A chemical-processing line has two chambers at the same pressure. A substance passes through chamber 1 at −25 ∘C-25\,^{\circ}\mathrm{C}−25∘C and then through chamber 2 at 20 ∘C20\,^{\circ}\mathrm{C}20∘C. For the process to work, the substance must be a liquid in chamber 1 and a gas in chamber 2.
| Substance | Melting point in ∘C^{\circ}\mathrm{C}∘C | Boiling point in ∘C^{\circ}\mathrm{C}∘C |
|---|---|---|
| P | -55 | -5 |
| Q | -15 | 45 |
| R | -70 | 30 |
Suggest which substance should be used. Explain your answer using the data in the table.
122 exam-style questions on OCR GCSE Chemistry 2.3 Properties of materials, covering 2.3.1 Carbon bonding and the variety of organic compounds, 2.3.2 Diamond, graphite, fullerenes and graphene, 2.3.3 Bond strength, changes of state and predicting states, 2.3.4 Bulk properties and types of bonding, and 2.3.5 Nanoparticles: scale, surface area, uses and risks. Each one has a worked solution and a mark scheme showing where the marks go.