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

Chemistry of transition elements — practice question

Transition-element ions make complexes when they combine with ligands.
(a(i))

State the meaning 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 the structures in the boxes and name the shapes.

(a(iii))[7]

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

(b(i))[2]

Complete the electronic structures for these ions. Cu(II) $[\text{Ar}]$ ................................. Cu(I) $[\text{Ar}]$ .................................

(b(ii))[3]

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

(c(i))[2]

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

(c(ii))[2]

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: $\text{2CuO}(s) \rightleftharpoons \text{Cu}_2\text{O}(s) + \frac{1}{2}\text{O}_2(g)$ Hence suggest whether a low or a high temperature of oxidation would favour the production of copper(I) oxide. Explain your reasoning.

Worked solution & mark scheme

This 16-mark question has a full step-by-step worked solution and mark scheme. One marking point: A complex consists of a central metal atom/ion attached to one or more ligands

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