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

Chemistry of transition elements — practice question

Transition element ions form complexes when they react with ligands.
(a(i))

State the meanings of the terms: complex, ligand.

(a(ii))

Copper forms two complexes, $[\text{Cu(H}_2\text{O)}_6]^{2+}$ and $\text{CuCl}_4^{2-}$. Draw three-dimensional diagrams of their structures in the boxes and give their shapes.

(a(iii))[7]

Platinum forms square-planar complexes, where all four ligands are in the same plane as the Pt atom. There are two isomeric complexes with the formula $\text{Pt(NH}_3)_2\text{Cl}_2$. Suggest the structures of the two isomers and, by comparison with a similar type of isomerism in organic chemistry, suggest the type of isomerism shown here.

(b(i))

Fill in the electronic structures for these ions: Cu(II) $[\text{Ar}]\,\ldots$ ; Cu(I) $[\text{Ar}]\,\ldots$

(b(ii))[5]

Use these electronic structures to explain why copper(II) salts are generally coloured, and why copper(I) salts are generally white or colourless.

(c(i))

Copper(II) oxide can be obtained in pure form by heating copper(II) nitrate. Use suitable $\Delta H_f^\circ$ values from the table to calculate $\Delta H^\circ$ for this reaction: $\text{Cu(NO}_3)_2(s) \rightarrow \text{CuO}(s) + 2\text{NO}_2(g) + \tfrac{1}{2}\text{O}_2(g)$.

(c(ii))[4]

Copper(I) oxide can be made from copper(II) oxide. Use suitable $\Delta H_f^\circ$ values from the table to calculate $\Delta H^\circ$ for the reaction $2\text{CuO}(s) \rightleftharpoons \text{Cu}_2\text{O}(s) + \tfrac{1}{2}\text{O}_2(g)$. Hence suggest whether a low or a high temperature of oxidation would favour the formation of copper(I) oxide. Explain your answer.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: A complex is a species produced when a central metal atom/ion is bonded to ligands

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