A cell composed of a platinum indicator electrode and a silver-silver chloride reference electrode in a solution containing both Fe 2 + and Fe 3 + has a cell potential of 0.742 V. If the silver-silver chloride electrode is replaced with a saturated calomel electrode (SCE), what is the new cell potential?

0.697 V

Explanation:

The potential of the half-cell of silver-silver chloride (Ag/AgCl) is + 0.197 V vs SHE (Standard Hydrogen Electrode)

The potential of the half-cell of the saturated calomel electrode (SCE) is + 0.242 V vs SHE.

So the difference in potential between Ag/AgCl and SCE is 0.045 V. We substract that value from the readings made with Ag/AgCl to convert them to SCE readings:

0.742 V - 0.045 V = 0.697 V