A student heats three solids, P, Q and R, in separate test tubes. The table shows the student's observations.
| Solid | Observations on heating | Observations on cooling | Mass change |
|---|---|---|---|
| P | white solid turns into a colourless liquid at 53 °C | white solid forms again at 53 °C | none |
| Q | green solid turns black; a gas is given off that turns limewater milky | black solid stays black | decreases |
| R | grey-black crystals turn directly into a purple vapour | grey-black crystals form on the cool upper part of the tube | none |
Name the change of state when the crystals of R turn directly into a vapour.
Deduce which of the solids P, Q and R undergo only physical changes. Justify your answer using evidence from the table.
The mass of Q decreases on heating, but the mass of R does not change even though R also forms a vapour. Explain this difference.
Explain, in terms of particles and energy, what happens as liquid P cools and becomes a solid at 53 °C.
R is iodine. Suggest why the student heats R in a fume cupboard.
53 exam-style questions on Edexcel GCSE Chemistry 3.1 States of matter, covering 3.1.1 The three states of matter and changes of state. Each one has a worked solution and a mark scheme showing where the marks go.