Question 21.8: Calculate Ered and Eox at 25°C for the ClO3^- ion in neutral...

Calculate E_{red} and E_{ox} at 25°C for the {ClO_{3}}^{-} ion in neutral solution, at pH 7.00, assuming all other species are at standard concentration (E^{\circ}_{red} = +1.442\> V; E_{ox}^{\circ} = -1.226\> V). Will the {ClO_{3}}^{-} ion disproportionate at pH 7.00?

ANALYSIS

Information given:       {ClO_{3}}^{-}: (E^{\circ}_{red} (1.442 V); E_{ox}^{\circ} (-1.226 V)                                                                                                                                           pH (7.00); T (25°C)                                                                                                                                  All species besides {ClO_{3}}^{-} are at 1.00 M.
Asked for:                      Will {ClO_{3}}^{-} disproportionate at the given pH?

STRATEGY

1. Write a half-equation for the reduction of {ClO_{3}}^{-}.
2. Calculate E_{red} by substituting into the Nernst equation for 25°C.
E_{red} = E^{\circ}_{red} -\frac{ 0.0257}{n} \ln Q
3. Write a half-equation for the oxidation of {ClO_{3}}^{-}.
4. Calculate E_{ox} by substituting into the Nernst equation for 25°C.
E_{ox} = E_{ox}^{\circ}  –  \frac{ 0.0257}{n} \ln Q
5. Find E.
E = E_{red} + E_{ox}
If E > 0, {ClO_{3}}^{-} will disproportionate.