A cell composed of a platinum indicator electrode and a silver-silver chloride reference electrode in a solution containing both Fe2 + and Fe3 + has a cell potential of 0.727 V. If the silver-silver chloride electrode is replaced with a saturated calomel electrode (SCE), what is the new cell potential?

0.683 V

Explanation:

The saturated calomel electrode (SCE) is based on the following reaction:

0.5 Hg₂Cl₂ (s) + e⁻ → Hg (l) + Cl⁻

If compared to the Standard Hydrogen Electrode, this electrode has a potential of + 0.241 V, while the silver-silver chloride has a potential of + 0.197 V.

So the new cell potential would be:

0.727 - (0.241 - 0.197) = 0.683 V