IGCSE Chemistry: How to Answer 6-Mark Questions — Cambridge and Edexcel 2026
The 6-mark extended writing question is where many IGCSE Chemistry students lose crucial marks — not because they don't know the chemistry, but because they don't know how to write the answer the examiner wants to see.
This guide explains exactly what Cambridge (0620) and Edexcel (4CH1) examiners want — and how to consistently get 5 or 6 marks.
What Examiners Are Looking For
6-mark questions use a "levels of response" marking scheme. Examiners place your answer in one of three levels:
| Level | Marks | What It Means |
|---|---|---|
| Level 3 | 5-6 | Detailed, accurate, well-structured — covers all key points in logical order with correct terminology |
| Level 2 | 3-4 | Some detail — covers most points but may be incomplete or out of sequence |
| Level 1 | 1-2 | Limited — some correct chemistry but vague or missing key elements |
| Level 0 | 0 | No relevant chemistry |
The 5-Step Method for Every 6-Mark Question
- Read carefully — underline key words: "describe", "explain", "compare", "evaluate"
- Plan in 30 seconds — list the 5-6 points you want to make
- Use correct terminology — don't say "particles speed up", say "particles have greater kinetic energy and collide more frequently"
- Write in sequence — especially for experiments: what you set up, what you do, what you observe, what you conclude
- Include what you observe — examiners love specific observations: "a white precipitate forms"
Most Common 6-Mark Question Topics
1. Electrolysis
What to include: Identify the electrolyte, state what happens at anode and cathode, explain what ions are discharged and why (concentration, reactivity), state what you observe at each electrode, write the half-equations.
Example observation: "Bubbles of gas are produced at the anode" — never just say "gas is produced"
2. Rates of Reaction — Experiment Design
What to include: Independent variable, dependent variable, controlled variables (at least 3), method of measurement, how to ensure a fair test, what you would expect to observe.
Common mistake: Listing equipment without explaining how to use it, or forgetting to state what stays constant.
3. The Haber Process
What to include: Raw materials, conditions (450°C, 200 atm, iron catalyst), why these conditions are chosen (compromise between rate and yield), what happens to unreacted nitrogen and hydrogen (recycled), the equation.
4. Organic Chemistry Reactions
What to include: Reactants, conditions, products, type of reaction (addition/substitution/elimination), mechanism summary, observations.
5. Titration Procedure
What to include: Rinse the burette with the solution to be used, fill burette, record initial reading, add indicator, run the alkali from the burette, swirl the flask, approach the end-point dropwise, record final reading, calculate titre. Repeat for concordant results.
Words That Get Marks vs Words That Don't
| Weak Phrasing (loses marks) | Strong Phrasing (gets marks) |
|---|---|
| "Particles move faster" | "Particles have greater kinetic energy" |
| "More collisions" | "More frequent successful collisions with energy ≥ activation energy" |
| "Gas comes out" | "Colourless gas with a pungent smell is produced" / "Bubbles of gas at the cathode" |
| "It reacts with the acid" | "The metal displaces hydrogen ions from the acid to form a salt and hydrogen gas" |
| "The solution changes colour" | "The indicator changes from colourless to pale pink at the end-point" |
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