Argon is obtained from air. Air is cooled until it becomes a liquid, and then the liquid air is separated by fractional distillation.
The table shows information about three gases in dry air.
| Gas | Boiling point in °C | Percentage by volume in dry air |
|---|---|---|
| nitrogen | −196 | 78.1 |
| oxygen | −183 | 20.9 |
| argon | −186 | 0.93 |
The liquid air is warmed slowly. State which gas boils off first. Give a reason for your answer.
Suggest why it is difficult to separate argon from oxygen by fractional distillation.
Calculate the volume of argon in 500 dm3\mathrm{dm^{3}}dm3 of dry air.
Calculate the mass of argon in your answer to (c). Relative atomic mass: Ar = 40. One mole of any gas occupies 24 dm3\mathrm{dm^{3}}dm3 at room temperature and pressure.
The percentage of oxygen in the atmosphere has changed greatly since the Earth formed. Suggest why argon is not removed from the atmosphere by chemical reactions.
38 exam-style questions on Edexcel GCSE Chemistry 7.3 Group 0, covering 7.3.1 The noble gases. Each one has a worked solution and a mark scheme showing where the marks go.