Most redox reactions are performed under non-standard conditions. Consider the p

Question

Most redox reactions are performed under non-standard conditions. Consider the
permanganate to manganese (II) ion half-cell, represented by the reaction:
MnO4-(aq) + 8H+(aq) + 5e- ----> Mn2+(aq) + 4H2O(l) E= +1.51V

Suppose the pH is increased to 4.0, but the concentrations of MnO4- and Mn2+ are kept at 1.0
M (standard conditions). Using the Nernst equation, determine the half-cell potential under these
new conditions. Discuss the sensitivity of this reaction (or lack thereof) to pH. Is it large or small?

Explanation / Answer

Half cell potential,

E = Eo - 0.0592/5 ln([Mn2+]/[MnO4-][H+]^8)

    = 1.51 - (0.0592/5)ln(1/1 x 10^-4)^8 x 1)

    = 1.074 V

sensitivity to pH is large for the given half cell reaction.

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