The reaction between cerium(IV) ions and iodide ions in acidic solution produces…

CHEMISTRY · Multi-part · A Level · Chemistry · Oxidation, reduction and redox reactions · Oxidation, reduction and redox reactions

Problem

The reaction between cerium(IV) ions and iodide ions in acidic solution produces cerium(III) ions and iodine molecules:

\text{Ce}^{4+}(aq) + \text{I}^-(aq) \rightarrow \text{Ce}^{3+}(aq) + \tfrac12\,\text{I}_2(aq)

(The factor of

\tfrac12

merely reminds you that the iodine molecule contains two iodine atoms; the final balanced equation must contain only whole-number coefficients.) (a) Write separate oxidation and reduction half-reactions for the process in acidic solution, explicitly including electrons,

\text{H}^+

, and

\text{H}_2\text{O}

where required. (b) Combine the half-reactions to obtain the overall balanced ionic equation with the smallest whole-number coefficients. State the coefficient that appears in front of

\text{I}^-

. (Do not simply supply the entire balanced equation without indicating the specific coefficient.) (c) Justify, with reference to the electron bookkeeping you carried out in part (a), why the coefficient you reported in part (b) is necessary.

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