What moves through a salt bridge?

Ions move through the salt bridge. Electrons move through the external wire.

When is a platinum electrode needed in a half-cell?

An inert conducting electrode such as platinum is needed when the redox system has no conducting solid redox species, for example Fe3+/Fe2+ or the hydrogen electrode.

What are the standard conditions for electrode potentials at A-level?

298 K, 1.00 mol dm−3 for each relevant aqueous species and 100 kPa for each relevant gas.

AQA 3.1.11 · OCR A 5.2.3 · RP8 / PAG8

Electrochemical Cell Lab

Build real A-level half-cells, choose electrodes and the salt bridge, then work out polarity and electron flow. The lab marks each decision separately, so it can tell you exactly what went wrong.

Exam board

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Keep the two circuits separate

Electrons outside; ions inside

The electrodes are connected through the external circuit, where electrons move. The half-cell solutions are connected by the salt bridge, where ions move to prevent charge building up. The bridge electrolyte must be soluble and must not react significantly with either half-cell.

Metal/metal-ion half-cell: the metal itself is the conducting electrode.

Both redox species aqueous: use an inert conductor such as Pt.

Gas half-cell: Pt provides a conducting surface in contact with the gas and solution.

Measuring E: use a high-resistance voltmeter so very little current is drawn.

Then make it exam-like

Build the cell here, then switch to the RP8/PAG8 questions for method choices, salt bridges, standard conditions and practical evaluation.

Practise RP8 / PAG8