QCEVault

Chemical equilibrium — Question 94

Original QCE Vault practice · 6 marks

Q94 · Practice questionComplex unfamiliar6 marks

QUESTION 94 (6 marks)

A mixture initially contains 0.0100 mol L⁻¹ each of Cu²⁺ and Mg²⁺. Hydroxide is slowly added at 25∘C with negligible volume change. Ksp(Cu(OH)2)=2.2×10−20; Ksp(Mg(OH)2)=1.8×10−11; Kw=10−14. Ignore complex ions.

a) Calculate the pH at which each hydroxide just begins to precipitate. [4 marks]

b) Choose a pH strictly between the two thresholds that precipitates copper hydroxide but not magnesium hydroxide. Justify. [2 marks]

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