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

Chemistry of transition elements — practice question

(a)[2]

Complete the electronic configurations of the species below. $\text{Co}\ \ [\text{Ar}]\ \ldots$ $\text{Co}^{2+}\ \ [\text{Ar}]\ \ldots$

(b)[1]

In an isolated transition metal atom, all five $d$ orbitals have equal energy. When a transition metal ion forms a tetrahedral complex, the $d$ orbitals separate into two groups with different energies. Finish an orbital energy diagram to show this, stating how many orbitals are in each group.

(c(i))[1]

Cobalt(II) makes a six-coordinate complex containing three water molecules and three chloride ions. Write the formula for this complex, showing the overall charge if appropriate.

(c(ii))[2]

Explain, using diagrams, how many isomers the complex in (i) has.

(d(i))[1]

Platinum(II) makes a four-coordinate complex containing two ammonia molecules and two chloride ions. Write the formula for this complex, showing the overall charge if appropriate.

(d(ii))[3]

This complex has two isomers. Draw the structures of these isomers and name them.

(d(iii))[2]

One of the isomers in (ii) is used as an important anticancer drug. State which isomer it is and explain why it is effective.

(e(i))[2]

Transition metal ions are often present as hexa-aqua complexes in aqueous solution, and the ligand exchange reactions are reversible. $[\text{Cu}(\text{H}_2\text{O})_6]^{2+} + 4\text{NH}_3 \rightleftharpoons [\text{Cu}(\text{NH}_3)_4(\text{H}_2\text{O})_2]^{2+} + 4\text{H}_2\text{O}$ Write an expression for $K_{\text{stab}}$ for this equilibrium and state its units.

(e(ii))[1]

The numerical value of $K_{\text{stab}}$ for this equilibrium at $298\ \text{K}$ is $1.20 \times 10^{13}$. Explain how this value is connected to the relative stabilities of the two complexes.

(ii)[3]

This complex has two isomers. Draw the structures of these isomers and name them.

(iii)[2]

One of the isomers in (ii) is an important anticancer drug. State which isomer it is and explain why it works.

Worked solution & mark scheme

This 20-mark question has a full step-by-step worked solution and mark scheme. One marking point: Cobalt: $[Ar]3d^74s^2$; $Co^{2+}$: $[Ar]3d^7$

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