air and burning

7/23/2019 Air and Burning

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1Class-VI Chemistry Question Bank

5 AIR

I. Tick () the most appropriate answer.

1. Atmosphere consists of :

(a) air above land mass (b) air above oceans

(c) air around us (d) envelope of air around the earth.

2. The constituent of air which helps in combustion is :

(a) nitrogen (b) carbon dioxide (c) oxygen (d) helium

3. The composition of air is:

(a) 78% oxygen, 21% nitrogen and 1% of other gases

(b) 21% oxygen, 78% nitrogen and 1% of other gases

(c) 22% oxygen and 78% nitrogen(d) 78% oxygen and 22% nitrogen

4. The products of combustion of fuels are :

(a) nitrogen and carbon dioxide

(b) water vapour and carbon dioxide

(c) water vapour and nitrogen

(d) only carbon dioxide

5. Rusting of iron takes place due to the presence of :

(a) oxygen in air (b) nitrogen in air

(c) water vapour in air (d) oxygen and water vapour in air

6. Carbon dioxide produced by living beings is used during:(a) rusting (b) combustion (c) photosynthesis (d) respiration

7. Air is a mixture of :

(a) oxygen and hydrogen (b) colourless gases

(c) liquids (d) oxygen and nitrogen

8. Oxygen contained in the air is replenished by :

(a) both plants and animals (b) animals

(c) green plants (d) none of these

9. Rust is an oxide of :

(a) nitrogen (b) iron (c) carbon (d) none of these

10. The products of burning of fuels are:(a) oxygen and water (b) carbon dioxide

(c) kerosene (d) carbon dioxide and water



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11. Which of the following constituents of air is used during photosynthesis?

(a) Nitrogen (b) Oxygen (c) Carbon dioxide (d) Dust12. Which gas is released on photosynthesis?

(a) Nitrogen (b) Oxygen (c) Carbon dioxide (d) Water vapour 13. Which gas is released on respiration?

(a) Nitric oxide (b) Carbon monoxide(c) Carbon dioxide (d) Sulphur dioxide

14. On being burnt wood, produces(a) only carbon dioxide (b) only water vapour (c) a mixture of carbon dioxide and water vapour (d) none of these gases

15. On being burnt, LPG produces:

(a) only carbon dioxide (b) only water vapour (c) carbon dioxide and water vapour (d) none of these gases

16. The gas used in filling balloons is:(a) oxygen (b) helium (c) nitrogen (d) water vapour

17. Air pollution occurs due to:(a) carbon dioxide given out by living beings(b) cutting of green plants(c) smoke given out by factories (d) all the above

Ans. 1. (d) 2. (c) 3. (b) 4. (b) 5. (d) 6. (c) 7. (d) 8. (c) 9. (b) 10. (d)11. (c) 12. (b) 13. (c) 14. (c) 15. (c) 16. (b) 17. (d).

II. [A] Fill in the blank spaces by choosing the correct words from the

following list :

List: respiration, chlorophyll, controlled, energy, nitrogen, sunlight,

uncontrolled, oxygen, carbon dioxide, water vapour.

1. Air is a mixture of approximately 78.3% of ................... , 20.9%

of ........................ and 1% of other gases.

2. Oxygen of the air is absolutely essential for the ....................... of

animals and plants.

3. The products of combustion and respiration are .................. and

.................. .

4. Carbon dioxide and water react chemically in the presence of

.......................... and ........................ to produce sugar and oxygen.5. During combustion .................. amount of heat ...................... is

liberated but during respiration ........................ amount of heat

energy is liberated.




Ans. 1. nitrogen, oxygen 2. respiration 3. carbon dioxide, water vapour 4.

sunlight, chlorophyll 5. uncontrolled, energy, controlled.

[B] 1. A substance that burns in oxygen, burns in air to form ........................substances (different/the same).

2. The air we ........................ contains more carbon dioxide than the one we

........................ (inhale/exhale).

3. On being burnt in an insufficient supply of air, carbon will produce

........................ (carbon monoxide/carbon dioxide).

4. CNG contains mainly ................ and LPG ................... (methane/butane).

5. Photosynthesis takes place in the ........................ of chlorophyll (absence/

presence).

Ans. 1. the same 2. exhale, inhale 3. carbon monoxide 4. methane, butane 5.

presence

III. Fill in the blanks.

1. The major constituent of air is ........................ .

2. Air supports combustion because it contains ........................ .

3. Exhaled air contains ........................ .

4. Green plants need .............. and ............. to prepare their food.

5. Respiration is a ........................ process.

6. One-fifth part of the air is ........................ .

7. The layer of air around the earth is called the .................... .

8. Air is a ........................ of gases.

9. Plants and animals maintain the balance of ............... and ................ inair.

10. Polluted air is ........................ for health.

11. The supporter of combustion in air is ........................ .

12. Green plants need ........................ to prepare food.

13. Aquatic plants and animals use ........................ dissolved in water.

14. Air exerts ........................ .

15. The reddish brown powder on the surface of iron nails exposed to air

and moisture is called ........................ .

16. ........................ is related to burning and rusting.

Ans. 1. nitrogen 2. oxygen 3. carbon dioxide 4. carbon dioxide and sunlight5. continuous 6. oxygen 7. atmosphere 8. mixture 9. oxygen and carbon

dioxide 10. harmful 11. oxygen 12. carbon dioxide 13. oxygen

14. pressure 15. rust 16. Oxidation



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IV. Statements given below are incorrect. Write the correct statements:

1. The products of combustion of fuels are nitrogen and water vapour.Ans. The products of combustion of fuels are carbon dioxide and water vapour.

2. Respiration takes place only in animals.Ans. Respiration takes place in animals and plants both.

3. LPG and CNG are incombustible gases kept in homes for extinguishing fire.

Ans. LPG is liquefied petroleum gas and used as a household fuel. CNG iscompressed natural gas and used as a fuel in automobiles and bigfactories.

4. Water turns blue coloured anhydrous copper sulphate to hydrated copper sulphate which is green in colour.

Ans. Water turns white coloured anhydrous copper sulphate to hydrated

copper sulphate which is blue in colour.5. Stomata is a specialised cell through which insects breathe.

Ans. Stomata are specialised cells through which plants breathe.

V. Write true or false against the statements given below :1. Ratio of oxygen and nitrogen by volume in air, is 4 : 1.2. Biomass is a common household fuel in rural India.3. Photosynthesis is the reverse process of combustion.4. During respiration controlled amount of heat energy is released.5. Raw materials for combustion are carbon dioxide and water.6. Raw materials for respiration are sugars and oxygen.

7. The amount of oxygen in the air remains the same because of photosynthesis.8. Plants give out carbon dioxide during respiration.9. Carbon dioxide gas turns limewater milky.

10. Nitrogen in the air also helps in combustion.11. Air is not essential for life.12. Oxygen present in the air helps in burning.13. Nitrogen is the major component of air.14. The amount of water vapour present in air is the same everywhere.15. A candle will continue to burn in a closed space.16. Natural gas is obtained from petroleum wells.

17. Carbon dioxide is the product of burning but not of respiration.18. Photosynthesis takes place at night also.19. Air is a compound.20. Carbon dioxide is given out during photosynthesis.




21. The composition of air was discovered by Lavoisier.22. The major component of air is oxygen.

Ans. 1. F 2. T 3. T 4. T 5. F 6. T 7. T 8. T 9. T 10. F 11. F 12. T 13.T 14. F 15. F 16. T 17. F 18. F 19. F 20. F 21. T 22. F.

VI. (a) Match the statements in Column A with Column B.

Column A Column B

1. The products of combustion of fuels are a. combustible gas2. LPG is a b. water and carbon dioxide3. Amount of oxygen in air is c. 78%4. 0.04% carbon dioxide is present d. with water 5. Hydrated copper sulphate changes e. in air

to blue colour

6. Plants absorb carbon dioxide in f. oxygenthe presence of 7. Air supports combustion due to the g. sunlight

presence of 8. Amount of nitrogen present in air is h. 21%

Ans. 1. (b) 2. (a) 3. (h) 4. (e) 5. (d) 6. (g) 7. (f) 8. (c).

(b) Column A Column B

1. Nitrogen a. helps in burning

2. Oxygen b. plants use it to make food

3. Carbon dioxide c. reduces the activity of oxygen

4. Water vapour d. 1% of the total composition of air 5. Other gases in air, water e. accounts for the humidity in the air

vapour and dust particles

Ans. 1. (c) 2. (a) 3. (b) 4. (e) 5. (d).

(c) Column A Column B

1. Carbon monoxide a. An inactive gas.

2. Rusting b. A low level of the gas in air is maintained byincreased plantation.

3. Nitrogen c. A poisonous gas.

4. Carbon dioxide d. Takes place in moist air.5. Oxygen e. A gas which is essential for respiration and combustion.

Ans. 1. (c) 2. (d) 3. (a) 4. (b) 5. (e).



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VII. Give reasons for the following.

1. When you water a plant, air bubbles come out from the dry soil.Ans. In dry soil, intermolecular spaces are full of air. So, when we water

a plant, these intermolecular spaces are covered by water and air bubbles come out from the dry soil.

2. Lime water kept in a beaker turns milky.Ans. Lime water kept in a beaker turns milky due to the presence of carbon

dioxide.3. LPG and CNG are called eco-friendly fuels.

Ans. LPG and CNG both are called eco-friendly fuels because both thefuels do not pollute our atmosphere.

4. Plants take in carbon dioxide.Ans. During photosynthesis, plants use carbon dioxide gas from the

atmosphere as a raw material to prepare their food. Photosynthesisdoes not take place in animals.

5. Animals depend on plants for respiration.Ans. Animals depend on plants for respiration because during

photosynthesis, plants take in carbon dioxide and give out oxygenwhich is used by animals for respiration.

6. Aquatic animals and plants are able to survive.Ans. Aquatic animals and plants have some specialised organs which are

modified to take in air which is dissolved in water. Due to the presenceof air dissolved in water aquatic plants and animals are able to survive.

7. A burning candle stops burning if covered with a glass tumbler.Ans. Oxygen helps in the burning of fuels. When a burning candle is

covered with a glass tumbler the supply of oxygen is cut off and theflame extinguishes.

8. Mountaineers and divers carry oxygen cylinders with them.Ans. Mountaineers and divers carry oxygen cylinders with them because at

higher and lower altitudes the air is thin and it becomes less dense.So, there is difficulty in breathing.

VIII. Answer the following questions.1. Name the four most important constituents of air and state their

appropriate percentage composition.

Ans. The most important constituents of air are nitrogen (78.3%), oxygen(20.9%), carbon dioxide (0.03%) and water vapour.

2. (i) Name a major constituent of air which does not take part incombustion.




(ii) Name a constituent of air which is essential for combustion and

respiration.

(iii) Name a constituent of air which is essential for photosynthesis.

Ans. (i) Nitrogen is the major constituent of air which does not take part

in combustion.

(ii) Oxygen is the main constituent of air which is essential for

respiration and combustion.

(iii) Carbon dioxide is the constituent of air which is essential for

photosynthesis.

3. (i) What do you understand by the term fuel?

(ii) Name any four common household fuels.

(iii) Name the products formed during the combustion of fuels?

Ans. (i) Fuel. Any substance which burns in air and release a large amount

of heat and light energy is called a fuel. For example, petrol, wood,diesel, coal, etc.

(ii) Four household fuels. Wood, coal, LPG and kerosene oil are

some common household fuels.

(iii) During combustion of fuels, oxygen of the air reacts with carbon

and hydrogen present in fuels to form carbon dioxide and water

vapour.

Fuel + air (Oxygen) → Carbon dioxide + Water vapour + heat.

4. How will you prove that air is necessary for the combustion of fuels?

Ans. We can prove that air is necessary

for the combustion of fuels by thefollowing experiment.

Take a plastic trough and pour

water in it.

Fix a candle in the trough and light

it.

Now invert a glass tumbler over

the burning candle. We see that

after a few seconds, the flame

starts flickering and finally goes

off.This is due to the reason that the

candle does not receive any fresh

supply of air on account of the water seal. Thus, this activity proves



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that air is necessary for combustion of fuels.

5. (i) What do you understand by the term respiration?

(ii) Briefly describe, how the respiration takes place in human

beings.

Ans. (i) The collective process of absorption of oxygen into the blood

stream and then oxidation of food materials in the cells with the

release of heat energy, carbon dioxide and water in the exhaled

air is called respiration.

(ii) In human beings, the food materials break down by the digestive

system to form simpler compounds. These are carried to the

individual cells through blood. At the same time oxygen dissolves

in the blood and is carried to the individual cells. In the cells, the

simpler compounds react with oxygen to form carbon dioxide

and water with the release of heat energy.7. How will you prove experimentally that the product of respiration in

our body are:

(i) carbon dioxide (ii) water vapour?

Ans. Exhaled air contains more carbon dioxide than inhaled air. We can

prove it by the following experiment:

Set up an apparatus as shown in the figure above. Open the pinch

cock A and keep the pinch cock B closed. Suck in air with the help of the mouth so that fresh air enters flask F1 and after bubbling through

lime water this air then enters the mouth and the lungs.

Now close pinch cock A and open pinch cock B. Exhale out air




from the lungs such that it bubbles through the lime water in flask F2.

Repeat these processes for about 10 times.

It is observed that lime water in flask F1 turns slightly milky

whereas in flask F2 it turns milky rapidly. It shows that exhaled air

contains more carbon dioxide than inhaled air.

Exhaled air also contains water vapour. We can prove it by the

following experiment: Take a clean mirror. Now pump an empty

spray over it. It is observed that the mirror remains clean.

Now, blow out air by the mouth from your lungs over the mirror.

We observe that mirror turns misty rapidly.

Thus, this experiment proves that exhaled air contains more water

vapour than fresh air.

8. How will you prove experimentally that plants produce carbon dioxidegas during respiration?

Ans. Plants produce carbon

dioxide gas during

respiration like human

beings. This can be proved

by an experiment. Take a

glass plate and place 25

gm of germinating seeds

on it. Along with the seeds

also place a dish withclear limewater.

Now place an inverted

funnel over the

germinating seed and lime

water as shown in the

figure. Plug the stem of the funnel with cotton wool and seal the rim of

funnel with grease to prevent the entry of fresh air. Leave this apparatus

undisturbed overnight.

We find that lime water turns milky. This proves that the

germinating seeds give off carbon dioxide during respiration.

9. Give three differences between respiration and combustion.

Ans. Three differences between respiration and combustion:



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Respiration Combustion

1. It is a biological process 1. It is a physical process and

which requires a coloured no biological pigment is pigment called haemoglobin. required.

2. It is a natural continuous 2. It is not a natural continuous process and takes place process.continuouly during day and night as long as a livingorganism lives.

3. During respiration, small 3. During combustion, largeamount of heat energy is amount of heat and lightevolved which is used energies are evolved.

by the organism.

10. Explain briefly how the amount of oxygen in air does not deplete, inspite of the fact that large amount of it is used in combustion and respiration.

Ans. In spite of excessive use of oxygen during respiration and combustion,oxygen in the air does not get depleted. This is due to a process called photosynthesis. By this process, plants synthesise food from carbondioxide and moisture in presence of sunlight. In this process oxygen isliberated and goes into the air. Thus, the percentage of oxygen in theatmosphere remains constant.

11. Where would you expect a high proportion of carbon dioxide in air?Ans. Carbon dioxide is released into the air by the burning of fossil fuels

such as coal, CNG, diesel, petrol etc. So, carbon dioxide is present inhigher proportion in air near factories operated by coal and in citieswith more oil-operated vehicles.

12. In which season would you expect a higher proportion of water vapour in air?

Ans. Higher proportion of water vapour is present in the summer season. Itis due to the fact that in this season rate of evaporation increases dueto rise in temperature. So, there is more vapour in the atmosphere.

13. Which gas is formed when carbon is burnt in oxygen? Which gas is

formed when carbon is burnt in an insufficient amount of air?Ans. Carbon dioxide is formed when carbon is burnt in a free supply of

oxygen. Carbon monoxide is formed when carbon is burnt in can not befilled insufficient amount of air.




14. Which substance do plants store as food after photosynthesis?Ans. Plants store carbohydrates as food after photosynthesis.

15. On digestion of food, which substance is produced that reacts with

oxygen during respiration?Ans. After digestion of food, glucose is produced that reacts with oxygen

during respiration.16. What are the products formed when CNG is burnt?

Ans. On burning of CNG, carbon dioxide and water vapour are formed.17. Which of the two — coal and LPG will you prefer as a household fuel

and why?Ans. LPG is preferred as a household fuel because it is eco-friendly and

does not pollute the atmosphere. On the other hand, coal produces both solid and gaseous residue on burning which causes pollution.

18. What is the phenomenon called that is caused by the increase in theamount of carbon dioxide in air?

Ans. Global warming is caused by the increase in the amount of carbondioxide in air.

19. Name a substance that you can use to keep the air dry in a closed space.Ans. Fused calcium chloride is used to keep the air dry in a closed space.

20. Why do you expect rusting to occur in ordinary air?Ans. Rusting takes place in moist air. If either air (oxygen) or moisture is

absent rust does not form. Since ordinary air contains both air and moisture, rusting takes place in it.

21. Mention five uses of air.Ans. Uses of Air.

(i) Air is used for respiration in plants and animals.(ii) Air is necessary for photosynthesis in plants.

(iii) Air is necessary for burning of fuels.(iv) Air is used in the tyres of vehicles.(v) Nitrogen present in the air is essential for the growth of plants.

22. What is air pollution? How can it be controlled?Ans. Air pollution. The release of substances in the air that cause a variety

of harmful effects to the natural environment is called air pollution.Air pollution can be controlled by taking the following steps—

(i) By planting more trees.(ii) Providing factories and power stations with tall chimneys.

(iii) Using catalytic converters in cars which convert hydrocarbon and carbon monoxide into harmless carbon dioxide and water vapour.

(iv) Using unleaded petrol in automobiles which is less harmful.

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air and burning

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