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

Chemistry of transition elements — practice question

(a(i))[2]

What do the terms bidentate and ligand mean?

(a(ii))[3]

Three isomeric complex ions have the formula $[\text{Cr(en)}_2\text{Cl}_2]^+$. Finish the three-dimensional diagrams of the isomers in the boxes. en may be used as the abbreviation for en.

(b(i))[3]

Write the expressions for the stability constants, $K_{\text{stab}1}$ and $K_{\text{stab}2}$, for equilibria 1 and 2, and include units in your answers. Equilibrium 1: $\text{Cu}^{2+}\text{(aq)} + 4\text{NH}_3\text{(aq)} \rightleftharpoons [\text{Cu(NH}_3)_4]^{2+}\text{(aq)}$ Equilibrium 2: $\text{Cu}^{2+}\text{(aq)} + 2\text{en(aq)} \rightleftharpoons [\text{Cu(en)}_2]^{2+}\text{(aq)}$

(b(ii))[1]

Give an expression for the equilibrium constant, $K_{\text{eq}3}$, in terms of $K_{\text{stab}1}$ and $K_{\text{stab}2}$, for equilibrium 3. $[\text{Cu(NH}_3)_4]^{2+}\text{(aq)} + 2\text{en(aq)} \rightleftharpoons [\text{Cu(en)}_2]^{2+}\text{(aq)} + 4\text{NH}_3\text{(aq)}$

(b(iii))[2]

The stability constants are given as $K_{\text{stab}1} = 1.2 \times 10^{13}$ and $K_{\text{stab}2} = 5.3 \times 10^{19}$. Calculate the value of $K_{\text{eq}3}$ and state its units.

(c(i))[1]

Explain why $\Delta S^\circ_{\text{eq}2}$ is so different from $\Delta S^\circ_{\text{eq}1}$.

(c(ii))[2]

Calculate the value of $\Delta G^\circ_{\text{eq}2}$ at $298\,\text{K}$.

(c(iii))[1]

What conclusion can be drawn about the relative feasibility of equilibria 1 and 2? Explain your answer.

(c(iv))[1]

Using the data in the table, suggest a value of $\Delta H^\circ$ for equilibrium 3.

(c(v))[1]

State the reaction type taking place in equilibrium 2.

Worked solution & mark scheme

This 17-mark question has a full step-by-step worked solution and mark scheme. One marking point: A bidentate ligand makes two dative bonds / donates two lone pairs

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