Exercise 5.1 - QUESTIONS ONLY - FULL AS IT IS FOLLOWED BY ANSWERS
Exercise 5.1 - FULL
A. Fill in the blank spaces by choosing the correct words in brackets.
Oxygen is necessary for respiration and ___________ [photosynthesis/combustion]
The envelope of air which surrounds the earth is known as ___________ [exosphere/atmosphere]
The life supporting constituent of air is ___________ [nitrogen/oxygen]
When products of combustion are passed through anhydrous copper sulphate, it turns ___________ [yellow/blue]
When clear limewater is exposed to air for some time it turns ___________ [milky/pink]
B. Statements given below are incorrect. Write the correct statements :
The products of the combustion of a fuel are nitrogen and water vapour.
Coal is a household fuel.
LPG is an incombustible gas kept in home to extinguish fire.
Water turns blue coloured anhydrous copper sulphate to colourless substance.
Oxygen is not necessary for the respiration of plants.
C. Match the statements :
| Column I | Column II |
| 1. The products of combustion of a fuel. | (a) 78% |
| 2. Percentage of oxygen in air. | (b) Carbon dioxide |
| 3. Percentage of nitrogen present in air. | (c) Kerosene oil |
| 4. A gas present in air which turns limewater milky. | (d) Water and carbon dioxide |
| 5. A petroleum product commonly used as household fuel. | (e) 21% |
D. Write ‘True’ or ‘False’ :
The ratio of oxygen and nitrogen by volume in air is about 1:4.
Biomass is common household fuel in rural India.
Raw materials for combustion are carbon dioxide and water.
Coal is used as an industrial fuel.
Nitrogen in the air helps in combustion.
E. Tick (✓) the most appropriate answer.
Atmosphere consists of : (a) air above land mass (b) air above oceans (c) air around us (d) envelope of air around the earth
The constituent of air which helps in combustion is : (a) nitrogen (b) carbon dioxide (c) oxygen (d) helium
A gas which is commonly used as household fuel is : (a) CNG (b) LPG (c) oxygen (d) nitrogen
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
The products of the combustion of a fuel are : (a) nitrogen and carbon dioxide (b) water vapour and carbon dioxide (c) water vapour and nitrogen (d) only carbon dioxide
F. Answer the following questions:
Name four important constituents of air and state their appropriate percentage in composition.
(a) Name a major constituent of air which does not take part in the process of combustion. (b) Name a constituent of air which is essential for combustion and respiration. (c) Name the constituent of air which is essential for photosynthesis.
Briefly describe how you will prove the presence of following in air : (a) water vapour (b) carbon dioxide
(a) What do you understand by the term fuel? (b) Name any four common household fuels. (c) Name the products formed during the combustion of a fuel.
How will you prove that air is necessary for the combustion of fuel?
How will you prove experimentally that products of the combustion of a candle are : (a) carbon dioxide gas (b) water vapour?
State the main uses of the following gases : (a) nitrogen (b) oxygen
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ANSWERS
Exercise 5.1: Air and Atmosphere
A. Fill in the Blanks
Choose the correct words from the brackets to complete the sentences.
Oxygen is necessary for respiration and combustion.
The envelope of air which surrounds the earth is known as atmosphere.
The life-supporting constituent of air is oxygen.
When products of combustion are passed through anhydrous copper sulphate, it turns blue.
When clear limewater is exposed to air for some time it turns milky.
B. Correcting the Statements
The following statements are incorrect. Here are the correct versions:
Incorrect: The products of the combustion of a fuel are nitrogen and water vapour.
Correct: The products of the combustion of a fuel are carbon dioxide and water vapour.
Incorrect: Coal is a household fuel.
Correct: Coal is generally used as an industrial fuel.
Incorrect: LPG is an incombustible gas kept in home to extinguish fire.
Correct: LPG is a combustible gas used as a household fuel.
Incorrect: Water turns blue coloured anhydrous copper sulphate to colourless substance.
Correct: Water turns white anhydrous copper sulphate into a blue coloured substance.
Incorrect: Oxygen is not necessary for the respiration of plants.
Correct: Oxygen is necessary for the respiration of plants.
C. Match the Following
| Column I | Column II |
| 1. The products of combustion of a fuel | (d) Water and carbon dioxide |
| 2. Percentage of oxygen in air | (e) 21% |
| 3. Percentage of nitrogen present in air | (a) 78% |
| 4. A gas present in air which turns limewater milky | (b) Carbon dioxide |
| 5. A petroleum product commonly used as household fuel | (c) Kerosene oil |
D. True or False
The ratio of oxygen and nitrogen by volume in air is about 1:4. — True
Biomass is common household fuel in rural India. — True
Raw materials for combustion are carbon dioxide and water. — False (These are the products; raw materials are fuel and oxygen).
Coal is used as an industrial fuel. — True
Nitrogen in the air helps in combustion. — False (Nitrogen does not help in burning).
E. Multiple Choice Questions (MCQs)
Atmosphere consists of:
(d) envelope of air around the earth
The constituent of air which helps in combustion is:
(c) oxygen
A gas which is commonly used as household fuel is:
(b) LPG
The composition of air is:
(b) 21% oxygen, 78% nitrogen and 1% of other gases
The products of the combustion of a fuel are:
(b) water vapour and carbon dioxide
F. Descriptive Answers
1. Name four important constituents of air and state their appropriate percentage.
Nitrogen: 78.03%
Oxygen: 20.9%
Noble gases (Argon, etc.): 0.94%
Carbon dioxide: 0.03%
2. Identify the constituent of air that is:
(a) Major constituent that does not take part in combustion: Nitrogen
(b) Essential for combustion and respiration: Oxygen
(c) Essential for photosynthesis: Carbon dioxide
3. Briefly describe how you will prove the presence of the following in air:
(a) Water vapour: Place crushed ice in a clean glass tumbler. After a few minutes, tiny droplets of water appear on the outer surface, proving that water vapour in the air condensed on the cool surface.
(b) Carbon dioxide: Pass air through freshly prepared limewater using a suction tube. The limewater will turn milky, proving the presence of carbon dioxide.
4. Fuel and its properties:
(a) Fuel: Any cheap material which burns in air or oxygen with the release of a large amount of heat and light energy without forming harmful products is called fuel.
(b) Four household fuels: Wood, LPG, Kerosene oil, and Coal.
(c) Products of combustion: Carbon dioxide, water vapour, and heat energy.
5. How will you prove air is necessary for the combustion of fuel?
Fix a burning candle in a plastic trough containing water and invert a glass tumbler over it. The candle burns for a few seconds and then goes out because the supply of fresh air (oxygen) is cut off by the water seal.
6. Prove experimentally that a burning candle produces $CO_2$ and water vapour.
Place a burning candle under a funnel connected to a U-tube containing white anhydrous copper sulphate. The copper sulphate turns blue, proving the presence of water vapour. Connect the other end of the tube to limewater; the limewater turns milky, proving the presence of carbon dioxide.
7. State the main uses of:
(a) Nitrogen: It is used to manufacture plant food (nitrates) and to preserve packaged foods by driving out oxygen.
(b) Oxygen: It is essential for the respiration of all living things and for the combustion of fuels to produce energy.
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