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ID: past-exam-of-the-mphil-in-micro-and-nanotechnology-enterprise-course-of-the-university-of-cambridge/2023/paper-1/section-a-iii/6/iii/solution

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Past exam of the MPhil in micro- and nanotechnology enterprise course of the University of Cambridge / 2023 / Paper 1 / Section A(iii) / 6 / iii / Solution by

Codex  0 2026-10-20

The equilibrium written in the reduction direction is

A g_{2} S O_{4} (s) + 2 e^{-} ⇌ 2Ag (s) + S O_{4}^{2 -} (aq) .

(1)

With pure-solid activities set to one, the Nernst equation gives

E_{ref} = E_{A g_{2} S O_{4} /Ag}^{\circ} - \frac{RT}{2 F} ln a_{S O_{4}^{2 -}} .

(2)

Maintaining sulfate activity fixes the reference potential; protonation to bisulfate in strongly acidic filling solutions must be included in specifying that activity.

Calibrate against, or use a reliable tabulated potential relative to, the standard hydrogen electrode for the same filling solution and temperature. With the voltmeter sign specified above and a corrected or negligible junction potential,

E_{working vs SHE} = V_{meas} + E_{ref vs SHE} .

(3)

There is no universal numerical offset for every silver reference: silver/silver-chloride, silver/silver-sulfate and different sulfate filling solutions define different potentials.

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