Pearson International A Level Chemistry Core Practical 12: Investigate electrochemical cells

This core practical is part of Pearson's practical-learning programme. The method below is one defensible implementation, not a confidential instruction sheet. Centres may adapt equipment while preserving the scientific purpose, controls, measurements and safety requirements.

Aim and scientific principle

Construct half-cells, measure cell potential under controlled conditions and relate polarity to redox direction.

Begin by translating the title into a testable question. Identify what is deliberately changed, what is measured directly, what is calculated and what must remain controlled. Predict a relationship only after naming the mechanism. A prediction without a reason is weak; a reason without measurable variables cannot guide a practical design.

Apparatus and setup

Use metal and ion half-cells, inert electrodes where required, salt bridge, high-resistance voltmeter, clean leads and standard solutions. Select every measuring instrument by range and resolution, not by name alone. Draw a labelled scientific setup that shows the working geometry and exactly where readings are taken. Include a control or blank when it distinguishes the target effect from drift, contamination or background response.

Before collecting results, check zero readings, calibration, leaks, alignment or sterility as relevant. Record the instrument resolution beside the first raw-data table. If a digital device displays more digits than its underlying accuracy supports, do not treat every digit as equally certain.

Method

1. Clean electrodes consistently and prepare labelled half-cells at known concentrations.
2. Connect them through a fresh salt bridge and a high-resistance voltmeter.
3. Record magnitude and sign only after the reading stabilises, then repeat or vary one defined factor.
4. Write reduction half-equations and calculate the predicted standard cell potential for comparison.

Plan the analysis before starting. This reveals whether an additional measurement is needed for a derived quantity and prevents a completed experiment from lacking a mass, length, concentration, background or calibration value. A method should be detailed enough for another trained student to reproduce, while avoiding decorative steps that do not affect validity.

Variables and controls

• Independent variable: half-cell identity or ion concentration.
• Dependent variable: cell potential and polarity.
• Important controls: