Practice Problem 9

Calculate the potential at 25oC for the following cell.

Cu | Cu2+(0.024 M) || Ag+(0.0048 M) | Ag



We start by translating the line notation into an equation for the reaction.

Cu(s) + 2 Ag+(aq) ----> Cu2+(aq) + 2 Ag(s)

We then look up the standard-state potentials for the two half-reactions and calculate the standard-state cell potential.

Oxidation:   Cu ----> Cu2+ + 2 e-   Eoox = -(0.3402 V)
Reduction:   Ag+ + e- ----> Ag   Eored = 0.7996 V
        Eo = Eored + Eoox = 0.4594 V

We now set up the Nernst equation for this cell, noting that n is 2 because two electrons are transferred in the balanced equation for the reaction.


Substituting the concentrations of the Cu2+ and Ag+ ions into this equation gives the value for the cell potential.