Hydrogen, the lightest gas
In this last section we take three gases — how they are prepared, their properties and their uses. The first is hydrogen.
A very small part of the atmosphere
Hydrogen is a gas present in a very small percentage of the ordinary composition of the atmosphere. It is nonetheless of great use to us.
The lightest gas
Hydrogen is the lightest gas. Its relative molecular mass is only 2, and no gas has a smaller one.
Compared with air
The relative molecular mass of nitrogen (N2), the main constituent of air, is 28, and that of oxygen (O2) is 32.
For hydrogen (H2) it is only 2 — so it is very much lighter than air.
This matters later
Precisely because it is lighter than air, hydrogen can be collected by a special method — one we shall meet over the next few pages.
On the next page we look at the six physical and chemical properties of hydrogen gas.