Chemistry 9701 · AS & A Level · Group 2

Group 2 — practice question

(a(i))[1]

If water is added to magnesium nitride, $\text{Mg}_3\text{N}_2$, a white suspension of $\text{Mg(OH)}_2$ and an alkaline gas are formed. Write the equation for this reaction.

(a(ii))[2]

A sample of $2.52\,\text{g}$ of $\text{Mg}_3\text{N}_2$ is placed in excess water. Determine the mass of $\text{Mg(OH)}_2$ produced.

(b)[4]

State and explain how the solubility of the Group 2 hydroxides changes down the group.

(c(i))[1]

Magnesium hydroxide is only slightly soluble in water. The concentration of its saturated solution at $298\,\text{K}$ is $1.7 \times 10^{-4}\,\text{mol dm}^{-3}$. Write an expression for the solubility product, $K_{sp}$, of $\text{Mg(OH)}_2$.

(c(ii))[2]

Find the value of $K_{sp}$ for $\text{Mg(OH)}_2$ at $298\,\text{K}$ and give the units.

(d)[2]

The temperatures at which Group 2 hydroxides and carbonates begin to decompose increase down the group. Suggest why the decomposition temperature of the Group 2 hydroxides shows this pattern.

Worked solution & mark scheme

This 12-mark question has a full step-by-step worked solution and mark scheme. One marking point: The balanced equation is $\text{Mg}_3\text{N}_2+6\text{H}_2\text{O}\rightarrow3\text{Mg(OH)}_2+2\text{NH}_3$.

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