Using the Nernst Equation to Calculate Ecell
Problem: In a test of a new reference electrode, a chemist constructs a
voltaic cell consisting of a Zn/Zn2+ electrode and the H2/H+ electrode
under the following conditions:
Calculate Ecell at 25oC.
Plan: Find Eocell and Q: 1) write the spontaneous reaction,
2) calculate Eocell from standard electrode potentials (Table 21.2),
3) use the given pressure and concentrations to find Q.
Solution: Determining the cell reaction and Eocell:
[Zn2+] = 0.010 M [H+] = 2.5 M PH2 = 0.30 atm
2 H+(aq) + 2 e- H2 (g) Eo = 0.00 V
Zn(s) Zn2+(aq) + 2 e- -Eo = 0.76 V
2 H+(aq) + Zn(s) H2 (g) + Zn2+(aq) Ecell = 0.76 V
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