C4 is a big, varied topic, but most of it sorts into three areas: the reactivity series, the chemistry of acids, and electrolysis. They look quite different on the page, yet underneath each one the same thing is happening. Atoms are being rearranged into new substances, whether a metal is pulled from its ore, an acid is neutralised by a base, or a compound is split apart by electricity.
Oxidation and reduction run through the whole topic, so it’s worth getting them clear early. Learn them first in terms of oxygen gained or lost, then, if you’re on Higher Tier, in terms of electrons.
🧭 How this topic splits by tier
C4 is a long topic and not all of it is for everyone — check what your tier needs:
- Everyone — the reactivity series and reactions with water and acids, displacement, extracting metals with carbon, acids with metals/bases/carbonates, making soluble salts, the pH scale and neutralisation, and the products of electrolysis (including the extraction of aluminium).
- Higher Tier H — oxidation and reduction in terms of electrons, ionic and half equations (for displacement, acid–metal reactions and electrolysis), and strong vs weak acids.
- Triple (Chemistry only) T — titrations (the method is Triple; the calculations are also Higher Tier).