CAIE A Level Chemistry 9701 · Group 2
The carbonates of the Group 2 metals decompose on heating to form the metal oxide and carbon dioxide gas. A student heats samples of magnesium carbonate, calcium carbonate and strontium carbonate separately and measures the temperature at which each decomposes. The results are shown.
| carbonate | decomposition temperature / °C |
|---|---|
| 540 | |
| 900 | |
| 1290 |
Compare the thermal stability of these carbonates and explain the trend in terms of the metal ions and the carbonate ion.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Compare means: Give similarities or differences between two things, and say which side each point belongs to. Write each point as a pair, for example: A is X, whereas B is Y. Two separate descriptions rarely earn the marks.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.