air

Air

Air is a mixture of different gases and water vapour. It covers the earth. The thick layer of air that surrounds the earth is called atmosphere. The atmosphere lies within 16 km from the earth’s surface. It also contains dust particles. The air is also found in the soil, water and porous materials such as sponges, bricks, wood, breads, etc. It cannot be seen but can be felt. Living things cannot survive without air. It is the most important things to all the living things. All the living things take in oxygen from the air and give out carbon dioxide during respiration. All the green plants use carbon dioxide of the air to make their food during photosynthesis.

 


Composition of air

We learn that air is mixture of gases. The main gases of air are nitrogen and oxygen. Nearly four-fifth of the air is nitrogen and oxygen whereas one-fifth of air contains oxygen. Besides these gases, the other gases present in the air are carbon dioxide, water vapour and the inert gases like neon, argon, helium, krypton, xenon and radon.
 The given figure shows the composition of the air on the earth. Plants use nitrogen in the form of fertilizer. Carbon dioxide and oxygen gases are exchanged between atmosphere and photosynthesis. Carbon dioxide is formed in the air by the combustion of fuel. In this way, the composition of the gases in the atmosphere is generally constant everywhere on the earth. However, the amount of water vapour and carbon dioxide may differ from place to place.

Various activities have shown that the composition of air on the earth by volume is as given in the table.

S.N
Gases in air
Percentage by volume
1.
2.
3.
4.
5.
6.
7.
Nitrogen
Oxygen
Carbon dioxide
Argon
Neon
Other inert gases
Water vapour
78.07
20.98
0.03
0.85
0.002
0.008
0.06

Rusting

We may have noticed that when shiny iron rods are exposed in a moist place for few days, their outer surface becomes reddish brown. The reddish brown layer on the surface of the iron rod is called rust. This brown rust is reddish due to the oxides of the iron. Thus, the process of formation of rust by the slow oxidation of iron into oxide due to the atmospheric oxygen in the presence of water vapour is called rusting.

Rusting

                      Rusting of iron


Presence of oxygen in air

 Oxygen is an important gas found in the air.  It constitutes one fifth of the air by volume. All the living thing uses it during the process of respiration. Oxygen in the air also helps in the process of burning.
Presence of oxygen in air

            Presence of oxygen in air


Carbon dioxide in air

Carbon dioxide in the air is used by plants to make their food during  the process of photosynthesis. It is given off during the process of respiration by all living things. It is also produced when fuels are burnt in air.

Carbon-dioxide

                Carbon-dioxide


Properties of air

1.Air is mixture of different gases. It is composed of nitrogen, oxygen, carbon dioxide, inert gases and water vapour.
2.Air occupies spaces and has weight.
3.Pure air is colorless, tasteless and odorless.
4.Air exerts pressure and can be compressed.
5.Air can blow from one place to another.
6.Air expands on heating.


Uses of air

1.Air helps to burn things as it contains oxygen. Oxygen is a supporter of burning.
2.Almost the all animals and plants use oxygen during the process of respiration.
3.All the green plants take carbon dioxide to prepare their food during the process of photosynthesis.
4.All the living things need nitrogen. It is the most essential gas that is used to make protein by all the living things. Proteins are essential for life.
5.The larger amount of nitrogen in the air prevents constant fire as it is neither a combustible nor a burning supporter.
6.Air is used to fill in the tires of vehicles, bladder of football, etc.
7.Air helps in the dispersal of seeds and pollination of flowers.
8.The moving air is used in wind-mills as it is a source of energy.
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