LIWA

Air and Atmosphere

ICSE Class 6 · Chemistry · Chapter 6

What this chapter covers

Key definitions

Air is a mixture of gases, mainly nitrogen and oxygen, with small amounts of carbon dioxide, water vapour and some other gases.

Oxygen is the gas in air that is needed for burning and for breathing.

Nitrogen is the gas that makes up the largest part of air and does not help things to burn.

Lime water is a clear, colourless liquid that turns milky when carbon dioxide passes through it.

Carbon dioxide is a gas in air that turns lime water milky and is given out when fuels burn and when living things breathe out.

Water vapour is water in the form of an invisible gas.

The percentage composition of air is the amount of each gas present in every 100 parts of air.

The atmosphere is the layer of air that surrounds the Earth.

A pollutant is a harmful substance that gets mixed into air, water or soil and makes it unclean.

Air pollution is the making of air dirty and harmful by adding pollutants to it.

Dust is made of tiny solid particles that float in the air.

Smoke is a mixture of harmful gases and tiny particles of unburnt carbon that is given out when things burn.

Key points

Questions answered

Describe one activity that shows air takes up space.
Push an empty bottle upside down into water; very little water enters. When it is tilted, bubbles of air come out and water goes in.
Name the two gases that make up most of the air, with their approximate amounts.
Nitrogen, about 78 parts in 100, and oxygen, about 21 parts in 100.
A burning candle is covered with an upside-down glass. Why does it go out after some time?
The candle needs oxygen to burn. It uses up the oxygen inside the glass, so the flame cannot continue.
How can you show that your breath contains carbon dioxide?
Blow through a straw into lime water. The lime water turns milky, which shows carbon dioxide is present.
Drops of water form on the outside of a glass of iced water. Where does this water come from?
From the water vapour in the air, which turns into liquid on the cold surface.
Why are pea and gram plants useful to farmers for the soil?
Bacteria on their roots change nitrogen from the air into a form plants can use, so the soil becomes richer in nitrogen.
What is the atmosphere?
The atmosphere is the layer of air that surrounds the Earth.
Name two pollutants in air and one source of each.
Dust, from bare ground or building sites; smoke, from vehicles or burning rubbish.