Chemistry 9701 · AS & A Level · Chemistry of transition elements

Chemistry of transition elements — practice question

The usual oxides of tin and lead are $\text{SnO}$, $\text{SnO}_2$, $\text{PbO}$ and $\text{PbO}_2$. Two broad patterns for Group IV oxides are: • As the elements become more metallic down the Group, their oxides show greater basic character. • Oxides with the elements in higher oxidation states are more acidic than the oxides with the elements in lower oxidation states.
(a(i))

Apply these patterns to decide which of the oxides of tin or lead above is most likely to react with $\text{NaOH(aq)}$. In each case, give a balanced equation for the reaction.

(a(ii))[4]

Apply these patterns to decide which of the oxides of tin or lead above is most likely to react with $\text{HCl(aq)}$. In each case, give a balanced equation for the reaction.

(b)[2]

'Red lead' is used as a pigment, and as a metal primer paint to prevent the corrosion of steel. It is an oxide of lead that contains $9.30\%$ oxygen by mass. Calculate to $3$ significant figures the number of moles of oxygen and lead contained in a $100.0\,\text{g}$ sample of red lead. Hence calculate its empirical formula.

(c(i))

Write down an expression for the solubility product, $K_{sp}$, of lead(II) chloride and state its units, given that $\text{PbCl}_2(s) \rightleftharpoons \text{Pb}^{2+}(aq) + 2\text{Cl}^-(aq)$ and $K_{sp} = 2.0 \times 10^{-5}$.

(c(ii))

Calculate $[\text{Pb}^{2+}(aq)]$ in a saturated solution of $\text{PbCl}_2$.

(c(iii))

An excess of $\text{PbCl}_2(s)$ is stirred with $0.50\,\text{mol dm}^{-3}$ $\text{NaCl}$ until equilibrium has been established. The excess $\text{PbCl}_2(s)$ is then filtered off. Assuming $[\text{Cl}^-]$ remains at $0.50\,\text{mol dm}^{-3}$ throughout, calculate the $[\text{Pb}^{2+}(aq)]$ in the remaining solution.

(c(iv))[4]

Suggest an explanation for the difference between this value and the value that you calculated in (ii).

Worked solution & mark scheme

This 10-mark question has a full step-by-step worked solution and mark scheme. One marking point: Balanced equation: $\mathrm{2NaOH + SnO_2 \rightarrow Na_2SnO_3 + H_2O}$

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