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Cambridge International AS & A Level Chemistry – Physical Chemistry (A Level)

Topic 24
Electrochemistry

Topic 24 covers electrolysis (24.1): predicting the substances liberated, the Faraday constant and F = Le, calculations with Q = It and finding the Avogadro constant by electrolysis; and standard electrode potentials (24.2): the standard hydrogen electrode, standard cell potentials, the polarity of the electrodes and the direction of electron flow, feasibility, relative strengths of oxidising and reducing agents, redox equations from half-equations, the Nernst equation and ΔG⦵ = −nE⦵cellF.

Exam Paper
Paper 4
9701 A Level
Learning Outcomes
24.1.1 – 24.2.10
Electrolysis and electrode potentials
Sub-topics
7 lessons
Revision notes available
Exam Board
Cambridge
9701 (2025 onwards)

Revision Notes

7 revision notes, in the order the specification teaches them.

Electrons moving from one particle to another
1

Redox, Oxidation Numbers and Half-Equations

Redox: electron transfer, oxidation numbers, oxidising and reducing agents and constructing redox equations from half-equations.

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A platinum electrode under a glass hood with gas bubbling
2

Standard Electrode Potentials and the Hydrogen Electrode

The standard electrode (reduction) potential: half-cells, standard conditions of 298 K, 101 kPa and 1.00 mol dm⁻³, and the standard hydrogen electrode.

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An electrochemical cell with a voltmeter
3

Electrochemical Cells and Cell Potentials

Electrochemical cells: half-cells, the salt bridge, measuring cell potentials and calculating the standard cell potential.

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A ladder of half-cells at different heights
4

The Electrochemical Series and Feasibility of Reactions

The electrochemical series: oxidising and reducing agents, predicting feasibility from E⦵ values.

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Two half-cells at different concentrations with a voltmeter
5

The Nernst Equation and Gibbs Free Energy

The Nernst equation and ΔG⦵ = −nE⦵cellF: electrode potentials under non-standard conditions and Gibbs free energy.

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An electrolysis cell with two electrodes and a battery
6

Electrolysis: Predicting the Products

Electrolysis: predicting the products at each electrode for molten and aqueous electrolytes using E⦵ values and concentration.

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A copper-plated electrode on a balance beside a battery
7

Electrolysis Calculations and the Faraday Constant

Electrolysis calculations: Q = It, F = Le, masses and volumes liberated and the determination of the Avogadro constant.

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Summary Map

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Summary map

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Summary map · PDF

Electrochemistry Map

Cambridge International AS & A Level Chemistry · Topic 24 Electrochemistry

The whole section on one A4 page: half-equations, standard electrode potentials, cells and E⦵cell, the electrochemical series and feasibility, the Nernst equation and ΔG⦵, and electrolysis.

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24.1.1

  1. a

    predict the identities of substances liberated during electrolysis from the state of electrolyte (molten or aqueous)

    Revise
  2. b

    predict the identities of substances liberated during electrolysis from the position in the redox series (electrode potential)

    Revise
  3. c

    predict the identities of substances liberated during electrolysis from the concentration

    Revise

24.1.2

  1. 24.1.2

    state and apply the relationship F = Le between the Faraday constant, F, the Avogadro constant, L, and the charge on the electron, e

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24.1.3

  1. a

    calculate the quantity of charge passed during electrolysis, using Q = It

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  2. b i

    calculate the mass of substance liberated during electrolysis

    Revise
  3. b ii

    calculate the volume of substance liberated during electrolysis

    Revise

24.1.4

  1. 24.1.4

    describe the determination of a value of the Avogadro constant by an electrolytic method

    Revise

24.2.1

  1. a

    define the term standard electrode (reduction) potential

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  2. b

    define the term standard cell potential

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24.2.2

  1. 24.2.2

    describe the standard hydrogen electrode

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24.2.3

  1. a

    describe methods used to measure the standard electrode potentials of metals or non-metals in contact with their ions in aqueous solution

    Revise
  2. b

    describe methods used to measure the standard electrode potentials of ions of the same element in different oxidation states

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24.2.4

  1. 24.2.4

    calculate a standard cell potential by combining two standard electrode potentials

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24.2.5

  1. a i

    use standard cell potentials to deduce the polarity of each electrode of a simple cell

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  2. a ii

    use standard cell potentials to explain/deduce the direction of electron flow in the external circuit of a simple cell

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  3. b

    use standard cell potentials to predict the feasibility of a reaction

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24.2.6

  1. a

    deduce from E⦵ values the relative reactivity of elements, compounds and ions as oxidising agents

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  2. b

    deduce from E⦵ values the relative reactivity of elements, compounds and ions as reducing agents

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24.2.7

  1. 24.2.7

    construct redox equations using the relevant half-equations

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24.2.8

  1. 24.2.8

    predict qualitatively how the value of an electrode potential, E, varies with the concentrations of the aqueous ions

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24.2.9

  1. 24.2.9

    use the Nernst equation, e.g. E = E⦵ + (0.059/z) log([oxidised species]/[reduced species]), to predict quantitatively how the value of an electrode potential varies with the concentrations of the aqueous ions; examples include Cu2+(aq) + 2e– ⇌ Cu(s), Fe3+(aq) + e– ⇌ Fe2+(aq)

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24.2.10

  1. 24.2.10

    understand and use the equation ΔG⦵ = –nE⦵cell F

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