Standard potentials are measured against the standard hydrogen electrode (S.H.E.

Question

Standard potentials are measured against the standard hydrogen electrode (S.H.E.) Because it is not always convenient to use a S.H.E., often other reference electrodes are used. The saturated calomel electrode (S.C.E.) is one commonly used reference electrode, with a potential of +0.242 V versus the S.H.E. Using a table of standard reductions, determine what the potential of each reduction below would be versus the S.C.E. a) Cu^2+ (aq) + 2e^- doubleheadarrow Cu(s) E degree = b) Al^3+ (aq) + 3e^- doubleheadarrow Al(s) E degree =

Explanation / Answer

a)

Cu+2 (aq) + 2e-   ---------> Cu (s)

Eo (S.H.E) = + 0.34 V

Eo (vs S.C.E) = + 0.34 - 0.242 = 0.098 V

Eo (vs S.C.E) = 0.098 V

b)

Al+3 + 3e   ---------------> Al (s)

Eo (S.H.E) = - 1.66 V

Eo (vs S.C.E) = - 1.66 - 0.242 = - 1.902 V

Eo (vs S.C.E) = - 1.902 V

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