Chemistry 9701 · AS & A Level · States of matter

States of matter — practice question

The oxides of tin and lead most often encountered are $\text{SnO}$, $\text{SnO}_2$, $\text{PbO}$ and $\text{PbO}_2$. From the oxides of Group IV elements, two broad trends follow: • The farther down the Group the elements are, the greater their metallic character, so their oxides are more basic. • In a higher oxidation state, an element’s oxide is more acidic than the oxide of that element in a lower oxidation state.
(a(i))

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

(a(ii))[4]

Use these trends to decide which of the above oxides of tin or lead is most likely to react with $\text{HCl(aq)}$. For each one, write a balanced equation for the reaction.

(b)[2]

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

(c)[10]

Lead(II) chloride dissolves only slightly in water. $\text{PbCl}_2(s) \rightleftharpoons \text{Pb}^{2+}(aq) + 2\text{Cl}^-(aq) \quad K_{sp} = 2.0 \times 10^{-5}$ (i) Write the solubility product expression, $K_{sp}$, for lead(II) chloride and state the units. (ii) Work out $[\text{Pb}^{2+}(aq)]$ in a saturated $\text{PbCl}_2$ solution. An excess of $\text{PbCl}_2(s)$ is mixed with $0.50\,\text{mol dm}^{-3}$ $\text{NaCl}$ until equilibrium is reached. The extra $\text{PbCl}_2(s)$ is then removed by filtration. (iii) Assuming $[\text{Cl}^-]$ stays at $0.50\,\text{mol dm}^{-3}$ throughout, calculate the $[\text{Pb}^{2+}(aq)]$ in the solution left behind. (iv) Suggest why this value is different from the value you found in (ii).

Worked solution & mark scheme

This 16-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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