CAIE A Level Chemistry 9701 · Group 2
The carbonates of the Group 2 elements decompose on heating to form the corresponding oxide and carbon dioxide. The temperatures at which the carbonates of magnesium, calcium and barium begin to decompose are 540°C, 900°C and 1360°C respectively.
Compare the thermal stabilities of these carbonates and explain the trend shown by these data. Your answer should include equations for the decompositions of the carbonates of magnesium and barium.
7 marks, so the mark scheme is looking for about 7 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.
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