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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/ii/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 / ii / Solution by

Codex  0 2026-10-20

Use a silver wire or strip in contact with excess solid silver sulfate, immersed in a sulfate filling solution of known, stable activity. A porous frit connects the filling solution ionically to the sample while limiting bulk mixing. The reference housing should maintain the salt/electrolyte composition rather than letting the sample directly determine it.

Connect the unknown working electrode to the positive input and the silver reference to the negative input of a high-input-impedance voltmeter. The frit or sulfate-compatible salt bridge completes the ionic circuit. At negligible measuring current,

V_{meas} ≃ E_{working} - E_{reference} + E_{junction} .

(1)

A stable, small junction contribution is desirable. The reference electrode should not carry the counterelectrode current in a driven experiment: a separate counterelectrode is used when current is passed.

Figure 1.
A sulfate-compatible silver reference measures a potential difference with negligible current
. Original circuit schematic. Silver, excess silver sulfate and controlled sulfate electrolyte define the reference compartment; the frit provides ionic contact. The voltmeter polarity fixes the sign of the measured working-minus-reference potential. **Details**.

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