Gce Model Questions Vol1 2024 Chemistry Question 29

The standard reduction potentials for the half‑reactions \(\text{Cl}_2 + 2e^- \rightarrow 2\text{Cl}^-\) and \(\text{Br}_2 + 2e^- \rightarrow 2\text{Br}^-\) are \(E^\circ_{\text{Cl}_2/\text{Cl}^-}=+1.36\ \text{V}\) and \(E^\circ_{\text{Br}_2/\text{Br}^-}=+1.07\ \text{V}\) respectively. A solution contains \(0.10\ \text{M}\) \(\text{Cl}^-\) and \(0.10\ \text{M}\) \(\text{Br}^-\). If an external potential of \(+1.20\ \text{V}\) is applied, (a) which halogen will be preferentially reduced? (b) Using the Nernst equation, calculate the equilibrium concentrations of the molecular halogens \(\text{Cl}_2\) and \(\text{Br}_2\) at that potential. Express your answers in mol L\(^{-1}\) and comment on their relative magnitudes.