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CHEMISTRY [3 Mark Question Answer]

Air and Atmosphere · ICSE STD 6 (ICSE - English Medium). 8 questions.

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[3 Mark Question Answer]

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8 questions · timed · auto-graded

Question 13 Marks
Name the processes which maintain the balance between oxygen and carbon dioxide in the air. How is it done?
Answer
Respiration and combustion are the processes which maintain the balance between oxygen and CO2 in the air.
  1. Respiration: Respiration is a chemical process that takes place in all living beings. In this process, oxygen present in the inhaled air reacts with the digested food material in the body. This results in the release of energy, carbon dioxide, and water.
  2. Combustion: Burning or combustion is a process in which a substance reacts chemically with oxygen and gets oxidised, with the release of energy in the form of heat and light. It is a fast process. During the process of burning, along with energy, carbon dioxide, and water vapour are also produced.
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Question 23 Marks
Why is air called a mixture? Give five facts in support of your answer.
Answer
Air is a mixture because:
  1. Air has no formula, a mixture has no formula whereas the compound has a formula.
  2. No energy changes are involved to form air from various gases.
  3. When air is formed out of its constituents no change in mass and no change in volume takes place.
  4. Properties of air vary from place to place and from time to time. i.e. there is more $CO _2$ in towns as compared to villages where more oxygen prevails as compared to towns.
  5. Components of air can be separated by simple physical methods.
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Question 33 Marks
Describe a simple experiment with the help of a diagram to show that Air is highly compressible
Answer
Air is highly compressible

A leak-proof syringe filled completely with air only (i.e. empty) is taken.
Observation: On pressing the piston of the syringe, the piston moves inwards. Air (gas) inside the syringe has maximum inter-molecular space and is highly compressible.
Conclusion: Air is highly compressible.
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Question 43 Marks
Describe a simple experiment with the help of a diagram to show that Air exerts pressure
Answer
Air exerts pressure

Take an open can, fill it with water, and heat it. On the formation of steam, place the cap on tightly and keep the can aside.
Observation: On condensation of the steam the pressure inside the can reduce. The air outside exerts pressure on the can which crumples slowly.
Conclusion: Air exerts pressure.
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Question 53 Marks
Describe a simple experiment with the help of a diagram to show that Air has mass
Answer
Air has mass

An inflated balloon is placed on one side of the scale.
Observation: It is seen that the scale moves towards one side. It moves on the side on which the inflated balloon was placed.
Conclusion: Air has mass.
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Question 63 Marks
Describe a simple experiment with the help of a diagram to show that Air occupies space
Answer
Air occupies space

•Press an inverted glass
•Tilt the tumbler to one side, tumbler over the water.
Observation: On tilting the tumbler, bubbles of air are seen coming out. Water slowly enters the tumbler to take place of the trapped air in the tumbler.
Conclusion: Air occupies space (the space in the tumbler was occupied by air)
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Question 73 Marks
State a reason why there is a balance in the amount of carbon dioxide in the air, even though carbon dioxide is released into the atmopshere by various processes.
Answer
By the way of photosynthesis in plants which occurs during daytime, carbon dioxide and water in the presence of sunlight and chlorophyll is changed into carbohydrates and oxygen is released out.
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Hence, oxygen in the air is renewed by photosynthesis, and therefore the amount of oxygen in the air does not get depleted or removed from the air.
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Question 83 Marks
A mixture has a variable composition. Give three other reasons why air is considered a mixture and not a compound.
Answer
Air is a mixture because :
  1. Air has no formula, a mixture has no formula whereas the compound has a formula.
  2. No energy changes are involved to form air from various gases.
  3. When air is formed out of its constituents no change in mass nor change in volume takes place.
  4. Properties of air vary from place to place and from time to time. i.e. there is more $CO _2$ in towns as compared to villages where more oxygen prevales as compared to towns.
  5. Components of air can be separated by simple physical methods.
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