Composition of air


•           Until the eighteenth century, people thought that air was just one substance.

•           But experiments have proved that air is a mixture of several gases.

•           Air contains mainly nitrogen, oxygen, and remaining includes carbon dioxide, noble gases, water vapour, dust particles, and traces of other gases.


Nitrogen and Oxygen:

•           Air contains about 78% nitrogen and 21% oxygen.

•           Oxygen in air supports burning whereas nitrogen does not.


78% nitrogen, 21% oxygen, 1% other gases


Carbon Dioxide:

•           Air contains about 0.03% of carbon dioxide.

•           Plants and animals take in oxygen and give out carbon dioxide during respiration.

•           During burning, carbon dioxide is also produced.


Water Vapour:

•           Air contains varying amounts of water vapour depending on the weather of a place.

•           In water cycle, the sun heats the water in oceans and seas.

•           This water evaporates and forms water vapour.

•           The presence of water vapour in air can be verified by observing wet clothes drying on a clothesline.

•           The water in wet clothes forms water vapour and disappears into the air.


Dust and Smoke:

•           When sun rays enter a dark room, we can observe tiny particles in these rays. These are dust particles as air contains dust and it also contains smoke.

Dust and smoke in the air