CJC H2 Chem 2013 Prelim P2 Soln

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2 9647/02/CJC JC2 Preliminary Exam 2013 1 Planning (P) Natural water that contains calcium and magnesium ions is said to be 'hard'. Tap water in England is hard water, which is evident from the limescale found in kettles. The main source of calcium and magnesium ions in hard water is limestones. However, neither calcium carbonate nor magnesium carbonate is appreciably soluble in water. It is said that the solubility is partly the result of carbon dioxide present in rain water. You are to design an experiment to investigate whether the presence of carbon dioxide in water, indeed, increases the solubility of magnesium carbonate. In addition to the standard apparatus available in a school laboratory, you are provided with the following materials,  magnesium carbonate  distilled water  distilled water saturated with carbon dioxide  methyl orange indicator  phenolphthalein indicator  standard hydrochloric acid (a) Write an expression for the solubility product, Ksp, of magnesium carbonate, stating its units. ……………………………………………………………………………………………....[1] (b) When a solution is saturated, the undissolved solid is in equilibrium with its aqueous solution. X(s) + aq X(aq) Describe briefly how you would prepare a saturated solution of magnesium carbonate at room temperature. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………….. ………………………………………………………………………………………………. [3]