The saturated calomel electrode, SCE, is often used as a reference electrode in

Question

The saturated calomel electrode, SCE, is often used as a reference electrode in making electrochemical measurements. The SCE is composed of mercury in contact with a saturated solution of calomel (Hg2Cl2). The electrolyte solution is saturated KCL. ESCE is +0.242V relative to the standard hydrogen electrode. Calculate the potential for each of the following galvanic cells containing a saturated calomel electrode and the given half-cell components as standard conditions. In each case, indicate whether the SCE is the cathode or the anode.

a) Cu2+ + 2e- --> Cu

b) Fe3+ + e- --> Fe2+

Explanation / Answer

a) a) Cu2+ + 2e- --> Cu , Eo = 0.34 V

SCE vs this cell potential = Eo = 0.34 - 0.242 = 0.098 V

cell potential = 0.1 V

it is cathode

b) Fe3+ + e- ---------------> Fe2+ , Eo = 0.771 V

Eo cell = Eo highest - Eo lowest

            = 0.771 - 0.242

           = 0.53 V

cell potential = 0.53 V

it is anode

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