Iodine is an essential element for proper thyroid health. Seawater contains trace amounts of iodide, and you are exploring electrolysis of solutions of iodide as a means to purify the element. You need to know whether iodide or water will be oxidized at lower potentials. Suppose that an aqueous solution with pH = 7 and containing I^– ions at 1 mol · L^–1 is being electrolyzed. Will O₂ or I^– be produced at the anode?

PLAN Decide which oxidation requires the lower potential. Then, provided the overpotentials are similar, that redox couple will be preferentially oxidized.