Concept: Composition and Properties of Air
What is air?
Air is a mixture of gases that is present around us. We cannot see air, but we can feel it. The blanket of air surrounding our earth is called the atmosphere. Air is vital for us as it contains oxygen which is necessary for breathing.
Composition of air:
The constituent gases present in the air are briefly described below—
- 78% of air consists of nitrogen, making it the most abundant gas present in the air.
- Nitrogen is released into the air due to the nitrogen cycle, a process that involves some specific living organisms and the atmosphere.
- It is a vital component for sustaining life on this planet.
- About 22% of the air consists of oxygen.
- It helps in breathing, combustion and respiration.
- It is the third most abundant gas in the air.
- 0.93% of air contains argon.
- It is a colourless, tasteless as well as odourless gas.
4. Carbon dioxide:
- Only 0.04 % of air contains carbon dioxide.
- Carbon dioxide is produced through respiration and the decomposition of organic materials.
- It is also released through some natural sources like volcanoes and hot springs.
- Various human activities like deforestation, burning of fossil fuels and industrial activities lead to the emission of carbon dioxide into the atmosphere.
- Apart from the above-mentioned gases, air also has water vapour, smoke, dust particles and germs.
Properties of air:
1. Air is colourless and odourless:
Pure air has no colour or odour. It is also invisible but can be felt.
Example: When we feel the wind, it is actually moving air.
2. Air takes up space:
As air is a mixture of gases, it occupies space just like other states of matter.
- When we take a balloon and inflate it, the balloon expands as we blow air into it.
- The more air we blow, the more it will expand as air fills up the space inside the balloon.
3. Air possesses mass:
Air has mass. Mass means the amount of matter contained in an object.
- Take a rod suspended by a string in the middle. Tie an empty balloon on each side to prove they weigh the same. Inflate one balloon and rehang it.
- The side of the balance with the inflated balloon will be heavier and come down.
- If the air had no mass, there would’ve been no change.
4. Air exerts pressure:
The particles of air flow in all directions and exert a force called air pressure.
We find it easier to row a boat when the wind blows behind us. The reason is that wind exerts pressure, making it easier to row the boat towards the direction in which wind is blowing. In this case, the wind pressure supports the rowing motion.
5. Air expands on heating:
On heating, air expands and occupies more space and also becomes lighter.
- Take an empty bottle and then attach a rubber balloon to its neck. You will see that the balloon is deflated.
- Now, place the bottle in a wide container filled with boiling water.
- After some time, you will see that the balloon gets inflated.
- It happens because the air inside the bottle expands on heating, and it fills the balloon.
Combustion: A unique reaction that includes oxygen, usually accompanied by the emission of heat and light.
Pressure: A way of measuring how much force is acting on an area.
Did You Know?
- The atmosphere is divided into several layers—troposphere, stratosphere, mesosphere, thermosphere and exosphere.
- We feel high air pressure at sea level because the whole atmosphere pushes down on us. However, the air pressure is relatively low on a mountain top since there is less atmosphere pushing down on us.
- The difference in air pressure causes our ears to pop when we take off in an aeroplane or drive up a hill.