Chemistry 9701 · AS & A Level · Group 2

Group 2 — practice question

(a(i))[4]

Describe how the solubilities of the hydroxides of magnesium, calcium and strontium change. Explain your answer. Put them in order from most soluble to least soluble.

(a(ii))[1]

Suggest how the pH of saturated solutions of the hydroxides of magnesium, calcium and strontium varies. Explain your answer.

(b)[4]

Barium hydroxide, $\text{Ba(OH)}_2$, is a strong base. A $250.0\,\text{cm}^3$ solution of $\text{Ba(OH)}_2$ with a pH of $12.2$ is prepared by dissolving $\text{Ba(OH)}_2$ in distilled water. Calculate the mass of $\text{Ba(OH)}_2$ required to make this solution. Show your working. $[M_r\!:\,\text{Ba(OH)}_2 = 171.3]$

(c(i))[1]

The solubility of iron(II) hydroxide, $\text{Fe(OH)}_2$, is $5.85 \times 10^{-6}\,\text{mol dm}^{-3}$ at $298\,\text{K}$. Write the expression for the solubility product, $K_{sp}$, of $\text{Fe(OH)}_2$.

(c(ii))[2]

Calculate the value of $K_{sp}$ of $\text{Fe(OH)}_2$. Include its units.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: Reactivity order: strontium > calcium > magnesium

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