Lesson: Chapter 16 — Changes of Matter

16.5. Hydrogen and oxygen 2 of 8

Properties of hydrogen

Hydrogen gas has six physical and chemical properties.

Property	Why it matters
Less dense than ordinary air	can be collected by downward displacement of air
Relative molecular mass is 2	the lowest of any gas
A combustible gas	identified by a "pop"; usable as a fuel
Slightly soluble in water	can be collected by downward displacement of water
Colourless	cannot be identified by sight
Has no smell	cannot be identified by smell either

Combustible or supporter of combustion?

Hydrogen is combustible — it burns itself. But it does not support combustion. Oxygen is exactly the reverse: it does not burn, but it helps other things to.

The last two properties are a problem

Being colourless and odourless, hydrogen cannot be identified in a tube by looking at it or smelling it. So a test is needed — and we meet it in activity 16.8.