Oxygen and its properties
The second gas is oxygen. Unlike hydrogen, it is present in the atmosphere in large amounts.
A fifth of the atmosphere
By the ordinary composition of the atmosphere, about 20% of it is oxygen gas.
The properties of oxygen gas
| Property | Compared with hydrogen |
|---|---|
| Denser than ordinary air | hydrogen is lighter than air — the opposite |
| Relative molecular mass is 32 | 16 times hydrogen's 2 |
| Supports combustion | hydrogen is combustible — the opposite |
| Slightly soluble in water | the same for both |
| Colourless; has no smell | the same for both |
Combustible and supporting combustion
Oxygen supports combustion; it is not itself combustible — it does not burn, but it helps other things to. So putting a lighted splint into a tube of oxygen gives no "pop".
Density decides the collection method
Because oxygen is heavier than air, the downward displacement of air used for hydrogen will not work for it.