Living Science Chemistry Class 6 ICSE Solutions Chapter 6 Air

ICSE Living Science Chemistry for Class 6 Solutions Chapter 6 Air

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Answer these questions.
Question 1.
What is atmosphere ?
Answer:
The blanket of air that envelopes the earth is called atmosphere.

Question 2.
Name the main components of air.
Answer:
The main components of air are nitrogen (78%) and oxygen (21%). It also contains small amounts of carbon dioxide, water
vapour, inert gases and dust particles.

Question 3.
Is air a mixture or a compound ?
Answer:
Air is a mixture (of gases, water vapour, dust particles, etc)

Question 4.
What happens when carbon dioxide is passed through lime water ?
Answer:
When carbon dioxide is passed through lime water, the lime water turns milky.

A. Tick the most appropriate answer.

Question 1.
Which of the following is the major constituent of air ?
a. Oxygen
b. Nitrogen
c. Carbon dioxide
d. None of these
Answer:
b. Nitrogen

Question 2.
Which of the following is not a greenhouse gas ?
a. Carbon dioxide
b. Methane
c. Nitrous oxide
d. Oxygen
Answer:
d. Oxygen

Question 3.
Which of these gases is released during the process of respiration ?
a. Oxygen
b. Nitrogen
c. Carbon dioxide
Answer:
c. Carbon dioxide

Question 4.
The fuel used in public transport to reduce pollution is
b. CNG
d. petrol
Answer:
b. CNG

Question 5.
Rusting takes place in the presence of
a. nitrogen and oxygen
b. carbon dioxide and nitrogen
c. oxygen and water vapour
d. nitrogen and water vapour
Answer:
c. oxygen and water vapour

Question 6.
In galvanization, iron metal is coated with a thin layer
b. copper
d. chromium
Answer:
a. zinc

B. Fill in the blanks.

Question 1.
The blanket of air that surrounds the earth is called the ………….
Answer:
The blanket of air that surrounds the earth is called the atmosphere.

Question 2.
………….. controls the rate of burning.
Answer:
Nitrogen controls the rate of burning.

Question 3.
…………… gas is necessary for burning or combustion.
Answer:
Oxygen gas is necessary for burning or combustion.

Question 4.
During respiration ………….. and ………… are released along with energy.
Answer:
During respiration carbon dioxide and water vapour are released along wkn energy.

Question 5.
………….. are burned to cook food, generate heat and run
vehicles.
Answer:
Fuels are burned to cook food, generate heat and run vehicles.

Question 6.
The process in which green plants use carbon dioxide and water to prepare food with the help of chlorophyll and in the presence of sunlight is called ………………
Answer:
The process in which green plants use carbon dioxide and water to prepare food with the help of chlorophyll and in the presence of sunlight is called photosynthesis.

C. State if the following statements are true or false. Correct the statement if it is false.

Question 1.
Oxygen is the main component of air in terms of percentage by volume.
Answer:
False. Nitrogen is the main component of air in terms of percentage by volume.

Question 2.
Burning and respiration require oxygen.
Answer:
True

Question 3.
Excess water vapour increases the rate of evaporation.
Answer:
False. Excess water vapour decreases the rate of evaporation.

Question 4.
Respiration takes place only in animals.
Answer:
False. Respiration takes place in all living organisms (plants and animals).

Question 5.
During photosynthesis carbon dioxide is released.
Answer:
False. During photosynthesis oxygen is released.

Question 6.
Tin and chromium are used for electroplating.
Answer:
True

D. Match the following.

Column A	Column B
1. Oxygen	a. needed for photosynthesis
2. Nitrogen	b. supports combustion
3. Carbon dioxide	c. hydrated iron oxide
4. Water vapour	d. helps in protein synthesis
5. Rust	e. determines climatic conditions
	f. burns to produce energy

Answer:

Column A	Column B
1. Oxygen	b. supports combustion
2. Nitrogen	d. helps in protein synthesis
3. Carbon dioxide	a. needed for photosynthesis
4. Water vapour	e. determines climatic conditions
5. Rust	c. hydrated iron oxide

E. Define the following terms.
1. Respiration
2. Combustion
3. Photosynthesis
Answer:
1. Respiration – Respiration is a chemical process that takes place in all living organisms by which they take in oxygen and use it to break down food and release energy, carbon dioxide and water vapour.

2. Combustion – Combusion or burning is a chemical process in which substances combine with oxygen (of the air) and produce new substances called oxide along with energy in the form of heat and light.

3. Photosynthesis – Photosynthesis is the process by which green plants make their own food (in the form of carbohydrates) (from air) and water (absorbed from soil) in the presence of sunlight and with the help of chlorophyll.

F. Answer the following in short.

Question 1.
Write down the composition of air by volume.
Answer:
Component of air – Percentage by volume
Nitrogen – 78 per cent
Oxygen – 21 per cent
Carbon dioxide – 0.02-0.03 per cent
Inert gases – about 0.9 per cent
Water vapour – variable
Dust particles – variable
Impurities – variable

Question 2.
Name the product obtained when fuels are burned.
Answer:
Fuels bum to produce energy in the form of heat and light.
Carbon-dioxide and water vapour are released as by products.

Question 3.
What are the two main processes that maintain the oxygen-carbon dioxide balance in nature ?
Answer:
Respiration and photosynthesis

Question 4.
What is rusting of iron ? State the conditions required for rusting.
Answer:
The process,by which iron gets covered with reddish-brown flaky substance (rust) in the presence of moist air is called rusting of iron. Conditions required for rusting are:
1. Presence of air (or oxygen)
2. Presence of water (or moisture)

Question 5.
Explain galvanization.
Answer:
Galvanization is the process of depositing a thin layer of zinc metal on the surface of iron objects to prevent rusting of iron. Zinc metal does not corrode on exposure to damp air.

Question 6.
Explain electroplating.
Answer:
Electroplating is a method to prevent rusting of iron by coating iron objects by thin layer of tin or chromium metal. Tin and chromium metals are resistant to corrosion.

G. Answer the following in detail.

Question 1.
How will you show by an experiment that air contains carbon dioxide ?
Answer:
Aim : To show that air contains carbon dioxide.
Materials Required : A boiling tube, a two-holed cork, delivery tubes, lime water.
Procedure:
1. Take some fresh lime water in a boiling tube. Close it with a two-holed cork, carrying two delivery tubes as shown in figure.
2. Suck in air through one delivery tube so that fresh air enters the lime water through the other tube.
Observation : After sucking air for some time, the lime water turns milky.
Conclusion : This shows that air contains carbon dioxide which turns lime water milky.

Question 2.
State the importance of the following components of air.
(a) Nitrogen
(b) Oxygen
(c) Carbon dioxide
Answer:
(a) Importance of nitrogen:
1. Controls rate of combustion of substances. In the absence of nitrogen, burning would be very fast and uncontrollable.
2. Helps in protein synthesis – Nitrogen helps in the formation of proteins which is essential for the growth and development of the plants.

(b) Importance of oxygen:
1. Supports combustion or burning of substances.
2. Essential for respiration by all living organisms. Respiration bums food in our body to release energy.

(c) Importance of carbon dioxide :

1. Needed for photosynthesis by plants to manufacture their food.
2. It is non-supporter of combustion so is used in fire – extinguishers.
3. Used to make fizzy drinks (soda water and carbonated drinks)
4. Used as refrigerant – Liquid and solid carbon dioxide (dry ice) are used as refrigerants and to store frozen foods.

Question 3.
Describe an experiment to show that exhated air contains more carbon dioxide that inhaled air.
Answer:
Aim : To show that exhaled air contains more carbon dioxide than inhaled air
Materials Required : Two conical flasks, lime water, corks, pinch clamps, glass tubes
Procedure :
1. Set up the apparatus as shown in figure.
2. Keeping pinch clamp A open and clamp B closed, such air in through opening C. This causes fresh air to be drawn into flask
3. Keeping pinch clamp A closed and clamp B open, below air out through opening C. This causes exhaled air to bubble into flask
Observation : The lime water in flask Q turns milky more rapidly than the lime water in flask P.
Conclusion : Exhaled air contains more carbon dioxide than inhaled air.

Question 4.
Describe an experiment to show that air is necessary for burning.
Answer:
Aim : To show that air is necessary for burning.
Materials Required : A candle, a bell jar, a matchbox
Procedure :
1. Take a candle and fix it on a table.
2. Now light the candle. It bums and gives a flame.
3. Now cover the burning candle with a bell jar.
Observation : The candle under the jar continues burning for some time and then gets extinguished.
Conclusion : When the oxygen inside the inverted bell jar is used up, the candle gets extinguished. This proves that air (oxygen) is necessary for burning.

Question 5.
State the similarities and differences between respiration and burning.
Answer:
Respiration :

1. Oxygen is required
2. Carbon dioxide and water vapour are released.
3. It is a natural and continuous process.
4. It is a slow process.
5. It takes place at body temperature (37 °C).
6. Small amount of energy is released in the form of heat.

Burning (Combustion) :

1. Oxygen is required.
2. Carbon dioxide and water vapour are released.
3. It is mostly an artificial and discontinuous process.
4. It is a quick process.
5. It takes place at high temperature.
6. Large amount of energy is released in the form of heat and light.

Question 6.
Draw a set-up for showing that oxygen gas is given out during photosynthesis. How will you test that the gas evolved is oxygen ?
Answer:
Aim : To show that green plants produce oxygen during photosynthesis.
Materials required : A trough, a Hydrilla plant, a glass funnel, a test tube, water, wooden splinter.
Procedure:
1. Fill a trough to about three-fourths with water. Place a few cuttings of a Hydrilla plant in it and cover diem with a funnel.
2. Fill a test tube with water, cover its mouth with your thumb and place it over the stem of the,funnel.
3. Place the whole set-up in sunlight for a few hours.
Observation :
1. Bubbles of a gas are seen collecting in the test tube by the displacement of water. When the test tube is filled with the gas, remove it covering its mouth with the thumb.
2. Bring a glowing wooden splinter near the mouth of the test tube filled with the gas. The splinter starts burning with a bright flame.

Conclusion : This shows that the gas in the test tube is oxygen. Thus, oxygen is produced during photosynthesis by green plants.

H. Give reasons for the following.

Question 1.
Drops of water are seen on the outer surface of a vessel containing chilled water.
Answer:
The chilled water cools the surface of the vessel. As a result, water vapour in the air condenses on the cold surface of the vessel and drops of water are seen.

Question 2.
LPG and CNG are preferred as fuels.
Answer:
LPG (Liquified Petroleum Gas) is preferred to other fuels as it release more heat energy and less carbon dioxide.
CNG (Compressed natural Gas) is a clean fuel and gives out significantly fewer pollutants.

Question 3.
Animals depend on plants for respiration.
Answer:
Animals need oxygen for respiration. Oxygen is given out as a by-product during photosynthesis by plants. So animals depend on plants for respiration.

Question 4.
Planting more trees reduces pollution of air.
Answer:
Trees absorb carbon dioxide during photosynthesis to make their own food. Carbon-dioxide in excess amount in air is a major air pollutant causing global warming and other damages. Planting more trees would mean more absorpti on of carbon dioxide by them and hence less air pollution.

Question 5.
A galvanized iron object does not rust.
Answer:
The thin layer of zinc on iron (galvanized iron) does not rust because zinc metal does not corrode on exposure to damp air.

I. Complete these chemical processes. Also name these processes.

Question 1.
food + …………. → ………….. + water vapour + energy
Answer:
food + oxygen → carbon dioxide + water vapour + energy

Question 2.
carbon dioxide + ………….→ …………. + oxygen
Answer:
carbon dioxide + water → glucose + oxygen

Living Science Chemistry Class 6 ICSE Solutions