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
• 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.
• 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