Cambridge O Level · 5070 · Data 2020–2025
Most-tested topics in O-Level Chemistry
Just 3 chapters — Experimental techniques and chemical analysis, Organic chemistry, Acids, bases and salts — carry about 49% of all the marks. Revise those first.
Based on 95 real Cambridge past papers and 15,138 tagged marks, 2020–2025. Ranked by marks, not guesswork.
Historical counts from past papers — not an exam prediction. Download the data (CSV)
Revise these first
The topics that carry the most marks, highest first. Each opens the free past-paper questions.
- 1Practise →Acids, bases and saltsEvery year
- 2Practise →3.3 The mole and the Avogadro constant7% of marksStoichiometryEvery year
- 3Practise →12.5 Identification of ions and gases7% of marksExperimental techniques and chemical analysisEvery year
- 4Practise →3.1 Formulae6% of marksStoichiometryEvery year
- 5Practise →12.1 Experimental design6% of marksExperimental techniques and chemical analysisEvery year
- 6Practise →12.2 Acid-base titrations5% of marksExperimental techniques and chemical analysisEvery year
- 7Practise →5.1 Exothermic and endothermic reactions3% of marksChemical energeticsEvery year
- 8Practise →6.2 Rate of reaction3% of marksChemical reactionsEvery year
See the full breakdown — all 49 topics across 12 chapters
Experimental techniques and chemical analysis
20% of marks- 12.5 Identification of ions and gasesEvery year1060 marks · 108 qs
- 12.1 Experimental designEvery year856 marks · 98 qs
- 12.2 Acid-base titrationsEvery year765 marks · 64 qs
- 12.4 Separation and purificationEvery year279 marks · 54 qs
- 12.3 ChromatographyEvery year33 marks · 18 qs
Organic chemistry
15% of marks- 11.1 Formulae, functional groups and terminologyEvery year410 marks · 75 qs
- 11.6 AlcoholsEvery year355 marks · 71 qs
- 11.5 AlkenesEvery year321 marks · 60 qs
- 11.7 Carboxylic acidsEvery year284 marks · 58 qs
- 11.2 Naming organic compoundsEvery year242 marks · 36 qs
- 11.4 AlkanesEvery year242 marks · 63 qs
- 11.3 FuelsEvery year223 marks · 38 qs
- 11.8 PolymersEvery year214 marks · 55 qs
Acids, bases and salts
14% of marks- 7.1 The characteristic properties of acids and basesEvery year1523 marks · 176 qs
- 7.3 Preparation of saltsEvery year394 marks · 78 qs
- 7.2 OxidesEvery year221 marks · 35 qs
Stoichiometry
14% of marks- 3.3 The mole and the Avogadro constantEvery year1061 marks · 133 qs
- 3.1 FormulaeEvery year958 marks · 134 qs
- 3.2 Relative masses of atoms and moleculesEvery year96 marks · 37 qs
Chemical reactions
9% of marks- 6.2 Rate of reactionEvery year526 marks · 100 qs
- 6.4 RedoxEvery year500 marks · 88 qs
- 6.3 Reversible reactions and equilibriumEvery year250 marks · 53 qs
- 6.1 Physical and chemical changesRecurring41 marks · 11 qs
Atoms, elements and compounds
8% of marks- 2.5 Simple molecules and covalent bondsEvery year331 marks · 72 qs
- 2.4 Ions and ionic bondsEvery year304 marks · 82 qs
- 2.2 Atomic structure and the Periodic TableEvery year175 marks · 51 qs
- 2.7 Metallic bondingEvery year174 marks · 39 qs
- 2.6 Giant covalent structuresEvery year107 marks · 27 qs
- 2.3 IsotopesEvery year90 marks · 35 qs
- 2.1 Elements, compounds and mixturesEvery year42 marks · 19 qs
The Periodic Table
5% of marks- 8.4 Transition elementsEvery year283 marks · 36 qs
- 8.2 Group I propertiesEvery year169 marks · 35 qs
- 8.3 Group VII propertiesEvery year158 marks · 28 qs
- 8.1 Arrangement of elementsEvery year74 marks · 31 qs
- 8.5 Noble gasesRecurring62 marks · 17 qs
Metals
5% of marks- 9.4 Reactivity seriesEvery year260 marks · 49 qs
- 9.6 Extraction of metalsEvery year162 marks · 52 qs
- 9.5 Corrosion of metalsEvery year89 marks · 28 qs
- 9.1 Properties of metalsEvery year87 marks · 18 qs
- 9.3 Alloys and their propertiesRecurring87 marks · 21 qs
- 9.2 Uses of metalsRecurring23 marks · 5 qs
Chemical energetics
3% of marks- 5.1 Exothermic and endothermic reactionsEvery year528 marks · 81 qs
Chemistry of the environment
3% of marks- 10.3 Air quality and climateEvery year300 marks · 64 qs
- 10.2 FertilisersEvery year78 marks · 28 qs
- 10.1 WaterEvery year70 marks · 28 qs
Electrochemistry
2% of marks- 4.1 ElectrolysisEvery year292 marks · 81 qs
- 4.2 Hydrogen-oxygen fuel cellsRecurring41 marks · 13 qs
States of matter
2% of marks- 1.1 Solids, liquids and gasesEvery year245 marks · 45 qs
- 1.2 DiffusionEvery year53 marks · 19 qs
Turn the data into practice
Every topic above is drawn from real Cambridge O Level Chemistry papers, tagged to the syllabus. Students can drill the high-frequency topics in the free bank; teachers can turn any of them into a ready-to-print worksheet in seconds. Or explore the full six-year trends in the interactive records.