We live, move and breathe at the bottom of an immense ocean of air called the atmosphere. Air is an invisible mixture of gases made up of a teeming mass of millions of tiny gas molecules that move about randomly and at high speed. Without air, the earth would be a lifeless planet, because the gases air contains are vital to plants and animals.

Carbon dioxide (CO2):

Carbon dioxide is vital for plant life. Plants absorb carbon dioxide from the air and combine it with water gathered by their roots to form sugars which they use for growth.

Nitrogen (N2):

Every living cell contains nitrogen. Plants cannot take nitrogen from the air, so they get it from the soil. Fertilizers contain nitrogen to replenish what plants remove from the soil.

The Uses of Air:

Scuba divers use compressed air to breathe underwater. However, the gases in air can also be used separately. Nitrogen is used in explosives and oxygen in medicine. Gases are extracted from air by a process called Fractional Distillation. Air is cooled and compressed until it forms a blue liquid. When the liquid expands and warms up, each gas boils off at a different temperature and is collected separately.

Composition of Air:

Any volume of pure, dry air is 78.09% nitrogen, 20.95% oxygen, 0.93% argon and 0.03% carbon dioxide and other gases. These colored balls represent the proportions of the different gases in air.

Oxygen (O2):

Burning is a chemical reaction of a substance with oxygen as this experiment shows. The candle burns in the jar of air until it has used up all the oxygen. Humans and other animals use oxygen from the air to burn food inside their bodies and produce energy.

Argon (Ar):

The gas Argon is called an Inert Gas because it is so unreactive. Electric light bulbs are often filled with argon. It prevents the bulb’s filament from burning up as it would in air, giving the bulb a much longer life.

Air Pollution:

Air is not naturally pure and contains varying amounts of other substances such as dust, water, vapor, bacteria, pollen and polluting gases. Air pollution from industry and traffic can cause serious health problems ii towns and cities as well as long – term damage to the environment.


The hazy air pollution that hangs over an urban area is called smog. Sumptuous smog is the result of burning fuels with high sulphur content, such as coal. Photochemical smog occurs when sunlight causes car exhaust fumes to react together.

Water Vapour:

Up to 4 per cent of Volume of air may be water vapour. Warm air can hold more water vapour than cool air. A can of cold drink absorbs heat from the air around it. As the air cools, water vapour condenses out of the air to form droplets on the outside of the can.

Air Pressure:

Air exerts a force on objects because its moving molecules are constantly colliding with them. Air pressure is a measure of this force. The pressure of the open air is called atmospheric pressure. It is lower at high altitudes where the air is less dense.


A device that measures atmospheric pressure is called a barometer. It can be used to forecast a change in the weather, because air pressure varies slightly from day to day with changes in the air’s temperature and humidity.


When a person sucks on one end of a drinking straw, the lungs reduce the air pressure inside the straw. Atmospheric pressure on the liquid’s surface does the rest, pushing down on the liquid and making it rise up through the straw.

Compressed Air:

The pressure of air can be increased by compressing it – that is, pumping more and more of it into limited space. Bicycle tires are filled with compressed air to give a smooth, comfortable ride.

Weight of Air:

Air has weight, as this simple experiment proves. Identical empty ballons are attached to both ends of a stick. The balloon balance when the stick is suspended from its middle. Inflating one of the balloons tips the balance, because the balloon full of compressed air weighs more than the empty balloon.

Joseph Priestley:

English scientist and clergyman Joseph Priestley (1733 – 1804) discovered oxygen in 1774. He also discovered many other gases, including nitrous oxide (laughing gas) and ammonia. Priestley studied carbon dioxide and devised a way to make carbonated (fizzy) water.

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