Methodology

This list is based on analysis of Cambridge IGCSE Chemistry 0620 past papers (2019–2025), examiner reports, mark schemes and syllabus weightings. Topics are ranked by frequency of appearance and mark allocation.

Top 10 most frequently tested topics

1. Electrolysis

Evidence: Examiner reports repeatedly highlight electrolysis errors (products at electrodes, aqueous vs molten). Appears in Papers 2, 4 and 6.

Covers: electrolysis of molten compounds; aqueous solutions; products at anode and cathode; rules for discharge.

2. Stoichiometry and mole calculations

Evidence: Mole calculations appear in almost every paper. Examiner reports note limiting reagent and ratio errors.

Covers: mole concept; reacting masses; empirical and molecular formula; percentage purity.

3. Acids, bases and salts

Evidence: Titration, pH, salt preparation and neutralisation feature regularly. Core to Paper 5 and 6 practicals.

Covers: acids and bases; pH; salts; titration calculations.

4. Organic chemistry (alkanes, alkenes, alcohols)

Evidence: Organic reactions, formulae and functional groups appear frequently. Examiner reports note confusion on combustion vs oxidation.

Covers: homologous series; alkanes, alkenes, alcohols; reactions; cracking; polymerisation.

5. Chemical bonding and structure

Evidence: Ionic, covalent and metallic bonding; structure of compounds. Foundation for many questions.

Covers: ionic and covalent bonding; giant structures; properties linked to bonding.

6. Periodic table and reactivity

Evidence: Group properties, reactivity series and displacement appear regularly. Examiner reports note metal reaction errors.

Covers: Group 1, 7, 0; reactivity series; displacement reactions.

7. Energetics (exothermic and endothermic)

Evidence: Energy changes and temperature effects appear across papers. Examiner reports highlight confusion on direction of energy change.

Covers: exothermic and endothermic; bond energy; enthalpy calculations.

8. Rates of reaction

Evidence: Factors affecting rate; collision theory; experiments. Common in theory and practical papers.

Covers: factors affecting rate; collision theory; catalysts; graphs.

9. Chemical tests and identification

Evidence: Cations, anions, gases; flame tests. Essential for Paper 6.

Covers: flame tests; cation and anion tests; gas tests; notes provided in Paper 6.

10. Separation techniques

Evidence: Filtration, crystallisation, chromatography, distillation. Examiner reports note chromatography and solvent errors.

Covers: filtration; crystallisation; distillation; chromatography; choosing correct method.

Revision priority

Electrolysis, mole calculations and acids/bases appear most often and carry high marks. Check common mistakes for examiner-reported errors.

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Sources: Cambridge past papers 2019–2025, examiner reports, syllabus 2026–2028.

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