Which of the following ions cannot act as a homogeneous catalyst for the reaction between iodide ions (I−\text{I}^-I−) and peroxodisulfate ions (S2O82−\text{S}_2\text{O}_8^{2-}S2O82−)?
Use the standard electrode potential data in the table below to help you answer this question.
Half-equationEθ/VS2O82−+2e−→2SO42−+2.01Co3++e−→Co2++1.82VO2++2H++e−→VO2++H2O+1.00Fe3++e−→Fe2++0.77I2+2e−→2I−+0.54Sn4++2e−→Sn2++0.15 \begin{array}{|c|c|} \hline \textbf{Half-equation} & E^\theta / \text{V} \\ \hline \text{S}_2\text{O}_8^{2-} + 2\text{e}^- \rightarrow 2\text{SO}_4^{2-} & +2.01 \\ \hline \text{Co}^{3+} + \text{e}^- \rightarrow \text{Co}^{2+} & +1.82 \\ \hline \text{VO}_2^+ + 2\text{H}^+ + \text{e}^- \rightarrow \text{VO}^{2+} + \text{H}_2\text{O} & +1.00 \\ \hline \text{Fe}^{3+} + \text{e}^- \rightarrow \text{Fe}^{2+} & +0.77 \\ \hline \text{I}_2 + 2\text{e}^- \rightarrow 2\text{I}^- & +0.54 \\ \hline \text{Sn}^{4+} + 2\text{e}^- \rightarrow \text{Sn}^{2+} & +0.15 \\ \hline \end{array} Half-equationS2O82−+2e−→2SO42−Co3++e−→Co2+VO2++2H++e−→VO2++H2OFe3++e−→Fe2+I2+2e−→2I−Sn4++2e−→Sn2+Eθ/V+2.01+1.82+1.00+0.77+0.54+0.15Co2+\text{Co}^{2+}Co2+
VO2+\text{VO}^{2+}VO2+
Fe2+\text{Fe}^{2+}Fe2+
Sn2+\text{Sn}^{2+}Sn2+
