CAIE A-Level Chemistry A2 26.2.3 Mode of Action of a Homogeneous Catalyst Questions

Practise explaining how homogeneous catalysts are consumed in one step and regenerated in a later step.

Exam points

explain homogeneous catalyst cycles with paired equations
explain catalyst regeneration and lower activation-energy pathways

[Maximum number: 2]

Iodine is found naturally in compounds in many different oxidation states.

The reaction of $\mathrm{I}^{-}$ ions with persulfate ions, $\mathrm{S}_{2} \mathrm{O}_{8}{ }^{2-}$ , can be catalysed by $\mathrm{Fe}^{3+}$ ions.

2 \mathrm{I}^{-}+\mathrm{S}_{2} \mathrm{O}_{8}^{2-} \rightarrow \mathrm{I}_{2}+2 \mathrm{SO}_{4}^{2-}

Write equations to show how $\mathrm{Fe}^{3+}$ catalyses this reaction.

$\begin{aligned} \text { Reduction of } \mathrm{Fe}^{3+}: \quad 2 \mathrm{Fe}^{3+}+2 \mathrm{I}^{-} \rightarrow 2 \mathrm{Fe}^{2+}+\mathrm{I}_{2}[1] \text { Regeneration of } \mathrm{Fe}^{3+}: 2 \mathrm{Fe}^{2+}+\mathrm{S}_{2} \mathrm{O}_{8}^{2-} \rightarrow 2 \mathrm{Fe}^{3+}+2 \mathrm{SO}_{4}^{2-}[1] \end{aligned}$

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CAIE A-Level Chemistry A2 26.2.3 Mode of Action of a Homogeneous Catalyst Questions question 1