Edexcel IGCSEChemistryGeneral Applications12 Marks

This question is about salts.

(a)(i)Describe how to prepare a pure, dry sample of magnesium sulfate crystals starting from magnesium carbonate and dilute sulfuric acid.[6]
(a)(ii)Suggest why the method used to prepare magnesium sulfate cannot be used to prepare barium sulfate.[1]
(b)Zinc chloride solution can be prepared by reacting zinc oxide with hydrochloric acid. A student adds 6.0 g of zinc oxide to 50 cm³ of 2.0 mol/dm³ hydrochloric acid. The equation for the reaction is ZnO(s) + 2HCl(aq) → ZnCl₂(aq) + H₂O(l) Calculate the maximum mass of zinc chloride (ZnCl₂) that can be formed. [Mᵣ: ZnO = 81, HCl = 36.5, ZnCl₂ = 136][5]

Mark scheme

Marking points from the official mark scheme. The mark or mark type is shown in brackets.

M1 for (a)(i) add excess magnesium carbonate (to sulfuric acid)
A1 for (a)(i) filter (to remove unreacted magnesium carbonate)
M1 for (a)(i) heat / evaporate (some of the water / solution)
A1 for (a)(i) leave to cool / crystallise
M1 for (a)(i) blot dry / dry (crystals) between filter paper
A1 for (a)(i) wash (with distilled water) (before drying) / allow to dry in warm place / in desiccator
B1 for (a)(ii) barium sulfate is insoluble / barium carbonate is insoluble / sulfuric acid is strong / sulfuric acid forms insoluble precipitate (with barium)
M1 for (b) moles of ZnO = 6.0 / 81 (= 0.074)
M1 for (b) moles of HCl = 50 / 1000 × 2.0 (= 0.10)
M1 for (b) (HCl is limiting) 0.10 / 2 (= 0.05)
A1 for (b) moles of ZnCl₂ = 0.05 (ECF from previous step if logical)
A1 for (b) mass of ZnCl₂ = 0.05 × 136 (= 6.8 g) (ECF from previous step if logical)

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