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

Chemistry of transition elements — practice question

(a)[1]

Complete the electronic configuration for the $\text{Cu}^{2+}$ ion below. $1s^2\ 2s^2\ 2p^6$ …

(b(i))

Explain the reason for this effect.

(b(ii))

How does this splitting account for the fact that transition metal complexes are often coloured?

(b(iii))[5]

Why does the colour of a transition metal complex vary with the identity of the ligands around the transition metal ion?

(c)[5]

Draw a fully labelled diagram of the apparatus that could be used to measure the $E^\circ$ of a cell made from the $\text{Fe}^{3+}/\text{Fe}^{2+}$ electrode and the $\text{Cu}^{2+}/\text{Cu}$ electrode.

(d(i))

Describe the type of reaction occurring between $\text{Cu}^{2+}(aq)$ and $\text{NH}_3(aq)$.

(d(ii))

Write an equation for the reaction.

(d(iii))

Describe the colour change of the solution.

(d(iv))[4]

Predict and explain how $E_{\text{electrode}}$ could change when $\text{NH}_3(aq)$ is added.

(e(i))

Name the functional group involved.

(e(ii))

Describe what a positive result looks like in this test.

(e(iii))[3]

Write an equation for the reaction between $\text{Cu}^{2+}$ and $\text{OH}^-$ ions and a two-carbon compound containing the functional group you named in (i).

(f)[2]

A mixture of tartaric acid and its sodium salt can act as a buffer in some ready-made food dishes. Calculate the pH of a solution containing $0.50\ \text{mol dm}^{-3}$ tartaric acid and $0.80\ \text{mol dm}^{-3}$ sodium tartrate. $K_a(\text{tartaric acid}) = 9.3 \times 10^{-4}\ \text{mol dm}^{-3}$.

Worked solution & mark scheme

This 20-mark question has a full step-by-step worked solution and mark scheme. One marking point: Electron arrangement $(1s)^2(2s)^2(2p)^6(3s)^2(3p)^6(3d)^9$

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