Chemistry 9701 · AS & A Level · Group 2

Group 2 — practice question

(a)[3]

Describe and explain how the solubilities of the sulfates of the Group II elements change down the group.

(b(i))

Use the data above to determine values of $\u0006H^\u000b_\text{solution}$ for $\text{Mg(OH)}_2$ and for $\text{Sr(OH)}_2$.

(b(ii))

Use your results in (i) to suggest whether $\text{Sr(OH)}_2$ is more or less soluble in water than $\text{Mg(OH)}_2$. State any assumptions you make.

(b(iii))[5]

Suggest whether $\text{Sr(OH)}_2$ would be more or less soluble in hot water than in cold water. Explain your answer.

(b)

The table below gives some enthalpy changes for magnesium and strontium compounds.

(c)

Calcium hydroxide, $\text{Ca(OH)}_2$, has only slight solubility in water.

(c(i))

Write an expression for $K_{sp}$ for calcium hydroxide, and state its units.

(c(ii))

A $25.0\,\text{cm}^3$ portion of a saturated solution of $\text{Ca(OH)}_2$ needed $21.0\,\text{cm}^3$ of $0.0500\,\text{mol dm}^{-3}$ $\text{HCl}$ for complete neutralisation. Calculate $[\text{OH}^-(aq)]$ and $[\text{Ca}^{2+}(aq)]$ in the saturated solution, and hence determine a value for $K_{sp}$.

(c(iii))[6]

Compare the solubility of $\text{Ca(OH)}_2$ in $0.1\,\text{mol dm}^{-3}$ $\text{NaOH}$ with its solubility in water. Explain your answer.

Worked solution & mark scheme

This 14-mark question has a full step-by-step worked solution and mark scheme. One marking point: Solubility falls down the group

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