Class 8

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 15 Sound Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 15 Sound

Class 8 Science Chapter 15 Sound Textbook Questions and Answers

1. Fill in the blank with appropriate word:

Question a.
The region in a sound wave, with higher pressure and density is called ………….. and that with low pressure and density is called ……….. .
Answer:
The region in a sound wave, with higher pressure and density is called compression and that with low pressure and density is called rarefaction.

Question b.
Medium is …………… for generation of sound.
Answer:
Medium is needed (or necessary) for generation of sound.

Question c.
The total number of compressions and rarefactions produced per second in a sound wave is 1000. The frequency of the sound wave is ………… .
Answer:
The total number of compressions and rarefactions produced per second in a sound wave is 1000. The frequency of the sound wave is 500 Hz.
[Note: Total number: 100. ∴ 500 compressions and 500 rarefactions are produced per second.]

Question d.
Different sound notes have different ………………. .
Answer:
Different sound notes have different frequencies.

Question e.
In a loudspeaker, …………… energy is converted into ………….. energy.
Answer:
In a loudspeaker, mechanical energy is converted into sound energy.

2. Give scientific reasons:

Question a.
It is essential to change the tension in the vocal cords, as we produce different sound notes from our larynx.
Answer:
Different sound notes correspond to different frequencies. The frequency of sound depends on the tension in the vocal cords. Hence, it is essential to change the tension in the vocal cords, as we produce different sound notes our larynx.

Question b.
Astronauts on the moon cannot hear each other directly.
Answer:
Two astronauts on the moon talking to each other directly, will be unable to listen to each other, even if they are very close to each other. The moon does not have atmosphere. Since there is no medium which is necessary for generation and propagation of sound, between the astronauts, direct sound propagation between them is not possible. Therefore, the astronauts use some technology like the one used in our cell-phones to communicate with each other. The waves used in cell-phone do not need any medium for propagation.

Question c.
As the sound wave propagates from one place to the other in air, the air itself is not required to move from one place to the other.
Answer:
Propagation of sound through air occurs due to energy transfer by vibrating air molecules in one region to those in the adjacent region away from the source. The molecules simply vibrate about their mean positions. Hence, the air itself is not required to move from one place to the other.

3. How are different sound notes generated in musical instruments like guitar, which uses strings for sound generation, and flute, which uses blown air for sound generation?

Question a.
How are different sound notes generated in musical instruments like guitar, which uses strings for sound generation, and flute, which uses blown air for sound generation?
Answer:
1. Guitar: It is a string based, flat- backed instrument. It has usually six strings, the strings are plucked or strummed with the fingers or a small piece of plastic, wood, etc. It has a flat sounding board with a circular sound hole in the centre. Also it has a fretted fingerboard. Its frequency range is more than three octaves. The frequency of vibration of the string is changed by changing the tension in the string or changing the vibrating length of the string. As the tension is increased, the frequency increases. As the vibrating length is increased, the frequency decreases. This is how different sound notes are generated.
[Note: The acoustic guitar has hollow body and six or twelve strings while the electric guitar usually has solid body and six strings. The electric bass guitar has four strings.]

2. Flute: It is a wind instrument where air is blown against the edge or rim of the blowing hole. The frequency of the sound produced depends upon the length of the vibrating air column in the tube. The greater the length of the vibrating air column, the less is the frequency of the sound produced. This is how different sound notes are produced. The flute has six or seven or eight holes to generate sounds of different frequencies. Different notes can be generated also by changing the way of air-blowing.

4. How is sound produced in the human larynx and a loudspeaker?

Question a.
How is sound produced in the human larynx and a loudspeaker?
Answer:
1. Sound production in the human larynx:
In the humans, sound is produced in the voice box called the larynx. It is located at the upper end of the windpipe. Two vocal cords (chords) are stretched across it with a narrow slit between them for the passage of air (Fig. 15.5). When the lungs force air through the slit, the cords start vibrating.

The frequency of the sound produced depends upon the length and thickness of the cords, and the tension in the chords. The frequency increases with the increase in tension and the more the length or the thickness of the cord, the less is the frequency. Muscles attached to the cords can make the cords tight (more tension) or loose (less tension).

2. Sound produced in a loudspeaker:
Figure shows the internal construction of a loudspeaker. Here, a coil is wound around a permanent magnet. The conical screen of the loudspeaker is attached to the coil.

When a current is passed through the coil, a magnetic field is produced. Its interaction with the permanent magnet results in the back and forth motion of the coil. The frequency and the amplitude of the motion of the coil depends on the variation in the current through the coil.

As the coil moves, the conical screen also moves back and forth. The vibrations of the screen produce sound waves in air. Very loud sound can be produced by changing the current.
[Note: If you gently touch the vibrating screen, you can feel the vibrations.]

5. Explain the experiment, with0 a neat diagram, to prove the following:
‘Sound needs a material medium for propagation.’

Question a.
Explain the experiment, with0 a neat diagram, to prove the following:
‘Sound needs a material medium for propagation.’
Answer:

Figure shows part of the set up used in this experiment. What is not shown is the electric circuit in which the electric bell is connected. A vacuum tight bell jar contains an electric bell connected to a power supply through the lid of the jar. The jar is placed on a smooth horizontal surface such as that of glass.

Initially the vacuum pump is off and the jar contains air. The circuit containing the bell is completed using the key or the switch so that the bell starts ringing. This can be heard outside the jar.

Then the vacuum pump is switched on so that it starts removing the air from the jar. We find that the level of ringing sound heard goes on decreasing as the quantity of air in the jar becomes less and less.

When the pump is operated for a sufficiently long time interval, the quantity of air in the jar becomes so less that the level of ringing sound becomes very low; sound is hardly audible. But we can see the striker in the bell hitting the gong. By extrapolation, we conclude that sound generation and propagation needs a medium.

6. Match the following:

Question a.

Answer:

Column I	Column II
Human larynx	Vibrations in vocal cords
Loudspeaker	Vibrations of screen
Jaltarang	Vibrations in air column
Tuning fork	Vibrations of metal arms
Sitar	Vibrations in strings

Can you recall?

Question a.
How is sound produced?
Answer:
Sound is produced by the vibrations of an object such as a stretched membrane or a string under tension.

Project:

Question 1.
Take two plastic glasses and tie a thread between them to make a toy phone. Does the voice of your friend reach you through the thread? Take metal wire instead of the thread and also change the length of the thread wire and repeat the activity. Discuss with your friends and teacher about your conclusions.

Question 2.
Take a plastic or tin can or a plastic glass. Remove its bottom. Stretch a piece of rubber balloon across one end and fix it with a rubber band. Put a few grains of say ragi or bajra on the stretched rubber. Now ask your friend to shout ‘Hoorrey ……… Hoorrey ………… ‘ from the open end of the glass. Observe the dancing of the grains up and down. Discuss the reason behind this.

Class 8 Science Chapter 15 Sound Important Questions and Answers

Select the correct option and write the completed statements:

Question 1.
Sound waves cannot travel through a ………… .
(a) solid
(b) liquid
(c) gas
(d) vacuum
Answer:
Sound waves cannot travel through a vacuum.

Question 2.
If the frequency of a sound wave is 512 Hz, the number of rarefactions produced per second is ……………… .
(a) 256
(b) 512
(c) 1024
(d) 128
Answer:
If the frequency of a sound wave is 512 Hz, the number of rarefactions produced per second is 512.

Question 3.
In the experiment to show that a medium is necessary for propagation of sound, as the quantity of air inside the bell jar decreases, the level of ringing sound heard outside ……………… .
(a) increases
(b) decreases
(c) fluctuates randomly
(d) changes at regular intervals
Answer:
In the experiment to show that a medium is necessary for propagation of , sound, as the quantity of air inside the bell jar decreases, the level of ringing sound heard outside decreases.

Find the odd one out and give the reason:

Question 1.
Sound waves, Waves on the surface of water, Waves on a stretched string, Light waves
Answer:
Light waves. Light waves can travel in a vacuum. Other waves need a medium for propagation.

Question 2.
Sitar, Violin, Guitar, Flute.
Answer:
Flute. It is not a string based instrument. Others are string based instruments.

State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)

Question 1.
If the vibrating length of a stretched string is kept constant and the tension in the string is increased, the frequency of the sound produced increases.
Answer:
True.

Question 2.
In Jaltarang, the frequency of sound produced is independent of the height of the air column inside the glass cup.
Answer:
False. (In Jaltarang, the frequency of sound produced depends on the height of the air column inside the glass cup; the more the height of the air column, the less is the frequency of the sound produced.)

Answer the following questions in one sentence each:

Question 1.
What is sound?
Answer:
Sound is a form of energy which produces sensation of hearing in our ears.

Question 2.
What is vibration?
Answer:
Vibration is a rapid, to and from periodic motion of an object about its mean position.

Question 3.
What is compression?
Answer:
As a sound wave travels through air, the region in which air is at high pressure and high density is called compression.

Question 4.
What is rarefaction?
Answer:
As a sound wave travels through air, the region in which air is at low pressure and low density is called rarefaction.

Question 5.
What is the relation between the frequency of vibration and the vibrating length (or height) of the air column?
Answer:
The greater the vibrating length (or height) of the air column, the less is the frequency of vibration of the column.

Question 6.
For a particular string (given material and radius), what are the factors on which its frequency of vibration depends?
Answer:
For a particular string (given material and radius), the frequency of vibration of the string depends upon its vibrating length and the tension in the string.
[Note: in the above case, frequency is proportional to the square root of the tension and inversely proportional to the length.]

Question 7.
Name an instrument in which a stretched skin is used to produce musical sound.
Answer:
Tabla.

Answer the following questions:

Question 1.
Explain the production and propagation of sound in air.
Answer:
Let us consider production of sound by using a tuning fork. A tuning fork is made of a metal. It has a stem and two prongs (Fig). Figure (a) shows the state of air in the absence of propagation sound through it. Equally spaced vertical lines show that the average distance between the air molecules is the same everywhere. It means average pressure and average density in the regions A, B and C are the same.

Suppose the tuning fork is held vertical, its stem is fixed in a stand (not shown in the figure) and its prongs are struck lightly using a light hammer with a piece of rubber at the top. The prongs then start vibrating.
Figure (b) shows what happens when the prongs move away from each other. The air outside the prongs is compressed (layers in the region A). The pressure and density increase in this region.

Figure (c) shows what happens when the prongs move close to each other. The air molecules near the prongs move away from each other resulting in lower pressure and lower density.

This region is called rarefaction. Meanwhile, the compression produced earlier moves forward, i.e., away from the prongs because the air molecules in this region transfer their energy to the air molecules in the region B producing a compression there. The periodic formation of compression and rarefaction results in propagation of sound waves away from the prongs.

Eventually, these sound waves reach our ears, the ear-drum vibrates, and we get a sense of hearing a sound as the specific signals reach the brain.

Use your brain power:

Question a.
If sound waves are generated in air, what moves away from the source? Is it the air itself or the state of compression and rarefaction created in the air?
Answer:
If sound waves are generated in air, the state of compression and rarefaction created in the air moves away from the source.
[Note: The air does not move away from the source because air is elastic and the force due to the tuning fork varies periodically with time.]

Question 2.
Explain the term frequency of a sound wave.
Answer:
Sound travels in the form of waves. A wave consists of cycles of alternate compression and rarefaction. The number of cycles produced in the air (or any other medium) per second is called the frequency of the sound wave. It is expressed in hertz (Hz). 1 hertz = 1 cycle per second or 1 vibration per second or 1 oscillation per second.

[Note: The SI unit of frequency, the hertz, is named in honour of Heinrich Hertz (1857-94), German physicist.]

Question 3.
State the factors on which the frequency of a tuning fork depends.
Answer:
The frequency of a tuning fork depends on the dimensions of the prongs, i.e., length and thickness, and the material used for making the fork.

Try this:

Question a.
Take 6 – 7 glass cups. Arrange them in a line and fill them with water with gradually increasing water level from one end to other. Take a pencil and strike the cups sequentially. The sound generated by each cup will be different. Why is it so?
Use of ICT:
Download videos of Jaltarang from youtube and send them to your friends by email.

Answer:
When a cup is struck, waves are set up in the air column above the water level in the cup. The frequency of the generated wave depends on the height of the air column inside the glass cup. Since the water level in each glass is different, the height of the air column in each glass is also different. Therefore, the frequency of sound generated by each glass cup will also be different. So, the sound generated is different.

Question b.
An ‘app’ for measurement of sound frequency may be available on cellphones. With the help of your teacher, use the app to measure the frequency of the sound generated from each glass cup. Do you observe any relation between the frequency of generated sound and the height of the air column in the glass cup?
Answer:
Yes. The greater the height of the air column in the glass cup, the less is the frequency of the sound produced.

Question c.
This is your simple ‘Jaltarang’! Can this experiment be performed with stainless steel pots of different size?
Answer:
Do it. See what happens as the stainless steel pot itself starts vibrating producing a sound. Also see how this sound is damped by water.

Do you know?

Question a.
What are the frequencies of musical notes ‘sa’, ’re’, ‘ga’, ‘ma’, ‘pa’, ‘dha’, ‘ni’ in the ‘madhya saptak’?
Answer:

[Note: The diatonic scale:


Such a simple fraction is pleasing to the ear and is called a musical interval. Frequency ratios 2 : 1, 3 : 2, 4 : 3 are examples of musical interval.

Observe and discuss:

Question 1.
Identify the instruments and discuss sound production in them. [Students should see these musical instruments.]

Answer:

1. Sitar
2. Shehnai
3. Flute
4. Tabla
5. Santoor
6. Bugle
7. Mandoline or Mandolin
8. Saxophone.

Question i.
Sitar, Santoor and Mandoline or mandoline (String instruments):
Answer:
Vibrating strings produce the sound. The greater the tension in the string, the higher is the frequency of the sound. The greater the vibrating length and the diameter of the string, the lower is the frequency of the sound.

Question ii.
Flute, Saxophone and Shehnai (Wind instruments):
Answer:
Vibrating air column produces the sound. The greater the length of the column, the lower is the frequency of the sound.

Question iii.
Tabla (Percussion instrument):
Answer:
Vibrating skin produces the sound. The greater the tension in the skin, the higher is the frequency of the sound. The greater the thickness of the skin, the lower is the frequency of the sound.

Try this:
‘Apps’ for generation of different sound notes (sound note generator app) may be available on cellphones. With the help of your teacher, using such an app, generate sound notes listed in the table.

Vocal cords are 20 cm in length in male, about 15 cm in female and even smaller in children. Therefore the voice of male, female and children are different.
[Note: Vocal cords are 20 mm in length in male, about 15 mm in female and even smaller in children. Reference NCERT textbook Std. VIII, published in 2017.]

Question 1.
Produce a sound ‘bho … bho …’ just like a dog-barking and ‘meow … meow…’ just like a mewing cat. Carefully notice the tension on the vocal cords, when you produce these sounds. Do you feel that the tension on the vocal cords changes when you produce these two different sounds?
Answer:
Yes.

Question 2.
An ‘app’ may be available on cell-phones to measure the loudness of sound in decibel. With the help of your teacher, use the app to measure the sound level of a sound from a loudspeaker at some public place. Measure the sound level at different distances from the loudspeaker. Do you observe some relation between the distance from the loudspeaker and the sound level?
Answer:
Yes. As the distance increases, the sound level decreases.

Always remember:

We should take care that others are not disturbed when we study sound and its production. Sound pollution is a major cause affecting the environment and social health. Hence we should find ways to avoid sound pollution.

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 14 Measurement and Effects of Heat Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 14 Measurement and Effects of Heat

Class 8 Science Chapter 14 Measurement and Effects of Heat Textbook Questions and Answers

1. A. Whom should I pair with?

Question a.

Group ‘A’	Group ‘B’
1. Temperature of a healthy human body	a. 296 K
2. Boiling point of water	b. 98.6 °F
3. Room temperature	c. 0°C
4. Freezing point of water	d. 212 °F

Answer:

Group ‘A’	Group ‘B’
1. Temperature of a healthy human body	b. 98.6 °F
2. Boiling point of water	d. 212 °F
3. Room temperature	a. 296 K
4. Freezing point of water	c. 0°C

B. Who is telling the truth?

Question a.
The temperature of a substance is measured in joule.
Answer:
False. (The temperature of a substance is measured in °C or °F or K.)

Question b.
Heat flows from an object at higher temperature to an object at lower temperature.
Answer:
True.

Question c.
The joule is the unit of heat.
Answer:
True.

Question d.
Objects contract on heating.
Answer:
False. (In general, objects expand on heating. There are some exceptions to this, you will learn about them in Standard X.)

Question e.
Atoms of a solid are free.
Answer:
False. (Atoms of a solid are bound to each other due to the forces acting between them.)

Question f.
The average kinetic energy of atoms in a hot object is less than the average kinetic energy of atoms in a cold object.
Answer:
False. (The average kinetic energy of atoms in a hot object is more than the average kinetic energy of atoms in a cold object.)

C. You will find if you search.

Question a.
A thermometer is used to measure ……………. .
Answer:
A thermometer is used to measure temperature.

Question b.
The apparatus used to measure heat is called a ………… .
Answer:
The apparatus used to measure heat is called a calorimeter.

Question c.
Temperature is the measure of the …………. kinetic energy of the atoms in a substance.
Answer:
Temperature is the measure of the average kinetic energy of the atoms in a substance.

Question d.
The heat contained in a substance is the measure of the ………….. kinetic energy of the atoms in the substance.
Answer:
The heat contained in a substance is the measure of the total kinetic energy of the atoms in the substance.

2. Nishigandha kept a vessel containing all the ingredients for making tea in a solar cooker. Shivani kept a similar vessel on a stove. Whose tea will be ready first and why?

Question a.
Nishigandha kept a vessel containing all the ingredients for making tea in a solar cooker. Shivani kept a similar vessel on a stove. Whose tea will be ready first and why?
Answer:
Shivani’s tea will be ready first.
Reason: In a given time, the amount of heat received by the vessel on a stove is far greater than that received by the vessel kept in a solar cooker.

3. Write brief answers.

Question a.
Describe a clinical thermometer. How does it differ from the thermometer used in a laboratory?
Answer:
A clinical thermometer has a narrow stem and a long bulb filled with mercury (or alcohol). There is a small constriction in the stem above the bulb. When the bulb of the thermometer is held in the armpit or the mouth of a patient, the mercury (or alcohol) in the bulb rises in the stem.

When it is taken out of the patient’s body, the small constriction does not allow the mercury (or alcohol) from the stem to retreat into the bulb. Thus, this arrangement enables us to read the temperature of the patient’s body at ease after the removal of the thermometer from his body.

The clinical thermometer is graduated from 35 °C to 42 °C (or from 95 °F to 108 °F). At 37 °C (98.6 °F), there is a red arrow mark which indicates the temperature of a healthy person.

The thermometer used in a laboratory has wider range and does not have constriction like a clinical thermometer.

Question b.
What is the difference between heat and temperature?
Answer:
Heat is related to the total kinetic energy of the atoms in a substance while temperature is related to the average kinetic energy of the atoms in the substance. Heat flows from a body at higher temperature to a body at lower temperature. Thus, temperature is a quantity that determines the direction of flow of heat. It is a quantitative measure of the degree of hotness or coldness of a body.

Higher temperature does not mean higher heat content. Suppose a vessel A contains 2 litres of water at 90 °C and a vessel B contains 100 ml of water at 91 °C. Then the heat content of water in A is greater than that of water in B, but the temperature of water in B is higher than that of water in A.

Units of heat:
Heat is usually expressed in calorie, kilocalorie and joule. It can also be expressed in erg as heat is a form of energy.

Question c.
Explain the construction of a calorimeter. Draw the necessary figure.
Answer:

Figure shows the construction of a calorimeter. Like a thermo flask, a calorimeter has two vessels. The inner vessel, made of copper, is (practically) thermally isolated from the surroundings. The outer vessel is made of wood and is covered with a heat resistant lid. The lid has two holes, one for the thermometer and the other for the stirrer. The inner and outer surfaces of the inner vessel are polished for minimizing exchange of heat with the surroundings by radiation. A heat resistant ring covers the inner vessel.

Question d.
Explain why rails have gaps at specific distances.
Answer:
The rails expand in summer due to increase in the temperature of the atmosphere. Also, they expand due to rise in temperature caused by the friction between the rails and the wheels of the running train. If there is no gap between successive rails of a railway line, the rails would bend due to expansion. This bending and twisting of the rails would cause accidents. Hence, a gap is kept between successive rails of a railway line to make provision for their expansion in summer.

Do you know:

Have you seen rails? They are not continuous. A small gap is kept between them at regular intervals. This is shown in the figure. This is kept to accommodate the change in the length of the rails with change in temperature. If this gap is not kept, then the rail will get distorted due to expansion in summer which may lead to accidents.

Similar to rails, the length of bridges can also increase due to expansion in summer. The length of the 18 km long great belt bridge in Denmark increases by 4.7 m in summer. Therefore, provision in made in the construction of the bridges to accommodate this expansion.

Question e.
Explain with the help of formulae the expansion coefficients of liquid and gas.
Answer:
1. A liquid is held in a container. When it is heated, both the container and the liquid expand. The expansion of the container is usually very small compared to that of the liquid in it. Often, it can be ignored.
Suppose a liquid is heated so that its temperature rises by ΔT (very small) and its volume increases from V₁ to V₂. Experimentally, it is found that the increase in volume, V₂ – V₁, is proportional to V₁ and ΔT.
Hence, (V₂ – V₁) α V₁ΔT.
∴ V₂ – V₁ = β V₁ΔT, where β is a constant of proportionality called the volumetric expansion coefficient of the liquid.
β = \(\frac{V_{2}-V_{1}}{V_{1} \Delta T}\).
It is expressed in per °C.
We have V₂ = V₁ + βV₁ΔT = V₁(1 + β ΔT).
β is the increase in the volume of a liquid per unit original volume per unit rise in its temperature.

2. A gas is enclosed in a container. When it is heated at constant pressure, both the container and the gas expand. Suppose a gas is heated at constant pressure so that its temperature rises by ΔT (very small) and its volume increases from V₁ to V₂. Experimentally, it is found that the increase in volume, V₂ – V₁ is proportional to V₁ and ΔT. Hence, (V₂ – V₁) a V₁ΔT.
∴ V₂ – V₁ = β V₁ΔT, where β is a constant of proportionality, the volumetric expansion coefficient, called the constant pressure expansion coefficient.
β = \(\frac{V_{2}-V_{1}}{V_{1} \Delta T}\).
It is expressed in per °C.
We have V₂ = V₁ + βV₁T = V₁(1 + β ΔT).
β is the increase in the volume of a gas per unit original volume per unit rise in its temperature when the pressure is kept constant.

4. Solve the following examples.

Question a.
What must be the temperature in Fahrenheit so that it will be twice its value in Celsius?
Solution:
Data: F = 2 C ∴ C = F/2, F = ?

∴ F – 0.9 F = 32
∴ 0.1 F = 32
∴ F = \(\frac{32}{0.1}\) = 320 °F.

Question b.
A bridge is made from 20 m long iron rods. At temperature 18 °C, the distance between two rods is 0.4 cm. Up to what temperature will the bridge be in good shape?
Solution:
Data: l₁ = 20 m, l₂ – l₁ = 0.4 cm
= 4 × 10^-3 m, T_i = 18 °C, λ for iron = 11.5 × 10^-6/°C
l₂ – l₁ = λl₁ Δt

= \(\frac{400}{23}\) °C = about 17.39 °C
Now, ΔT= T_f – T_i ∴ T_f = T_i + ΔT
∴ T_f = 18 °C + 17.39 °C = 35.39 °C.
The bridge will be in good shape up to 35.39 °C.

Question c.
At 15 °C the height of Eiffel Tower is 324 m. If it is made of iron, what will be the increase in length in cm, at 30 °C?
Solution:
Data: ΔT = 30 °C – 15 °C = 15 °C, l₁ = 324 m, λ for iron = 11.5 × 10^-6/°C l₂ – l₁ = λl₁ ΔT
= 11.5 × 10^-6/°C × 324 m × 15 °C
= 55890 × 10^-6 m
= 55890 × 10^-6 × 10² cm
= 55890 × 10^-4 cm
= 5.589 cm (nearly 5.6 cm)
This is the increase in the length, i.e., the increase in the height of Eiffel Tower.

Question d.
Two substances A and B have specific heats c and 2 c respectively. If A and B are given Q and 4Q amounts of heat respectively, the change in their temperatures is the same. If the mass of A is m, what is the mass of B?
Solution:
Data: c (A) = c, c (B) = 2c,
Q (A) = Q, Q (B) = 4Q, ΔT same,
m (A) = m, m (B) = ?

∴ m(B) = 2m.
This is the mass of B.

Question e.
When a substance having mass 3 kg receives 600 cal of heat, its temperature increases by 10 °C. What is the specific heat of the substance?
Solution:
Data: m = 3 kg = 3000 g,
Q = 600 cal, ΔT = 10 °C, c = ?
Q = mcΔT

= 0.02 cal/(g.°C)
This is the specific heat of the substance.

Can you recall?

Question a.
Which sources do we get heat from?
Answer:

1. Sun
2. earth
3. fuels like wood, coal, petrol
4. electricity
5. atomic energy
6. air.

Question b.
How is heat transferred?
Answer:
Heat is transferred by conduction, convection and radiation.

Question c.
Which effects of heat do you know?
Answer:
Expansion, change of state, rise in temperature, emission of light, burning.

Question d.
Some effects of heat are shown in Fig. What are they?

Answer:
Rise in temperature/boiling, melting, burning, expansion.

Question e.
What are potential and kinetic energies?
Answer:
The energy stored in a body because of its specific state or position is called its potential energy. The energy possessed by a body because of its motion is called it’s kinetic energy.

Project:

Question a.
Collect information about bimetallic strips and discuss in your class how a fire alarm is made using it.

Class 8 Science Chapter 14 Measurement and Effects of Heat Important Questions and Answers

Rewrite the following statements by selecting the correct options:

Question 1.
32°F is equal to …………….. .
(a) 212 °C
(b) 212 K
(c) 273.15 K
(d) 273.15 K
Answer:
32°F is equal to 273.15 K.

Question 2.
-40°C is equal to ………….. .
(a) -40 °F
(b) 40 °F
(c) -8°F
(d) 40K
Answer:
-40°C is equal to -40 °F.

Question 3.
The boiling point of water is ………… .
(a) 212 K
(b) 212 °F
(c) 273.15 K
(d) 32 °F
Answer:
The boiling point of pure water is 212 °F.

Question 4.
Specific heat is expressed in …………… .
(a) J/(kg. °C)
(b) kg/(J C)
(c) J/kg
(d) cal/g
Answer:
Specific heat is expressed in J/(kg.°C).

Question 5.
The freezing point of water is …………….. .
(a) OK
(b) 212°F
(c) 32°F
(d) 0°F
Answer:
The freezing point of water is 32 °F.

Find the odd one out and give the reason:

Question 1.
0°C, 32°F, 273.15K, 212°F.
Answer:
212 °F. This is the boiling point of water; others correspond to the freezing point of water.

Question 2.
373.15 K, 100 °C, 212 °F, 32 °F.
Answer:
32 °F. This is the freezing point of water others correspond to the boiling point of water.

Answer the following questions in one sentence each:

Question 1.
Name the biggest source of heat received by the earth.
Answer:
The Sun is the biggest source of heat received by the earth.

Question 2.
What is the relation between the temperature in °C and the temperature in °F?
F – 32 °C
Answer:
\(\frac{F-32}{9}\) = \(\frac{C}{5}\), where C denotes temperature in °C and F denotes temperature in °F.

Question 3.
Name the quantity expressed in cal/(g.°C).
Answer:
Specific heat is expressed in cal/(g.°C).

Question 4.
State the formula for the coefficient of linear expansion of a solid substance.
Answer:
λ = (l₂ – l₁]) / (l₁ ΔT).

Question 5.
State the formula for the coefficient of areal expansion of a solid.
Answer:
σ = (A₂ – A₁)/ (A₁ ΔT).

Question 6.
State the formula for the volumetric expansion coefficient of a solid.
Answer:
β = (V₂ – V₁) / (V₁ ΔT).

Question 7.
State the relation between λ and σ (if ΔT is very small).
Answer:
σ = 2 λ.

Answer the following questions:

Question 1.
How is heat generated in the Sun?
Answer:
In the interior of the Sun, at the centre, hydrogen nuclei fuse together to form helium nuclei. A lot of heat is generated in this process.

Question 2.
What is geothermal energy?
Answer:
Heat within the interior of the earth, e.g., that coming from the molten core of the earth, is called geothermal energy.
[Note: Volcanoes, geysers, hot springs are sources of this energy.]

Question 3.
What is atomic energy or nuclear energy?
Answer:
Energy released or obtained in nuclear fission or nuclear fusion is called atomic energy or nuclear energy.

Question 4.
Name three sources of chemical energy.
Answer:
Fuels like wood, coal and petrol are sources of chemical energy.

Try this:

1. Take three similar vessels. Let us call them ‘A’, ‘B’ and ‘C’.
2. Fill A with hot water and B with cold water. Put some water from A and B in C.
3. Dip your right hand in A and left hand in B and keep them immersed for 2 to 3 minutes.
4. Now dip both the hands in C. What do you feel?

Even though, both the hands are dipped in water in the same vessel, i.e., water at the same temperature, your right hand will find the water to be cold while the left hand will find it to be hot. What is the reason for this? Think about it.
Answer:
The right hand finds the water cold because it loses heat to water in C. The left-hand feels the water hot because it gains heat from water in C. (This shows that we cannot determine the temperature of an object accurately by simply touching it)

Question 5.
State the units in which temperature is expressed.
OR
What are the units of temperature?
Answer:
Temperature is expressed in °C (degree Celsius), °F (degree Fahrenheit) and K (kelvin).

Question 6.
Draw diagrams to illustrate motion of atoms in a gas and a solid. Also explain the type of motion.
Answer:
Atoms of a gas are comparatively free and move at random. Figures a and b show the velocities of atoms in a gas at high and low temperature, respectively. The direction and the length of the arrows show respectively the direction and the magnitude of the velocity of the atoms. The velocity of atoms in the gas at higher temperature is larger in magnitude than the velocity of atoms in the gas at lower temperature.

The velocities of atoms in a solid are shown by arrows in Fig. (c). The atoms in a solid are tied to one another because of the forces acting between them. This is indicated by drawing springs between adjacent atoms. Because of heat, they oscillate around their fixed mean positions. The higher the temperature of a solid, the greater is their velocity of oscillation.

Try this:

1. Take two steel vessels A and B of the same size.
2. Fill some water in A and double that amount in B. Make sure that the water in both vessels is at the same temperature.
3. Raise the temperatures of water in both vessels by 10 CC using a spirit lamp. Did it take the same time to increase the temperature in the two vessels?
Answer:
No.
You must have required more time to raise the temperature of water in B. This means that for the same increase in temperature, you had to give more amount of heat to B. Thus, even though the water in A and in B have the same temperature, the amount of heat in B is more than that in A.

Question 7.
How are the different units of temperature-related?
Answer:
1. The SI unit of temperature is the kelvin (K). Temperature is also expressed in °C (degree Celsius) and °F (degree Fahrenheit).

Here, C denotes temperature in °C, F denotes temperature in 0F and K denotes temperature in K (kelvin).
[Notes: (i) The unît degree Celsius is named in honour of Anders Celsius (1701 – 44) Swedish astronomer. He devised a temperature scale in 1742.
(ii) The unit degree Fahrenheit is named in honour of Gabriel Daniel Fahrenheit (1686 – 1736) German physicist. He developed the mercury thermometer and devised the temperature scale.
(iii) The unit kelvin is named in honour of William Thomson, 1st Baron Kelvin (of Largs) (1824 – 1907) British physicist and electrical engineer. He made significant contribution in thermodynamics and electromagnetic theory. He proposed a scale of temperature now known as the Kelvin scale or thermodynamic scale.]

Question 8.
What is a liquid (mercury or alcohol) thermometer?
Answer:
A thermometer in which the change in the volume of a liquid (mercury or alcohol) with temperature is used for measurement of temperature is called a liquid thermometer.

Question 9.
Why has mecury been replaced by alcohol in a thermometer?
Answer:
Because mercury is harmful for us, it has been replaced by alcohol in a thermometer.
[Notes: (i) Mercury thermometers are still widely used in laboratories in schools and colleges.
(ii) A thermometer is a device to measure temperature. A thermometer containing mercury in its bulb is called a mercury thermometer. There are other types of thermometer such as a thermocouple thermometer, a platinum resistance thermometer, a thermistor thermometer, etc.]

Question 10.
Describe the construction of mercury thermometer.
Answer:

1. For constructing a thermometer, a thick-walled capillary tube with a uniform bore is taken. The tube has a thin-walled glass bulb at one end.
2. The bulb and a small part of the tube is filled with mercury. The other end of the tube is sealed after removing air from it.
3. The tube is then calibrated and the temperature of the substance can be read with it.

[Note: The range of an alcohol thermometer is different from that of a mercury thermometer.]

Question 11.
How does a mercury thermometer work?
Answer:
1. When the bulb of the thermometer is brought in contact with the substance whose temperature is to be measured, there is an exchange of heat between the substance and the mercury in the bulb.

2. The mercury expands or contracts depending upon whether it gains heat or loses heat. Accordingly there is a rise or fall of the level of mercury in the tube of the thermometer indicating the temperature of the substance when the mercury and the substance are in thermal equilibrium.

Question 12.
Why is the bore of a thermometer made very small?
Answer:
The bore of a thermometer is made very small so that even a slight variation in the temperature may cause noticeable variation in the mercury level in the tube of the thermometer. As a result, the sensitivity of the thermometer increases and even small changes in the temperature can be recorded.

Question 13.
Why does the bulb of a thermometer have a thin glass wall?
Answer:
The bulb of a thermometer is made of a thin glass so that it can easily conduct the heat from the substance in contact with the mercury in the bulb.

Question 14.
Why does a thermometer usually break at the bulb?
Answer:
The bulb of a thermometer has a thin glass wall. Therefore, a thermometer usually breaks at the bulb.

Question 15.
Explain why the capillary tube of a clinical thermometer has a constriction.
Answer:
When the temperature of a patient is measured with a clinical thermometer, the mercury in the bulb expands and rises in the tube. The small constriction in the thermometer prevents the mercury thread from retreating into the bulb. Thus, the patient’s temperature can be read at ease after removing the thermometer from his body.

Question 16.
Explain why a clinical thermometer should not be washed with hot water.
Answer:
A clinical thermometer is constructed for the purpose of recording the temperature of the human body. Hence, its stem is such that it can allow the mercury to rise up to a temperature of about 42 °C. The temperature of hot water may be more than 42 °C. Therefore, when a clinical thermometer is washed with hot water, mercury will not have enough room for expansion and the thermometer would break.

[Note: (1) A digital thermometer has a sensor that detects the heat coming out from the body directly and displays the temperature.
(2) The maximum-minimum temperature has two scales, one against each arm of the thermometer. One scale indicates the maximum temperature reached (generally during the day) and the other scale indicates the minimum temperature reached (generally during the night).]

Question 17.
Explain what happens when there is exchange of heat between two objects.
Answer:
When there is an exchange of heat between a hot object and a cold object, the temperature of the hot object falls and the temperature of the cold object rises. If this system of two objects is isolated from the surroundings so that no heat enters or leaves the system, then, heat lost by the hot object = heat gained by the cold object. After some time, the average kinetic energies of the atoms in the two objects become equal, i.e., the two objects attain the same temperature.

Question 18.
Define specific heat.
Answer:
The specific heat of an object (substance) is the amount of heat required to increase the temperature of unit mass of that substance through one degree.

Question 19.
Write the formula for specific heat. Hence, obtain its unit.
Answer:
Specific heat of a substance,
c = \(\frac{Q}{m\left(T_{\mathrm{f}}-T_{\mathrm{i}}\right)}\), where m is the mass of the substance and Q is the amount of heat supplied to the substance to increase its temperature from Ti to Tf.

The SI unit of heat is the joule (J), that of mass is kg and that of temperature is kelvin (K).
∴ The SI unit of specific heat = \(\frac{\mathrm{J}}{(\mathrm{kg} \cdot \mathrm{K})}\)
[Note: Specific heat is also expressed in J/(kg°C) and cal/(g°C).]

Question 20.
The specific heat of aluminium is 0.21 cal/(g°C). What do you understand by this statement?
Answer:
The amount of heat required to raise the temperature of 1g of aluminium through 1 °C is 0.21 cal.

Question 21.
The specific heat of gold is 0.03 cal/(g°C). Express it in J/(kg°C).
Answer:
1 cal = 4.18 joules (J)
1 gram = 10^-3 kg
∴ 1 cal/(g°C) = 4.18 J/(10-3 kg°C)
= 4180 J/(kg°C)
∴ 0.03 cal/(g°C) = 0.03 × 4180 J/(kg°C)
= 125.4 J/(kg °C)

Question 22.
Arrange the following materials in increasing order of specific heat: aluminium, gold, iron, water.
Answer:
Gold, iron, aluminium, water.

Use your brain power!

Question 1.
Why does your mother put folded cloth strips soaked in cold water on your forehead when you have high fever?
Answer:
To remove heat quickly from our body and thereby lower the temperature of the body (as water has high specific heat).

Question 2.
Why is the calorimeter made of copper?
Answer:
Copper is a good conductor of heat and has low specific heat. Also copper is durable and not highly reactive.

Question 23.
How will you determine the specific heat of a metal using a calorimeter?
OR
Describe the experiment to determine the specific heat of iron using an iron ball, calorimeter and water.
Answer:
1. Find the mass (m_i) of the iron ball.
2. Find the total mass (m_c) of the calorimeter (metal container) and the stirrer.

3. Fill the calorimeter to two-thirds of its capacity with water and find its mass (m’_c) along with the stirrer. Hence, find the mass (m_w) of the water in the calorimeter (m_w = m’_c – m_c).
4. Keep the calorimeter in the wooden box and note the temperature (T₁) of the water in the calorimeter with the thermometer.

5. Suspend the iron ball in water in a beaker. Heat the beaker so that the water starts boiling. Note the temperature (T₂) of the boiling water.
6. Transfer the iron ball quickly to the calorimeter and cover the calorimeter with the lid immediately.

7. Stir the water in the calorimeter gently and continuously for uniformity of temperature and note the maximum temperature (T₃) attained by the mixture.

8. Find the specific heat capacity of iron using the following formula:
heat lost by the iron ball = heat gained by the calorimeter, stirrer and water
[assuming that there is no exchange of heat between the system (calorimeter, stirrer, water and iron ball) and the surroundings].

where cc = specific heat of the material of the calorimeter and stirrer and c_w = specific heat of water.
Hence, the specific heat of iron (c_i) can be determined when other quantities are known.

Question 24.
Why is a calorimeter used in the study of the exchange of heat between a solid and liquid or between two liquids?
Answer:
When a hot body is kept in contact with a cold one, there is an exchange of heat between the two. Hence, the temperature of the hot body decreases while that of the cold body increases till both the bodies attain the same temperature. During this process, if there is no exchange of heat between the surrounding and the bodies, the heat lost by the hot body is equal to the heat gained by the cold body.

As a calorimeter ensures that there is hardly any exchange of heat between the contents of the calorimeter and the surroundings, the calorimeter is used in the study of the exchange of heat between a solid and liquid or between two liquids.

Question 25.
Explain why the inside and outside of a calorimeter are polished.
Answer:

1. A calorimeter is used for the measurement of heat. Hence, it is essential to minimize the exchange of heat between the vessel and the surroundings.
2. A polished surface is a good reflector of heat. Hence, by polishing the inside and outside of a calorimeter, the loss or gain of heat due to radiation is reduced to a considerable extent.

Question 26.
Explain with the help of a formula the coefficient of linear expansion of a solid.
Answer:
Suppose a rod of length l₁ at temperature T₁ is heated to temperature T₂ such that ΔT = T₂ – T₁ is very small. Let l₂ be the length of the rod at temperature T₂.
Experimentally, it is found that the increase in the length of the rod (linear expension), l₂ – l₁, is proportional to l₁ and ΔT. Therefore, (l₂ – l₁) α, l₁ΔT
∴ l₂ – l₁ = λl₁ ΔT, where X is the constant of proportionality, called the coefficient of linear expansion of the solid.
λ = \(\frac{l_{2}-l_{1}}{l_{1} \Delta T}\) It is expressed in per °C.
We have l₂ – l₁ + λΔT = l₁ (1 + λΔT).

Question 27.
Define coefficient off linear explansion of a solid. Write the formula for it and obtain its unit.
Answer:
Coefficient of linear expansion of a solid is defined as the increase in the length of a rod of the solid per unit initial length per unit rise in its temperature.
Coefficient of linear expansion of a solid,
λ = \(\frac{l_{2}-l_{1}}{l_{1} \Delta T}\), where l₁ and l₂ are respectively the initial and final length of the rod of the solid and ΔT is the rise in its temperature.
Unit of λ = \(\frac{\text { unit of length }}{\text { unit of length } \times \text { unit of temperature }}\)

Question 28.
The coefficient of linear expansion of silver is 18 ×10^-6 per °C. What do you understand by this statement?
Answer:
If the temperature of a silver rod of length lm is increased by 1 °C, the length of the rod increases by 18 × 10^-6 m.

Question 29.
Explain with the help of a formula the coefficient of areal expansion of a solid.
Answer:
Suppose a sheet of a solid with surface area A₁ at temperature T₁ is heated to temperature T₂ such that ΔT = T₂ – T₁ is very small. Let A₂ be the surface area of the sheet at temperature T₂. Experimentally, it is found that the increase in the surface area of the sheet (areal expansion), A₂ – A₁, is proportional to A₁ and ΔT. Therefore,
(A₂ – A₁)α A₁ ΔT
∴ A₂ – A₁ = σ Al₁ΔT, where a is the constant of proportionality, called the coefficient of areal expansion of the solid.
σ = \(\frac{A_{2}-A_{1}}{A_{1} \Delta T}\). It is expressed in per °C.
We have A₂ = A₁ + σA₁ΔT = A₁ (1 + σΔT).
σ is the increase in the area of a solid per unit original area per unit rise in its temperature.
[Note: Consider a thin square metal plate of length l. Area of one face of the plate = A = l₂. Suppose the plate is heated so that the rise in its temperature is ΔT (assumed to be very small). Then in the usual notation, Δl = l λΔT and ΔA =
AσΔT = l² σΔT. Also, ΔA = (l + Δl)² – l² = l² + 2l.Δl + Δl² – l2 = 2l.Δl + Δl² . As Δl² << 2l.Δl, we can write ΔA = 2l.Δl(approximately)
∴ ΔA = 2l(l λΔT) = 2l²λΔT but ΔA = l²σΔT
∴ σ = 2.λ]

Question 30.
Explain with the help of a formula the volumetric expansion coefficient of a solid.
Answer:
Suppose a solid with volume V₁ at temperature T₁ is heated to temperature T₂ such that T₁ = T₂ – T₁ is very small. Let V₂ be the volume of the solid at temperature T₂. Experimentally, it is found that the increase
in the volume of the solid (volumetric expansion), V₂ – V₁, is proportional to V₁ and ΔT. Therefore, (V₂ – V₁)α V₁ΔT.
∴ V₂ – V₁ = βV₁ΔT, where β is the constant of proportionality, called the volumetric expansion coefficient of the solid.
β = \(\frac{V_{2}-V_{1}}{V_{1} \Delta T}\) It is expressed in per °C.
We have V₂ = V₁ + βV₁ ΔT = V₁ (1 + βΔT).
is the increase in the volume of a solid per unit original volume per unit rise in its temperature.
[Note: It can be shown that β = \(\frac{3}{2}\) σ 3λ.]

Question 31.
Obtain an expression for the variation of the density of a solid with temperature.
Answer:

As the temperature increases, density decreases.

Use your brain power!

Question 1.
Which use of the expansion of liquids in daily life do you know?
Answer:
Use of a thermometer. The effect of heat on water is somewhat different from that for other liquids. This is called anomalous behaviour of water. We are going to learn about it in higher standard.

Can you recall?

Expansion of gases:

A gas does not even have a fixed volume. Gas expands on heating but if the gas is kept in a closed box, its volume cannot increase but its pressure increases. This is shown in Fig. Observe Fig. and find out answers to the questions.

Question 1.
Using the formula density = mass/volume, explain what will be the effect of heat on the gas kept in a closed bottle.
Answer:
The density of the gas will remain the same as there is no change on the mass and volume of the gas.

Question 2.
If the bottle is not closed but has a movable piston attached to its open end (see the figure), what will be the effect of heating the gas in the bottle?
Answer:
The piston will move upwards as the gas expands.
Therefore, the expansion of a gas is measured by keeping its pressure constant.

Use your brain power!

Question 1.
The density of a gas decreases on heating. Which of the pictures in Fig. makes use of this?
Answer:
Students should be able to answer this question.

Write short notes on the following:

Question 1.
The Celsius temperature scale:
Answer:
In this case, the temperature at which pure ice melts at normal atmospheric pressure is taken as zero degree (0°C) and the temperature at which pure water boils at normal atmospheric pressure is taken as hundred degree (100 °C). The interval between them is divided into loo equal parts. Each part corresponds to a temperature difference of 1 °C.

Question 2.
The Fahrenheit temperature scale:
Answer:
In this case, the normal melting point of pure ice is taken as 32 °F and the normal boiling point of pure water is taken as 212 °F. The interval between these two points is divided into 180 equal parts. Each part corresponds to a temperature difference of 1°F. If C is the temperature of a body on the Celsius scale and F is the corresponding temperature on the Fahrenheit scale, the two are related by
C = \(\frac{5}{9}\) (F – 32) or F = \(\frac{9}{5}\) C + 32.

Question 3.
The Kelvin temperature scale:
Answer:
In this case, the melting point of pure ice at normal atmospheric pressure is taken as 273.15 kelvin (273.15 K) and the boiling point of pure water at normal f atmospheric pressure is taken as 373.15 I kelvin (373.15 K). The lowest possible temperature (called the absolute zero) on this scale corresponds to -273.15 °C.

Give scientific reasons:

Question 1.
We heat the neck of a glass bottle in order to remove the firmly fitted stopper.
Answer:
When we heat the neck of the glass bottle, it expands. Due to this, the stopper becomes loose and can be removed with ease.

Question 2.
A clinical thermometer has to be jerked before re-use.
Answer:
The constriction above the bulb of the clinical thermometer prevents the mercury thread once risen from falling down to the bulb. Hence, in order to force the mercury thread back into the bulb, the 1 clinical thermometer has to be jerked before re-use.

Question 3.
Instead of the mercury thermometer, alcohol thermometer is used for measurement of very low temperature.
Answer:
Mercury freezes at – 39 °C and turns to a solid. Hence, the mercury thermometer cannot be used to measure temperature below -39°C. The freezing point of alcohol is -117°C. Hence, the alcohol thermometer is used for i measurement of very low temperature.

Solve the following examples:

Question 1.
The normal armpit temperature in humans is 98.6 °F. What is this temperature in (i) degree Celsius (ii) kelvin ?
Solution:
Data: F = 98.6 °F, C = ?, K = ?

(ii) K = C + 273.15
= 37 + 273.15 = 310.15 K.

Question 2.

Find the heat needed to raise the temperature of 2.5 kg of water from 30 °C to 40 °C. Write the answer in calorie as well as joule.
Solution:
Data: m = 2.5 kg = 2500 g,
ΔT = 40 °C-30 °C, Q = ?
Heat needed to raise the temperature of 1 g of water through 1°C is 1 calorie.
∴ Q = 2500 × 10 = 25000 calories
Now, 1 calorie = 4.18 joules
∴ Q = 25000 × 4.18 joules = 104500 joules
Heat needed, Q = 25000 calories = 104500 joules.

Question 3.
If the temperature of water rises by 5 °C when 500 cal of heat is supplied to it, what is the mass of water?
Solution:
Mass of water = \(\frac{500}{5}\) = 100 g.

Question 4.
How much heat is required to raise the temperature of 500 g of mercury from 20 °C to 100 °C? [Specific heat of mercury = 0.033 kcal/(kg °C)]
Solution:
Data: m = 500 g = 0.5 kg,
T₁ = 20 °C,
T₂ = 100 °C, c = 0.033 kcal/(kg . °C), Q = ?
Q = mc (T₂ – T₁)
= 0.5 kg × 0.033 kcal/(kg . °C) × (100 °C – 20 °C)
= 0.5 × 0.033 × 80 kcal
= 0.033 × 40 kcal
∴ Q = 1.32 kcal
Heat required = 1.32 kcal.
[Note: 1kcal/(kg-°C) = 1 cal/(g.°C)]

Question 5.
A certain mass of water at 84 °C is poured into an equal mass of water at 24 °C. What will be the resulting temperature of the mixture ?
Solution:
Data: mx = m2 = m (say),
T₁ = 84 °C, T₂ = 24 °C, T = ?
Heat lost by the hot water = heat gained by the cold water

Resulting temperature of the mixture = 54 °C.

Question 6.
A bucket contains 8 kg of water at 20 °C. When 4 kg of hot water is mixed with it, the temperature of the mixture becomes 40 °C. Calculate the temperature of the hot water. (Ignore the heat absorbed by the bucket.)
Solution:
Data: m₁ = 8 kg, T₁ = 20 °C, m₂ = 4 kg, T = 40 °C, T₂= ?
Heat lost by the hot water = heat gained by the cold water (ignoring the heat absorbed by the bucket)
∴ m₂c (T₂ – T) = m₁c (T – T₁)
∴ 4 kg × c × (T₂ – 40°C)
= 8 kg × c × (40°C – 20°C)
∴ T₂ – 40°C = 2 × 20°C = 40°C
∴ T₂ = 40 °C + 40 °C = 80 °C
Temperature of the hot water = 80 °C.

Question 7.
A blacksmith plunges a 2 kg horseshoe at 400 °C into 1 kg of water at 20 °C. Find the maximum temperature of the water. [Specific heat of iron = 0.11 kcal/(kg-°C)]
Solution:
Data: mx = 2 kg,
c₁ = 0.11 kcal/(kg.°C), T₂ = 400 °C, m₂ = 1 kg,
c₂ = 1 kcal/(kg.°C), T₂ = 20 °C, T = ?
Heat lost by the horseshoe = heat gained by the water
∴ m₁c₁ (T₁ – T) = m₂c₂(T – T₂)
∴ 2 kg × 0.11 kcal/(kg.°C) × (400 °C – T)
= 1 kg × 1 kcal/(kg.°C) × (T – 20 °C)
∴ 0.22 × (400 °C – T) = T – 20 °C
∴ 1.22 T= 108 °C
∴ T = \(\frac{108}{1.22}\)°C = 88.52 °C
Maximum temperature of the water = 88.52 °C.

Question 8.
A copper sphere of mass 500 g is heated to 100 °C and then introduced into a copper calorimeter containing 100 g of water at 20 °C. Find the maximum temperature of the mixture, if the mass of the calorimeter is 100 g and the specific heat of the calorimeter is 0.1 cal/(g.°C).
Solution:
Data: m = 500 g, c = 0.1 cal/(g.°C), T’= 100 °C, m₁ = 100 g, c₁ = 1 cal/(g.°C), T₁ = 20°C, m₂ = 100 g, c₂ = 0.1 cal/(g.°C), T₂ = 20 °C, T= ?
Heat lost by the sphere = heat gained by the water and the calorimeter.
∴ mc (T’ – T) = m₁c₁ (T – T₁) + m₂c₂ (T – T₂)
∴ 500 g × o.l cal/(g.°C) × (100 °C – T)
= 100 g × 1 cal/(g.°C) × (T – 20 °C) + 100 g × 0.1 cal/(g.°C) × (T – 20 °C)
∴ 50 (100 °C – T) = 100 × (T – 20 °C) + 10 × (T – 20 °C)
∴ 50 (100 °C – T) = 110 × (T – 20 °C)
∴ 500 °C – 5T = 11T – 220 °C
∴ 16T = 720 °C
∴ T = \(\frac{720^{\circ} \mathrm{C}}{16}\) = 45 °C
Maximum temperature of the mixture = 45 °C.

Question 9.
A metal rod 1.8 m long, increases ( in length by 1.4 mm, when heated from 0 °C to 50 °C. Find the coefficient of linear expansion of the metal.
Solution:
Data: l₁ = 1.8 m, l₂ – l₁ = 1.4 mm = 1.4 × 10^-3 m.
T₁ = 0 °C, T₂ = 50 °C.
l₂ – l₁ = l₁ λ (T₂ – T₁)
∴ The coefficient of linear expansion of the metal is

Question 10.
A thin metal disc of surface area 500 cm2 at 0 °C is heated to 40 °C. Find the increase in the surface area of the disc. (σ = 4 × 10^-5 °C ^-1)
Solution:
Data: A₁ = 500 cm², T₁ = 0 °C,
T₂ = 40 °C, σ = 4 × 10^-5 °C^-1, A₂ – A₁ = ?
The increase in the surface area of the disc is
A₂ – A₁ = A₁σ(T₂ – T₁)
= (500 cm²) (4 × 10^-5 °C^-1) (40 °C – 0 °C)
= 500 × 4 × 10^-5 × 40 = 0.8 cm².

Question 11.
The surface area of a metal plate is 2.4 × 10^-2m² at 20 °C. When the plate is heated to 185 °C, its area increases by 0.8 cm². Find the coefficient of areal expansion of the metal.
Solution:
Data: A₁ = 2.4 × 10^-2 m²,
T₁ = 20 °C, T₂ = 185 °C, ΔA = 0.8 cm² = 0.8 × 10^-4 m², σ = ?
ΔA = A₂ – A₁ = A₁ σ(T₂ – T₁)
∴ The coefficient of areal expansion of the metal is

Question 12.
A lead bullet has a volume of 25 cm³ at 0 °C, and 25.21 cm³ at 90 °C. Find the volumetric expansion coefficient of lead.
Solution:
Data: V₁ = 25 cm³, T₁ = 0 °C,
V₂ = 25.21 cm³, T₂ = 90 °C
T₂ – T₁ = 90 °C – 0 °C = 90 °C β = ?

The volumetric expansion coefficient of lead is 9.333 × 10^-5 °C^-1.

Example Questions for practice:

Question 1.
The temperature of a body is 30 °C. Express it in (i) degree Fahrenheit (ii) kelvin.
Answer:
86 °F, 303.15 K

Question 2.
The temperature of a body is 283.15 K. Express it in °C and °F.
Answer:
10 °C, 50 °F

Question 3.
The temperature of a body is 68 °F. Express it in °C and K.
Answer:
20 °C, 293.15 K

Question 4.
Find the heat needed to raise the temperature of 5 kg of water from 20 °C to 25 °C. Write the answer in calorie as well as joule.
Answer:
25 × 10³ cal, 1.045 × 10⁵ J

Question 5.
When a substance having mass 2 kg absorbs 2000 cal of heat, its temperature increases by 10 °C. Find the specific heat of the substance.
Answer:
0.1 cal/(g.°C)

Question 6.
Find the heat needed to raise the temperature of 100 g of a metal through 10 °C if the specific heat of the metal is 0.1 cal/g. °C.
Answer:
100 cal

Question 7.
If water of mass 80 g and temperature 40 °C is mixed with water of mass 20 g and temperature 25 °C, what will be the maximum temperature of the mixture?
Answer:
37 °C

Question 8.
A metal rod 2.5 m long, increases in length by 1.25 mm when it is heated from 10 °C to 60 °C. Find the coefficient of linear expansion of the metal.
Answer:
1 × 10^-5 °C^-1

Question 9.
The surface area of a metal plate is 2 × 10^-2 m² at 10 °C. When the plate is heated to 60 °C, its area increases by 0.2 m². Find the coefficient of areal expansion of the metal.
Answer:
2 × 10^-5 °C^-1

Question 10.
A metal ball has volume 50 cm3 at 0 °C and 50.4 cm3 at 100 °C. Find the volumetric expansion coefficient of the metal.
Answer:
8 × 10^-5 °C^-1

Project:

Ref. Project. Useful information:
A bimetallic strip: A bimetallic strip consists of two strips of equal lengths but of different metals rivetted together. At room temperature the strip is straight.

Question 1.
The principle on which a bimetallic strip works:
Answer:
When two different metal strips of the same length at a given temperature are heated to the same higher temperature, they expand in different proportion.
A bimetallic strip of brass and iron is straight at room temperature. The expansion of brass is nearly 1.5 times that of iron. Hence, when this bimetallic strip is heated, it bends, making the iron side concave.

Question 2.
How a bimetallic strip is used in fire alarm:
Answer:
A bimetallic strip of brass and iron is

connected to a battery and an electric bell as shown in the diagram. One terminal of the bell is connected to a screw which is at a very small distance from the iron side of the strip. In case, there is an accidental fire, the bimetallic strip bends towards iron and touches the screw. Thus, the circuit is completed and the bell rings, thereby warning the people of the accidental fire.

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 16 Reflection of Light Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 16 Reflection of Light

Class 8 Science Chapter 16 Reflection of Light Textbook Questions and Answers

1. Fill in the blanks:

Question i.
The perpendicular to the mirror at the point of incidence is called …………. .
Answer:
The perpendicular to the mirror at the point of incidence is called the normal.

Question ii.
The reflection of light from a wooden surface is ……….. reflection.
Answer:
The reflection of light from a wooden surface is irregular reflection.

Question iii.
The working of a kaleidoscope is based on the properties of …………… .
Answer:
The working of a kaleidoscope is based on the properties of reflection of light.

2. Draw a figure describing the following: The reflecting surfaces of two mirrors make an angle of 90° with each other. If a ray incident on one mirror has an angle of incidence of 30°, i draw the ray reflected from the second mirror. What will be its angle of reflection?

Question a.
Draw a figure describing the following: The reflecting surfaces of two mirrors make an angle of 90° with each other. If a ray incident on one mirror has an angle of incidence of 30°, draw the ray reflected from the second mirror. What will be its angle of reflection?
Answer:
For the ray C, the angle of reflection = 60°.

3. How will you explain the statement ‘We cannot see the objects in a dark room’?

Question a.
How will you explain the statement ‘We cannot see the objects in a dark room’?
Answer:
In a room that is completely dark, no light falls on objects. Hence, no light enters our eyes. Hence, there is no sensation of vision, i.e., we cannot see the objects.

4. Explain the difference between regular and irregular reflection of light.

Question a.
Explain the difference between regular and irregular reflection of light.
Answer:
For regular reflection of light, the angles of incidence as well as the angles of reflection are the same for all parallel rays of light incident on the plane and smooth surface. Hence, the reflected rays are also parallel to one another.

For irregular reflection of light, the angles of incidence for parallel rays of light incident on the rough surface are not equal, and hence the angles of reflection are also not equal. Here, the reflected rays are not parallel to one another and spread over a large surface.

5. Draw a figure showing the following:
(a) Incident ray, (b) Normal, (c) Angle of incidence, (d) Angle of reflection, (e) Point of incidence, (f) Reflected ray.

Question a.
Draw a figure showing the following:
(a) Incident ray
(b) Normal
(c) Angle of incidence
(d) Angle of reflection
(e) Point of incidence
(f) Reflected ray.
Answer:

6. Study the following incident.

Swara and Yash were looking in a water-filled vessel. They could see their images clearly in the still water. At that instant, Yash threw a stone in the water. Now their images were blurred. Swara could not understand the reason for the blurring of the images.
Explain the reason for blurring of the images to Swara by answering the following questions:

Question i.
Is there a relation between the reflection of light and the blurring of the images?
Answer:
Yes.

Question ii.
Which types of reflection of light can you notice from this?
Answer:
Regular reflection of light when light is incident on the still water and irregular reflection of light when light is incident on the water as ripples are produced on its surface when a stone is thrown in the water.
Still water behaves as a plane and smooth surface while oscillating water behaves as a rough surface.

Question iii.
Are the laws of reflection followed in these types of reflection?
Answer:
Yes.

7. Solve the following examples.

Question a.
If the angle between the plane mirror and the incident ray is 40°, what are the angles of incidence and reflection?
Solution:
The angle between the plane mirror and the incident ray is 40°. Therefore, the angle of incidence (i) = the angle made by the incident ray with the normal to the plane mirror = 90° – 40° = 50°. The angle of reflection, r – i – 50°.

Question b.
If the angle between the mirror and reflected ray is 23°, what is the angle of incidence of the incident ray?
Solution:
The angle between the mirror and the reflected ray is 23°. Therefore, the angle of reflection (r) = the angle made by the reflected ray with the normal to the plane mirror = 90° – 23° = 67°.
∴ The angle of incidence, i = r = 67°.

Project:

Question a.
Apollo astronauts who stepped on the moon have kept some large mirrors there. Collect information about how the distance to the moon is measured using these.

Class 8 Science Chapter 16 Reflection of Light Important Questions and Answers

Rewrite the following statements by selecting the correct option:

Question 1.
If the angle made by the incident ray with the surface of a plane mirror is 30°, the angle of reflection must be …….. .
(a) 30°
(b) 90°
(c) 60°
(d) 15°
Answer:
If the angle made by the incident ray with the surface of a plane mirror is 30°, the angle of reflection must be 60°.

Question 2.
If the angle of incidence is 40°, the angle made by the reflected ray with the surface of the plane mirror must be ……. .
(a) 40°
(b) 50°
(c) 20°
(d) 80°
Answer:
If the angle of incidence is 40°, the angle made by the reflected ray with the surface of the plane mirror must be 50°.

Question 3.
If the angle of incidence is 20°, the angle made by the reflected ray with the normal to the surface must be ……… .
(a) 20°
(b) 70°
(c) 10°
(d) 40°
Answer:
If the angle of incidence is 20°, the angle made by the reflected ray with the normal to the surface must be 20°.

Question 4.
In a kaleidoscope, the mirrors are inclined to each other at ……. .
(a) 60°
(b) 30°
(c) 45°
(d) 90°
Answer:
In a kaleidoscope, the mirrors are inclined to each other at 60°.

Question 5.
In a periscope, the mirrors are ………….. .
(a) parallel to each other
(b) at right angles to each other
(c) inclined at 45° to each other
(d) inclined at 60° to each other
Answer:
In a periscope, the mirrors are parallel to each other.

Find the odd one out and give the reason:

Question 1.
Plane mirror, Plywood, Wood, Rough tile.
Answer:
Plane mirror. In this case, regular reflection of light takes place. In other cases, reflection of light is irregular.

State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)

Question 1.
The sense of vision is the most important among our five senses.
Answer:
True.

Question 2.
In a periscope, the angle between the incident ray and the normal to the mirror is 30°.
Answer:
False. (In a periscope, the angle between the incident ray and the normal to the mirror is 45°.)

Answer the following questions in one sentence each:

Question 1.
What is an incident ray?
OR
Define incident ray.
Answer:
A ray of light falling on a surface is called an incident ray.

Question 2.
What is the point of incidence?
OR
Define point of incidence.
Answer:
The point at which the incident ray strikes the surface is called the point of incidence.
[Note: It is also the point of reflection.]

Question 3.
What is the normal?
OR
Define normal.
Answer:
The perpendicular to a surface at the point of incidence is called the normal.

Question 4.
What is the reflected ray?
OR
Define reflected ray.
Answer:
The ray of light that leaves the surface at the point of reflection (the same as the point of incidence) is called the reflected ray.

Question 5.
What is the angle of incidence?
OR
Define angle of incidence.
Answer:
The angle between the incident ray and the normal is called the angle of incidence.

Question 6.
What is the angle of reflection?
OR
Define angle of reflection.
Answer:
The angle between the reflected ray and the normal is called the angle of reflection.

Try this:

Switch off the light in your room at night for some time and then turn it on again.

Question 1.
Could you see the objects in the room clearly when the light was switched off?
Ans.
No.

Question 2.
What did you feel when it was turned on again?
Answer:
We could see the objects clearly. From the above activity you can notice that there is some connection between the sense of vision and light. When we switch off the light at night, the objects in the room cannot be seen and they can be seen as before when the light is switched on again. Thus, we can see objects when the light coming from these objects enters our eyes.

Answer the following questions:

Question 1.
What is reflection of light?
Answer:
When light rays fall on an object, their direction changes and they turn back. This is called the reflection of light.

Try this:

Material:
Torch light, mirror, a stand for hanging the mirror, black paper, comb, white paper, drawing board.
Activity :
1. Fit a white paper tightly over a table or drawing board.
2. Leaving out some portion in the middle of the comb, cover the rest with black paper so that light can only pass through the open central portion.
3. Hold the comb perpendicular to the white paper and throw torch light on its central portion.
4. Adjust the comb and torch so as to get light rays on the white paper. Now keep a mirror in the path of this ray of light as shown in the figure.
5. What do you observe?

Answer:
Light rays which fall on the mirror get reflected and travel in a different direction.

Question 2.
State the laws of reflection of light.
Answer:

1. The angle of reflection is equal to the angle of incidence.
2. The incident ray, the reflected ray and the normal lie in the same plane.
3. The incident ray and the reflected ray are on the opposite sides of the normal.

Try this:

Verification of the laws of reflection of light.
Equipment: Mirror, drawing board, pins, white paper, protractor, scale, pencil.
Activity:

1. Fit a white paper on the drawing board tightly as possible.
2. On the paper draw a line PQ indicating the position of the mirror.
3. Draw a perpendicular ON to PQ at point O.
4. Draw a ray AO making an angle of 30° with ON.
5. Fix two pins S and R along AO.
6. Fix the mirror to a stand and place it along PQ perpendicular to the drawing board.
7. Fix pins at T and U along the line joining the bottom of the reflected images of the pins at S and R.
8. Remove the mirror and join the points T and U and extend it up to O.
9. Measure ZTON.
10. Repeat steps 4 to 9 for angle of incidence equal to 45° and 60° and write down the angles in the following table.

What relation do you find between the angle of incidence and the angle of reflection? If you have done the experiment carefully, you will find that the angle of incidence is equal to the angle of reflection in all three cases. This verifies the laws of reflection.

Question a.
What will happen when a light ray is incident perpendicular to the mirror?
Answer:

Here,
r = i = 90°.
Hence the light ray, on reflection, will retrace the path.

Question 3.
Figures (a) and (b) show three parallel rays, shown in grey, incident on smooth and rough surfaces. The reflected rays drawn using laws of reflection are shown in red.
1. Rays reflected from which surface are parallel to one another?
2. What conclusion can you draw from the figure?
Answer:
1. Rays reflected from the smooth surface are parallel to one another.

2.When the reflecting surface is plane and smooth, the angles of incidence (i) as well as of reflection (r) are the same for all parallel rays incident on the surface. If i₁, i₂, i₃, … are the angles of incidence for incident parallel rays, and r₁, r₂, r₃, …, are the corresponding angles of reflection, then, i₁ = i₂ = i₃ = ……. = r₁ = r₂ = r₃ = ….. This is called regular reflection. Here, the reflected rays are parallel to one another. If the reflecting surface is rough and parallel rays are incident on it, then the angles of incidence are not equal and hence the angles of reflection are also not equal. Here, i₁ ≠ i₂ ≠ i₃ … and r₁ ≠ r₂ ≠ r₃ …, but r₁ = i₁, r₂ = i₂, r₃ = i₃ … as laws of reflection are obeyed. This is called irregular reflection. [Fig.(b)]. Here, the reflected rays are not parallel to one another and spread over a large surface.

Question 4.
What is regular reflection of light?
Answer:
The reflection of light from a plane and smooth surface is called regular reflection of light.

Question 5.
What is irregular reflection of light?
Answer:
The reflection of light from a rough surface is called irregular reflection of light.

Always remember:

1. Laws of reflection are followed in both and regular and irregular reflection.
2. The reflection of light in irregular reflection has not been obtained because the laws of reflection are not followed. They are obtained because the surface is rough (irregular).
3. In irregular reflection, the angles of incidence at different points are different. But at any one point, the angles of incidence and reflection are equal, i.e. i₁ = r₁, i₂ = r₂ …..

Can you recall?

Reflection of reflected light :

Question 1.
How do you see if the barber m a saloon has cut the hair on your neck properly or not?
Answer:
In a saloon, there are mirrors in your front and at back. The image of the back of your head is formed in the mirror at the back. The image of this image is formed in the mirror in front of you. Thus you can see how the hair at the backside of your head is cut.

Question 2.
What type of image do we see in a mirror? What happens to the left and right sides?
Answer:
The image in a plane mirror is upright (erect) and of the same size as the object, but the left and right sides are interchanged. Our right hand appears to be the left hand in the image and the left hand appears to be the right hand in the image. (This is called lateral inversion.)

Question 3.
How do we see the image of the moon in water?
Answer:
The moon is not self luminous. The sunlight falling on the surface of the moon is reflected. This reflected light is again reflected by water to give us the image of the moon.

Try this:

Kaleidoscope:

Activity:

1. Take three rectangular mirrors of the same size.
2. Using sticking tape, stick the mirrors together making a triangle with the reflecting surface facing inwards (see Fig.).
3. Take a white paper of triangular shape and fix it with a tape at one end of the mirrors closing that end.
4. Insert 4 – 5 coloured glass pieces in the hollow of the mirrors.
5. Close the other end also with a paper and make a hole in it.
6. Look through the hole towards light. You will see innumerable images of the glass pieces. These are formed due to reflections by the three mirrors.

You can see different designs in the kaleidoscope. The speciality of a kaleidoscope is that the designs do not easily repeat themselves. Every time the design is different. People making wall papers which are used to decorate walls and cloth designers use a kaleidoscope for making new designs.

Periscope:
Activity:

1. Take a cardboard box. Make slits in the top and bottom sides of the box and place two mirrors so that they make an angle of 45° with the sides of the box and are parallel to each other. Fix them with a sticking tape.
2. Make two windows of 1 inch each near the two mirrors. Now see through the bottom window.
3. Make note of what you see.

From the bottom window, one can see what is in front of the top window. This device is called a periscope. This is used in submarines to see objects above the surface of water. It is also used to observe and keep a watch on the objects or persons on the ground from an underground bunker. The kaleidoscope and periscope both use the properties of reflection of light.

[Note: In a periscope, the angle of incidence is 45° and the two plane mirrors are parallel to each other. Hence, the emergent ray is parallel to the incident ray.]

Example questions for practice:

Question 1.
If the angle between the plane mirror and the incident ray is 20°, what is the angle between the reflected ray
and the plane mirror?
Answer:
20°.

Question 2.
See Fig. In terms of O, what are the angles (i) AON (ii) BON (iii) AOB (iv) BOQ?

Answer:
(i) 90° – θ (ii) 90° – θ (iii) 180° – 2θ

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 12 Introduction to Acid and Base Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 12 Introduction to Acid and Base

Class 8 Science Chapter 12 Introduction to Acid and Base Textbook Questions and Answers

1. Identify the following solutions, whether they are acid or base.

Question a.

Answer:

2. Write chemical names from given formulae.
H₂SO₄, Ca(OH)₂, HCl, NaOH, KOH, NH₄OH

Question a.
Write the chemical names from given formulae: H₂SO₄, Ca(OH)₂, HCl, NaOH, KOH, NH₄OH
Answer:

1. H₂SO₄ – Sulphuric acid
2. Ca(OH)₂ – Calcium hydroxide
3. HCl – Hydrochloric acid
4. NaOH – Sodium hydroxide
5. KOH – Potassium hydroxide
6. NH₄OH – Ammonium hydroxide

3. Sulphuric acid has highest importance in chemical Industry. Why?

Question a.
Sulphuric acid has highest importance in chemical Industry. Why?
Answer:
Answer:
Sulphuric acid has highest importance in the chemical industry because it is used in the manufacturing of fertilizers like ammonium sulphate and superphosphate of lime. It is used in the manufacturing of hydrochloric acid, nitric acid, phosphoric acid, ether, plastics and metal sulphates. It is also used in the manufacturing of dyes, drugs, perfumes, disinfectants and glue.

4. Give answers.

Question a.
Which acid is used for getting chloride salt?
Answer:
Hydrochloric acid is used for getting chloride salt.

Question b.
By squeezzing lemon on a piece of rock the gas liberated turned lime water milky. Which compound is present in the rock?
Answer:
Metal carbonate is present in the rock.

Question c.
The label on the bottle of chemical is spoiled. How will you find whether the chemical is acidic or not?
Answer:
The chemical is tested with blue litmus paper. If it turns red it is an acidic otherwise tested with red litmus paper, if it turns blue, it is an alkaline.

5. Answer the following questions. 

Question a.
Explain the difference between acid and base.
Answer:
Acids:

1. Acids have sour taste.
2. Acids turn blue litmus red.

Bases:

1. Bases have bitter taste.
2. Bases turn red litmus blue.

Question b.
Why indicator does not affect by salt?
Answer:
Mostly indicators are organic compounds which do not react with a salt.

Question c.
Which substances are produced i by neutralization process?
Answer:
Salt and water are produced in the f neutralization process.

Question d.
Which are the industrial uses of acids?
Answer:
Acids which are used in the industry are:

1. Sulphuric acid
2. Hydrochloric acid
3. Nitric acid.;

1. Sulphuric acid: Sulphuric acid is 5 used (a) in the manufacture of chemical? fertilizers like ammonium sulphate, (b) for cleaning gold and silver articles and (c) in car batteries.

2. Hydrochloric acid: Hydrochloric acid is used (a) to clean toilets and (b) to obtain glucose from starch and also for producing gelatine.

3. Nitric acid: Nitric acid is used (a) in the manufacture of perfumes (b) for engraving on copper, brass or silver and (c) in the manufacture of paints and explosives.

6. Select proper word given in bracket and fill in the blanks.

Question a.
Main constituent of acid is ……………. .
Answer:
Main constituent of acid is H⁺ ion.

Question b.
Main constituent of alkali is …………….. .
Answer:
Main constituent of alkali is OH^– ion.

Question c.
Tartaric acid is a …………… acid.
Answer:
Tartaric acid is a weak acid.

7. Match the pairs. 

Question a.

Group A	Group B
1. Tamarind	a. Acetic acid
2. Curd	b. Citric acid
3. Lemon	c. Tartaric acid
4. Vinegar	d. Lactic acid

Answer:

Group A	Group B
1. Tamarind	c. Tartaric acid
2. Curd	d. Lactic acid
3. Lemon	b. Citric acid
4. Vinegar	a. Acetic acid

8. State true or false.

Question a.
Oxides of metals are alkaline in nature.
Answer:
True.

Question b.
Salt is acidic.
Answer:
False. (Salt is neutral)

Question c.
Metal corrodes due to salts.
Answer:
False. (Acids and bases corrode metals)

Question d.
Salts are neutral.
Answer:
True. (Not all salts neutral)

9. Classify the following substances into acidic, basic and neutral group:
HCl, NaCl, MgO, KCl, CaO, H₂SO₄, HNO₃, H₂O and Na₂CO₃.

Question a.
Classify the following substances into acidic, basic and neutral group:
HCl, NaCl, MgO, KCl, CaO, H₂SO₄, HNO₃, H₂O and Na₂CO₃.
Answer:

Group	Substances
Acid	HCl, H2SO4, HNO3
Base	CaO, MgO, Na2CO3
Neutral	H2O, NaCl, KCl.

Project:

Question a.
Write in your own language the uses and importance of neutralization reaction in daily life.

Class 8 Science Chapter 12 Introduction to Acid and Base Important Questions and Answers

Fill in the blanks:

Question 1.
Acid reacts with metal to form …………. gas.
Answer:
Acid reacts with metal to form hydrogen gas.

Question 2.
DNA is an acid present in our body, it decides …………. properties.
Answer:
DNA is an acid present in our body, it decides heredity properties.

Question 3.
The chemical formula of milk of magnesia is ………….
Answer:
The chemical formula of milk of magnesia is Mg (OH)₂.

Question 4.
…………. are used to control hyperacidity.
Answer:
Antacids are used to control hyperacidity.

Question 5.
Alkali has …………. taste.
Answer:
Alkali has bitter taste.

Question 6.
Proteins are made up of ………….
Answer:
Proteins are made up of amino acids.

Question 7.
…………. is used in batteries.
Answer:
Dil. H₂SO₄ is used in batteries.

Rewrite the following statements by selecting the correct options:

Question 1.
The colour of phenolphthalein indicator in alkaline solution is ………….
(a) yellow
(b) green
(c) orange
(d) pink
Answer:
The colour of phenolphthalein indicator in alkaline solution is pink.

Question 2.
…………. is sour to taste.
(a) An acid
(b) An alkali
(c) A salt
(d) Alcohol
Answer:
An acid is sour to taste.

Question 3.
When phenolphthalein is added to NaOH, the colour of the solution will become ……………… .
(a) colourless
(b) red
(c) pink
(d) yellow
Answer:
When phenolphthalein is added to 5 NaOH, the colour of the solution will become pink.

Question 4.
When phenolphthalein is added to HCl, the colour of the solution will be ………….. .
(a) red
(b) pink
(c) green
(d) colourless
Answer:
When phenolphthalein is added to HCl, the colour of the solution will be colourless.

Question 5.
…………. is a natural indicator.
(a) Phenolphthalein
(b) Methyl orange
(c) Litmus
(d) Methyl red
Answer:
Litmus is a natural indicator.

Question 6.
The litmus paper or the litmus solution is obtained from …………. plants.
(a) moss
(b) rose
(c) hibiscus
(d) lichen
Answer:
The litmus paper or the litmus solution is obtained from lichen plants.

Question 7.
…………. is not an alkali.
(a) Sodium hydroxide
(b) Potassium hydroxide
(c) Copper hydroxide
(d) Calcium hydroxide
Answer:
Copper hydroxide is not an alkali.

Question 8.
…………. is a weak acid.
(a) Hydrochloric acid
(b) Nitric acid
(c) Carbonic acid
(d) Sulphuric acid
Answer:
Carbonic acid is a weak acid.

Question 9.
When methyl orange is added to HCl, the colour of the solution will be …………… .
(a) red
(b) pink
(c) yellow
(d) colourless
Answer:
When methyl orange is added to HCl, the colour of the solution will be pink.

Question 10.
When blue litmus paper is added to NaOH, the colour of the litmus paper will be ……………. .
(a) blue
(b) red
(c) pink
(d) yellow
Answer:
When blue litmus paper is added to NaOH, the colour of the litmus paper will be blue.

State whether the following statements are true or false. If a statement is false, correct it and rewrite:

Question 1.
Red cabbage is a natural indicator.
Answer:
True

Question 2.
Fats of our body are formed by fatty acids.
Answer:
True.

Question 3.
Ammonium hydroxide is used in the production of fertilizers.
Answer:
True.

Question 4.
Lime water is a weak acid.
Answer:
False. (Limewater is a weak base)

Question 5.
Orange colour of methyl orange turns yellow in acid.
Answer:
False. (Orange colour of methyl orange turns pink in acid)

Question 6.
Methyl red turns yellow in alkali.
Answer:
True.

Question 7.
Oxalic acid is used in aerated cold drinks.
Answer:
False. (Carbonic acid is used in aerated cold drinks).

Find the odd one out and justify:

Question 1.
Acetic acid, carbonic acid, hydrochloric acid, nitric acid.
Answer:
Acetic acid. (Others are mineral acids.)

Question 2.
Hydrogen chloride, sodium hydroxide, calcium oxide, ammonia.
Answer:
Hydrogen chloride. (Others are bases.)

Question 3.
HCl, CH₃COOH, H₂SO₄, HNO₃
Answer:
CH₃COOH. (Others are strong acids.)

Question 4.
NaOH, Ca(OH)₂, NH₄OH, Ba(OH)₂
Answer:
NaOH (Others are weak bases.)

Question 5.
H₂SO₄, H₂CO₃, HCl, HNO₃
Answer:
H₂CO₃ (Others are strong acids.)

Question 6.
Citric acid, formic acid, lactic acid, nitric acid.
Answer:
Nitric acid. (Others are organic acids.)

Question 7.
Lime, litmus, phenolphthalein, methyl orange.
Answer:
Lime. (Others are indicators.)

Match the following:

Question 1.

Column ‘A’	Column ‘B’
1. Strong acid	a. Magnesium hydroxide
2. Weak alkali	b. Carbonic acid
3. Weak acid	c. NaOH
4. Strong alkali	d. Nitric acid

Answer:

Column ‘A’	Column ‘B’
1. Strong acid	d. Nitric acid
2. Weak alkali	a. Magnesium hydroxide
3. Weak acid	b. Carbonic acid
4. Strong alkali	c. NaOH

Question 2.

Column ‘A’	Column ‘B’
1. Sodium hydroxide	a. Whitewashing
2. Magnesium hydroxide	b. Fertilizers
3. Calcium hydroxide	c. Washing soap
4. Ammonium hydroxide	d. Antacid

Answer:

Column ‘A’	Column ‘B’
1. Sodium hydroxide	c. Washing soap
2. Magnesium hydroxide	d. Antacid
3. Calcium hydroxide	a. Whitewashing
4. Ammonium hydroxide	b. Fertilizers

Define the following:

1. Acid: A substance which gives H⁺ ions in water is called an acid.

2. Alkali: A substance which gives OH^– ions in water is called an alkali.

3. Indicator: Substances which change their colours in presence of acid or base are called indicators.

4. Neutralization: The reaction between an acid and an alkali to form the r salt and water is termed as neutralization.

Answer the following questions in one sentence each:

Question 1.
What are natural acids?
Answer:
Acids present in foodstuffs are called natural acids.

Question 2.
State three vegetables from which natural indicators can be prepared.
Answer:
Natural indicators: Red cabbage, radish, tomato.

Question 3.
State names of any three strong acids.
Answer:

1. Hydrochloric acid
2. Sulphuric acid
3. Nitric acid.

Question 4.
State the names of the acids found in lemon juice, Amla, tamarind water and curd.
Answer:

1. Lemonuice – citric acid
2. Amla – ascorbic acid
3. tamarind water – tartaric acid
4. curd – lactic acid.

Question 5.
State names of any three alkalis.
Answer:

1. sodium hydroxide
2. potassium hydroxide
3. calcium hydroxide.

Question 6.
State the names of three indicators.
Answer:

1. Litmus paper
2. Methyl orange
3. Phenolphthalein.

Question 7.
State the names of three weak alkalis.
Answer:

1. Calcium hydroxide
2. ammonium hydroxide
3. magnesium hydroxide.

Question 8.
From which plant is litmus obtained?
Answer:
Litmus is obtained from plants called lichens.

Question 9.
Name the antacid which is used to control the hyper acidity.
Answer:
Milk of magnesia [Mg(OH)₂] is used to control the hyper acidity.

Question 10.
How will you neutralize the excess of acid present in the soil?
Answer:
Lime stone or lime water is mixed in the soil to neutralize the excess of acid.

Question 11.
When lemonuice falls on a marble kitchen counter, which is the gas that bubbled out?
Answer:
Carbon dioxide.

Answer the following questions:

Question 1.
What are indicators?
Answer:
Substances which change their colours in presence of acid or base are called indicators.

Question 2.
State two acid-base indicators and mention their colour change.
Answer:
Phenolphthalein and methyl orange are two acid-base indicators. Phenolphthalein is colourless in an acidic solution while it turns pink in a basic solution. Methyl orange gives orange colour with an acidic solution and yellow colour with a basic solution.

Question 3.
State the colour change for each of the following solutions with red litmus, blue litmus, phenolphthalein and methyl orange solutions.
Answer:

Question 4.
Name the acid present in (1) Orange (2) Vinegar (3) Tamarind (4) Curd (5) Tomato (6) Lemon.
Answer:

Substance	Acid
Orange	Citric acid
Vinegar	Acetic acid
Tamarind	Tartaric acid
Curd	Lactic acid
Tomato	Oxalic acid
Lemon	Citric acid

Question 5.
Classify the following into acidic substances, basic substances and salts.
(1) Lime water, (2) soda water, (3) soap water, (4) sea water, (5) sweet limeuice, (6) sugar caneuice, (7) buttermilk, (8) a mixture of ash in water, (9) tamarind water.
Answer:
a. Acidic substances: (1) Soda water, (2) sweet limeuice, (3) buttermilk, (4) tamarind water.
b. Basic substances: (1) Lime water, (2) Soap water, (3) a mixture of ash in water.
c. Salts: (1) Sea water, (2) sugar caneuice.

Question 6.
What happens when sour substances like limeuice, tamarind water falls on shahabad stones or kitchen platform? Why?
Answer:
When sour substances like limeuice, tamarind water falls on shahabad stones or kitchen platform, citric acid present in limeuice and tartaric acid in tamarind water reacts with metal carbonates present in shahabad stones or kitchen platform, carbon dioxide gas is evolved resulting in the formation of uneven surface.

Question 7.
Collect soil samples from your surroundings and find out whether it is acidic or alkaline or neutral?
Answer:
Soil samples collected from the surroundings are acidic in nature.

Question 8.
Which substances are used to clean greenish stains on copper vessels and to shine blackish silver utensils?
Answer:
Tamarind pulp is used to clean greenish stains on copper vessels. To shine blackish silver utensils, ammoniacal solution or limeuice or detergent is used.

Question 9.
Why toothpaste is used for brushing teeth?
Answer:

1. Toothpaste contains fluorides and alkali to neutralize the mouth acid.
2. Hence, the tooth paste, which is generally alkaline, is used for cleaning the teeth as it can neutralize the excess acid in i the mouth and prevent tooth decay.

Question 10.
State the properties of acids.
Answer:

1. Acids are sour in taste.
2. Acid molecules contain hydrogen ion (H⁺) as a main constituent.
3. Acid reacts with metal to form hydrogen gas.
4. Acid reacts with carbonates and liberates CO₂ gas.
5. Blue litmus turns red in acid.

Question 11.
State the uses of acids.
Answer:

1. Acids are used in the production s of chemical fertilizers.
2. Acids are used in the production of explosives, oil purification, medicines, dyes and paints.
3. Hydrochloric acid is used for the preparation of different types of chloride salts.
4. Dil. H₂SO₄ acid is used in the batteries (electric cell).
5. Dil. HCl is used for sterilization of water.
6. Acid is used for making of white paper from wood pulp.

Question 12.
The iron knife shines better after cutting the sour fruits like lemon, raw mangoes. Why?
Answer:
Acids present in sour fruits clean and dissolves the salts present on the surface of iron knife as a result iron knife shines better after cutting the sour fruits.

Question 13.
What is meant by neutralization? Give example.
Answer:
When an acid reacts with an alkali to form a salt and water, it is called neutralization.

Give scientific reasons:

Question 1.
When we have stomachache, doctors prescribe medicine containing magnesium hydroxide.
Answer:

1. There is hydrochloric acid in our stomach which helps in the digestion of food.
2. Sometimes in the stomach, there is more hydrochloric acid than we need.
3. This excess acid causes acidity and indigestion resulting in stomachache.
4. When magnesium hydroxide is administered it neutralizes the extra acid in the stomach.
5. Therefore, magnesium hydroxide is the best cure for stomachache.
6. So, when we have stomachache, doctors prescribe medicine containing magnesium hydroxide.

Question 2.
Quicklime or slaked lime is added to the soil.
Answer:

1. When chemical fertilizers are added to the soil, the soil becomes acidic.
2. To reduce its acidity quicklime or slaked lime is added to the soil.

Question 3.
Tarnished and stained copper vessels are brought to a shine by using tamarind pulp.
Answer:
In due course, unus6d copper vessels
are covered with a coating of black copper oxide and other compounds of copper which tarnish the vessel. Tamarind contains tartaric acid. When the vessel is rubbed with tamarind pulp, tartaric acid reacts with copper oxide and removes the layer. Thus, the copper vessel regains its shine.

Question 4.
Copper and brass utensils are tinned.
Answer:
Copper and brass reacts with i organic acids present in food materials and poisonous salts are formed. Tin does not react with organic acids present in food materials. Therefore, copper or brass vessels are tinned.

Distinguish between acid and alkali. OR Distinguish between the following:

Question 1.
Acid and Alkali:
Answer:

Acid	Alkali
1. Acid has sour taste.	1. Alkali has bitter taste.
2. Acid turns blue litmus red.	2. Alkali turns red litmus blue.
3. An acid in an aqueous solution gives H+ ions.	3. An alkali in an aqueous solution gives OH+ ions.
4. Oxides of non – metals form acids.	4. Oxides of metals form bases.

Activity-based questions:

Activity 1:
Apparatus: Hibiscus, rose, turmeric, red cabbage leaves, filter paper, etc.
Activity: Rub red petals of hibiscus flower on the white filter paper. This gives hibiscus indicator paper. Similarly rub, rose petals on the white filter paper. Cut strips of this paper, it is a rose indicator paper. Take turmeric powder, add a little water in it. Dip filter paper or ordinary paper in the turmeric water for some time.

After drying make strips of that paper. Prepare turmeric indicator paper in this way. Put leaves of red cabbage in small quantity of water and heat it. Once solution of cabbage leaves cool down, dip papers in it and dry it. Make strips of dried paper. In this way prepare red cabbage indicator paper. Put some drops of following substances on the indicator papers prepared by the above method and write the effect in the following table:

Substance	Effect on turmeric paper	Acidic/basic
1. Lime juice	Yellow	Acidic
2. Lime water (calcium hydroxide)	Red	Basic
3.

Activity 2:
Take baking powder. Add a little water to it. Add this solution on to limeuice, vinegar, orangeuice, appleuice, etc. and note the findings.
What do you observe on addition of baking soda solution in the fruituice? Whether bubbles formed or effervescence came out of fruituice?
From the above first activity we came to know that yellow turmeric indicator paper’s turns red in certain solutions. Similarly on addition of baking soda solution in the acidic solution bubbles come out or effervescence is produced.
By these simple and easy activity we can identify acidic or alkaline substance:
[Note for Activity 1 and Activity 2: Students should perform the experiments under the guidance of school teachers and record their observations.]

Activity 3:
Under the guidance of teacher take limeuice, ammonium hydroxide (NH₄OH), dil. hydrochloric acid (dil. HCl) and nitric acid (HNOs) in different test-tubes. Add drops of following indicators in them. Also dip litmus papers in the solutions. Observe and record in the following table.

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 13 Chemical Change and Chemical Bond Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 13 Chemical Change and Chemical Bond

Class 8 Science Chapter 13 Chemical Change and Chemical Bond Textbook Questions and Answers

1. Complete the statement by filling the gaps using appropriate term from the terms given in the brackets:
(slow, coloured, arrow, fast, smell, milky, physical, product, chemical, reactant, covalent, ionic, octet, duplet, exchange, sharing, equality sign)

Question a.
An ……….. is drawn in between the reactants and products while writing the equation for a chemical reaction.
Answer:
An arrow is drawn in between the reactants and products while writing the equation for a chemical reaction.

Question b.
Rusting of iron is a ……….. chemical change.
Answer:
Rusting of iron is a slow chemical change.

Question c.
The spoiling of food is a chemical change which is recognized from the generation of certain …………. due to it.
Answer:
The spoiling of food is a chemical change which is recognized from the generation of certain smell due to it.

Question d.
A colourless solution of calcium hydroxide in a test tube turns ………….. on blowing in it through a blow tube for some time.
Answer:
A colourless solution of calcium hydroxide in a test tube turns milky on blowing in it through a blow tube for some time.

Question e.
The white particles of baking soda disappear when put in lemon juice. This means that it is a ……….. change.
Answer:
The white particles of baking soda disappear when put in lemon juice. This means that it is a chemical change.

Question f.
Oxygen is a …………….. in respiration.
Answer:
Oxygen is a reactant in respiration.

Question g.
Sodium chloride is …………… compound while hydrogen chloride is compound.
Answer:
Sodium chloride is ionic compound while hydrogen chloride is covalent compound.

Question h.
Electron …………….. is complete in each hydrogen in a hydrogen molecule.
Answer:
Electron duplet is complete in each hydrogen in a hydrogen molecule.

Question i.
Chlorine (Cl₂) molecule is formed by ………….. of electrons between two chlorine atoms.
Answer:
Chlorine (Cl₂) molecule is formed by sharing of electrons between two chlorine atoms.

2. Explain by writing a word equation. 

Question a.
Respiration is a chemical change.
Answer:
Respiration is a biological process, in this process air is inhaled, oxygen present in this inhaled air reacts with glucose present in the cells of the body forming carbon dioxide and water. Moreover, we cannot obtain glucose and oxygen from carbon dioxide and water. Hence, respiration is a chemical change.
Word equation:

Question b.
Hard water gets softened on mixing with a solution of washing soda.
Answer:
Hard water does not form lather with soap and is brackish to taste. This is because hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state. When a solution of washing soda is added to hard water, it forms a precipitate of calcium carbonate and magnesium carbonate, which is removed by filtration thus water is softened.
Word equation:

Question c.
Limestone powder disappears on adding to dilute hydrochloric acids.
Answer:
In the reaction of dil. HCl and limestone powder (CaCO₃), limestone disappears slowly and carbon dioxide (CO₂) liberates slowly.
Word equation:

Question d.
Bubbles are seen on adding lemon juice to baking soda.
Answer:
When baking soda is added to lemon juice a chemical change takes place in citric acid present in the lemon juice and carbon dioxide gas is formed. Word equation:

This is a neutralization reaction.

3. Match the pairs.

Question a.

Column I	Column II
1. Photosynthesis	a. Tendency to lose electrons
2. Water	b. Reactant in combustion process
3. Sodium chloride	c. Chemical change
4. Dissolution of salt in water	d. Covalent bond
5. Carbon	e. Ionic bond
6. Fluorine	f. Physical change
7. Magnesium	g. Tendency to form anion

Answer:

Column I	Column II
1. Photosynthesis	c. Chemical change
2. Water	d. Covalent bond
3. Sodium chloride	e. Ionic bond
4. Dissolution of salt in water	f. Physical change
5. Carbon	b. Reactant in combustion process
6. Fluorine	g. Tendency to form anion
7. Magnesium	a. Tendency to lose electrons

4. Show with the help of diagram of electronic configuration how the following compounds are formed from the constituent atoms.

Question a.
Sodium Chloride:

Answer:
1. Sodium has atomic number 11 and electronic configuration 2, 8, 1.
2. Sodium atom has 1 electron in its outermost shell.

3. It loses one electron from its outermost shell, i.e., M shell. Then its L shell becomes the outermost shell with a stable octet. The nucleus of sodium atom has 11 protons but the number of electrons in the atom has become 10. So, there is a net unit positive charge giving a sodium cation (Na⁺).

4. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet.
5. Thus, the electron lost by sodium is taken up by chlorine.

6. When chlorine atom gains one electron, octet of chlorine is completed and its K, L, M shells have together 18 electrons and the nucleus has 17 protons. This leads to the formation of an ion (CP).

7. Thus, a chlorine atom accepts one electron from a sodium atom and consequently a chloride ion with one unit negative charge and a sodium ion with one unit positive charge are formed.

8. Sodium and chloride ions, being oppositely charged, attract each other due to the electrostatic force of attraction. An ionic bond is formed and this results in the formation of sodium chloride (NaCl) molecule.

Question b.
Potassium fluoride:
Answer:
1. Potassium has atomic number 19 and electronic configuration 2, 8, 8, 1.
2. Potassium atom has 1 electron in its outermost shell.

3. It loses one electron from its outermost shell, i.e. N shell. Then its M shell becomes the outermost shell with a stable octet. The nucleus of potassium atom has 19 protons but the number of electrons in the atom has become 18. So there is a net unit positive charge giving a potassium cation (K⁺).

4. On the other hand, fluorine has electronic configuration 2, 7. Fluorine has 7 electrons in the outermost shell and requires one electron to complete its octet.

5. Thus, the electron lost by potassium is taken up by chlorine.

6. When fluorine atom gains one electron, octet of fluorine is completed, its K and L shells have together 10 electrons and the nucleus has 9 protons. This leads to the formation of an ion (F^–).

7. Thus, a fluorine atom accepts one electron from a potassium atom and consequently a fluoride ion with one unit negative charge and a potassium ion with one unit positive charge are formed.

8. Potassium and fluoride ions, being oppositely charged, attract each other due to electrostatic force of attraction. An ionic bond is formed and this results in the formation of potassium fluoride (KF) molecule.

Question c.
Water:
Answer:

1. Hydrogen has atomic number 1 and electronic configuration 1.
2. Hydrogen has 1 electron in its K shell.

3. Oxygen has atomic 8 and electronic configuration 2, 6. There are 6 electrons in the valence shell of oxygen atom. It means that the electron octet in oxygen is short of two electrons and the valency of oxygen is two.

4. In the H₂O molecule, the oxygen atom complete its octet by sharing two electrons one each with two hydrogen atoms, thus, forming two covalent bonds. While this happens, the duplets of two hydrogen atoms are completed.

Question d.
Hydrogen chloride:
Answer:
1. Hydrogen has atomic number 1 and electronic configuration 1, that means it has 1 electron in its K shell and its duplet is short of one electron therefore, the valency of hydrogen is one.

2. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet.

3. The two atoms, hydrogen and chlorine share one electron with each other. As a result, the electron duplet of hydrogen and octet of chlorine is complete and a covalent band is formed between them.

Can you recall?

Question a.
What are the methods of classification of changes?
Answer:
The methods of classification of changes: Physical change and chemical change.

Question b.
What is the difference between physical and chemical change?
Answer:

1. In physical change, the composition of substance does not change. No new substance is formed.
2. In chemical change, the composition of compounds change and new compounds are formed.

Question c.
Classify the following changes into physical and chemical change. Ripening of mango, melting of ice, boiling of water, dissolution of salt in water, Ripening of banana, fragrance on ripening fruit, darkening of a cut potato, bursting of an inflated balloon, sound of bursting fire cracker, foul smell from a portion of spoiled food.
Answer:

• Physical change: Melting of ice, boiling of water, dissolution of salt in water.
• Chemical change: Ripening of mango, ripening of banana, fragrance of ripening fruit, darkening of a cut potato, bursting of an inflated balloon, sound of bursting firecracker, foul smell from a spoiled food.

Project:

Question a.
Prepare a list of the chemical changes that occur in your house and surroundings and discuss these in the class.

Class 8 Science Chapter 13 Chemical Change and Chemical Bond Important Questions and Answers

Fill in the blanks:

Question 1.
……………. is a continuously occurring biological process.
Answer:
Respiration is a continuously occurring biological process.

Question 2.
The reaction between citric acid and sodium bicarbonate is a ……………. reaction.
Answer:
The reaction between citric acid and sodium bicarbonate is a neutralization reaction.

Question 3.
Combustion of fuel is a ………… and ……………. chemical change.
Answer:
Combustion of fuel is a fast and irreversible chemical change.

Question 4
Electronic configuration of sodium is …………….
Answer:
Electronic configuration of sodium is 2, 8, 1.

Question 5.
Electronic configuration of chlorine is …………….
Answer:
Electronic configuration of chlorine is 2, 8, 7.

Question 6.
A chemical bond formed by sharing of valence electrons of two atoms with each other is called a …………….
Answer:
A chemical bond formed by sharing of valence electrons of two atoms with each other is called a covalent bond.

Question 7.
Hard water contains the chloride and sulphate salts of ……………. and ……………. in dissolved state.
Answer:
Hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state.

Question 8.
Electronic configuration of fluorine is …………….
Answer:
Electronic configuration of fluorine is 2, 7.

Question 9.
Green plants perform ……………. in sunlight.
Answer:
Green plants perform photosynthesis in sunlight.

Question 10.
Melting of ice is a ……………. change.
Answer:
Melting of ice is a physical change.

Question 11.
The chloride ion has a ……………. charge.
Answer:
The chloride ion has a negative charge.

Question 12.
A covalent bond between two atoms is also represented by ……………. joining their symbols.
Answer:
A covalent bond between two atoms is also represented by dash joining their symbols.

Rewrite the following statements by selecting the correct options:

Question 1.
Sodium atoms and sodium ions ………….. .
(a) are chemically the same
(b) have the same number of protons
(c) have the same number of electrons
(d) form covalent bond
Answer:
(b) have the same number of protons

Question 2.
An ionic bond is formed when …………….. .
(a) two metallic elements react
(b) two nonmetallic elements react
(c) a metallic element reacts with a non-metallic element
(d) a pair of elements react
Answer:
(c) a metallic element reacts with a non-metallic element

Question 3.
…………….. tries to establish the duplet state in its outermost orbit by sharing electrons.
(a) Sodium
(b) Potassium
(c) Hydrogen
(d) Magnesium
Answer:
(c) Hydrogen

Question 4.
…………… is an electron donor.
(a) Helium
(b) Iodine
(c) Chlorine
(d) Magnesium
Answer:
(d) Magnesium

Question 5.
………………. combine to form an ionic compound.
(a) Hydrogen and chlorine
(b) Hydrogen and oxygen
(c) Potassium and chlorine
(d) Nitrogen and oxygen
Answer:
(c) Potassium and chlorine

Question 6.
……………. is an example of chemical change.
(a) Magnetism of iron
(b) Rusting of iron
(c) Heating of iron till it becomes red hot
(d) Dissolution of salt in water
Answer:
(b) Rusting of iron.

State whether the following statements are True or False. (If a statement is false, correct it and rewrite it.)

Question 1.
The preparation of cold drink soda- lemon is a physical change.
Answer:
False. [The preparation of cold drink soda-lemon is a chemical change.]

Question 2.
Hard water contains the chloride and sulphate salts of calcium and magnesium in dissolved state.
Answer:
True.

Question 3.
Combustion of fuel is a fast and irreversible man-made chemical change.
Answer:
True.

Question 4.
Photosynthesis reaction is a man-made chemical change.
Answer:
False. [Photosynthesis reaction is a natural chemical change.]

Question 5.
The atoms with incomplete electron octet/duplet form chemical bonds.
Answer:
True.

Question 6.
Electronic configuration of chlorine is 2, 8, 6.
Answer:
False. (Electronic configuration of chlorine is 2, 8, 7.)

Question 7.
One ionic bond is formed due to the electrical change +1 or -1 on an ion.
Answer:
True.

Question 8.
H₂O Molecule is an ionic compound.
Answer:
False. (H₂O molecule is a covalent compound.)

Question 9.
The bond between two chlorine atoms is a covalent band.
Answer:
True.

Question 10.
Arrow indicates the direction of the reaction.
Answer:
True.

Consider the correlation between the words of the first pair, match the third word/words with the most appropriate answer:

Question 1.
K : 2, 8, 8, 1 : : Mg : ………………
Answer:
2, 8, 2

Question 2.
MgCl₂ : Ionic bond : : CaO : ……………..
Answer:
Covalent bond

Question 3.
Photosynthesis : Natural chemical change : : Cold drink, soda lemon : ………
Answer:
Man-made chemical change

Question 4.
Respiration: Glucose + Oxygen : : Neutralization : ………….
Answer:
Acid + alkali.

Match the columns:

Question 1.

Column I	Column II
1. Respiration	a. Potassium and fluorine
2. Acid + Base	b. Glucose and oxygen
3. Photosynthesis	c. Carbon dioxide and water
4. Ionic bond	d. Salt and water

Answer:

Column I	Column II
1. Respiration	c. Carbon dioxide and water
2. Acid + Base	d. Salt and water
3. Photosynthesis	b. Glucose and oxygen
4. Ionic bond	a. Potassium and fluorine

Define the following:

• Chemical change: In a chemical change, the chemical composition of the original matter changes and new substances having different properties and different chemical composition are formed.
• Ionic bond: The chemical bond formed due to an electrostatic force of attraction between the oppositely charged cation and anion is called an ionic bond or an electrovalent bond.
• Covalent bond: The chemical bond formed by sharing of valence electrons of two atoms with each other is called a covalent bond.

Answer the following questions in one sentence each:

Question 1.
Name the reactants in respiration.
Answer:
Glucose and oxygen are the reactants in respiration.

Question 2.
Name the products of respiration.
Answer:
Carbon dioxide and water are the products of respiration.

Question 3.
Name the reactants in photosynthesis.
Answer:
Carbon dioxide and water are the reactants in photosynthesis.

Question 4.
Name the products of photosynthesis.
Answer:
Glucose and oxygen are the products of photosynthesis.

Question 5.
Name the salts present in hard water.
Answer:
Salts present in hard water are calcium chloride, magnesium chloride, calcium sulphate and magnesium sulphate.

Question 6.
Give two examples of ionic compounds.
Answer:
Ionic compounds: Sodium chloride (NaCl), Potassium fluoride (KF).

Question 7.
Give two examples of covalent compounds.
Answer:
Covalent compounds: Hydrogen (H₂), Water (H₂O).

Question 8.
Name an acid used for cleaning Shahabad tile.
Answer:
An acid used for cleaning Shahabad tile is dilute hydrochloric acid (HCl).

Question 9.
Write a chemical equation for combustion of fuel.
Answer:
Chemical equation:
C + O₂ → CO₂

Question 10.
Write a chemical equation for photosynthesis.
Answer:
Chemical equation:

Answer the following questions:

1. Explain by writing a word equation.

Question 1.
Combustion of fuel is a fast and irreversible chemical change.
Answer:
Wood, coal, petrol or cooking gas are burnt for producing energy. Carbon is the common substance that burns in all these fuels. The product carbon dioxide is formed when carbon combines with oxygen in the air during the combustion process. We cannot obtain fuel from carbon dioxide by employing any other method. Properties of carbon dioxide are altogether different from those of fuel. Hence, this change is a irreversible chemical change.
Word equation:
Carbon + Oxygen → Carbon dioxide

Question 2.
Dilute hydrochloric acid is used for cleaning Shahabad tiles.
Answer:
The main constituent of Shahabad tile is calcium carbonate. During its cleaning with hydrochloric acid, the upper layer of the tile reacts with hydrochloric acid and three products are formed. One of them is calcium chloride, which being soluble in water, gets washed away with water. The second product is carbon dioxide, it mixes with air. The third product is water.
Word equation:

2. Write a chemical equation (unbalanced) for the following reactions:

Question 1.

Answer:
Chemical equation:
CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

Question 2.

Answer:
Chemical equation:
CaCO₃ + HCl → CaCl₂ + CO₂ + H₂O

Question 3.
Magnesium salts during the softening of hard water.

Answer:
Chemical equation:
MgCl₂ + Na2CO₃ → MgCOg + 2NaCl

3. Show with the help of diagram of electronic configuration how the following compounds are formed from the constituent atoms.

Question 1.
Hydrogen molecule:
Answer:
1. Hydrogen has atomic number 1 and electronic configuration 1. That means it has 1 electron in its K shell and its duplet is short of one electron therefore, the valency of hydrogen is one.

2. The two atoms of hydrogen are identical, they share their electrons with each other.
3. As a result, the electron duplet of both the hydrogen atoms is complete and a covalent band is formed between them.

4. There is one covalent bond between the component atoms H and Cl of the molecule HCl. Use this information to represent the formation of HCl molecules from H and Cl atoms diagrammatically.
(Use your brainpower)
Answer:
Hydrogen chloride:
1. Hydrogen has atomic number 1 and electronic configuration 1, that means it has 1 electron in its K shell and its duplet is short of one electron therefore, the valency of hydrogen is one.

2. On the other hand, chlorine has electronic configuration 2, 8, 7. Chlorine atom has 7 electrons in its outermost shell and requires one electron to complete its octet.

3. The two atoms, hydrogen and chlorine share one electron with each other. As a result, the electron duplet of hydrogen and octet of chlorine is complete and a covalent band is formed between them.

5. Show the formation of the following ionic compounds from the corresponding elements using two methods namely, numerical and diagrammatic representation of electronic configuration.
(a) K⁺ F^–, from 19K and 9F, (b) Ca²⁺ O^2- from ₂₀Ca and ₈O.
(Use your brainpower)
Answer:
(a) K⁺F^– from ₁₉K and ₉F
Potassium fluoride:
1. Potassium has atomic number 19 and electronic configuration 2, 8, 8, 1.
2. Potassium atom has 1 electron in its outermost shell.

3. It loses one electron from its outermost shell, i.e. N shell. Then its M shell becomes the outermost shell with a stable octet. The nucleus of potassium atom has 19 protons but the number of electrons in the atom has become 18. So there is a net unit positive charge giving a potassium cation (K⁺).

4. On the other hand, fluorine has electronic configuration 2, 7. Fluorine has 7 electrons in the outermost shell and requires one electron to complete its octet.

5. Thus, the electron lost by potassium is taken up by chlorine.

6. When fluorine atom gains one electron, octet of fluorine is completed, its K and L shells have together 10 electrons and the nucleus has 9 protons. This leads to the formation of an ion (F^–).

7. Thus, a fluorine atom accepts one electron from a potassium atom and consequently a fluoride ion with one unit negative charge and a potassium ion with one unit positive charge are formed.

8. Potassium and fluoride ions, being oppositely charged, attract each other due to electrostatic force of attraction. An ionic bond is formed and this results in the formation of potassium fluoride (KF) molecule.

(b) Ca²⁺O^2- from ₂₀Ca and ₈O.

Distinguish between the following:

Question 1.
Physical change and Chemical change:
Answer:

Physical change	Chemical change
1. In this change, the composition of the substance does not change. No new substance is formed.	1. In this change, the composition of the compounds change and new compounds are formed.
2. In this case, physical properties such as state, colour, density, etc. are changed.	2. In this case, physical and chemical properties are entirely changed.
3. This change is temporary.	3. This change is permanent.
4. In this case, the original substance can be recovered by simple means or by merely reversing the process.	4. In this case, the original substance cannot be recovered by easy means or by reversing the process.

Question 2.
Ionic bond and Covalent bond:
Answer:

Ionic bond	Covalent bond
1.  Ionic bond is formed due to the transfer of electrons from one atom to another.	1. Covalent bond is formed due to the sharing of electrons between two or more atoms.
2. Atoms of metals and nonmetals combine to form ionic bonds.	2. Atoms of nonmetals combine to form covalent bonds.
3. Molecules of the compounds formed due to ionic bond split up into ions in aqueous solution.	3. Molecules of the compounds formed due to covalent bond so not split up into ions in a solution.

Give scientific reasons:

Question 1.
Ionic compounds are formed due to the combination of metallic and nonmetallic atoms.
Answer:
Metallic atoms have a tendency to lose electrons from their outermost orbits to establish the octet state in their penultimate orbits. Conversely, nonmetallic atoms gain electrons to establish the octet state of their outermost orbits.

When a metallic atom and a nonmetallic atom come close together, the metallic atom loses electrons and gets c converted into positively charged ion, while the nonmetallic’ atom gets converted into negatively charged ions so formed, develop an ionic bond and this results in the formation of an ionic compound. Hence, ionic compounds are formed due to the combination of metallic and nonmetallic atoms.

Activity-based questions:

Activity 1:

Take the lemon juice in a clean glass. Take two drops of the lemon juice in a spoon and taste. Add a pinch of baking soda in the glass of lemon juice. Did you notice bubbling around the particles of soda? Did you hear a sound on taking your ear near the glass? Now again taste it. Did it taste as sour as it was in the beginning? (Above activity is to be done using clean apparatus and edible material. Then only it is possible to test the ’taste’, otherwise keep in mind that the testing of ‘taste’ cannot be done.)

Activity 2:
Take some freshly prepared lime water (solution of calcium hydroxide) in a test tube. Keep on blowing in it with a blow tube. What is seen after some time? Did the colourless lime water turn milky? After some more time you will find that a white insoluble solid settles at the bottom of the test tube. This is a precipitate of calcium carbonate. The turning lime water milky means that the blown gas mixed in it was carbon dioxide.

Write a chemical equation for the above word equation.
Chemical equation:
CO₂ + Ca(OH)₂ → CaCO₃ + H₂O

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 11 Human Body and Organ System Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 11 Human Body and Organ System

Class 8 Science Chapter 11 Human Body and Organ System Textbook Questions and Answers

1. Find out my partner.

Question a.

Group ‘A’	Group ‘B’
1. Heartbeats	a. 350 ml
2. RBC	b. 7.4
3. WBC	c. 37° C
4. Blood donation	d. 72 per min
5. Normal body temperature	e. 50 – 60 lakh/mm3
6. pH of oxygenated blood	f. 5000 – 6000 per mm3

Answer:

Group ‘A’	Group ‘B’
1. Heartbeats	d. 72 per min
2. RBC	e. 50 – 60 lakh/mm3
3. WBC	f. 5000 – 6000 per mm3
4. Blood donation	a. 350 ml
5. Normal body temperature	c. 37° C
6. pH of oxygenated blood	b. 7.4

2. Complete the following table.

Question a.

Answer:

3. Draw neat and labeled diagrams. 

Question a.
Respiratory system.
Answer:

Question b.
Internal structure of heart.
Answer:

4. Explain with reasons.

Question a.
Human blood is red coloured.
Answer:
The red colour of human blood is due to hemoglobin which is a red coloured conjugated protein with iron that is present on the red blood cells. Therefore, it looks red.

Question b.
Upward and downward movement of diaphragm occurs consecutively.
Answer:
The breathing movements are possible due to contraction and relaxation of the diaphragm. The rib muscles also help in these movements. When the ribs rise and diaphragm is lowered at the same time, then there is a decrease in pressure on lungs.

This causes movement of air into the lungs at the time of inhalation. On the other hand, when ribs come back to their normal position and diaphragm is risen, then pressure on the lungs increases. This causes movement of the air out of the body through the nose in the form of exhalation. These movements are possible only due to consecutive upward and downward movement of the diaphragm.

b

Question c.
Blood donation is considered to be superior of all donations.
Answer:
Blood cannot be manufactured by any artificial chemical process. The only way to obtain blood is by donations of blood from a live donor. Blood is needed at times of emergency. The life of person can be saved if timely blood transfusion is given to the needy victim or a patient. Since such donation can save a valuable human life, it is called superior of all donations.

Question d.
Person with ‘O’ blood group is considered as ‘universal donor’.
Answer:
Person with ‘O’ blood group does not have any antigen on his/her RBCs. The ‘O’ type blood thus cannot cause clotting reactions in the body of the recipients. Such persons with ‘O’ blood group can donate blood to any person having any blood group therefore they are considered as ‘universal donor’.

Question e.
Food must have limited amount of salts.
Answer:
More salt in diet means more sodium ions. These extra sodium salts cause rise in blood pressure. Such condition is called hypertension. This condition can be dangerous and fatal in some cases. Therefore, one must keep control over sodium content of the food.

5. Answer the following questions in your own words.

Question a.
Explain the functional correlation of circulatory system with respiratory, digestive and excretory system.
Answer:
1. Three systems viz. respiratory, digestive and circulatory always work in coordination.
2. Digestive system helps in breaking down complex food molecules into simple soluble nutrients at the end of the digestion process.
3. The soluble nutrients are absorbed in the circulating blood in the villi of the intestine.
4. The blood carries these nutrients to each cell during its circulation.
5. The respiratory system helps the oxygen from the air to be absorbed in the blood.
6. This process takes place in alveolus present in lungs. The oxygen is absorbed in the blood and through haemoglobin it is taken to every cell of the body. At the same time the unwanted carbon dioxide produced in each cell is given out in a process of gaseous exchange.
7. The soluble nutrients, and chiefly glucose is metabolized with the help of oxygen-producing energy. Thus, all the three systems bring about coordinated functions to keep the body alive.

Question b.
Explain the structure and function of human blood.
Answer:
I. Structure, i.e. components of the human blood: Human blood is a fluid connective tissue consisting of blood plasma and blood corpuscles suspended in it.

1. Plasma: Plasma is the fluid part of the blood which is pale yellow in colour. It is slightly alkaline in nature. It has 90-92% water, 6-8 % proteins and 1-2 % inorganic salts.
It contains proteins such as albumin, globulin, fibrinogen, etc. There are inorganic ions such as Ca, Na and K.

2. Blood cells:
a. Blood cells are mainly of three types, viz. RBCs, WBCs and blood platelets. They are produced in the red bone marrow.
b. RBCs are small, circular and enucleated cells. They are full of haemoglobin which is essential in transporting oxygen. RBCs are red blood cells which are 50 to 60 lakh per cubic millimetre. Their life span is 100 to 127 days.
c. WBCs are large, nucleated and colourless. They are of five subtypes, viz. neutrophils, basophils, eosinophils, monocytes and lymphocytes. They are 5 to 10 thousands per millimetre of blood.
d. Platelets are very small disc-shaped blood cells which are 2.5 to 4 lakh per cubic millimetre of blood.

II. Function of human blood:

1. Transport functions:

• Gases: Oxygen is carried via blood from lungs to cells in various parts of body and carbon dioxide from tissues to lungs.
• Nutrients: Simple nutrients like glucose, amino acids, fatty acids are taken up by blood from wall of alimentary canal and transported up to each cell in the body.
• Waste materials: Nitrogenous wastes like ammonia, urea, creatinine are released by tissues into blood which carries those to kidney for excretion.
• Enzymes and hormones: Blood transports the enzymes and hormones from the site of their production to the site of their action.

2. Protection: Antibodies are produced in the blood and they protect the body from microbes and other harmful particles.
3. Thermoregulation: Body temperature is maintained constant at 37 °C by vasodilation and vasoconstriction.
4. Maintaining the balance of minerals like Na, K in the body.
5. If bleeding occurs at the injury, platelets and a protein called fibrinogen of the blood form a clot and seal the injury.
6. Functions of blood cells:

• RBCs: With haemoglobin it carries out transport of respiratory gases.
• WBCs: Soldiers of the body. Produce antibodies and give immunity to body.
• Platelets: Help in blood clotting.

Question c.
Explain the importance and need of blood donation.
Answer:
Blood can never be synthesized artificially. There is no substitute for natural blood. Every healthy person possesses about 5 litres of blood in his or her body. In case of haemorrhage i.e. blood loss, the blood volume may reduce which can result into threat to life. Moreover, the loss of blood should be immediately taken care of, otherwise it may cost the life.

Therefore blood transfusion is very crucial in case of victims of accidents, patients of surgeries or mothers who suffer from blood loss during childbirth (parturition). Some diseases such as thalassemia, blood cancer, etc. also need regular transfusions. Therefore, blood is always needed in many such conditions. Blood donation is only option for such transfusions.

6. Explain the differences.

Question a.
Arteries and veins.
Answer:

Arteries	Veins
1. Arteries carry blood away from the heart to the tissues of the body.	1. Veins carry blood from the tissues of the body back to the heart.
2. Arteries are located deeper within the body.	2. Veins are usually located superficially beneath the surface of the skin.
3. Arteries are thick walled	Veins are thin walled.
4. Arteries do not have valves.	4. Veins have valves.
5. Arteries would generally remain open if blood flow stopped, due to their thick muscular layer.	5. Veins would collapse if blood flow stops.
6. Except pulmonary artery, all arteries carry oxygenated blood.	6. Except pulmonary vein, all veins carry deoxygenated blood.
7. Arteries are more muscular than veins, which helps in transporting blood that is full of oxygen efficiently to the tissues.	7. Veins are less muscular than arteries, but contain valves to help keep blood flowing in the right direction, usually toward the heart.
8. There is maximum blood pressure in the arteries.	8. There is minimum blood pressure in the veins.

Question b.
External and internal respiration.
Answer:

External respiration	Internal respiration
1. Intake of air from the outside into the body and release of air from the body to outside is called external respiration.	1. Exchange of gases between cells and tissue fluid is called internal respiration.
2. External respiration occurs between cells and the external environment.	2. Internal respiration occurs only in the cells of the body.
3. It involves processes of inspiration and expiration.	3. It involves movement of O2 from blood into tissue fluid and movement of CO2 from tissue.
4. External respiration involves breathing and gaseous exchange.	4. Internal respiration involves neither breathing nor gaseous exchange.
5. Oxygen combines with haemoglobin in external respiration.	5. Chemical reactions occur in the cells to form energy.

7. Which health parameters of blood donor should be checked? 

Question a.
Which health parameters of blood donor should be checked?
Answer:
Blood donor should be healthy. He or she should have good haemoglobin’s content. The RBC and WBC count should also be normal. They should not carry any parasites in their blood such as malarial parasite or dengue virus. The donor should not be HIV positive or should not have any infectious diseases. He should not have any addictions such s drug-abuse or alcohol consumption.

8. Fill in the blanks using appropriate words given in the bracket.
(hemoglobin, alkaline, diaphragm, red bone marrow, acidic, voluntary, involuntary,)

Question a.
RBCs of the blood contain ……….., an iron compound.
Answer:
RBCs of the blood contain haemoglobin, an iron compound.

Question b.
……………….. is present between thoracic and abdominal cavity.
Answer:
Diaphragm is present between thoracic and abdominal cavity.

Question c.
Cardiac muscles are …………… .
Answer:
Cardiac muscles are involuntary.

Question d.
pH of oxygenated blood is …………… .
Answer:
pH of oxygenated blood is alkaline.

Question e.
Production of RBCs occurs in ……………… .
Answer:
Production of RBCs occurs in red bone marrow.

8. Find odd one out.

Question a.
A, O, K, AB, B.
Answer:
K (All others are blood groups.)

Question b.
Blood plasma, platelets, blood transfusion, blood corpuscles.
Answer:
Blood transfusion (All others are components of blood.)

Question c.
Trachea, alveoli, diaphragm, capillaries.
Answer:
Capillaries (All others are parts of respiratory system. Capillaries exist throughout the body.)

Question d.
Neutrophils, globulins, albumins, prothrombin.
Answer:
Neutrophils (All others are proteins present in the plasma.)

10. Read the following paragraph and identify the disease.

Today, her child became one and half year old. However, that child does not seem to be healthy and happy. It was continuously crying and gradually becoming weak. It has shortness of breath. Its nails have become blue.
Answer:
The heart of the child is not functioning properly. Bluish nails show lack of oxygen, thus the baby may be suffering also from respiratory problems.

11. Your neighboring uncle has been diagnosed with hypertension. What should he do to keep his blood pressure within normal range?

Question a.
Your neighboring uncle has been diagnosed with hypertension. What should he do to keep his blood pressure within normal range?
Answer:
Hypertension has many causes. Try to find out what is the exact cause. Is it lack of exercise, obesity, lots of fast and junk food consumption, over-intake of salt, mental tension, etc. He should visit a proper physician and take prescribed blood pressure control medicines. He should never miss a single tablet. He should avoid salty and preserved food. He should practice yoga and meditation. He should also undertake some stress- management techniques.

Project:

Question a.
Collect information about various modern treatments on heart diseases.

Class 8 Science Chapter 11 Human Body and Organ System Important Questions and Answers

Rewrite the statements after correcting them:

Question 1.
Cells need supply of insoluble nutrients and oxygen for the energy production.
Answer:
Cells need the supply of soluble nutrients and oxygen for the energy production.

Question 2.
Respiratory system and respiration begins with mouth.
Answer:
Respiratory system and respiration begins with nose.

Question 3.
A lung is present on either sides of heart in abdominal cavity.
Answer:
A lung is present on either sides of heart in thoracic cavity.

Question 4.
Continuous upward and downward movement of diaphragm is necessary to bring about the beating of heart.
Answer:
Continuous upward and downward movement of diaphragm is necessary to bring about the breathing.

Question 5.
Blood vessels which carry the blood away from heart are called veins.
Answer:
Blood vessels which carry the blood away from heart are called arteries.

Question 6.
William Harvey described the blood groups in man.
Answer:
William Harvey described the mechanism of circulation in the body.

Question 7.
Capillaries unite together to form the arteries.
Answer:
Capillaries unite together to form the veins.

Match the columns/Find out my partner:

Question 1.

Group ‘A’	Group ‘B’
1. William Harvey	a. Blood group AB.
2. Carl Landsteiner	b. A, B, O blood group system.
3. Decastello and Sturli	c. Mechanism of circulation of blood.

Answer:

Group ‘A’	Group ‘B’
1. William Harvey	c. Mechanism of circulation of blood.
2. Carl Landsteiner	b. A, B, O blood group system.
3. Decastello and Sturli	a. Blood group AB.

Complete the following table:

Question 1.

Answer:

Type	Systolic pressure	Diastolic pressure
Normal blood pressure	90 – 119 mmHg	60 – 79 mmHg
Primary hypertension	120 – 139 mmHg	80 – 89 mmHg
Hypertension stage – I	140 – 159 mmHg	90 – 99 mmHg
Hypertension stage – II	> 160 mmHg	> 100 mm

Define the following terms:

1. Inhalation: Inhalation is taking in air through the nose from the surrounding
2. Exhalation: Exhalation is giving out the air back to the outer environment.
3. External respiration: The processes of inhalation and exhalation both together are called external respiration.
4. Internal respiration: Exchange of gases between cells and tissue fluid is called internal respiration.
5. Cellular respiration: Production of energy in the form of ATP from oxidation of glucose and other soluble nutrients is called cellular respiration.
6. Thermoregulation: Maintenance of the body temperature to a constant level by performing vasoconstriction or vasodilation is called thermoregulation.
7. Blood pressure: Pressure exerted by the flowing blood on the blood vessel wall is called blood pressure.
8. Systolic pressure: The maximum blood pressure exerted by the flowing blood when the heart is contracting is called systolic pressure.
9. Diastolic pressure: The minimum blood pressure exerted by the flowing blood when the heart is not contracting but receiving (i.e. relaxing) the blood is called diastolic pressure.
10. Hypertension or High Blood Pressure: The blood pressure value of 140 – 159 mm Hg which is more than the normal blood pressure is called hypertension or high blood pressure.
11. Sphygmomanometer: The instru¬ment used for measuring blood pressure is called sphygmomanometer.
12. Hematology: The branch of medical science in which the blood, haemapoietic organs (organs that produce blood cells) and blood disorders are studied is called haematology.

Answer the following questions in one or two sentences each:

Question 1.
What are the heart sounds and why are they produced?
Answer:
There are two types of heart sounds, one is ‘lubb’ and other is ‘dub’. These are produced due to closure of the heart valves.

Question 2.
What is blood circulation?
Answer:
The process of pumping the blood to all the parts of the body and bringing it back again to the heart is called the blood circulation.

Question 3.
Name any four proteins present in the blood plasma.
Answer:
The proteins present in the blood plasma are albumin, globulins, fibrinogen and prothrombin.

Question 4.
Which inorganic ions control the function of muscles and nerves?
Answer:
Calcium, sodium and potassium control the functions of muscles and nerves.

Question 5.
What is the basis on which blood group is determined?
Answer:
The antigen present on the RBCs: and the antibodies present in the plasma of I the blood determine the type of blood group. The genes of parents are responsible for the type of blood group that the child inherits.

Question 6.
Under which conditions, blood is required for donation?
Answer:
Whenever there is hemorrhage, the patient requires blood. Such patients are accident victims, those who excessively bleed, women during childbirth (parturition) and for patients undergoing surgeries.

Question 7.
How much blood is collected from a person during donation?
Answer:
About 350 ml of blood is collected from a person during donation.

Question 8.
When is National Voluntary Blood Donation Day observed?
Answer:
National Voluntary Blood Donation Day is observed on 1st October every year.

Explain the differences:

Question 1.
Atria and ventricles:
Answer:

Atria	Ventricles
1. Atria are the upper chambers of the heart.	1. Ventricles are the lower chambers of the heart.
2. Atria are the smaller receiving chambers.	2. Ventricles are the larger distributing chambers.
3. Atria are thin walled chambers having lesser blood pressure.	3. Ventricles are thick walled chambers with greater blood pressure.
4. Atria do not have inlet valves.	4. Ventricles have inlet valves.
5. Right atrium receives deoxygenated blood from whole body through the inferior vena cava (lower body), superior vena cava (from upper body). It pumps blood into right ventricle.	5. Right ventricle pumps deoxygenated blood received from right atrium to lungs for oxygenation which is known as pulmonary circulation.
6. Left atrium receives oxygenated blood from lungs through pulmonary veins. It pumps blood into left ventricle.	6. Left ventricle pumps oxygenated blood received from left atrium to whole body. This is called systemic circulation.

Question 2.
RBCs and WBCs:
Answer:

RBCs	WBCs
1. RBCs are red in colour due to haemoglobin present in them.	1. WBCs are colourless as there is no pigment in them.
2. RBCs are produced in red bone marrow.	2. WBCs are produced mostly in bone marrow. But they are also produced in lymph nodes, spleen, etc.
3. RBCs are smaller in size and rounded in .shape.	3. WBCs are larger in size and are of different shapes.
4. RBCs have an average lifespan of 120 days.	4. Life span of WBCs vary according to their role. They have a life span from a few days to 3 weeks.
5. Normal RBC count is 50 – 60 lakh RBCs per cubic mm. of blood.	5. Normal WBC count is 5 thousands to 10 thousands per cubic mm. of blood.
6. Their function is to transport the respiratory gases (Oxygen and Carbon Dioxide).	6. Their main function is to produce antibodies and fight against the infections. Thus they are called soldiers of the body.

Give scientific reasons:

Question 1.
A very large number of alveoli is present in lungs, which are covered over by capillary network.
Answer:
Due to very large number of alveoli the surface area of the lungs is increased many a times for the gaseous exchange. The alveoli are covered over by capillary network for rapid gaseous exchange. The oxygen is taken in the body and at the same time carbon dioxide is given out of the body only by the gaseous exchange occurring at the alveolar surface.

Question 2.
Heart is covered by double layered pericardial membrane.
Answer:
Pericardium is the protective double membrane that covers the heart. In between the two layers of this membrane there is protective fluid. The pericardium and the fluid together protect the heart from friction and mechanical shock. Since heart is a vital organ, it is well protected by such pericardial membrane.

Question 3.
Veins are provided with valves.
Answer:
Valves prevent the backflow of the blood. Blood in the veins is not under great pressure so it is likely that it may flow back. But valves prevent such movements. Therefore they are provided with valves.

Write short notes on the following:

Question 1.
Cellular respiration:
Answer:

1. During respiration, the glucose molecules along with some other soluble nutrients are slowly oxidized with the help of oxygen in each cell.
2. In this process the energy is released in the form of ATP, CO₂ and water vapours are produced.
3. These products are not needed for the body and hence given out of the body in exhalation.
4. This process of cellular respiration is shown by the following reaction:
   C₆H₁₂O₆ + 6O₂ = 6CO₂ + 6H₂O + Energy (38ATP)

Question 2.
Lung:
Answer:

1. Pair of lungs is the main respiratory organ in the human body. They are located in thoracic cavity.
2. They are present on either sides of heart.
3. Each lung has double layered pleural membranes.
4. Trachea bifurcates into two bronchi. Each bronchus enters lung on its side and S divide and re-divide into fine bronchioles.
5. At the end of each bronchiole there is alveolus. Alveolus is surrounded by capillary network.
6. Each alveolus is extremely thin walled and hence gaseous exchange can occur through diffusion here. Due to thousands of alveoli, the lung surface is increased many a times.
7. Deoxygenated blood coming from heart by pulmonary arteries is purified here in the lungs.
8. It is mixed with oxygen due to gaseous exchange and returned back to the heart by pulmonary veins. Lungs thus continuously help in oxygenation of blood with the help of all of the alveoli.

Question 3.
Diaphragm:
Answer:

1. Diaphragm is a muscular partition that divides the thoracic and abdominal cavity.
2. Located at the base of thoracic cage, it is very important in breathing movements.
3. Diaphragm can undergo consecutive upward and downward movements.
4. These movements along with movements of thoracic cage cause rise and fall of the pressure in the thoracic cavity.
5. Rising up of ribs and lowering of diaphragm causes the decrease in air pressure which makes the air to move into the lungs through nose. This is inhalation.
6. When the pressure rises in the thoracic cavity again, the air is given out. This is exhalation.
7. This is caused due to ribs returning to their original position and rising diaphragm. This simultaneously increases the pressure in thoracic cavity.

Question 4.
Structure of human heart:
Answer:

1. Human heart is four chambered muscular organ.
2. The size of the heart is about one’s own fist and its weight is about 360 gm.
3. For protection, it is covered over by double-layered pericardium.
4. The wall of the heart is made up of cardiac muscles which are involuntary in nature. They have the capacity of rhythmic beating.
5. The upper two chambers are called right and left atrium and lower two chambers are called right and left ventricle.
6. Between right atrium and right ventricle there is tricuspid valve which guards the opening. Similarly between left atrium and left ventricle there is bicuspid valve.
7. On entire right side of the heart there is deoxygenated blood.
8. On entire left side of the heart there is oxygenated blood.
9. Right atrium receives deoxygenated blood by superior and inferior vena cava. These two major veins bring deoxygenated blood from entire body to the heart.
10. Left atrium receives oxygenated blood from lungs by pulmonary vein.
11. Right ventricle sends the deoxygenated blood to lungs for oxygenation, through pulmonary artery.
12. Left ventricle supplies oxygenated blood to entire body through systemic aorta.

Question 5.
Human Blood Groups:
Answer:

1. The A, B, O blood group system is the most popular and medically important blood group system of human beings.
2. The blood group is determined due to antigenic protein present on the RBCs and the antibody present in the plasma.
3. The four main groups of human blood are A, B, AB and O.
4. According to the presence or absence of Rh antigen the blood groups are further said to be Rh-positive or Rh-negative.
5. This makes total eight blood groups which are taken into consideration at the time of blood transfusions.
6. Blood groups are dependent on genes and are thus hereditary in nature.

Answer the following:

Question 1.
How do the organisms like amoeba, earthworm, cockroach, plants, various aquatic animals, bird, respire? Prepare a chart.
Answer:

Diagram – based questions:

Question 1.
Sketch and label structure of alveolus showing gaseous exchange.
Answer:

Question 2.
Sketch and label artery and vein showing structural difference between the two.
Answer:

Question 3.
Draw a diagram to show formation of capillaries. Also show how capillaries form a vein.
Answer:

MCQs based on experiments:

I. Human respiratory system:

Question 1.
From which organ does respiratory system of man begin?
(a) Trachea
(b) Lungs
(c) Alveolus
(d) Nose
Answer:
(d) Nose

Question 2.
Which of the statement given below is correct?
(a) Wind pipe is present in front of food pipe.
(b) Food pipe is present in front of wind pipe.
(c) Wind pipe and food pipe are not near each other.
(d) Wind pipe is same as oesophagus and food pipe is called trachea.
Answer:
(a) Wind pipe is present in front of food pipe.

Question 3.
Which type of respiration includes inhalation and exhalation?
(a) Internal respiration
(b) External respiration
(c) Cellular respiration
(d) None of the above
Answer:
(b) External respiration

Question 4.
How many molecules of ATP are produced from one molecule of glucose ?
(a) 26
(b) 36
(c) 38
(d) 40
Answer:
(c) 38

Question 5.
Where is sound box located in the body?
(a) At the beginning of the wind pipe.
(b) At the beginning of the food pipe.
(c) At the end of the wind pipe.
(d) At the end of the food pipe.
Answer:
(a) At the beginning of the wind pipe.

II. Structure of heart:

Question 1.
What is the location of a bicuspid valve in human heart?
(a) Between right and left ventricle.
(b) Between left and right atrium.
(c) Between left atrium and left ventricle.
(d) Between right atrium and right ventricle.
Answer:
(c) Between left atrium and left ventricle.

Question 2.
Which blood vessels bring deoxygenated blood to the right atrium?
(a) Superior and inferior vena cava
(b) Pulmonary veins
(c) Pulmonary artery
(d) Systemic aorta
Answer:
(a) Superior and inferior vena cava

Question 3.
Which artery carries deoxygenated blood and which vein carries the oxygenated blood respectively?
(a) Dorsal aorta and inferior vena cava respectively.
(b) Pulmonary vein and pulmonary artery respectively
(c) Pulmonary artery and pulmonary vein respectively
(d) Superior vena cava and inferior vena cava respectively.
Answer:
(c) Pulmonary artery and pulmonary vein respectively

Question 4.
Under which of the following condition will rate of heartbeat be faster?
(a) Sleeping
(b) Resting
(c) Running
(d) Sitting
Answer:
(c) Running

Question 5.
Which chambers of the heart are called receiving chamber?
(a) Both atria
(b) Right ventricle
(c) Left ventricle
(d) Only left atria
Answer:
(a) Both atria

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 10 Cell and Cell Organelles Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 10 Cell and Cell Organelles

Class 8 Science Chapter 10 Cell and Cell Organelles Textbook Questions and Answers

1. Who am I?

Question a.
I am ATP producing factory.
Answer:
Mitochondria

Question b.
I am single-layered but maintain cellular osmotic pressure.
Answer:
Vacuole

Question c.
I support the cell, but I am not cell wall. I have a body resembling net.
Answer:
Endoplasmic reticulum

Question d.
I am chemical factory of the cell.
Answer:
Chloroplasts in case of plant cells can be called chemical factory as they synthesise carbohydrates. Ribosomes also synthesise proteins, so those can also be called chemical factory. Golgi complex is secretory in function, hence it can be also called factory. Mitochondria though mainly referred to as powerhouse of the cell, it is also mentioned as chemical factory by some authors.

Question e.
Leaves are green because of me.
Answer:
Chloroplast.

2. What would have happened? If……….

Question a.
RBCs had mitochondria.
Answer:
Mitochondria continuously carry out oxidation and form energy inside the cell. They produce energy-rich compound, ATP. In this process, they utilize carbohydrates, fats and proteins present in the cell. If RBCs has mitochondria, they would have used oxygen for this purpose than carrying it to all the cells of the body. The cells would not have obtained oxygen.

Question b.
There had been no difference between mitochondria and plastids.
Answer:
Mitochondria carry out oxidation of carbohydrates, fats, etc. with the help of enzymes. Plastids are synthesising carbohydrates with the help of solar energy and chlorophyll. Both the cell organelles have their own sets of different enzymes as per their role. If there would have been no difference between mitochondria and plastids, the specific functions would not have been taken place.

Question c.
Genes had been absent on the chromosomes.
Answer:
Genes are functional segments on the chromosomes which are responsible for transmitting the hereditary information.

Question d.
Plasma membrane had not been selectively permeable.
Answer:
Selectively permeable membrane allows some substances to enter the cell, while prevents other unwanted or harmful substances. If plasma membrane would not have been selectively permeable, there would be no control over entry and exit of any substances. The process of osmosis would also be erroneous in such case.

Question e.
Plants lacked anthocyanin.
Answer:
If plants lacked anthocyanin, no part of the plant would display purple or blue colour. Anthocyanin attracts the insects for pollination and seed dispersal. These processes will be affected due to lack of anthocyanin. These pigments are also said to be protective in nature for the plant. This protection will not be given to the plant in absence of anthocyanin.

3. Who is odd man among us? Give reason.

Question a.
Nucleolus, mitochondria, plastids, endoplasmic reticulum
Answer:
Nucleolus. (All the others are cell organelles but nucleolus is not a cell organelle present in cytoplasm.)

Question b.
DNA, Ribosomes, Chlorophyll
Answer:
Chlorophyll. (DNA and Ribosomes are present in plant as well as in animal cells. Chlorophyll is present only in plant cells.)

4. Give functions.

Question a.
Plasma membrane.

Answer:

1. Plasma membrane acts as a selectively permeable membrane. It allows entry of those useful substances which are needed for the cell. It does not allow entry of the harmful and unwanted substances.
2. Plasma membrane keeps the homeostasis in the cell. The cell is kept in steady state even if the external environment changes.
3. Plasma membrane is responsible for processes of endocytosis and exocytosis.
4. The processes of diffusion and osmosis are possible only due to plasma membrane.
5. In animal cells, plasma membrane is the outermost protective covering of the cell.

Question b.
Cytoplasm.
Answer:

1. All the cell organelles are spread in the cytoplasm of a cell.
2. The cytoplasm is the medium for many cellular chemical reactions.
3. The cytosol which is the part of cytoplasm other than cell organelles stores many vital substances like amino acids, glucose, vitamins, etc.
4. Cytosol also helps in the cellular movements.

Question c.
Lysosome.

Answer:

1. Lysosome helps in the destruction of attacking viruses and bacteria and thereby help in the immune response.
2. Lysosomes act as demolition squads. They destroy worn-out cellular organelles and organic debris. This process is called autolysis which All Pagesmeans self-destruction.
3. They are also called suicide bags as in a worn out, damaged or old cell, lysosomes automatically burst. The lytic enzymes present in the lysosome digest their own cells.
4. Lysosomes can digest stored proteins, fats during starvation.

Question d.
Vacuole.

Answer:

1. Vacuoles maintain the osmotic pressure of the cell.
2. Various metabolic byproducts and end products such as glycogen, proteins, water, etc. are stored in the lysosome.
3. In food vacuole of amoeba, the food is temporarily stored till digestion. In other animal cells, vacuoles can store waste products and food.
4. Vacuoles of plant cells can provide turgidity and rigidity as it contains good amount of cell sap.

Question e.
Nucleus.

Answer:

1. Nucleus is the controlling centre for the entire cell.
2. It controls all metabolic activities of the cell.
3. The cell division is possible due to the nucleus.
4. The chromosomes present in the nucleus carry the genes. These genes are responsible for the transmission of hereditary characters from parental generation to the next generations.

5. Who gives me the colour? (Select the correct option).

Question a.

Column ‘A’	Column ‘B’
1. Red tomato	a. Chlorophyll
2. Green leaf	b. Carotene
3. Carrot	c. Anthocyanin
4. Violet	d. Lycopene

Answer:

Column ‘A’	Column ‘B’
1. Red tomato	d. Lycopene
2. Green leaf	a. Chlorophyll
3. Carrot	b. Carotene
4. Violet	c. Anthocyanin

Project:

Question 1.
Prepare model of a cell using different ecofriendly materials.

Question 2.
Study osmosis using parchment paper or a similar membrane.

Question 3.
Form a friends’ group in your class. Give each one role of a cell organelle. Present a skit accordingly.

Class 8 Science Chapter 10 Cell and Cell Organelles Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
Cell wall is mainly composed of carbohydrates like ……….. and …………. .
Answer:
Cell wall is mainly composed of carbohydrates like cellulose and pectin.

Question 2.
Plasma membrane is said to be a ……………. …………….. membrane as it allows some substances to enter the cell, while prevents other substances.
Answer:
Plasma membrane is said to be a selectively permeable membrane as it allows some substances to enter the cell, while prevents other substances.

Question 3.
Homeostasis is maintained in the cell by ………….. .
Answer:
Homeostasis is maintained in the cell by plasma membrane.

Question 4.
An …………… is a specialized subunit having specific function within the cell.
Answer:
An organelle is a specialized subunit having specific function within the cell.

Question 5.
……………. has ribosome granules on its outer surface.
Answer:
Rough ER has ribosome granules on its outer surface.

Question 6.
During starvation, ………………… digest stored proteins, fats.
Answer:
During starvation, lysosomes digest stored proteins, fats.

Question 7.
……………….. is the secretory organ of the cell.
Answer:
Golgi complex is the secretory organ of the cell.

Question 8.
……………. compound ATP is produced in the mitochondria.
Answer:
Energy-rich compound ATP is produced in the mitochondria.

Given below are incorrect statements. Rewrite them after correcting them:

Question 1.
In mitochondria, the inner membrane is porous and the outer membrane is deeply folded.
Answer:
In mitochondria, the outer membrane is porous and the inner membrane is deeply folded.

Question 2.
Vacuole is bound by double membrane.
Answer:
Vacuole is bound by single membrane.

Question 3.
If fruit pieces are kept in thick saturated sugar solution, the water from fruit pieces enter the sugar solution resulting into their swelling.
Answer:
If fruit pieces are kept in a thick saturated sugar solution, the water from fruit pieces enter the sugar solution resulting into their shrinking.

Question 4.
Raisins kept in water shrink after an hour.
Answer:
Raisins kept in water swell after an hour.

Question 5.
Lysosome produces vacuoles and secretory vesicles.
Answer:
Golgi complex produces vacuoles and secretory vesicles.

Who gives me the colour? (Select the correct option)

Question 1.

Column ‘A’	Column ‘B’
1. Nucleus	a. Pipelines of the cell
2. Endoplasmic reticulum	b. Powerhouse of the cell
3. Golgi complex	c. Suicidal bags
4. Mitochondria	d. Packing department
5. Lysosomes	e. Controlling centre

Answer:

Column ‘A’	Column ‘B’
1. Nucleus	e. Controlling centre
2. Endoplasmic reticulum	a. Pipelines of the cell
3. Golgi complex	d. Packing department
4. Mitochondria	b. Powerhouse of the cell
5. Lysosomes	c. Suicidal bags

Find the odd one out by giving suitable reasons:

Question 1.
Demolition squads, Suicide Bags, Immune system, Powerhouse of the cell.
Answer:
A powerhouse of the cell. (All the others are descriptions of the lysosomes.)

Question 2.
Lignin, Suberin, Cutin, Iodine
Answer:
Iodine. (All the others are polymers present in the cell wall.)

Question 3.
Nucleolus, Genes, Chromosomes, Ribosomes
Answer:
Ribosomes. (All the others are inclusions in the nucleus.)

Write definitions/Give meanings:

1. Homeostasis: The tendency of the cell to keep the cellular environment constant in spite of changes in the outer: environment is called homeostasis.

2. Endocytosis: To take in the food or any other substance from outer environment into the cell is called endocytosis.

3. Exocytosis: To give out the unwanted substances from the cell to the outer « environment is called exocytosis.

4. Diffusion: The movement of the molecules from region of higher concentration to the region of lower concentration is called diffusion.

5. Osmosis: The movement of solute from low concentration to high concentration and the movement of solvent from high concentration to the region of low concentration across semipermeable membrane is called osmosis.

6. Plasmolysis: When the cell is kept ?! in hypertonic medium, the water exits through the process of exosmosis causing shrinkage of the cytoplasm, this is known as plasmolysis.

7. Isotonic solution: When the concentration of the cell and that of the medium in which the cell is kept is same, then such solution is called isotonic solution.

8. Hypotonic solution: When the concentration of the water in the cell is less than that of the concentration of the water in the surrounding medium in which the cell is kept, then such solution is called hypotonic solution.

9. Hypertonic solution: When the concentration of the water in the cell is more than that of the concentration of water in the surrounding medium then such solution is called hypertonic solution.

Distinguish between the following:

Question 1.
Prokaryotic and eukaryotic cell:
Answer:

Prokaryotic cell	Eukaryotic cell
1. Nucleoid is present instead of a well-formed nucleus.	1. Nucleus is well-formed with nuclear membrane, chromatin network and nucleolus.
2. Chromosome number is always one.	2. Chromosome number is more than one and is specific for every species.
3. Membrane-bound cell organelles are absent.	3. There are membrane-bound cell organelles.
4. The size of the cell is 1 to 10 micrometre. Example: Bacteria	4. The size of the cell is 5 to 100 micrometre. Example: All highly evolved unicellular and multicellular plants and animals.

Question 2.
Plant cell and animal cell
Answer:

Plant cell	Animal cell
1. The cell wall is the outermost covering on the cell. The plant cells have both cell wall and the cell membrane	1. The cell membrane or plasma membrane is the outermost covering of the cell. The animal cells do not have cell wall
2. The vacuoles are large and centrally placed.	2. The vacuoles are small and uniformly distributed in the cytoplasm.
3. There are plastids in the plant cells. The chloroplasts have chlorophyll.	3. The plastids are absent in the animal cells.
4. The lysosomes are absent in the plant cells.	4. Lysosomes are present in the animal cells. They contain digestive enzymes.
5. The cytoplasm is thin and pushed to the periphery due to central vacuole.	5. The cytoplasm is dense and granular. It is uniformly spread throughout the cell.

Answer the following questions in one sentence:

Question 1.
What are the components of plasma membrane?
Answer:
In plasma membrane, protein molecules are embedded in two layers of phospholipids.

Question 2.
Which part of the cell maintains the homeostasis?
Answer:
Plasma membrane of the cell maintains the homeostasis.

Question 3.
What are genes?
Answer:
Genes are the functional segments on the chromosomes that carry hereditary i information from the parental generation to the offspring.

Question 4.
What is meant by rough ER?
Answer:
The endoplasmic reticulum that has ribosomes on its outer membrane is called rough ER.

Question 5.
Write the examples of plant pigments.
Answer:
Chlorophyll, Carotene, Xanthophyll, Anthocyanin, Betalains and Lycopene are some of the plant pigments.

Question 6.
What are the inclusions in the stroma of chloroplasts?
Answer:
Enzymes, DNA, ribosomes and carbohydrates that are necessary for photosynthesis are present in the stroma of the chloroplasts.

Question 7.
Which staining technique was developed by Camilio Golgi? Where was this technique used?
Answer:
Camilio Golgi developed the staining technique called ‘Black reaction’ which was used in the study of nervous system.

Question 8.
What type of work is done by National Centre for Cell Science?
Answer:
National Centre for Cell Science – NCCS is involved in research in cytology and research about cancer treatment and it also provides services for National Animal cell repository.

Question 9.
Ripe tomatoes appear red.
Answer:
When green tomatoes become ripe they lose chlorophyll and develop red pigment in them called lycopene. Therefore, ripe tomatoes appear red.

Give scientific reasons:

Question 1.
Raisins swell after keeping in plain water.
Answer:
When raisins are placed in plain water, there is action of endosmosis. The outer skin of raisins acts like selectively permeable membrane. Since the concentration of water inside the raisin is lesser than the concentration of water in the outer medium, water enters in the raisin. This causes raisins to swell after keeping them in plain water.

Question 2.
The fruit pieces kept in sugar syrup show shrinking.
Answer:
There is more concentration of water in the fruit pieces as compared to the concentration of water in the sugar syrup. Therefore, water is lost out by exosmosis. The membranes of the fruit pieces act as selectively permeable membranes. Thus the process of plasmolysis occurs resulting into shrinking of the fruit pieces.

Question 3.
The nucleus of the sieve tubes of the plant phloem is lost.
Answer:
The sieve tubes of the plant phloem conduct the food in plants. To make this transport easier, the nucleus of the sieve tubes of the plant phloem is lost,

Question 4.
Plant cells have less mitochondria than those of animal cells.
Answer:
Mitochondria are the cell organelles which are called powerhouse of the cell. They produce energy in the form of ATP. Animals are motile and need more energy for walking, running and moving. Plants are stationary. They do not need energy to greater extent. Therefore, they have lesser number of mitochondria.

Question 5.
Vacuoles do not have any typical size or shape.
Answer:
Vacuoles change their shape and size as per the need of the cell. Thus they do not have any fixed shape or size.

Question 6.
Ripe tomatoes appear red.
Answer:
When green tomatoes become ripe they lose chlorophyll and develop red pigment in them called lycopene. Therefore, ripe tomatoes appear red.

Give functions:

Question 1.
Endoplasmic reticulum.

Answer:

1. Endoplasmic reticulum or ER is the supporting framework of the cell.
2. The ribosomes attached to the membrane of the ER synthesize proteins. These proteins are conducted by ER.
3. The detoxification process is done by ER. The toxins that enter the cell through food, air and water are removed out by making them water soluble.

Question 2.
Golgi complex.

Answer:

1. Different secretions are prepared in the Golgi complex. Hence it is called the secretory organ of the cell.
2. The secretions are modified and sorted out as per their functions. They are further packed.
3. The enzymes, mucus, proteins, pigments, etc. are sorted and then dispatched to various target regions like plasma membrane, lysosome, etc.
4. Golgi complex also produces vacuoles and secretory vesicles.
5. Formation of cell wall, plasma membrane and lysosomes is aided by Golgi complex.

Question 3.
Plastids.
Answer:

1. Chloroplasts contain chlorophyll. They carry out the process of photosynthesis. They convert solar energy to chemical energy in the form of food.
2. Chromoplasts with different pigments can impart different colours to flowers and fruits.
3. Leucoplasts are responsible for the synthesis and storage of food like starch, oils and proteins.

Answer the following questions:

Question 1.
How does endosmosis and exosmosis occur in the cell?
Answer:

1. When the water concentration inside the cell is less as compared to the medium in which it is present, then the endosmosis takes place. This makes the water to enter inside the cell.
2. When water concentration inside the cell is more than the water concentration in the medium in which it is present, then the water comes out of the cell. This is called exosmosis.
3. Since the cell membrane acts as a semipermeable membrane, the processes of endosmosis and exosmosis takes place in the cell.

Question 2.
What is cytoplasm? What are the constituents of cytoplasm?
Answer:

1. The jelly like material present between the cell membrane and nucleus is called cytoplasm.
2. Cytoplasm without cell organelles is called cytosol.
3. All the cell organelles are spread in the cytoplasm.
4. Cytosol stores many vital constituents such as amino acids, glucose, vitamins, etc.
5. The cytoplasm of animal cells is dense and granular while that of plant cells is thin and peripheral. It is pushed to sides due to large central vacuole.

Question 3.
Describe the structure of the nucleus in the cell.

Answer:

1. Nucleus is the most important part of the eukaryotic cell.
2. Inside the nucleus there is round darkly stained nucleolus.
3. The nucleus is covered over by double membrane which is porous.
4. The nuclear pores allow the transport of different substances in and out of the nucleus to cytoplasm.
5. Inside the nucleus is the chromatin network which contains chromosomes. Chromatin fibres are thin which condense to form chromosomes. The chromosomes become clear and distinct at the time of cell division.
6. In every cell there are specific number of chromosomes. Chromosomes contain genes which are bearers of hereditary characters.

Question 4.
Why is endoplasmic reticulum compared with the pipelines?
Answer:

1. The endoplasmic reticulum works as pipelines to carry different substances in the cell.
2. It is a net like structure consisting of interconnected small tubes and sheets filled with fluid.
3. On the inner side the E.R. is connected to nucleus while at the outer side it is in contact with plasma membrane. Therefore, it works like a pipeline.

Question 5.
Write an account of the different structures seen in Golgi complex.
Answer:

1. Golgi complex is made up of 5-8 hollow and flat sacs called cisternae.
2. These are placed parallel to each other and are filled with different enzymes.
3. Golgi complex has two faces called forming face and maturation face.
4. The proteins packed in vesicles and coming from ER reach Golgi complex through cytoplasm.
5. They fuse with the formation face of the Golgi membranes for emptying their contents in the cisternae.
6. When these contents pass through the cisternae, they are chemically modified with the help of enzymes and are again packed in the vesicles.
7. These vesicles come out of Golgi ‘ complex at the maturation face.

Question 6.
How is energy produced in the mitochondria? How the structures of mitochondria help in this process?
Answer:

1. Around every mitochondrion there is a double membrane.
2. The outer membrane of these is porous while the inner membrane is deeply folded.
3. These folds or ‘cristae’ enclose the matrix filled with proteinaceous gel containing ribosomes, phosphate granules and DNA. Protein synthesis takes place in this matrix.
4. Mitochondria carry out oxidation of carbohydrates and fats in the cell. This produces energy in the form of ATP, s i.e. Adenosine Tri Phosphate

Question 7.
What is the benefit of foldings of inner membrane in mitochondria?

Answer:
The structure of the inner mitochondrial membrane is extensively folded and compartmentalized. The numerous imaginations of the membrane are called cristae. This folded inner membrane increases the area which is about 5 times more than that the outer membrane due to cristae. Cristae membranes have small round protein complexes known as Fx particles. In these particles the process of energy production goes on.

Research:

Question 1.
Keep 4 – 5 raisins in water and observe after an hour. Afterward, keep the same raisins in sugar solution and observe after an hour. Note down the observations and discuss in the classroom.
Answer:
When raisins are kept in water its outer skin acts as a semi-permeable membrane. The water content inside the raisin is lesser as compared to the water content in the outside medium. Therefore the water enters in the raisins due to process of endosmosis. Thus if raisins kept in plain water are observed after one hour, they are seen to be swollen.

On the other hand, if raisins are kept in sugar solution, they show plasmolysis and they shrink. The sugar solution acts as hypertonic medium. Water content in the raisin is higher than that present in the sugary solution. Thus water exists from raisins and its content thus shrinks.

Question 2.
Wooden doors fit very tightly in rainy season. Why does it happen?
Answer:
During rainy season there is more humidity in air. The doors get soaked in rain water. Though wood is non-living, it has the ability to absorb water. As the moisture is more in the surrounding area, it enters the wood. This is a type of endosmosis. It causes the doors to swell. The swollen doors then fit very tightly.

Diagram based questions:

Question 1.
Structure of the cell:

Answer:

(iii) Complete the chart:

Answer:

Component	Animal cell	Plant cell
Cell membrane	Present	Present
Cell wall	Absent	Present
Lysosomes	Present	Absent
Plastids	Absent	Present
Endoplasmic reticulum	Present	Present
Vocuole	Present	Present
Golgi complex	Present	Present
Mitochondria	Present	Present

Question 2.
Sketch the diagrams to show how osmosis occurs in plant cell if kept separately in isotonic, hypotonic and hypertonic medium.
Answer:

Question 3.
Sketch the diagrams to show how osmosis occurs in animal cell if kept separately in isotonic, hypotonic and hypertonic medium
Answer:

Activity-based questions:

Question 1.
Experiment Activity – Take a drop of water on a clean glass slide. Using an ice-cream spoon, gently scrap the inner surface of your cheek. With a needle, transfer a little material from spoon to the water drop on the slide and spread it evenly. Put a drop of methylene blue stain on the smear. Put a cover slip and observe under microscope. Did you observe the cells with blue nucleus?
Answer:
Students should do this activity at school laboratory. There are squamous epithelial cells in the inner side of the cheek. When stained with methylene blue the nucleus takes up dark stain and can be seen clearly.

Question 2.
Experiment Activity – Take out a thin peel of Rheo or Croton leaf and observe the chromoplasts under the compound microscope.
Answer:
Students are expected to do the observations in the school laboratory.

Question 3.
Can you recall? Observe the cells of onion peel under the microscope. Have you seen the fully turgid, rectangular cells of onion peelings?

Answer:
Students are expected to do the observations in the school laboratory.

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 9 Disaster Management Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 9 Disaster Management

Class 8 Science Chapter 9 Disaster Management Textbook Questions and Answers

1. Answer the following in your own words.

Question a.
Explain the relation between continuous rains and landslide. Give reasons.
Answer:
Before the actual landslide, many changes occur in the surrounding hilly ground. The hard rocks develop cracks and crevices. These are natural changes but due to man-made activities, the cracks are widened due to erosion. These cracks make the big rocks to break into smaller stones. The cracks widen further due to excessive rainfall. These rocks further get eroded and they fall down along with soil from the slopes. The entire process is speeded up due to rainwater.

Question b.
Prepare a chart showing ‘Dos’ and ‘don’ts’ at the time of earthquake.
Answer:
At the time of earthquake

Dos	Don’ts
1. Go in the open grounds.	1. Don’t wait in the multi-storeyed buildings. Do not use lifts. Use stairs to descend.
2. Keep the electrical appliances and cooking gas closed.	2. Do not stand near buildings, trees or electric wires and poles.
3. Use battery or torch.	3. Do not light candles, lantern or match- sticks.
4. Stand silently at one place. Do not panic or get scared.	4. Do not sit in uncomfortable posture for a long time.
5. Take protection under some hard covering, especially to protect the head and face. Cover the face.
6. If, in vehicle, find a safe place and stop the vehicle, sit in the vehicle than coming out in open.

Question c.
What are the specifications of an earthquake-proof building?
Answer:
The earthquake-proof building is such that even if the earthquake is caused, it should not cause damage to the buildings due to these earth movements. There are some codes of conduct while constructing such buildings. Advanced technology is used for earthquake resistant construction. The foundation of earthquake-proof building is separated from lower land. The walls are of less weight or they are wooden. The house constructed with special light materials are preferred in earthquake-prone regions.

Question d.
Explain the effects of landslide.
Answer:
1. Mostly rivers originate in the hills and mountains. When there is landslide, the rivers naturally get flooded.
2. The paths of the riverine water changes due to landslide.
3. Waterfalls are displaced from their original positions.
4. New and artificial water reservoirs are created.
5. The falling debris, soil and rocks make the trees at the base of hillside uprooted. All the plant life is lost.
6. The constructions done by the villagers on the slope can be totally damaged due to landslide. There is large scale damage to property and life. In few cases like Malin the entire village was buried due to landslide and accompanied rainfall.
7. Transportation is affected as the roads and railway tracks are blocked due to debris.

Question e.
Is there any relation between dam and earthquake? Explain.
Answer:
There is abundant water stored in the dams. This water column puts additional weight on the ground. Initially there may not be any weight, but later due to construction of dam, suddenly the pressure of this weight is so high that this ground experiences the tension. If such area is already earthquake-prone, then there can be chances of earthquake. According to theory of plate tectonics, there are continuous movements in the earth’s surface. If over such fragile plates, the dams are constructed then the chances of earthquake are enhanced.

2. Give Scientific reasons.

Question a.
It is safer to find shelter under things like a bed, table at the time of earthquake.
Answer:
When earthquake takes place, due to the vibrations in the earth’s surface, there is possibility of the roof and walls of the house to fall. This collapse can cause severe head injury which can be fatal. Thus, one must take shelter below the hard-supporting structures such as bed or table. This precaution can save one’s life.

Question b.
In monsoon, don’t take shelter near hillside.
Answer:
The excessive rainfall can cause landslides. The soil and rocks from the hillside can be pushed down along with the flow of rainwater. This debris slides to the lower heights from the hills. This explains us that taking shelter near the base of the hillside can be disastrous as one can be buried in the debris due to sudden landslide. Therefore, in monsoon, one should not take shelter near hillside.

Question c.
Don’t use lifts at the time of earthquake.
Answer:
Lifts or elevators run on electricity. The electricity supply can be hindered due to earthquake. There may be chances of fire due to short circuit. We may get trapped in the elevator at such times. The building may also collapse due to earthquake. It is always better to use stairs at the time of such calamities, so that one can safely come out of the building. Therefore, it is said that lifts should not be used at the time of earthquakes.

Question d.
The foundation of earthquake- proof building is separated from lower land.
Answer:
The surface of the earth trembles at the time of earthquake. These tremors cause seismic waves which are responsible for the movements of the earth’s surface. The ground thus shakes or it goes up-down. These shocks and waves formed in the interior of the earth spread on the surface in all directions. This causes collapse of the building and other structures on the land.
To prevent such disasters the foundation of earth-quake proof building is separated from lower land.

3. If a crowd gathers at the place of earthquake, what would be the difficulties in relief work?

Question a.
If a crowd gathers at the place of earthquake, what would be the difficulties in relief work?
Answer:
If people flock in crowd, the rescue work will not be possible. The ambulances and the fire engines will not reach the spot where the help is needed. The personnel from disaster management cells cannot thus act in time. It will be difficult to manage the situation and thus such crowding should never be done.

4. Make a list of the institutes and organizations who provide help for disaster managment. Collect more information about their work.

Question a.
Make a list of the institutes and organizations who provide help for disaster management. Collect more information about their work.
Answer:
International government organisations working for disaster management are:
a. The United Nations and its organisations:
1. The Food and Agricultural Organisation of the UN (FAO): It gives early warning of impending food crises, and keep track of global food supply problems.
2. The United Nations Development Programme (UNDP): It helps disaster-prone countries with disaster mitigation, prevention and preparedness measures.
3. The World Food Programme (WFP): It is the main supplier of relief food aid.
4. The World Health Organisation (WHO): It gives global public health leadership by setting standards, monitoring health trends, and providing direction on emergency health issues. WHO’s role is to reduce avoidable loss of life and the burden of disease and disability.

b. The International Committee of the Red Cross ( ICRC): It gives physical rehabilitation to people injured by explosive weapons or other types of incident.

c. The International Federation of Red Cross and Red Crescent Societies ( IFRC): It coordinates and gives international help to victims of natural and technological disasters, to refugees and in health emergencies.

International non-governmental agencies working for disaster management are:
a. International Rescue Committee (IRC): It provides lifesaving care and life-changing help to refugees forced to flee from war or disaster.

b. IMA World Health: It, in collaboration with USAID, the World Bank and many other organisations, builds sustainable health care systems.

c. CARE: It is an organisation fighting global poverty. It works for women and puts efforts to improve their basic education, prevent the spread of HIV by providing awareness among them, give them increase access to clean water and sanitation, expand economic opportunity for them. It provides emergency aid to survivors of war and natural disasters, and helps people rebuild their lives.

Indian organisations and institutes working for disaster management are:
a. National Disaster Response Force (NDRF): The multi-disciplinary, multi-skilled, high-tech force of the NDMA are capable of dealing with all types of natural and man-made disasters.

b. National Disaster Management Authority (NDMA): It lay down the policies, plans and guidelines for Disaster Management to ensure timely and effective response to disasters.

c. National Institute of Disaster Management (NIDM): It has been given the responsibilities for human resource development, capacity building, training, research, documentation and policy advocacy in the field of disaster management.

5. Make a survey of your school according to the plan of disaster management an write the pointwise information.

Question a.
Make a survey of your school according to the plan of disaster managment an write the pointwise information.
Answer:

This an activity based questions. Kindly do it yourself. But make sure to involve the following points in your survey:

• Primary information of the school: It should include information such as name and address of the school and Head Master, total number of school staff and name and phone numbers of school management members.
• School disaster management committee: Get the information of the members involved in disaster management committee.
• Detailed information about school building: Note the number of rooms, classroom, age of the building, types of roofs under this point.
• Information about school ground: It should include information like distance of ground from the main road, types of play grounds.
• Daily routine of the school: It should include information like working time of the school, lunch break time for the school.
• Possible hazards in the school: It should information such as record of past disaster happened in school, current planning for overcoming disasters.
• Disaster management map of the school: It should have information regarding all the buildings of the school, entrances and exit gates, place of probable danger, safer place at the time of disaster.

6. Are there any possible places of landslide in your area? Collect information from experts.

Question a.
Are there any possible places of landslide in your area? Collect information from experts.
Answer:
This is an activity based question. kindly do it yourself.

7. With the help of the following pictures, explain your role in disaster management.

Question a.
With the help of following pictures, explain your role in the disaster management.
Answer:

The picture given is not very clear. It does not indicate the condition of disaster. Therefore, there are two alternatives for this answer.
Option 1 : The boy holds a paper on which is written, ‘I am at risk’! The boy is shocked to read this. Someone has given message to him. He must search that person and help him or her. He should therefore take help from some elder or from police force in such matter.

Option 2 : The boy shown in the picture is in danger. So, he is typing in his I – pad, “I am at Risk”. After receiving this message, someone will help him. It depends upon, to whom is he sending this message. If he sends this message to us, we can immediately try to help him. His message “I am at Risk”, shows that he is in danger and has to be saved.
It is not clear about which disaster is shown in the picture.

Project:

Question 1.
Make a collection of news, photos. and cuttings about landslides and rift collapse.

Question 2.
With the help of Internet, collect information about the latest gadgets and technology to forecast earthquake.

Question 3.
Collect information about NDRF, RPF, CRPF, NCC from Internet.

Question 4.
Discuss- Need of CCTV.

Class 8 Science Chapter 9 Disaster Management Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
Earthquakes cause ……………. waves leading to movements of the earth’s surface.
Answer:
Earthquakes cause seismic waves leading to movements of the earth’s surface.

Question 2.
The central point of earthquake is the point above the ……………. on the earth’s surface.
Answer:
The central point of earthquake is the point above the epicentre on the earth’s surface.

Question 3.
The accentuation of earthquake is measured in …………… .
Answer:
The accentuation of earthquake is measured in ‘Richter Scale’.

Question 4.
If there is earthquake at the bottom of ocean, it may create ……………… waves.
Answer:
If there is earthquake at the bottom of ocean, it may create tsunami waves.

Question 5.
…………….. is the best device to put off small fires.
Answer:
Stirrup pump is the best device to put off small fires.

Question 6.
………………. of waterfalls occurs due to landslides.
Answer:
Displacement of waterfalls occurs due to landslides.

State whether the following statements are True or False:

Question 1.
Every year nearly 2,400 to 4,000 earthquakes occur on the earth.
Answer:
False. (Every year nearly 12,400 to 14,000 earthquakes occur on the earth.)

Question 2.
Potassium, sodium and calcium are the metals that react with water at high room temperature.
Answer:
False. (Potassium, sodium and calcium are the metals that react with water at normal room temperature.)

Question 3.
A fire caused due to electrical components is extinguished by fire extinguishers like carbon dioxide are used.
Answer:
True.

Question 4.
Indiscriminate cutting of the trees results in improvement of soil quality.
Answer:
False. (Indiscriminate cutting of the trees results in soil erosion.)

Question 5.
Landslide results in loss of plant life.
Answer:
True.

Match the column:

Question 1.

Column ‘A’	Column ‘B’
1. Class A fire	a. Electrical components
2. Class B fire	b. Gaseous substances
3. Class C fire	c. Chemical substances
4. Class D fire	d. Liquid substances
5. Class E fire	e. Solid substances

Answer:

Column ‘A’	Column ‘B’
1. Class A fire	e. Solid substances
2. Class B fire	d. Liquid substances
3. Class C fire	b. Gaseous substances
4. Class D fire	c. Chemical substances
5. Class E fire	a. Electrical components

Question 2.

Column ‘A’	Column ‘B’
1. Earthquake	a. Formation of artificial water reservoir
2. Tsunami	b. Wildlife lost
3. Forest fire	c. Loss of coastal regions
4. Landslide	d. Change in the level of groundwater-table

Answer:

Column ‘A’	Column ‘B’
1. Earthquake	d. Change in the level of groundwater-table
2. Tsunami	c. Loss of coastal regions
3. Forest fire	b. Wildlife lost
4. Landslide	a. Formation of artificial water reservoir

Name the following:

Question 1.
Modern equipment to get prior intimation about earthquake:
Answer:

1. Laser ranging
2. Very long baseline
3. Geiger counter
4. Creep meter
5. Strain meter
6. Tide gauge
7. Tilt meter
8. Volumetric strain gauge.

Question 2.
Some code of conduct made by Indian Standard Institute for construction of buildings:
Answer:

1. IS 456
2. IS 1893
3. IS 13920

Question 3.
The subcommittees of School Disaster Management.
Answer:

1. Fire extinguisher
2. Awareness
3. Instructions
4. Traffic management
5. Safety
6. Communication committee.

Answer the following questions in one sentence:

Question 1.
Which is the instrument or machine that records the intensity of earthquake?
Answer:
The machine/Instrument which records the earthquakes is called ‘Seismograph’ or ‘Seismometer’.

Question 2.
Which is the most common and effective solution for extinguishing fire ?
Answer:
Spraying water is the most common and effective solution for extinguishing fire.:

Question 3.
Which type of fires can be extinguished by the method of suppressing?
Answer:
To extinguish the fires caused due to electricity or oil, the method of suppressing the fire can be used.

Question 4.
Which metals react with water at normal room temperature?
Answer:
Combustible metals like potassium, sodium and calcium, react with water at normal room temperature.

Question 5.
Which metals react with water at higher temperatures?
Answer:
Magnesium, aluminum and zinc react with water at high temperatures.

Question 6.
Which institutes have launched a program to forecast the landslides and its effects?
Answer:
The Government of India in collaboration with Indian Mountaineering Institute and International Centre for Integrated Mountain Development has launched a program to forecast the landslides and its effects.

Give scientific reasons:

Question 1.
The electric mains are shut off immediately after the earthquake.
Answer:
There is increased possibility of short circuit after the earthquake. This may result in fire. The earthquake has already – brought the disaster. To prevent further destruction, the electric mains are shut off immediately after the earthquake.

Write short notes:

Question 1.
Types of fire:
Answer:
There are five types of fire. This division is based on two criteria, viz.
(i) Which substance is being burnt, (ii) What is the method of extinguishing it.
1. Class A Fire: Commonly inflammable solid things such as wood, clothes, coal, papers can be burnt by this type of fire. This fire is extinguished by spraying water over it. This is also called cooling out. Water is effectively used to put off class A fire.

2. Class B Fire: Flammable liquid substances such as petrol, oil, varnish, solvents, cooking oil, paints, etc. catch fire and it is called class B fire. Since these substances are lighter than water, they can be extinguished only by foaming fire extinguishers.

3. Class C Fire: The fire caused due to gaseous substances is called class C fire. Domestic gas (L.P.G.) and acetylene can cause such kind of fire.

4. Class D Fire: Combustible metals catch class D fire. Metals such as potassium, sodium and calcium, can react with water at normal room temperature whereas magnesium, aluminium and zinc react with water at high temperature. When both these groups combine with water, it causes explosion.

5. Class E Fire: When electric components are subjected to fire, they form class C fire. Such fires can be caused by short circuit or due to problems in electric fittings. Such fire is extinguished with the help of carbon dioxide and non-conductive fire extinguishers.

Question 2.
Disaster relief – planning.
Answer:
Anyone can face disaster at any time. The only way to tackle with such disasters is to keep preparedness to deal with any calamity. Schools, colleges and various offices need to chalk out a detailed planning in case of possible disasters. With this purpose in mind, disaster relief planning is done.

E.g. In the disaster relief planning for school, primary information of the school, the structure of School Disaster Management Committee, detailed information about school building and information about school ground, daily routine of the school such as at what time the school starts and what time does it end, the possible hazards in the school, and disaster management map of the school is included.

Answer the following questions:

Question 1.
What are the different ways to extinguish fire? Write briefly about them.
Answer:
There are three main methods to extinguish the fire. These methods are used to stop the spread of fire and to avoid the financial and other losses.
1. Cooling out by use of water: Water is easily available and can be used for putting off fire instantly. Due to spraying of water, there is cooling effect produced which helps in reducing the loss by fire. Fire can be easily controlled by water.

2. Suppressing the fire by covering it: When there is a fire due to electricity or oil it has to be controlled by covering the fire by sand or soil. When the froth is spread on the fire, there is no contact between air and fire. This puts off the fire and stops the spread of fire caused due to oil.

3. Keep away Flammable Substances: Care is taken to keep away all flammable substances from the fire. Wooden articles and inflammable substances are kept in such as way the fire will not engulf it. Stirrup pumps are used to put off small fires by which the water is spread in all directions around the fire.

Question 2
What are the safety measures and precautions to stop the fire?
Answer:

1. Switching off the regulator of cooking gas cylinder when not in use. Put off the connections of all electrical appliances when not in use.
2. If there is fire, call others immediately for help. Take help of others by calling them. Also help others who are in need to save their lives from fire.
3. Get help from fire brigade by calling phone number 101.
4. Know details about working of the fire extinguishing apparatus.
5. Give first aid to the victim of fire. Seek immediate medical help,

Question 3.
What are the causes of landslide?
Answer:

1. Various types of natural disasters like earthquakes, tsunami, heavy rains, storms, floods can result into landslide.
2. The indiscriminate cutting down of the trees can result into soil erosion. Soil erosion in turn results into landslide.
3. The construction of roads, bridges, railway tracks, etc. on the mountain slopes result into lot of digging. Such activities make soil cover loose. From the slopes the soil and rocks then can slide easily. This results into landslides.

Draw a well labelled diagrams:

Question 1
Seismometer/Secismograph.
Answer:

Question 2.
Focal point and epicenter or earthquake.
Answer:

Open-Ended Questions:

Question 1.
Have you at any time faced with any disaster? What were your experiences during such condition? How did you get rescued?
Answer:
Students should write their own experiences about such incidents if any.

Question 2.
In Maharashtra where do the traffic jams occur due to landslides? Make a list of such places. Why does the landslide occur at those places only? Discuss in the classroom and suggest preventive measures.
Answer:
In Maharashtra, the landslides are very common in the hilly regions. The traffic is suspended often during rainy season when such calamity strikes. Malshej, Khandala, Kasara are some of the Ghats which are very prone to land-slide. On the tracks of Konkan railway, the landslides are very common during heavy downpour.

The regions where more landslides occur have many constructions and large scale deforestation. The traffic of Konkan railway comes to standstill after such landslide. Moreover, during heavy monsoon days, the speed of the running trains is kept very slow. The soil structure is also responsible for such landslides.

Preventive measures: There should be wire meshing done across the sides of the roads and railway tracks so that the collapsed rocks and other debris does not obstruct the traffic. Tree plantation should be carried out to prevent loosening of the soil and rock. It will also help in preventing the soil erosion.

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 8 Pollution Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 8 Pollution

Class 8 Science Chapter 8 Pollution Textbook Questions and Answers

1. Following are some statements about pollution. Which type of pollution do those express:

Question a.
Fog seems to be appearing in Delhi during day hours.
Answer:
Air pollution-Smog
(The sentence should have the word Smog and not fog. Smog is fog with smoke. Only fog cannot be polluting, but the smog is.)

Question b.
Many times, vomiting and dysentery occurs after eating ‘panpuri’.
Answer:
Water pollution-Contaminated food and water due to bacteria or virus

Question c.
Problem of sneezing occurs sometimes during visit to garden.
Answer:
Air pollution due to pollens

Question d.
Crop does not grow up in some areas.
Answer:
Soil pollution

Question e.
People living in the busy squares face the problems like short breathing and other respiratory problems.
Answer:
Air pollution due to traffic

2. Read the passage and identify the sentences expressing types of pollution.

Question a.
Nilesh is a student of Std. VII and lives in urban area. It takes about an hour to go to the school by bus. He faces the heavy traffic of two wheelers, four wheelers, rickshaws, buses while going to school. He is facing the problem of asthma since last few days, Doctors recommended him to stay away from urban area. Since then, his mother sent him to the village of his maternal uncle, Nilesh saw the heaps of garbage at many places in village. Foul smell of human and animal wastes was present at many places. Blackish water with foul smell was flowing in a stream. He developed some abdominal disease within few days.
Answer:

1. It takes about an hour to go to the school. (Due to traffic jam, Nilesh is spending more time in polluted, contaminated air.)
2. He faces the heavy traffic. (Large scale combustion of fossil fuel.)
3. He is facing the problem of asthma. (Air pollution – Harmful to human health.)
4. The heaps of garbage at many places. (Solid waste – Land pollution.)
5. Foul smell of human and animal wastes. (Biological pollution, air pollution.)
6. Blackish water with foul smell was flowing in a stream. (Improper sewage management – Water pollution.)
7. He developed some abdominal disease within few days. (Water pollution – Effect on human health.)

3. Match the pairs from ‘A’ and ‘B’ columns and explain the effect of pollution on human health.

Question a.

Column ‘A’	Column ‘B’
1. Water containing cobalt	a. Mental retardation
2. Methane gas	b. Paralysis
3. Water containing lead	c. Inflammation of lungs
4. Sulphur dioxide	d. Skin cancer
5. Nitrogen dioxide	e. Irritation of eyes

Answer:

Column ‘A’	Column ‘B’
1. Water containing cobalt	b. Paralysis
2. Methane gas	d. Skin cancer
3. Water containing lead	a. Mental retardation
4. Sulphur dioxide	e. Irritation of eyes
5. Nitrogen dioxide	c. Inflammation of lungs

4. True or false.

Question a.
Water does not get polluted by washing the clothes in running water of river.
Answer:
False. (Even if washing of soiled clothes is done in running water, it will cause pollution as the dirt and the waste materials will be added to water. This certainly will cause water pollution.)

Question b.
More the use of electric appliances, more will be the pollution.
Answer:
True. (Most of the electricity is generated in India by burning coal. The power generation plants thus cause lots of air pollution. More the electricity is used by using more appliances, there will be more pollution. However, only power generation through solar energy cannot cause pollution.)

5. Answer the following:

Question a.
What is pollution?
Answer:
Contamination of natural environment that can harmfully affect the environment is called pollution.

Question b.
What are Pollutants?
Answer:
The products which affect the normal functioning of ecosystem and have an adverse effect on plants, animals and humans are called pollutants.

Question c.
What is acid rain?
Answer:
1. When rainwater contains harmful amounts of nitric and sulphuric acids, it is called acid rain.
2. Burning of fossil fuels such as coal, wood, petroleum, etc. releases nitrogen oxide and sulphur oxide into the atmospheric air.
3. Since these oxides are soluble in water, they dissolve in rainwater. Nitrogen and sulphur oxides dissolved in large quantities of water vapour form acids like nitric acid, nitrous acid, sulphurous acid and sulphuric acid.
4. These acids mix with mist, drops of rainwater and snow. They change their composition and fall back on the ground in the form of acid rain.
5. Effects of acid rain are as follows:

• Increase in the acidity of soil and water bodies.
• Damage to the trees.
• Water becomes unsuitable for fish and wildlife.
• Buildings, statues, sculptures, bridges, monuments and fences are corroded due to acid rain. Thus, acid rain damages our national assets.
• Acid rain affects agriculture and crop lands.

Question d.
What is greenhouse effect?
Answer:

1. Greenhouse effect is the ; phenomenon due to which global warming and climate change occur.
2. The earth receives solar energy in the form of heat from the sun. The surface of earth absorbs this heat and reflects it back to the atmosphere as infrared radiation. Some of this heat energy goes directly into space.

Question e.
Which are visible pollutants known to you?
Answer:
1. The polluting substances that are seen easily with the naked eyes can be called as visible pollutants. E.g. Solid wastes, plastic articles, plastic bags, the suspended things in the water, metal refuse, etc.

Question f.
Which are invisible pollutants?
Answer:
The pollutants which are completely dissolved in water or mixed in the air, cannot be seen and hence they can be called invisible pollutants. Since they are not seen, we remain unaware about the presence of these pollutants. E.g. the insecticides spread f on the crops. Aerosols, many hazardous gases in the air, toxic compounds that are totally soluble in water, etc.

6. Answer the following.

Question a.
Give two examples of each of water, soil and air pollution from your residential area.
Answer:
Air pollution:

1. New buildings are constructed. Old structures are demolished. This is creating lots of dust pollution. The air is full of particulate matter.
2. The number of vehicles on the road has tremendously increased. This causes smoky environment.

Water pollution:

1. The sea shows lots of floating plastic and decaying flowers, etc. When beaches are visited it is a common sight.
2. Many fishes are seen dying in great numbers and are washed off to the shore.

Soil pollution :

1. Everywhere garbage heaps are seen. In that plastic bags, needles, old medicine vials and cartons are seen in abundance.
2. The sludge brought by rainwater is spread everywhere and that causes stink.

Question b.
How does the pollution occur due to vehicles? Give the names of vehicles causing least pollution.
Answer:

1. More than 50% of the air pollution is caused by vehicular traffic.
2. Particulate matter, unburnt hydrocarbons, CO, nitrogen oxides and carcinogenic hydrocarbons are present in the automobile exhausts.
3. Fossil fuels like petrol, diesel, natural gas, gasoline, etc. which are burnt to run the automobiles lead to the emission of CO₂ and other gases.
4. Therefore, vehicles are said to be the major contributors to air pollution.
5. The only vehicle which is non¬polluting is bicycle. The four-wheelers which are battery operated are also manufactured recently.

These two types of vehicles are eco-friendly. The cars that run on C.N.G. are also said to be lesser polluting.

Question c.
What are natural reasons causes for water pollution?
Answer:
The natural causes of the water pollution:
1. If organic pollutants are added to the water there is an overgrowth of weeds such as Eichhornia. The growth of algae also makes the water unsuitable for consumption. These aquatic plants release oxygen during daytime but by night they require oxygen thus depleting the dissolved oxygen level. The natural characters of water are then changed.

2. The decomposing matter when added to the water make it polluted and stinking.

3. Due to deposition of sludge or eroded soil, the rivers change their path and divert from original flow. The currents are also changed. Deposition of sludge makes the water polluted.

4. Due to soil erosion, surrounding the water bodies, the microbes, bacteria, protozoans and the worms and larvae of nematodes enter the water causing severe biological pollution. Many inorganic pollutants are also added to the water. The fungand bacteria present in the water make it non-potable. Such water spreads water-borne diseases.

Question d.
Suggest four preventive measures for air pollution.
Answer:
The following methods are adopted to control air pollution from the industries:

1. The source discharge is diluted by tall chimneys.
2. There are source correction methods like changing the raw material, equipment modification, process modification, etc.
3. Effective pollution controlling equipment like dust collectors, electrostatic precipitators, wet scrubbers, etc. should be used.
4. There should be ban and control over atomic tests and chemical weapons on the international level.

Question e.
Explain relation between greenhouse effect and global warming.
Answer:
Because of greenhouse effect, there is increase in the global temperature. The heat on the earth remains trapped due to envelope of greenhouse gases. The percentage of carbon dioxide and methane is constantly increasing and hence there is increase in the temperature too. Thus the greenhouse effect is directly related to the global warming.
Effects of this relation between greenhouse effect and global warming are as follows:

1. The polar ice caps and the glaciers at both the poles are melting due to increased temperature.
2. The oceans’ water is rising due to this melted ice. The sea level rise is causing coastal land submergence. The islands at various regions are threatened of drowning.
3. Many species of living organisms are already extinct due to global warming. The rest are also threatened.
4. Wild animals are showing weird migrations. Polar bear is endangered.
5. The increased temperature of the oceanic water is causing many changes in the tides and currents. This results into increased occurrence of cyclones, hurricanes and cloud bursting. The natural disasters are rising in last decade.
6. The agricultural production is decreasing. The regions with less rainfall are facing draughts.

Question f.
Construct two slogans each on air, water and soil pollution.
Answer:
Air pollution:

1. Be a part of the solution and not part of pollution.
2. Show your care, clean your air.

Water pollution:

1. Water, water everywhere, Not a drop to drink. The pollution is making all the water stink.
2. Save the fish and the little turtle. Don’t throw plastic or it will encircle.

Soil Pollution:

1. Don’t be mean, keep environment clean.
2. Let’s keep land clean, together only we can win.

7. Classify the following pollutants into natural and manmade categories.

Question
Classify the following pollutants into natural and manmade categories.
Sewage, dust, pollen grains, chemical fertilizers, vehicular smoke, algae, pesticides, waste of animals and birds.
Answer:

Man-made	Natural
1. Sewage	1. Dust (Natural)
2. Dust (Construction related)	2. Pollen grains
3. Chemical fertilizers	3. Algae
4. Vehicular smoke	4. Waste (Excreta) of animals and
5. Pesticides

Project:

Question 1.
Visit the water testing laboratory in your area and collect the information about tests for checking the purity of water.

Question 2.
Visit the square having heavy traffic in your area and report the pollution at different times of day and find out the duration of maximum pollution.

Class 8 Science Chapter 8 Pollution Additional Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
Natural pollutants are destroyed in due course of time by …………. .
Answer:
Natural pollutants are destroyed in due course of time by nature’s rule.

Question 2.
Air pollutants with ……….. cause colour change in paints, oil paintings, nylon, etc.
Answer:
Air pollutants with sulphur cause colour change in paints, oil paintings, nylon, etc.

Question 3.
Boards indicating the …………. are displayed in busy squares in metro cities.
Answer:
Boards indicating the air quality index are displayed in busy squares in metro cities.

Question 4.
Soil ………… decreases due to pollution.
Answer:
Soil fertility decreases due to pollution.

Question 5.
Problem of …………… pollution increases due to soil pollution.
Answer:
Problem of water pollution increases due to soil pollution.

State whether the following statements are True or False. Explain your statement:

Question 1.
Polluted water is responsible for diseases such as cholera, hepatitis, typhoid, skin diseases and diseases of the alimentary canal.
Answer:
True. (The water sources if they are contaminated with biological pollutants such as bacteria, viruses or protozoans, can cause variety of water-borne diseases.)

Question 2.
When water is mixed with natural or artificial unwanted material, the dissolved oxygen level of such water increases.
Answer:
False. (When water is mixed with natural or artificial unwanted material, the dissolved oxygen level of such water decreases. This causes harm to the resident animals. However when aquatic weeds and algae outgrow in number it causes rise in oxygen only during day time.)

Question 3.
Though any amount of pollutants are added to the soil, the toxic substances do not leach into water.
Answer:
False. (The toxic substances added to the soil can leach in the groundwater and cause water pollution.)

Identify the odd term:

Question 1.
Industrialization, Population explosion, Mining, Vehicular transport, Dust storms.
Answer:
Dust storms (All others are man-made causes environmental degradation.)

Question 2.
Poisoning, asthma, Silicosis, respiratory diseases.
Answer:
Silicosis (All others are effects of methane.)

Question 3.
Irritation of eyes, respiratory tract, excess mucus, mental weakness
Answer:
Mental weakness (All other are effects of sulphur dioxide.)

Question 4.
Volcanic eruption, Earthquake, Atomic explosion, Forest fires.
Answer:
Atomic explosion (All others are natural causes of air pollution.)

Question 5.
Uranium, Sulphur, Thorium, Plutonium.
Answer:
Sulphur (All others are elements which are used in the production of atomic energy.)

Consider the relation between the items in the first pair and write the correlation for second pair:

Question 1.
Industrialization: Sulphur compounds : :…………………. : Lead compounds
Answer:
Use of fuels/Transportation

Question 2.
City where smoke and soot caused it to be called black city : Petersburg : : Indian city where worst ever industrial accident has occurred : ……………….
Answer:
Bhopal

Question 3.
Arsenic and Cadmium : Inorganic water pollutants : : Weedicides and insecticides : ………….
Answer:
Organic water pollutants.

Write definitions:

Question 1.
Air pollution.
Answer:
Contamination of air by toxic gaseous and particulate pollutants in concentration which is harmful to human beings and his surroundings is called air pollution.

Question 2.
Water pollution.
Answer:
When toxic and unwanted substances enter, dissolve or remain suspended in the water bodies deteriorating the quality of water and affecting the aquatic ecosystem, then it is known as water pollution.

Question 3.
Soil pollution.
Answer:
Soil pollution is the phenomenon caused due to natural or man-made causes, which occurs when there are changes in its physical, biological and chemical properties of the soil leading to decreased fertility due to either natural or man-made reasons.

Distinguish between the following:

Question 1.
Degradable and Non-degradable pollutants:

Degradable pollutants	Non-degradable pollutants
1. Degradable pollutants can degrade on their own after some time.	1. non-degradable pollutants cannot degrade on their own.
2. Degradable pollutants are usually acted upon by microorganisms to reduce them to inorganic substances.	2. non-degradable pollutants are not acted upon by microorganisms and hence are not reduced to inorganic substances.
3. Degradable pollutants are not accumulated in nature.	3. non-degradable pollutants accumulate in nature and remain there for a long period of time.
4. Degradable pollutants emit foul odour when they are being decomposed.	4. non-degradable pollutants may not emit foul odour as they are not decomposed.
5. Vegetables and fruits, food refuse, organic matter, etc. form degradable pollutants.	5. Metals, plastic, glass, etc. form non-degradable pollutants.

Question 2.
Industrial waste and Domestic waste:

Industrial waste	Domestic waste
1. Most of the industrial waste contains non-degradable pollutants.	1. Most of the domestic waste contains bio-degradable pollutants.
2. Industrial wastes are produced during industrial and manufacturing processes.	2. Domestic wastes are produced in every home due to day to day activities.
3. Pollution monitoring and controlling bodies like MPCB keep a watch on the proportion of industrial wastes.	3. Pollution monitoring and controlling bodies like MPCB do not keep a watch on the proportion of domestic wastes. It is the individual responsibility of every citizen to reduce the amount of domestic waste that they produce.
4. Fly ash from thermal power plants, heavy metals, chemicals, etc. form the industrial wastes.	4. Garbage, domestic refuse, and discarded solid materials containing food waste, paper, cardboard, peels of fruits, vegetable matter, etc. form the domestic wastes.

Give scientific reasons:

Question 1.
Domestic sewage is harmful for all forms of life.
Answer:

1. Domestic sewage contains water
2. There are detergents and washing private vehicles. powders containing phosphate, which are used to soften the water.
3. These chemicals are harmful to aquatic animals.
4. They also contain disease. causing pathogenic bacteria and viruses.
5. Hence, domestic sewage is harmful for originating from kitchen, bathrooms, toilet, forms of

Question 2.
Use public transport instead of private vehicles.
Answer:

1. All the automobiles use fossil used to soften the water. fuels Burning of fossil fuels causes air pollution by gaseous pollutants as well as by particulates.
2. Toxic gases such as CO, CH₄, SO₂, etc. are emitted through automobile exhausts.
3. When each person uses private vehicles, the proportion of air pollution increases.
4. Instead, public transport helps to reduce air pollution it will also help to ease trafficams.
5. Therefore, as a role of citizen in pollution control, public transport should be used instead of private vehicles.

Question 3.
Due to agriculture, there can be a lot of air pollution.
Answer:

1. During agricultural practices, open field burning is done. Due to this burning there is emission of gases like SO₂, CO₂, CH₄, CO and oxides of nitrogen along with large amounts of particulate matter.
2. In agricultural practices, pesticides used emit toxic chemicals.
3. Industrial farms pollute air by emitting foul odour and airborne pollutants.
4. When manure is decomposed, there is production of greenhouse gases.

Question 4.
A hole has been observed in the ozone layer in the stratosphere near Antarctica.
Answer:

1. Ozone layer depletion is mainly caused due to the action of CFC (Chlorofluorocarbon) molecules in the air.
2. Due to various increased activities of humans, the magnitude of air pollution has been increasing in the last few decades.
3. CFC molecules were used as coolants in refrigerators, freezers and air conditioners.
4. They were also present in industrial solvents, dry cleaning agents and hospital sterilants, aerosols and foam. Due to such enhanced use, much of the CFCs were liberated in the last few years.
5. CFC molecules are decomposed by ultraviolet rays which release chlorine and fluorine molecules.
6. Chlorine and fluorine react with the ozone resulting in a hole in the ozone layer present in the stratosphere.

Therefore, a hole has been observed in the ozone layer in the stratosphere above Antarctica.

Answer the following.

Question 1.
What do you mean by ozone layer depletion? What are the causes of ozone layer depletion?
Answer:
1. The ozone layer is present at the top of the stratosphere. The stratosphere is the second layer of the atmosphere which is present 48 km above the earth’s surface.
2. Ozone layer is protective layer for living organisms of the earth, as it absorbs harmful UV rays from the sun. When this layer is reduced or destroyed, it is called ozone layer depletion.

3. Causes of the ozone layer depletion:

1. The main cause of ozone depletion are CFC molecules.
2. Chlorine atoms are present in chlorofluoro-carbons (CFC) molecules. They react with ozone and deplete it.
3. CFCs are used as coolants in refrigerators, freezers and air conditioners manufactured before 1995.
4. CFCs are also present in industrial solvents, dry cleaning agents and hospital sterilants (sterilizers), aerosols and foam. All the above materials release a lot of CFCs into the atmosphere.
5. CFC molecules are broken down by ultraviolet radiations which result in release of chlorine and fluorine, which further reduce the ozone layer.

Question 2.
What adverse effect does ozone depletion have?
Answer:

1. When the ozone layer is depleted, the ultraviolet radiations of the sun can reach the earth’s surface in greater proportion.
2. This results in damage to animal and plant life on the earth.
3. Ultraviolet rays cause skin cancer and cataract in human beings.
4. The ozone hole is seen in the stratosphere above Antarctica.

Question 3.
Describe the effects of air pollution on animals and plants.
Answer:
1. Effects of air pollution on animals:

• Air pollutants affect breathing of the animals.
• Particulate pollutants can cause problems to the wildlife.
• Particulate matter containing heavy metals is accumulated in the bodies of animals. The accumulated heavy metals at high levels in the body tissues, can cause problems. ‘
• Acid rain causes serious problems to animal life.

2. Effects of air pollution on plants:

• Various parts of the plant show reduced growth after coming in contact with air pollutants.
• The leaves show yellowing or chlorosis on exposure to air pollutants.

Question 4.
What are man-made reasons for water pollution?
Answer:
The effluents and other substances released by man into the surrounding water bodies together can be called man-made reasons for water pollution.
1. Domestic sewage: The excreta, urine and other domestic-use water is added to the water bodies in many cities and villages. In big metro-cities, the sewage is partially treated but these management practices are not enough.

2. Industrial effluent: Different industries and factories release effluents which may contain toxic and harmful components, such as various pigments, bleaching chemicals, leather pieces, fibres, mercury, lead, etc.

3. Oil pollution: Oil spillages are seen in the seas due to leakage of crude oil. The crude oil is hazardous as it contains cancer causing hydrocarbons.

4. Fertilizers and pesticides: These compounds when used in farm, may get washed off to nearby water body. The chemical fertilizer containing N, P, K cause water pollution. Pesticides such as endrin, chlorine, carbonate containing pesticides, etc. are mixed with water. They cause contamination of the aquatic animals.

5. The wrong behaviour of human beings causes water pollution. The addition of wastes, defecation near coasts, washing clothes, decomposing hemp and flax in water, disposal of ashes, floral offerings to god, dumping ashes all such activities result into water pollution.

6. The warm water released into the water body through thermal power plants cause thermal pollution.

Question 5.
What are the effects of water pollution on human beings?
Answer:
The water-borne diseases that are caused by different bacteria and viruses cause infections to human beings through contaminated water. Some bacterial and viral diseases are spread through epidemics. Cholera, hepatitis, enteritis, diarrhoea, typhoid are such diseases that can cause severe infections to man. Polluted water also cause skin diseases and deformities of bones, Some pollutants accumulated in vital organs cause their ailments. Liver, kidneys, brain, etc. are affected in this way. Person may develop hypertension too due to pollutants.

Question 6.
What are the effects of water pollution on the ecosystem?
Answer:
Biological effects:

1. Plants in the ecosystem show retarded growth, resulting into species loss.
2. Due to imbalance in the ecosystem, the food chain and food web is disturbed.
3. Pollutants cause mortality in fish and other aquatic animals.
4. Oil slick causes harmful impact on the marine birds.
5. Useful bacterial fauna in the water is lost.

Abiotic effects:

1. Pollutants cause changes in physical and chemical properties of water.
2. Salinity of the water changes.
3. Dissolved oxygen in the water is depleted, causing mortality of fishes.

Question 7.
Describe the effects of air pollution on the environment.
Answer:
Air pollution can cause the following serious effects on the environment:

1. Deforestation and fuel consumption bring about rise in CO₂ concentration.
2. Excess CO₂ in air causes rise in atmospheric temperature of the earth.
3. The increased temperature is called global warming.
4. The global warming results into melting of glaciers, subsequently causing rise in the sea level.
5. There is a change in the climate and pattern of rainfall. This may indirectly affect the agricultural production.

Question 8.
Describe the effects of soil pollution.
Answer:
Effect of soil pollution:

1. There are many pathogenic bacteria, viruses and parasitic intestinal worms in the sewage sludge. These are able to cause many diseases.
2. Soil and vegetable crops are contaminated by manure made from human and animal excreta containing pathogens. This can lead to various diseases.
3. There is loss of fertility and productivity of soil and land due to soil pollution.
4. Soil pollution leads to water pollution, when toxic chemicals leach into the groundwater. Similarly, when contaminated soil enters into streams or lakes, it also causes water pollution.
5. Radioactive materials and soil contaminants can travel through food chains. They move away from the soil into crops, livestock and human bodies.

Question 9.
How do biodegradable and non- biodegradable wastes cause land pollution?
Answer:

1. Biodegradable material is mainly present in the domestic waste.
2. It is in the form of food waste, peels of fruits, vegetables, etc.
3. Paper is also a main part of the domestic waste which is biodegradable.
4. Polythene bags, plastic waste and footwear, etc. are non-biodegradable waste from the domestic sources. All of these pollute the land.

Question 10.
How do you protect soil from being polluted?
Answer:

1. We should not throw domestic waste and industrial waste indiscriminately on the land, so that it contaminates soil.
2. Proper disposal of solid wastes and more importantly safe disposal of biomedical waste material should be practised.
3. Instead of throwing non-biodegradable materials on the land, they should be properly recycled and reused.
4. Biodegradable materials should be composted and converted into useful manure, rather than throwing them to cause pollution of the soil.
5. Excessive use of fertilizers and pesticides should be avoided so that the soil does not get contaminated.

Question 11.
What are the different laws to prevent pollution?
Answer:
The different laws to prevent pollution are as follows:

1. Water (Prevention and Control of Pollution) Act, 1974.
2. Air (Prevention and Control of Pollution) Act, 1981.
3. Environment (Protection) Act, 1986.
4. There are different laws and rules which have been made for the disposal of hazardous waste, biomedical waste, solid waste and prevention of noise pollution.

Question 12.
Who implements the laws related to pollution?
Answer:
The Central Pollution Control Board (CPCB) and Maharashtra Pollution Control Board (MPCB) check whether the organizations like factories, industrial estates, Municipalities, Zilla Parishads, Panchayat Samities and Gram Panchayats follow all the laws related to control of pollution.

Use your brain power!

Question 1.
Which types of pollutants are observed?
Answer:
Pollutants are of many varied types. They can be classified according to their sources, according to which ecosystem they are polluting, and according to their characteristics.

Question 2.
Whether the pollutants are degradable or non-degradable?
Answer:
Some pollutants are biodegradable while some are non-biodegradable. The pollutants that spread in the air are in the form of gases or particulate matter. Though they are non-degradable, they constantly make chemical reactions with each other.

The pollutants thrown in water and on land are of both the types. Pollutant like plastic is totally non-biodegradable. The biodegradable substances can be decomposed by various bacteria and fungand are converted back into elemental form. The pollutants added in S the water are also of two types. The heavy metals and colours are non-degradable.

Think about it:

Question 1.
If natural materials are pollutants, why do we not perceive their adverse effects during their use? When such materials are referred as pollutants?
Answer:
The natural pollutants are active only for a short duration. Due to natural reasons their activity is limited, and they are lost after a specific time. Their sources are not continuous and their spread too is not regular as in case of man-made pollutants which are emitted steadily.

Thus, we can avoid these substances. We also use them in limited quantity. Therefore, the natural substances, though may be polluting in nature, we are unable to perceive its toxicity. However, if we use them in abundance and create an imbalance, then its effect can be experienced as a great hazard.

Question 2.
What are the reasons other than those mentioned on the textbook page no. 55 mentioned responsible for air pollution?
Answer:
1. The automobile vehicles like two-wheelers and four-wheelers are increasing tremendously in numbers. This uncontrolled number of vehicles and their heavy traffic is causing air pollution to very high level in megacities.
2. Construction industries, demolition of the old buildings, digging the roads, are such activities which are adding to the particulate air pollution of the cities.
3. The bursting of firecrackers on the occasion of festivals and ceremonies, the spread of gulal during processions are also actions which result into unwanted air pollution.
4. Aeroplane traffic, rocket launching, industrial farming are the modern sources of air pollution.

Question 3.
Whether the vehicles with two- stroke engine cause more pollution than four stroke engine?
Answer:
Yes, they do. Scooters and motor cycles are more dominant source of air pollution as they emit soot and organic particles. In urban areas this proportion is high. These particles are toxic and they create heavy air pollution.

The two-wheelers have two-stroke engines. Such engines are far less efficient in burning the fuel that is used in the vehicles. The exhaust systems are also less effective at removing pollutants. On the contrary most of the four-wheelers have catalytic converters. Therefore, the exhaust fumes from scooters contain higher levels of the chemicals found in the fuel and oil they use.

The vehicles with two-stroke engine such as two wheelers emit significantly more primary organic aerosols and volatile organic compounds from incomplete burning of the fuel. They also produce significant secondary organic aerosols as gases released from the exhaust react with the air and microscopic particles of soot.

These pollutants increase the risk of heart and lung disease. Older two-stroke vehicles produced reactive oxygen molecules that are known to be potentially harmful for lung health. In recent times there is excessive use of two-wheelers which is deteriorating the air quality to great extent.

Question 4.
Give 5 examples of each of domestic waste, biological waste and agricultural waste and write in your own words about soil pollution due to those wastes.
Answer:
Domestic waste:

1. Empty containers of medicines, papers, bottles, etc.
2. Plastic
3. Glass pieces
4. Old utensils, clothes
5. Tins and cartons of used items, the discarded household items.

Biological waste:

1. Dead corpse of animals.
2. Urine and faeces
3. Peels of fruits, stalks of vegetables and fruits.
4. Food waste
5. Garlands and old bouquets.

Agricultural waste:

1. The stubs of crops after the grains are removed.
2. Cattle dung and urine
3. Some persistent amount of insecticides
4. Some amount of fertilizers
5. Empty containers, bags, cartons of insecticide, chemical fertilizers, seeds, gunny bags, etc.

Diagram based questions:

Question 1.
Given below is a diagram showing hazardous polluting event.
Explain what is this and what are its effects shown in the diagram.

Answer:
The above picture depicts the formation and effects of acid rain. The toxic gases such as SO2 , CO2 and NO2 are released through the chimneys of factories. These oxides are released in air. They get dissolved in the rainwater and reach back the earth’s surface in the form of acids. The plants, animals and houses are being damaged due to this acid rain.

Question 2.
Draw a well labelled diagram to show greenhouse effect.
Answer:

Activity based questions:

Question 1.
Discuss the issues like ‘dry waste-wet waste’ and ‘toilet in each home’ and write information in your own words.

MCQs based on practical:

Question 1.
Which fertilizers when used in excessive amounts cause soil pollution that spreads to neighbouring water bodies and cause water pollution too?
(a) Chemical
(b) Organic
(c) Artificial
(d) Compost
Answer:
(a) Chemical

Question 2.
What is the type of pollutants that are present in the industrial effluents that is released in the rivers and sea?
(a) Inorganic
(b) Organic
(c) Biological
(d) Biomedical
Answer:
(a) Inorganic

Question 3.
What grows in excess when eutrophication of the water bodies take place?
(a) Plants
(b) Algae
(c) Fishes
(d) Fungi
Answer:
(b) Algae

Question 4.
Which of the following is seen in the polluted water body?
(1) flowers used in pooja
(2) fruits
(3) fishes
(4) aquatic insects
(5) plastic bags
(6) turtles
(7) thick growth of algae
(8) light blue colour of water
(9) cattle wading in water
(10) broken idols
(a) (1) (3) (5) (6) (9) (10)
(b) (1) (2) (5) (7) (9) (10)
(c) (1) (3) (6) (8) (9) (10)
(d) (1) (2) (4) (7) (8) (9)
Answer:
(b) (1) (2) (5) (7) (9) (10)

Question 5.
Which is the easiest method to identify the polluted water?
(a) To taste the water
(b) To check the depth of water
(c) To observe colour and odour of the water
(d) To swim in the water
Answer:
(c) To observe colour and odour of the water

Formative Evaluation:

Question 1.
Which factors are responsible for pollution shown in the following pictures?

Question 2.
Compare the two neighbouring photographs.

Balbharti Maharashtra State Board Class 8 Science Solutions Chapter 7 Metals and Nonmetals Notes, Textbook Exercise Important Questions and Answers.

Maharashtra State Board Class 8 Science Solutions Chapter 7 Metals and Nonmetals

Class 8 Science Chapter 7 Metals and Nonmetals Textbook Questions and Answers

1. Complete the table:

Question a.

Answer:

Property of metal	Use in everyday life
i. Ductility	i. Gold, silver ornaments
ii. Malleability	ii. Aluminium sheets, galvanised sheets
iii. Conduction of heat	iii. Stainless steel vessels, copper vessels, boilers
iv. Conduction of electricity	iv. Copper wires
v. Sonority	v. Brass articles

2. Identify the odd term.

Question a.
Gold, Silver, Iron, Diamond.
Answer:
Diamond. (Others are metals.)

Question b.
Ductility, Brittleness, Sonority, Malleability.
Answer:
Brittleness. (Other properties are metallic properties.)

Question c.
Carbon, Bromine, Sulphur, Phosphorus.
Answer:
Bromine. (Others are solids.)

Question d.
Brass, Bronze, Iron, Steel.
Answer:
Iron. (Others are alloys.)

3. Give scientific reasons:

Question a.
The stainless steel vessels in kitchen have copper coating on the bottom.
Answer:

1. Stainless steel is an alloy of iron ; with carbon, chromium and nickel.
2. The conductivity of copper is higher than that of iron in steel. Copper heats uniformly and faster. The time for cooking is reduced, as a result it saves fuel. Hence, the stainless steel vessels in kitchen have copper coating on the bottom.

Question b.
Copper and brass vessels are cleaned with lemon.
Answer:

1. Copper undergoes oxidation in air to form black copper oxide. Copper oxide reacts slowly with carbon dioxide in air and gains a green coat. This green substance is copper carbonate.
2. Lemon contains acid. The acid dissolves the green coating of basic copper carbonate present on the surface of a tarnished copper and brass vessels and makes them shiny again.

Question c.
Sodium metal is kept in kerosene.
Answer:

1. Sodium reacts so vigorously with atmospheric oxygen and water that it catches fire if kept in the open.
2. It does not react with kerosene and sinks in it. Hence, to protect sodium and to prevent accidental fires it is always kept in kerosene.

4. Answer the following: 

Question a.
What is done to prevent corrosion of metals?
Answer:
By applying a layer of paint, oil, grease or varnish on the surface of a metal to prevent corrosion. Also plating with noncorroding metal is done. Iron is coated with thin layer of zinc. Due to these processes the contact of metal surface with air is lost and corrosion is prevented.

Question b.
What are the metals that make the alloys brass and bronze?
Answer:
The alloy brass is formed from copper and zinc and the alloy bronze is formed from copper and tin.

Question c.
What are the adverse effects of i corrosion?
Answer:

1. A reddish coloured deposit (rust) is formed on iron by reaction with oxygen gas.
2. A greenish coloured deposit (copper carbonate) is formed on copper by reaction with carbon dioxide.
3. A blackish coloured deposit is formed (silver sulphide) on silver.
4. Corrosion causes damages to car bodies, bridges, iron railings, ships specially those of iron, silver articles and copper vessels.

Question c.
What are the uses of noble metals?
Answer:
Uses of Noble Metals:

1. Gold, silver and platinum are used to prepare ornaments.
2. Silver is used in medicines. (It has antibacterial property).
3. Gold and silver are also used to make metals and few electronic devices.
4. Platinum, palladium metals are used as catalyst.

5. Three experiments to study the process of rusting are given below. Observe the three test tubes and answer the following questions.

Question a.
Why the nail in the test tube 2 is not rusted?
Answer:
In the test tube 2, oil cuts the supply of air to nail due to which oxidation of nail is prevented and boiled water is free from gases. Hence, the nail in the test tube 2 is not rusted.

Question b.
Why is the nail in the test tube 1 is rusted highly?
Answer:
The nail in the test tube 1 is highly rusted because nail is in contact with water and air. The oxidation process is fast.

Question c.
Would the nail in the test tube 3 get rusted?
Answer:
No change is observed in the test tube 3. Nail remains as it is because the calcium chloride absorbs moisture, making the air dry, thus preventing rusting of the nail.

Project:

Question a.
How is the Varkha or silver foil used in sweets made? Collect the information about which metals are used to make ‘Varkha’.

Class 8 Science Chapter 7 Metals and Nonmetals Additional Important Questions and Answers

Rewrite the sentences after filling the blanks:

Question 1.
Gold of 100% purity is …………… carat gold.
Answer:
Gold of 100% purity is 24 carat gold.

Question 2.
The stainless steel utensils used at home are made of an alloy of iron with carbon, …………… and ……….. .
Answer:
The stainless steel utensils used at home are made of an alloy of iron with carbon, nickel and chromium.

Question 3.
…………….. is used in medicines.
Answer:
Silver is used in medicines.

Question 4.
To prepare ornaments ………… carat gold is used.
Answer:
To prepare ornaments 22 carat gold is used.

Question 5.
Non-metals are ………… conductors of heat and electricity.
Answer:
Non-metals are bad conductors of heat and electricity.

Question 6.
Non-metals form ………….. oxides.
Answer:
Non-metals form acidic oxides.

Question 7.
Some element can be hammered into thin sheets. This property is called …………….. .
Answer:
Some element can be hammered into thin sheets. This property is called malleability.

Question 8.
Iodine and ……………. are the two non – metals having typical metallic lustre.
Answer:
Iodine and diamond are the two non¬metals having typical metallic lustre.

Question 9.
Non-metals form ………. ions by gain of electrons.
Answer:
Non-metals form negative ions by gain of electrons.

Question 10.
During formation of positively charged ion, atom of metal ………….. .
Answer:
During formation of positively charged ion, atom of metal lose electrons.

Rewrite the following statements by selecting the correct options:

Question 1.
Metalloids have properties of …………. .
(a) metals
(b) non-metals
(c) both metals and non-metals
(d) neither metals nor non-metals
Answer:
(c) both metals and non-metals

Question 2.
………….. is a metal.
(a) Hg
(b) S
(c) P
(d) Br
Answer:
(a) Hg

Question 3.
…………… is a non-metal.
(a) Aug
(b) Ag
(c) Br
(d) Cu
Answer:
(c) Br

Question 4.
……………. is a metalloid.
(a) Aluminium
(b) Antimony
(c) Zinc
(d) Mercury
Answer:
(b) Antimony

Question 5.
……………. is a metal which is in liquid form at ordinary temperature.
(a) Gallium
(b) Magnesium
(c) Sodium
(d) Scandium
Answer:
(a) Gallium

Question 6.
…………….. is an acidic oxide.
(a) Na₂O
(b) CO₂
(c) FeOs
(d) H₂O
Answer:
(b) CO₂

Question 7.
The valence electron in …………… atom is 1.
(a) magnesium
(b) sodium
(c) silicon
(d) aluminium
Answer:
(b) sodium

Question 8.
The electronic configuration of oxygen is …………….. .
(a) 2, 5
(b) 2, 6
(c) 2, 4
(d) 2, 8, 6
Answer:
(b) 2, 6

Question 9.
Pure ………… is soft.
(a) aluminium
(b) silver
(c) gold
(d) platinum
Answer:
(c) gold

Question 10.
…………… is a highly malleable metal.
(a) Iron
(b) Nickel
(c) Manganese
(d) Aluminium
Answer:
(d) Aluminium

Question 11.
22 carat gold is gold of …………… purity.
(a) 100%
(b) 91.66%
(c) 75%
(d) 44%
Answer:
(b) 91.66%

State whether the following statements are True or False:

Question 1.
Metals are sonorous.
Answer:
True.

Question 2.
Diamond is the softest natural substance.
Answer:
False. (Diamond is the hardest natural substance.)

Question 3.
The density of lithium is lower than water.
Answer:
True.

Question 4.
Sulphur is brown in colour.
Answer:
False. (Sulphur is yellow in colour.)

Question 5.
Germanium is a metalloid.
Answer:
True.

Question 6.
Ornaments are made from 24 carat gold.
Answer:
False. (Ornaments are made from 22 carat gold.)

Question 7.
A reddish coloured deposit is formed on iron by reaction with oxygen.
Answer:
True.

Question 8.
Paladium and rhodium are noble metals.
Answer:
True.

Question 9.
The metal oxides are acidic in nature.
Answer:
False. (The metal oxides are basic in nature.)

Question 10.
The metal reacts with dilute acids to form a metal salt.
Answer:
True.

Identify the odd term:

Question 1.
Magnesium, Mercury, Sodium, Iron.
Answer:
Mercury. (Others metals are in solid state at normal temperature.)

Question 2.
Magnesium, Aluminium, Sulphur, Copper.
Answer:
Sulphur. (Others are metals.)

Question 3.
Iron, Copper, Graphite, Phosphorus.
Answer:
Phosphorus. (Others are good conductors of electricity.)

Question 4.
Tin, Bronze, Steel, Stainless steel.
Answer:
Tin. (Others are alloys.)

Consider the relation between the items in the first pair and write the correlation for second pair:

Question 1.
Mercury : Metal : : Carbon : …………. .
Answer:
Non-metal

Question 2.
Wood : Bad conductor of electricity : : Copper : ………………… .
Answer:
Good conductor or electricity

Question 3.
Gold : Noble metal : : Copper: ……………. .
Answer:
Metal

Question 4.
Iron and carbon : Steel : : Copper and Tin : ……….. .
Answer:
Bronze

Question 5.
0 : 2, 6 : : Mg : …………….. .
Answer:
2, 8, 2.

Match the columns:

Question 1.

Column ‘A’	Column ‘B’
1. Copper	a. Low melting point
2. Sodium	b. Liquid
3. Magnesium	c. High melting point
4. Boron	d. Conduction of heat
	e. 2, 8, 2

Answer:

Column ‘A’	Column ‘B’
1. Copper	d. Conduction of heat
2. Sodium	a. Low melting point
3. Magnesium	e. 2, 8, 2
4. Boron	c. High melting point

Question 2.

Column ‘A’	Column ‘B’
1. Silver	a. Copper + tin
2. Mercury	b. Medicines
3. Platinum	c. Thermometer
4. Brass	d. Catalyst

Answer:

Column ‘A’	Column ‘B’
1. Silver	b. Medicines
2. Mercury	c. Thermometer
3.Platinum	d. Catalyst
4. Brass	a. Copper + tin

Define the following:

1. Ductility: The property due to which a substance can be drawn into a thin wire is called ductility.
2. Malleability: The property due to which a substance can be hammered into a thin sheet is called malleability.
3. Metalloids: The element which shows the properties of metals as well as those of non-metals is called a metalloid.
4. Corrosion: Gases in the air react with metals in presence of moisture to form metal compounds on its surface, this destroys the metal gradually and is called corrosion.
5. Alloy: A homogeneous mixture of two or more metals or a homogeneous mixture of metal with non-metals is called alloy.

Answer the following questions in one sentence:

Question 1.
Name an alloy of copper and tin.
Answer:
An alloy of copper and tin is termed as bronze.

Question 2.
Name a metal which is in liquid state at ordinary temperature.
Answer:
Mercury is in liquid state at ordinary temperature.

Question 3.
Name two metals which are malleable.
Answer:
Iron and aluminium are malleable metals.

Question 4.
Name two metals which are ductile.
Answer:
Gold and silver are ductile metals.

Question 5.
Name two metals which are good conductors of heat.
Answer:
Silver and copper are good conductors of heat.

Question 6.
Name two metals which are good conductors of electricity.
Answer:
Copper and aluminium are good conductors of electricity.

Question 7.
Name two non-metals which are in solid state at room temperature.
Answer:
Carbon and sulphur are solids at room temperature.

Question 8.
Name two non-metals which are in gaseous state at room temperature.
Answer:
Hydrogen and oxygen are in gaseous state at room temperature.

Question 9.
Name the non-metal having electrical conductivity.
Answer:
Graphite has electrical conductivity.

Question 10.
Name two non-metals which are lustrous.
Answer:
Iodine and diamond are lustrous in nature.

Question 11.
Name two non-metals having high melting points.
Answer:
Carbon and boron melt at high temperature.

Question 12.
State two metals which can be cut easily with a knife.
Answer:
Sodium and potassium are soft metals and can be cut easily with a knife.

Question 13.
Which is the hardest natural substance?
Answer:
Diamond, which is a form of carbon is the hardest natural substance.

Question 14.
State the property of the metals for which they can be drawn into wires.
Answer:
The property of the metals due to which they can be drawn into wires is called ductility.

Question 15.
State the property of the metals due to which they can be beaten into thin sheets.
Answer:
The property of the metals due to which they can be beaten into thin sheets is called malleability.

Question 16.
Which of the following metals react with cold water? Sodium, iron, copper, potassium.
Answer:
Sodium and potassium metals react with cold water.

Question 17.
Which of the following metals do not react with cold water or hot water?
Answer:
Aluminium and iron do not react with cold water or hot water.

Question 18.
What are the constituents of stainless steel?
Answer:
Iron with carbon, chromium and nickel are the constituents of stainless steel.

Question 19.
State the term used to express the purity of gold.
Answer:
The purity of gold is expressed in carat.

Question 20.
Name two metals having low melting points and boiling points.
Answer:
Sodium and potassium having low melting points and boiling points.

Question 21.
Name a non-metal which is in liquid state at room temperature.
Answer:
Bromine is in liquid state at room temperature.

Question 22.
State the atomic number and electronic configuration of sodium.
Answer:
Atomic number of sodium: 11.
Electronic configuration of sodium (Na): 2, 8, 1.

Question 23.
State the atomic number and electronic configuration of aluminium.
Answer:
Atomic number of aluminium: 13.
Electronic configuration of aluminium (Al): 2, 8, 3.

Question 24.
Give two example of metalloids.
Answer:
Metalloids: Arsenic (As),
germanium (Ge), antimony (Sb).

Question 25.
State the atomic number and electronic configuration of nitrogen.
Answer:
Atomic number of nitrogen: 7.
Electronic configuration of nitrogen (N): 2, 5.

Answer the following questions:

Question 1.
A metal can be drawn into a wire. Explain why.
Answer:

1. The property due to which a substance can be draw into a thin wire is called ductility.
2. Metals are ductile. Thus, a metal can be draw into a wire.

Question 2.
A metal can be hammered into a i thin sheet. Explain why.
Answer:

1. The property due to which a substance can be hammered (or rolled) into a thin sheet without cracking is called malleability.
2. Metals are malleable. Thus, a metal can be hammered to form a thin sheet.

Question 3.
State the properties of metals.
Answer:

1. Metals have a lustre.
2. Metals are malleable. They can be beaten into thin sheets.
3. Metals are ductile. They can be drawn into wires.
4. They are good conductors of heat and electricity.
5. At ordinary temperature, metals are generally solid. (Exception: Mercury is liquid.)
6. Metals usually have high density.

Question 4.
State the properties of non-metals.
Answer:

1. Non-metals lack lustre.
2. As non-metals are brittle, they are not malleable.
3. They are not ductile.
4. Non-metals are poor conductors of heat and electricity.
5. At ordinary temperature, non-metals are in the solid or gaseous state. (Exception: Bromine is liquid.)
6. Non-metals have low density in the solid state.

Question 5.
How are metal ions formed? Give two examples.
Answer:
Metals have a tendency to lose their valence electrons to form positively charged ions, called cations.
Examples:

Question 6.
Classify the following elements into metals and non-metals :
Silicon, gold, silver, sulphur, carbon, aluminium, copper and phosphorus.
Answer:
Metals: Gold, silver, aluminium and copper.
Non-metals: Silicon, sulphur, carbon and phosphorus.

Question 7.
How are metal oxides formed? Explain with an example.
Answer:
Metals combine with oxygen in the ’ air to form their oxides.
Metal + Oxygen → Metal oxide
[Note: Reaction/explanation given in the screen are for better understanding of students. The same are not given in the textbook.]
When magnesium burns in air, it combines with oxygen to form magnesium oxide.
2Mg + O₂ → 2MgO
Magnesium Oxygen Magnesium oxide

Question 8.
How will you show that metal oxides are basic in nature?
Answer:
1. Take magnesium oxide in a test S tube. Add water in the test-tube. Shake the test-tube. Test the solution with red and blue litmus paper. Blue litmus paper remains as it is while red litmus paper turns blue. This shows that metal oxides are basic in nature.

2. Metal oxides react with an acid to form salt and water. Therefore, metal oxides are basic in nature.
Metal oxide + Acid → + Water

Question 9.
How do metals react with acid? Explain with an example.
Answer:
The metals react with dilute acids to form metal salts. Metals liberate hydrogen gas from dilute acids.
Metal + Dilute acid → Metal salt + Hydrogen gas.
Magnesium reacts with dilute HCl to form magnesium chloride and hydrogen gas.

Question 10.
How do metals react with water? Explain with an example.
Answer:
Most metals do not react with cold water. But some metals like sodium and potassium react with cold water to form their hydroxides and hydrogen gas.
Sodium reacts with water to form sodium hydroxide.

Question 11.
How do non-metals react with oxygen? Explain with an example.
Answer:
Non-metals combine with oxyen to form their oxides.
Non-metal + Oxygen → Non-metal oxide
When carbon burns in air, it combines with oxygen to form carbon dioxide.

Question 12.
How will you show that non- metal oxides are acidic in nature?
Answer:
1. Take non-metal oxide in a test tube. Add water in the test tube. Test the solution with blue and red litmus paper. Red litmus paper remains as it is while blue litmus paper turns red. This shows that non¬metal oxides are acidic in nature.

2. The oxides of non-metals are acidic in nature. They react with bases to form soluble salt and water. Therefore, non-metal oxides are acidic in nature.
C + O₂ → CO₂
CO₂ + 2NaOH → Na2CO₃ + H₂O

Question 13.
How are non-metal ions formed? Give two examples.
Answer: Non-metals have a tendency to accept electrons in their valence shell to form negatively charged ions called anions.
Examples:

Question 14.
What is meant by noble metals? Give two examples.
Answer:
Some metals like gold, silver, platinum, paladium and rhodium are found in nature in the form of elements. They are not affected by air, water, acids and heat etc. Hence, they are called noble metals.

Give scientific reasons:

Question 1.
Ornaments are generally not made from 24-carat gold.
Answer:

1. 24-carat gold is considered as gold of 100% purity.
2. 24-carat pure gold is very soft. 100% pure gold breaks due to pressure or gets bent easily. Therefore, ornaments are generally not made from 24-carat gold.

c

Question 2.
Ships are painted at frequent intervals.
Answer:
1. The metal sheets of ships are made from iron.
2. Due to salty seawater, the metal sheets of ships get rusted and corroded. Paints contain metals like zinc or magnesium. This prevents the metal surface of the ship coming into direct contact with salty seawater. Therefore, ships are painted at frequent intervals.

Question 3.
Gold and platinum are called noble elements.
Answer:

1. The metals such as gold and platinum are found in nature in the form of elements.
2. They are not affected by water, air, acids, heat and also do not take part in chemical reactions. Hence, they are called noble metals.

Explain the following reactions with the help of balanced equations:

Question 1.
Magnesium combines with oxygen.
Answer:
Magnesium combines with oxygen to form magnesium oxide.

Question 2.
Magnesium oxide reacts with dilute HCl.
Answer:
When magnesium oxide reacts with dilute HCl, magnesium chloride (salt) and water are formed.

Question 3.
Magnesium reacts with dilute HCl.
Answer:
When magnesium reacts with dil.
hydrochloric acid, magnesium chloride is formed and hydrogen gas is evolved.

Question 4.
Sodium reacts with water.
Answer:
When sodium reacts with water, sodium hydroxide and hydrogen gas are formed.

Question 5.
Carbon burns in air.
Answer:
When carbon burns in air, carbon dioxide is formed.

Question 6.
Carbon dioxide reacts with sodium hydroxide.
Answer:
When carbon dioxide reacts with sodium hydroxide, soluble salt sodium ; carbonate and water are formed.

Question 7.
Carbon dioxide reacts with water.
Answer:
When carbon dioxide reacts with water, carbonic acid is formed.

Question 8.
Sulphur dioxide reacts with water.
Answer:
When sulphur dioxide reacts with water, sulphurous acid is formed.

Question 9.
Sulphur trioxide reacts with water.
Answer:
When sulphur trioxide reacts with water, sulphuric acid is formed.

Write short notes:

Question 1.
The noble metals.
Answer:
Some metals like gold, silver, platinum, paladium and rhodium are found in nature in the form of elements. They are not affected by air, water, acids and heat etc. Hence, they are called noble metals.

Uses of Nobel Metals:

1. Gold, silver and platinum are used to prepare ornaments.
2. Silver is used in medicines. (It has antibacterial property).
3. Gold and silver are also used to make metals and few electronic devices.
4. Platinum, palladium metals are used as catalyst. .

Question 2.
The purity of gold.
Answer:
1. The purity of gold is measured in carats.
2. Twenty-four carat gold is considered as gold of 100% purity.
3. 24-carat pure gold is very soft. 100% pure gold bends easily or breaks due to pressure. Therefore, copper or silver is added to gold in the necessary proportion (while making ornaments).
4. Generally, 22-carat gold is used in making ornaments.

Percentage of gold	Carat
100%	24
91.66%	22
75%	18
58.33%	14
50%	12
41.66%	10

Question 3.
Corrosion.
Answer:
Corrosion: Gases in the air react with metals in presence of moisture to form metal compounds on its surface, this destroys the metal gradually and is called corrosion.

By applying a layer of paint, oil, grease or varnish on the surface of a metal to prevent corrosion. Also plating with noncorroding metal is done. Iron is coated with thin layer of zinc. Due to these processes, the contact of a metal surface with air is lost and corrosion is prevented.

1. A reddish coloured deposit (rust) is formed on iron by reaction with oxygen gas.
2. A greenish coloured deposit (copper carbonate) is formed on copper by reaction with carbon dioxide.
3. A blackish coloured deposit is formed (silver sulphide) on silver.
4. Corrosion causes damages to car bodies, bridges, iron railings, ships specially those of iron, silver articles and copper vessels.

Question 4.
Alloys.
Answer:

1. A homogeneous mixture of two or more metals or of metals and non-metals is called an alloy.
2. They contain metals in specific proportions.
3. The physical properties of an alloy are different from those of its constituents, but chemical properties remain the same.
4. Copper and tin are used to make an alloy called bronze. It is hard and corrosion resistant.
5. When iron and carbon are mixed, an alloy steel is formed. It is a stronger material.
6. The alloy, stainless steel is made from iron, carbon, nickel and chromium. It is more durable, clean and does not rust.

Distinguish between the following:

Question 1.
Metals and Non-metals
Answer:

Metals	Non-metals
1. Metals have lustre.	1. Non-metals do not have lustre.
2. Metals are malleable.	2. Non-metals are not malleable.
3. Metals are ductile.	3. Non-metals are not ductile.
4. Metals are good conductors of heat and electricity.	4. Non-metals are poor conductors of heat and electricity.
5. At room temperature, metals are in the solid state. (Exception : Mercury is liquid.)	5. At room temperature, non-metals are in the solid, or gaseous state. (Exception Bromine. It is in liquid state.)
6. Generally, metals have high densities.	6. Generally, non-metals have lower densities.