If you want an A* in IGCSE Chemistry (0620), past papers are the quickest way to turn revision into marks. The same question patterns show up across Paper 2 multiple choice and Paper 4 theory, just dressed in new numbers and contexts. Once you learn a repeatable method for each pattern, you stop dropping marks to missing units, unbalanced equations, vague explanations, and rushed reading. This guide breaks down ten high-frequency IGCSE Chemistry past paper question types and gives a solving framework you can reuse in revision sessions.

1. Moles from a balanced equation
   Write the symbol equation and balance it first. Convert the given mass to moles using n = m ÷ Mr. Use the coefficients as the mole ratio. Convert your final moles into the requested value (mass, gas volume, or concentration) and finish with correct units.
2. Concentration (mol/dm³) from mass and volume
   Start with n = m ÷ Mr. Convert volume into dm³ by dividing cm³ by 1000. Use c = n ÷ V. If mass is required, rearrange to m = c × V × Mr and keep dm³ throughout.
3. Titration calculation (acid–alkali)
   Pick the accurate titres and calculate the mean. Convert the mean titre to dm³. Find moles of the standard solution using n = c × V, then apply the equation ratio to get moles of the unknown. Divide by the pipette volume (in dm³) to get the unknown concentration.
4. Limiting reactant
   Balance the equation. Convert each reactant to moles. Compare “reaction portions” by dividing each mole value by its coefficient. The smaller value is limiting. Use that reactant to calculate product, then calculate any excess left.
5. Percentage yield
   Calculate the theoretical yield from the limiting reactant using mole ratios. Use % yield = (actual ÷ theoretical) × 100. If the question mentions transfer losses or incomplete reaction, treat the collected amount as actual yield.
6. Percentage purity
   Work out how much pure substance is present, then use % purity = (pure ÷ impure sample) × 100. If an impure reactant is used, calculate moles from the pure part only, not the full mass.
7. Ionic equations
   Write the full ionic equation by splitting soluble ionic compounds into ions. Cancel spectator ions that appear unchanged on both sides. Check atom balance and charge balance. Final answers should show only reacting species, with charges included.
8. Electrolysis: aqueous vs molten
   List all ions present. In aqueous solutions, include H⁺ and OH⁻ from water. At the cathode, hydrogen is produced unless the metal is less reactive than hydrogen. At the anode, halides form halogens in many cases; oxygen forms from OH⁻ when halides are not discharged. Write half-equations to lock in accuracy.
9. Bonding and structure linked to properties
   Name the structure (ionic, simple molecular, giant covalent, metallic) and link it to a property with a reason. Use mark-scheme chains: strong electrostatic attraction gives high melting points in ionic lattices; mobile ions carry charge when molten or aqueous; delocalised electrons explain conduction in metals and graphite; weak intermolecular forces explain low boiling points in simple molecules.
10. Rates of reaction and graphs
    Read gradients: a steeper slope means a faster rate. A plateau shows completion. Use collision theory language: higher temperature increases successful collisions; greater surface area increases collision frequency; catalysts lower activation energy. Quote values from the graph when asked and label axes with units.

Common traps that cost marks
• Writing the ratio from an unbalanced equation
• Leaving volume in cm³ during concentration questions
• Rounding early in multi-step calculations
• Stating a trend without linking it to electrons or particles
• Giving conclusions without observations in tests

A 30-minute daily routine using these questions
Spend 15 minutes on IGCSE Chemistry Paper 2 MCQs daily, aiming for speed with zero unit mistakes. Then spend 15 minutes on one Paper 4 structured question set built around moles, electrolysis, acids and salts, bonding, or rates. Mark using the mark scheme and keep a mistake log. Each entry should include the topic, the error, and one fix you will practise tomorrow. Redo the same pattern until you can score full marks twice in a row, then move on.

Exam-day checklist: underline command words, write the equation before touching numbers, keep cm³↔dm³ conversions beside you, show units on every line, use state symbols only when asked, and for practical-style questions write observations first (colour change, gas, precipitate) before naming the test. Leave two minutes to scan for missed questions and sign errors. Check significant figures where the question gives a target.

If you revise these ten past paper question types with a fixed method, your answers become cleaner, faster, and more exam-safe, which is exactly what A* Chemistry demands.