What air is made of

Air is a mixture of several different gases

The most plentiful gas in air is nitrogen and most of the rest is oxygen

  The composition of airks2_air_clip_image002_0000 Nitrogen: 78%
Oxygen: 21%
Argon: 1%
Tiny amounts of carbon dioxide, helium and other gases

(See table)


How to show that air has weight


A metre rule is balanced at its center and an inflated balloon is hung from each end (see diagram labelled BEFORE)
When air is let out of one of the balloons we see the ruler move so that the side with the inflated balloon goes down.

This happens because the inflated balloon is heavier than the empty balloon showing is that air must have weight

The weight of air in an average room will be about 100kg!

How much do you weigh?
(in kilograms)
Find some bathroom scales and find out


Table showing the names of the main gases in the air and what they are used for

Name of gas






Nitrogen is the main gas in air.

Nitrogen is used to make plant food (fertilizer) and is also in explosives.





Without oxygen we cannot breath and fires wont burn.

Oxygen is used in hospitals to help us breathe.

It also used in welding and as rocket fuel.

Oxygen is produced by plants (during photosynthesis).




Argon is the gas inside electric light bulbs

Carbon dioxide


Carbon dioxide is the gas in fizzy drinks. It is also used in fire extinguishers.

All living organisms breath out carbon dioxide when they make energy (from food).

Carbon dioxide is needed by plants when they make food (during photosynthesis).





It is a very light gas and is used in balloons to help them float


Water vapour


Water vapour is formed when water evaporates.

When water vapour in the air cools down it forms clouds.

There is lots of water vapour in the air we breathe out.


A 10 year old will weigh about 25kg