Science · Chapter 5 · ICSE Class 5

Air and Water

Air and water are all around us, and both can change form. Drag the temperature slider to watch water change state.

The States of Water Machine
🧊
Ice (Solid)
Temperature: -10°C
Below 0°C, water freezes into solid ice.
-10°C

Try it: slide slowly past 0°C and 100°C to see water change state.

The composition of air: nitrogen, oxygen, and other gases A pie chart showing that air is made up of about 78 percent nitrogen, 21 percent oxygen, and about 1 percent other gases Nitrogen 78% Oxygen 21% + about 1% other gases
5.1

What is air?

Air is a mixture of invisible gases that surrounds the Earth. Even though we cannot see it, air takes up space and has weight.

Nitrogen
~78%

The largest part of air, though we don't use much of it directly when breathing.

Oxygen
~21%

The gas we breathe in to stay alive and that fuels burning.

Other gases
~1%

Includes carbon dioxide, water vapour, and other trace gases.

Try this — Wave your hand quickly in front of your face — you can feel the air moving even though you can't see it, proving air is real matter that takes up space.
5.2

Uses of air

1Breathing

All living things need the oxygen in air to breathe and release energy from food.

2Burning

Oxygen in the air is needed for things to burn — a candle flame will go out if it runs out of air.

3Moving things

Moving air (wind) can fill sails to move boats, turn windmills, and fly kites.

5.3

States of water

Water can exist in three states depending on temperature: solid (ice), liquid (water), and gas (water vapour/steam).

1Melting and freezing

Ice melts into liquid water above 0°C. Liquid water freezes into solid ice below 0°C.

2Boiling and condensation

Liquid water boils and turns into water vapour (gas) at 100°C. Water vapour condenses back into liquid water when it cools down, like droplets forming on a cold glass.

Watch out — Water vapour in the air is invisible — the white "steam" you see rising from a hot cup is actually tiny droplets of liquid water that have already condensed, not the gas itself.
5.4

Uses of water and saving it

We use water for drinking, cooking, washing, growing crops, and generating electricity. Since clean water is limited, it's important to use it wisely — for example, by turning off taps when not in use and fixing leaks quickly.

Practice

Exercises

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Sample tests

Two 20-mark, 30-minute tests. Reveal answers question by question.