Redox & Electrochemistry is a core part of A-Level Chemistry. Revise the key concepts and common mistakes below, then lock them in with the free games.
Key concepts
OxidationLoss of electrons; oxidation number increases.
ReductionGain of electrons; oxidation number decreases.
Oxidation numberA value showing how oxidised an atom is in a species.
Half-equationsShow electron loss or gain at each part of a redox reaction.
Oxidising & reducing agentsSpecies that accept or donate electrons.
Redox titrationUses a redox reaction to find an unknown concentration.
Oxidation & reductionElectron loss and gain (OIL RIG).
Electrode potentialTendency of a half-cell to gain electrons, measured against hydrogen.
Electrochemical cellTwo half-cells producing an EMF from a redox reaction.
ElectrolysisUsing electricity to drive a non-spontaneous redox reaction.
Common mistakes to avoid
Questions where students often pick the tempting wrong answer — make sure you know the right one:
What is reduction in terms of electrons?✗ Reduction means losing oxygen and oxidation means gaining oxygen — full stop. ✓ Gain of electrons (the oxidation number is reduced).
What does a mole of a substance represent?✗ A mole is a unit of mass equal to the relative molecular mass in grams of any substance. ✓ Avogadro's number (6.02 x 10^23) of particles of that substance.
In a standard hydrogen electrode used as a reference, what is the assigned electrode potential?✗ The standard hydrogen electrode actually has zero potential because hydrogen has no charge. ✓ Exactly 0 V by convention — all other electrode potentials are measured relative to it.
Is the oxidation state of an atom the same as its actual charge?✗ The oxidation state of an atom is exactly equal to its real ionic charge in every compound. ✓ Not necessarily — oxidation state is an accounting tool assuming all bonds are fully ionic; real charge is usually smaller.
OIL RIG: oxidation is.✗ Gain of electrons ✓ Loss of electrons
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