Collecting a dense gas
Because the density of carbon dioxide is greater than that of ordinary air, the gas can also be collected in another way.
Figure to be added
How it works
The carbon dioxide arriving through the tube is the denser gas, so it travels to the bottom of the gas jar.
The jar then fills with carbon dioxide.
The air that was in the jar is pushed upwards and out.
Upward displacement of air
This method of collecting a gas is therefore called the "upward displacement of air".
Which way up the jar goes
Hydrogen — inverted
The gas is light and rises — so the jar must be held upside down.
Carbon dioxide — upright
The gas is heavy and sinks — so the jar must be held the right way up.
How to choose the method
If the gas does not dissolve in water, downward displacement of water works. If it is lighter than air, downward displacement of air works; if heavier, upward displacement of air.