Deep-sea divers sometimes breathe a gas mixture called heliox instead of air. The heliox used in this question contains 80% helium and 20% oxygen by volume.
Helium is extracted from natural gas. The table shows the boiling points of the main gases in the natural gas used.
| Gas | Boiling point in °C |
|---|---|
| helium | −269 |
| nitrogen | −196 |
| methane | −162 |
Relative atomic masses: He = 4, O = 16. One mole of any gas occupies 24 dm3\mathrm{dm^{3}}dm3 at room temperature and pressure.
Hydrogen is less dense than helium. Explain why helium, not hydrogen, is mixed with oxygen for divers to breathe.
Calculate the density of heliox at room temperature and pressure, in g dm−3\mathrm{g\,dm^{-3}}gdm−3.
A diving cylinder contains heliox that would occupy 2400 dm3\mathrm{dm^{3}}dm3 at room temperature and pressure. Calculate the mass of helium in the cylinder.
Explain how helium can be separated from the other gases in natural gas. Use the data in the table.
Helium that escapes into the air rises and is eventually lost into space. Suggest why helium is described as a non-renewable resource.
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.