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

Chemistry of transition elements — practice question

Several copper compounds, for example $\text{CuSO}_4$ and $\text{Cu(NO}_3)_2$, contain $\text{Cu}^{2+}$ ions. In aqueous solution, this ion is present as the $[\text{Cu(H}_2\text{O)}_6]^{2+}$ complex ion, with water acting as a monodentate ligand.
(a)[1]

What is meant by the term monodentate ligand?

(b)[4]

Aqueous copper(II) sulfate, $\text{CuSO}_4\text{(aq)}$, shows noticeable changes in appearance with particular reagents. Fill in the table below.

(c)[3]

Adding water to concentrated aqueous cobalt(II) chloride changes the solution colour from blue to pink. Explain this observation. No equation is required, but your response should refer to electron movement between orbitals.

(d)[2]

When chlorine gas is bubbled into $\text{FeSO}_4\text{(aq)}$, the solution changes from pale green to yellow. Use information from the Data Booklet to explain why this happens. Include an equation in your answer. You do not need to mention electron movement between orbitals.

(e(i))[1]

When chloride ions are added to a solution containing $[\text{Fe(H}_2\text{O)}_6]^{3+}$, an equilibrium is set up. $[\text{Fe(H}_2\text{O)}_6]^{3+} + 4\text{Cl}^- \rightleftharpoons [\text{FeCl}_4]^- + 6\text{H}_2\text{O}$ Write an expression for the stability constant of $[\text{FeCl}_4]^-$, $K_{\text{stab}}$.

(e(ii))[1]

For the equilibrium above, $K_{\text{stab}} = 0.080$. Calculate the concentration of $[\text{Fe(H}_2\text{O)}_6]^{3+}$ in a solution where $\text{Cl}^-$ has a concentration of $2.0\,\text{mol dm}^{-3}$ and $[\text{FeCl}_4]^-$ has a concentration of $0.10\,\text{mol dm}^{-3}$.

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