CHEMISTRY 133

Spring, 2015 Homework Set 2.1

Additional Problem

1.  Calculate the potential for the cell describe bellow when [ZnSO₄] = 2.0 x 10^-3 M

Zn(s)|ZnSO₄(aq)|PbSO₄(s)|Pb(s).  Look up standard reduction potentials in Appendix H.

E_cell = E_reduction – E_oxidation

Reduction reaction in anode (note: this should occur as an oxidation, but we are giving the reduction reaction by convention).  Zn²⁺ + 2e^- → Zn(s) E° = -0.762 V

Reduction reaction at cathode: PbSO₄(s) + 2e^- → Pb(s) + SO₄^2- E° = -0.355 V

E_oxidation = E° - 0.05916/2log{1/[Zn²⁺]} = -0.762 V – 0.05916/2log(1/2.0 x 10^-3) =  

E_oxidation = -0.762 V – 0.080 V = -0.842 V

E_reduction = E° - 0.05916/2log[SO₄^2-] = -0.355 V – 0.05916/2log(2.0 x 10^-3) = -0.355 + 0.080 V

E_oxidation = -0.275 V

E_cell = E_reduction – E_oxidation = -0.275 – (-0.842V) = 0.567 V