Composition of Air

37 Grade 6 Integrated Science questions on Composition of Air, with worked marking schemes. 37 questions are available on this topic in full.

1. Question 1

   3 marks

   During a lesson the teacher said, 'Both breathing and burning use up the same gas from the air.'

   (a) Name this gas. (1 mark)

   (b) Explain what happens to a candle flame in a closed jar as this gas is used up. (2 marks)

   (3 marks)

   Marking scheme

   (a) Oxygen (1 mark). (b) As the oxygen in the jar is used up, the flame gets smaller/weaker and finally goes out because there is no more oxygen to support burning (2 marks).

2. Question 2

   1 mark

   Which gas makes up the largest part of the air we breathe?

   A. Carbon dioxide

   B. Water vapour

   C. Nitrogen

   D. Oxygen

   (1 mark)

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3. Question 3

   1 mark

   Air is a

   A. pure substance

   B. mixture of gases

   C. single element

   D. compound

   (1 mark)

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4. Question 4

   4 marks

   Learners set up an experiment to show that air contains water vapour.

   (a) Describe one simple way to show that the air contains water vapour. (2 marks)

   (b) State why air is described as a mixture and not a single substance. (2 marks)

   (4 marks)

   Marking scheme

   (a) Breathe onto a cold/shiny surface such as a mirror or glass and it becomes misty/foggy, OR place cold water/ice in a dry glass and drops of water form on the outside - showing water vapour in the air condenses (2 marks). (b) Because air is made up of two or more different gases (nitrogen, oxygen, carbon dioxide, rare gases, water vapour) that are simply mixed together and can be separated (2 marks).

5. Question 5

   1 mark

   A candle continues to burn only when there is enough of a certain gas. Which gas in the air supports burning?

   A. Carbon dioxide

   B. Water vapour

   C. Nitrogen

   D. Oxygen

   (1 mark)

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6. Question 6

   4 marks

   Air contains several gases each of a different proportion.

   (a) Arrange these three gases in order from the one present in the largest amount to the smallest: oxygen, nitrogen, carbon dioxide. (3 marks)

   (b) Which of the three is needed by animals for respiration? (1 mark)

   (4 marks)

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7. Question 7

   1 mark

   Air around us is best described as:

   A. A solid

   B. A liquid

   C. A mixture of gases

   D. A single gas

   (1 mark)

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8. Question 8

   4 marks

   A learner claimed that all of the air is used up when a candle burns inside a closed jar over water, because the flame goes out.

   (a) State whether the learner is correct. (1 mark)

   (b) Give a reason for your answer. (3 marks)

   (4 marks)

   Marking scheme

   (a) The learner is NOT correct / No (1 mark). (b) Only the oxygen part (about one fifth / 21%) is used up; the water rises by only about one fifth, and most of the jar is still filled with nitrogen and other gases which do not support burning, so the flame goes out even though most of the air remains (3 marks).

9. Question 9

   1 mark

   Which of the following correctly shows the two gases present in the LARGEST amounts in the air?

   A. Carbon dioxide and water vapour

   B. Oxygen and carbon dioxide

   C. Nitrogen and carbon dioxide

   D. Nitrogen and oxygen

   (1 mark)

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10. Question 10

    1 mark

    Green plants take in a certain gas from the air to make their food during the day. Which gas is this?

    A. Rare gases

    B. Carbon dioxide

    C. Nitrogen

    D. Oxygen

    (1 mark)

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11. Question 11

    1 mark

    When we breathe in, our bodies use one gas from the air to release energy. Which gas is this?

    A. Carbon dioxide

    B. Nitrogen

    C. Oxygen

    D. Rare gases

    (1 mark)

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12. Question 12

    1 mark

    The gas that makes up about 78% of the atmosphere is

    A. argon

    B. oxygen

    C. carbon dioxide

    D. nitrogen

    (1 mark)

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13. Question 13

    4 marks

    A boy left an iron nail outside for many days and it became covered with rust.

    (a) Name the gas from the air that is used up when iron rusts. (1 mark)

    (b) Explain why the nail did not rust when it was kept dry and coated with oil. (3 marks)

    (4 marks)

    Marking scheme

    (a) Oxygen (1 mark). (b) Rusting needs both oxygen (from the air) and water/moisture; coating the nail with oil keeps out air/oxygen and water, and keeping it dry removes the moisture, so rusting cannot take place (3 marks).

14. Question 14

    3 marks

    Air is a mixture of several gases.

    (a) Name the gas that is present in the greatest amount in air. (1 mark)

    (b) State the approximate percentage of this gas in air. (1 mark)

    (c) Name the gas in air that supports burning. (1 mark)

    (3 marks)

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15. Question 15

    4 marks

    A lit candle was placed in a basin of water and covered with a glass jar as shown in class. After some time the flame went out and the water rose inside the jar.

    (a) Explain why the candle flame went out. (2 marks)

    (b) State what the rise of water in the jar tells us about the air. (2 marks)

    (4 marks)

    Marking scheme

    (a) The candle used up the oxygen inside the jar; once the oxygen was finished the flame could no longer keep burning and went out (2 marks). (b) The water rose to fill the space left by the used-up oxygen, showing that oxygen makes up about one fifth (about 21%) of the air (2 marks).

16. Question 16

    1 mark

    When a metal spade is left outside in the rain, it slowly forms rust. Which gas in the air is used up during rusting?

    A. Water vapour

    B. Oxygen

    C. Carbon dioxide

    D. Nitrogen

    (1 mark)

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17. Question 17

    1 mark

    Which of the following is an effect of air pollution?

    A. Respiratory diseases like asthma

    B. Strong buildings

    C. Clean drinking water

    D. Healthy plants

    (1 mark)

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18. Question 18

    1 mark

    About what fraction of the air is made up of oxygen?

    A. Three quarters

    B. One fifth

    C. One half

    D. The whole

    (1 mark)

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19. Question 19

    1 mark

    In the candle-and-jar experiment, why does the candle finally go out even though the jar still has gas in it?

    A. The water put out the flame

    B. The candle became too short

    C. The oxygen has been used up and the remaining gases do not support burning

    D. All the gas has escaped from the jar

    (1 mark)

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20. Question 20

    1 mark

    Bubbling gas into limewater turns the limewater milky. Which gas found in small amounts in air turns limewater milky?

    A. Carbon dioxide

    B. Nitrogen

    C. Oxygen

    D. Water vapour

    (1 mark)

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21. Question 21

    6 marks

    Explain why:

    (a) A fire will go out when a glass jar is placed over it. (3 marks)

    (b) It is dangerous to sleep in a completely closed room with a burning charcoal jiko. (3 marks)

    (6 marks)

    Marking scheme

    (a) The jar traps a limited amount of air; the fire uses up the oxygen inside; once the oxygen is finished there is nothing to support burning, so the fire goes out (3 marks). (b) The burning jiko uses up the oxygen in the closed room and produces poisonous/harmful gas (carbon dioxide/carbon monoxide); with little fresh air/oxygen, a person can suffocate/be poisoned and die (3 marks).

22. Question 22

    1 mark

    During the day, green plants release a gas that living things need for breathing. Which gas do plants release into the air?

    A. Oxygen

    B. Nitrogen

    C. Water vapour

    D. Carbon dioxide

    (1 mark)

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23. Question 23

    1 mark

    Trees help reduce air pollution by

    A. absorbing carbon dioxide and releasing oxygen

    B. producing carbon dioxide

    C. making shade only

    D. blocking wind

    (1 mark)

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24. Question 24

    1 mark

    The component of air used by living things for respiration is

    A. carbon dioxide

    B. water vapour

    C. oxygen

    D. nitrogen

    (1 mark)

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25. Question 25

    1 mark

    Which of the following gases is present in air in the smallest proportion among those listed?

    A. Oxygen

    B. Nitrogen

    C. Rare gases

    D. Carbon dioxide

    (1 mark)

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26. Question 26

    4 marks

    Green plants and animals depend on the gases in the air.

    (a) Name the gas plants take IN during the day to make food. (1 mark)

    (b) Name the gas plants give OUT during the day. (1 mark)

    (c) Explain how this exchange of gases is useful to animals. (2 marks)

    (4 marks)

    Marking scheme

    (a) Carbon dioxide (1 mark). (b) Oxygen (1 mark). (c) Plants release oxygen which animals need for breathing/respiration, and they take in the carbon dioxide that animals breathe out, keeping the air fresh and balanced for animals to live (2 marks).

27. Question 27

    1 mark

    Two learners breathed out onto a cold mirror and it became misty. This shows that the air we breathe out contains:

    A. Smoke

    B. Water vapour

    C. Only nitrogen

    D. Rust

    (1 mark)

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28. Question 28

    4 marks

    Oxygen is an important gas in the air. State two uses of oxygen to living things. (4 marks)

    (4 marks)

    Marking scheme

    Award 2 marks per point (any two): oxygen is used for breathing/respiration to release energy in living things; oxygen supports burning/combustion; oxygen is used in hospitals for patients with breathing difficulties; oxygen is needed for rusting/decay (2 marks each, max 4).

29. Question 29

    1 mark

    Besides gases, air also contains a small amount of moisture. This moisture in the air is known as:

    A. Rust

    B. Water vapour

    C. Smoke

    D. Nitrogen

    (1 mark)

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30. Question 30

    4 marks

    Carbon dioxide is one of the gases found in small amounts in the air.

    (a) State one use of carbon dioxide to green plants. (2 marks)

    (b) Explain why carbon dioxide is used in some fire extinguishers. (2 marks)

    (4 marks)

    Marking scheme

    (a) Green plants use carbon dioxide to make their own food (during photosynthesis) in the presence of sunlight (2 marks). (b) Carbon dioxide does not support burning and it cuts off/blocks oxygen from reaching the fire, so the fire goes out (2 marks).

31. Question 31

    1 mark

    A lit candle was covered with an inverted glass jar standing in a basin of water. After the candle went out, the water rose about one fifth of the way up the jar. This shows that:

    A. Nitrogen supports burning

    B. All the air in the jar was used up

    C. Water was produced by the candle

    D. Oxygen used up by the candle makes up about one fifth of the air

    (1 mark)

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32. Question 32

    1 mark

    A fire extinguisher puts out a fire by cutting off oxygen. Which gas is commonly used in fire extinguishers because it does NOT support burning?

    A. Water vapour

    B. Carbon dioxide

    C. Oxygen

    D. Nitrogen

    (1 mark)

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33. Question 33

    1 mark

    The gas that is needed for breathing and burning is

    A. carbon dioxide

    B. oxygen

    C. hydrogen

    D. nitrogen

    (1 mark)

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34. Question 34

    1 mark

    Air pollution is caused by

    A. clean rain

    B. recycling waste

    C. smoke from factories and vehicles

    D. planting trees

    (1 mark)

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35. Question 35

    3 marks

    Give the approximate percentage of each of the following gases in air.

    (a) Oxygen ....... % (1 mark)

    (b) Nitrogen ....... % (1 mark)

    (c) State the approximate percentage of carbon dioxide in air. (1 mark)

    (3 marks)

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36. Question 36

    1 mark

    Plants use carbon dioxide during

    A. transpiration

    B. excretion

    C. respiration

    D. photosynthesis

    (1 mark)

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37. Question 37

    1 mark

    The percentage of nitrogen in air is about:

    A. 50%

    B. 0.03%

    C. 78%

    D. 21%

    (1 mark)

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