Class Notes NCERT Solutions for CBSE Students
Question: Explain why during an incident of fire, one is advised to wrap a woollen blanket over a burning object.
Answer: Blanket cuts the supply of oxygen to the object that is burning, thereby prevents it from further burning.
Question: What is air? Name the major constituents of air. Also give their volume proportions in air.
Answer: Air is a mixture of gases. The major constituents of air are nitrogen, oxygen, carbon dioxide and argon. The percentage composition of constituents of air are as given below:
Other components of air are water vapour and dust particles.
Question: Demonstrate through a simple experiment that the air mainly contains nitrogen and oxygen in the volume ratio of 4: 1.
Answer: Aim of experiment: To show that air contains nitrogen and oxygen in the ratio 4:1 by volume:
Procedure: Take a glass container and fix a candle at its centre. Put some quantity of water in the container. Place an empty, dry gas jar over it. Mark five marks above water surface on the jar at equal distances shown in the figure given below.
The candle is lightened and is covered with the gas jar. After some time the candle is extinguished and the water level is raised in gas jar. The raised level in water is 1/5 of the volume of air in the gas jar.
This proves that one part of the air of the jar is a gas which supports combustion, i.e., oxygen. Hence, 1/5 by volume is oxygen in air.
Question: Air is a mixture. Prove this statement.
Answer: The components of mixture can be easily separated and they retain their properties.
The components of air are: oxygen, nitrogen, water vapour and carbon-dioxide, all these gases can be easily separated and they retain their properties.
