IGCSE Chemistry Paper 4: how to approach the theory paper

For students on the Extended route of Cambridge IGCSE Chemistry (0620), Paper 4 carries the largest weighting, half the qualification, and it brings calculations, explanations and data questions together. This guide explains what Paper 4 is, what it tests and how to prepare for it, with worked examples of the calculations the syllabus requires.

What IGCSE Chemistry Paper 4 is

Cambridge IGCSE Chemistry has two routes. According to the syllabus for 2026, 2027 and 2028:

• Core candidates take Paper 1 (multiple choice, Core), Paper 3 (theory, Core) and one practical paper. They can be awarded grades C to G.
• Extended candidates take Paper 2 (multiple choice, Extended), Paper 4 (theory, Extended) and one practical paper. They can be awarded grades A* to G.

Cambridge says Extended entry is for candidates who have studied the Extended content (Core and Supplement) and are expected to achieve grade C or above.

Paper 4: Theory (Extended) is 1 hour 15 minutes long, carries 80 marks and counts for 50% of the qualification. It has compulsory short-answer and structured questions based on both the Core and Supplement content, and it's externally assessed.

The other two parts of the Extended route are:

• Paper 2: 45 minutes, 40 four-option multiple-choice questions, 40 marks, 30%.
• Paper 5 (Practical Test, 1 hour 15 minutes) or Paper 6 (Alternative to Practical, 1 hour): 40 marks, 20%.

Put together, Paper 4 carries as much weight as the other two papers combined.

That is why the rest of this guide focuses on it.

What Paper 4 tests

Paper 4 tests two of the three assessment objectives:

• AO1, Knowledge with understanding: 63% of the paper.
• AO2, Handling information and problem-solving: 37% of the paper.

AO3 (experimental skills) is tested only in Papers 5 and 6. So nearly two-thirds of Paper 4 is about knowing the syllabus content precisely. The rest is applying it to unfamiliar information: data, graphs, unfamiliar reactions and calculations.

Pace matters too. 75 minutes for 80 marks is just under a minute per mark, so there's no time to re-learn anything in the exam.

Read the command words

The 0620 syllabus defines the command words used in its exams. Several are easy to confuse:

• State: express in clear terms.
• Describe: state the points of a topic, or give characteristics and main features.
• Explain: set out purposes or reasons, make the relationships between things clear, say why and/or how, and support with relevant evidence.
• Suggest: apply knowledge and understanding to situations where there's a range of valid responses.
• Calculate: work out from given facts, figures or information.
• Deduce: conclude from available information.

Don't answer "explain" with a description. A description says what happens. An explanation says why it happens.

The calculations you must be able to do

The Supplement content for stoichiometry expects Extended students to calculate reacting masses, limiting reactants, volumes of gases at r.t.p., volumes and concentrations of solutions (in g/dm³ and mol/dm³, converting between cm³ and dm³), results from titration data, empirical and molecular formulae, and percentage yield, composition by mass and purity. The syllabus takes the molar gas volume as 24 dm³ at room temperature and pressure.

The worked examples below are practice questions written for this guide, not taken from an exam paper. They use relative atomic masses from the syllabus Periodic Table: Ca = 40, C = 12, O = 16, H = 1, Na = 23, S = 32, Mg = 24.

Example 1: masses, gas volume and percentage yield. 10.0 g of calcium carbonate is heated: CaCO₃ → CaO + CO₂.

• Mr of CaCO₃ = 40 + 12 + (3 × 16) = 100.
• Moles of CaCO₃ = 10.0 ÷ 100 = 0.100 mol.
• The equation is 1 : 1 : 1, so 0.100 mol of CO₂ forms. Its volume at r.t.p. = 0.100 × 24 = 2.40 dm³.
• Mr of CaO = 40 + 16 = 56, so the theoretical mass of CaO = 0.100 × 56 = 5.60 g.
• If 4.80 g of CaO is actually collected, the percentage yield = 4.80 ÷ 5.60 × 100 = 85.7%.

Example 2: a titration. 25.0 cm³ of 0.100 mol/dm³ sodium hydroxide is neutralised by 20.0 cm³ of sulfuric acid: 2NaOH + H₂SO₄ → Na₂SO₄ + 2H₂O. Find the concentration of the acid.

• Moles of NaOH = 0.100 × (25.0 ÷ 1000) = 0.00250 mol.
• The ratio is 2 NaOH : 1 H₂SO₄, so moles of H₂SO₄ = 0.00250 ÷ 2 = 0.00125 mol.
• Concentration of H₂SO₄ = 0.00125 ÷ (20.0 ÷ 1000) = 0.0625 mol/dm³.

Example 3: an empirical formula. A sample of an oxide contains 2.4 g of magnesium and 1.6 g of oxygen.

• Moles of Mg = 2.4 ÷ 24 = 0.10. Moles of O = 1.6 ÷ 16 = 0.10.
• The ratio is 1 : 1, so the empirical formula is MgO.

Three habits protect marks in every calculation: write the equation and the mole ratio, convert cm³ to dm³ before using concentration, and show each step so a method can still earn credit if the final number is wrong.

How to prepare for Paper 4

1. Learn the Supplement content, not just the Core. Paper 4 is set on both. Cambridge says candidates taught only the Core content can achieve a maximum of grade C, and candidates aiming for A* to C should be taught the Extended content.
2. Practise calculations until the method is automatic. Use the list above as a checklist and do a few of each type every week.
3. Practise extended answers against the command words. For each "explain" question, check that the answer gives a reason, not just a description.
4. Practise with the right papers. Cambridge publishes past papers, examiner reports and specimen papers on its website. Use Paper 4 papers (the Extended theory paper), and make sure they're for the 0620 syllabus. Our IGCSE past papers page explains how to work through them.
5. Read the examiner reports alongside the papers. Compare your child's answers with the examiners' comments to find the topics that keep costing marks.
6. Sit full papers under timed conditions. 80 marks in 75 minutes is tight, so practise the pace before exam day.

FAQ

How long is IGCSE Chemistry Paper 4?

1 hour 15 minutes, for 80 marks.

What percentage is Paper 4 worth?

50% of the qualification for Extended candidates.

What's the difference between Paper 3 and Paper 4?

Paper 3 is the Core theory paper, and Paper 4 is the Extended theory paper. Both are 1 hour 15 minutes and 80 marks, but Paper 4 also tests Supplement content, and only the Extended route can lead to grades A* and A.

Is a Periodic Table provided?

Yes. The syllabus includes the Periodic Table of Elements used in the exams, which gives relative atomic masses, and states that the volume of one mole of any gas is 24 dm³ at r.t.p.

Has the 0620 syllabus changed?

The current syllabus covers exams in 2026, 2027 and 2028. Cambridge published version 2 in August 2026, which updated the assessment overview. It says there are no substantial changes that would affect teaching.

Get help from an IGCSE Chemistry tutor

Our 124 tutors include 16 with examiner, marker or moderator experience, and 51% hold a teaching qualification. An IGCSE Chemistry tutor can build calculation fluency, work through Paper 4 questions with your child and turn examiner-report advice into practice. We'll match you with a tutor within a day, starting with a free, no-obligation Meet & Greet. There's no long-term contract.

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Sources

• Cambridge International, Cambridge IGCSE Chemistry 0620 syllabus for 2026, 2027 and 2028, version 2 (assessment overview, assessment objectives, stoichiometry content, Periodic Table, command words): https://www.cambridgeinternational.org/Images/697205-2026-2028-syllabus.pdf
• Cambridge International, 0620 syllabus update, August 2026: https://www.cambridgeinternational.org/Images/763304-2026-2028-syllabus-update.pdf
• Cambridge International, Cambridge IGCSE Chemistry 0620: https://www.cambridgeinternational.org/programmes-and-qualifications/view/cambridge-igcse-chemistry-0620/
• Cambridge International, past papers, examiner reports and specimen papers: https://www.cambridgeinternational.org/past-papers/