Chemistry study notes
Electrochemistry
Measure and combine electrode potentials, predict cell reactions, and calculate what electrolysis produces.
A-Level 9476 (2026-2027)
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7 topicsRedox and half-equations
Balance atoms, charge and electrons before using the data.
Measuring standard potentials
Build the reference and the three kinds of test half-cell.
Cell direction and real conditions
Use the potential difference and recognise its limits.
Gibbs energy and combined potentials
Use electron amounts to combine energy changes correctly.
Batteries and fuel cells
Compare voltage, useful energy, mass and size.
Electrolysis products and calculations
Choose a half-reaction, then convert charge into yield.
Copper purification and aluminium anodising
Connect electrode reactions to their industrial purpose.
Scope
Learning outcomes
12. Electrochemistry. Use the outcome map to find the explanation for a particular syllabus requirement.
See the learning outcome map
12(a) Explain redox using electrons and oxidation numbers.
- Electron loss/gain
- Increase/decrease of oxidation number
- Oxidising and reducing agent roles
12(b) Define standard electrode and standard cell potentials.
- (i) Standard reduction potential relative to SHE
- (ii) Standard cell electromotive force
- Standard states, negligible-current measurement and stated temperature
Measure every half-cell against the same referenceThe spontaneous cell sends electrons from anode to cathode
12(c) Describe the standard hydrogen electrode.
- Platinum with catalytic platinum surface
- Hydrogen at standard pressure
- Hydrogen-ion standard activity/concentration convention
- Reference potential and reversible half-equation
12(d) Describe standard electrode-potential measurements.
- (i) Metal/aqueous-ion and non-metal/aqueous-ion arrangements
- (ii) Same-element ions in different oxidation states
- SHE, salt bridge, high-resistance voltmeter, sign and standard conditions
12(e) Calculate standard cell potentials.
- Cathode reduction potential minus anode reduction potential
- Do not scale potentials with half-equation coefficients
12(f) Use cell potentials to predict electron flow and spontaneity.
- (i) Simple-cell electron direction
- (ii) Thermodynamic spontaneity for the reaction as written
- Electrode roles and signs in a galvanic cell
12(g) Recognise limits of standard-potential predictions.
- Non-standard composition, temperature, pressure and pH
- Kinetic barriers and passivation
- Complexation and precipitation affecting free ions
A standard prediction is not a guarantee of a rapid real reactionChoose the products from the species and conditions
12(h) Construct overall redox equations from half-equations.
- Atom and charge balances
- Acidic and alkaline balancing method
- Electron cancellation
- Cross-reference Topic 13 redox systems
12(i) Apply the Gibbs energy and potential relationship.
- DeltaG standard = -nFE standard
- Balanced-reaction electron count and units
- Combining half-reactions through additive Gibbs energies
- Electron-weighted combined potential
12(j) Predict concentration effects on electrode potentials.
- Metal-ion concentration
- Oxidised/reduced ion ratio
- Hydrogen-ion concentration
- Qualitative treatment at fixed other conditions
A standard prediction is not a guarantee of a rapid real reaction
12(k) Discuss possible advantages of improved cells.
- Hydrogen/oxygen fuel cell
- Improved batteries including electric vehicles
- Smaller size, lower mass and higher voltage
- Whole-system and capacity comparison
12(l) Relate Faraday, Avogadro and electron-charge constants.
- F = Le
- Charge per mole of electrons
- Units and rounded Data Booklet values
12(m) Predict electrolytic products.
- Molten versus aqueous electrolyte
- Redox-series/electrode-potential reasoning
- Ion concentration
- Competing water reactions and electrode material
12(n) Calculate charge and electrolysis yield.
- (i) Quantity of charge passed
- (ii) Mass and gas volume liberated
- Half-equation electron ratio
- Current efficiency and gas conditions
12(o) Explain industrial electrolysis through electrode reactions.
- (i) Aluminium anodising
- (ii) Electrolytic copper purification
- Electrode identities, products and purpose
- Technical plant details not required