CAIE A Level Chemistry 9701 · Atoms, molecules and stoichiometry

Atoms, molecules and stoichiometry: compare question

Compare5 marksStandard

Anhydrous magnesium sulfate, $\ce{MgSO4}$ , and hydrated magnesium sulfate, $\ce{MgSO4.7H2O}$ , are two forms of the same salt.

(a) Compare the formulas of these two compounds, using the terms anhydrous, hydrated and water of crystallisation in your answer.

(b) Write a balanced chemical equation with state symbols for the conversion of the anhydrous salt to the hydrated salt by adding water.

(c) When aqueous solutions of magnesium sulfate and barium chloride are mixed, a precipitate of barium sulfate forms. Write the ionic equation for this precipitation, and state which ions are spectator ions.

How this question is marked

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.

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