How to get an A* in IGCSE Chemistry 0620

Only Extended candidates can get an A*. Extended students sit Paper 2 (multiple choice), Paper 4 (theory) and one practical paper, usually Paper 6 (Alternative to Practical). The Core papers (1 and 3) are capped at grade C.

Paper 4 is worth half of your grade, so long structured answers matter most. Paper 2 is 30% and Paper 6 is 20%.

Tip: Supplement topics such as moles of gases, titration calculations, electrolysis of aqueous solutions and the Haber process appear only on Extended papers. Do not skip them.

• That is just over a minute per question. Do a first pass, answer everything you are sure of, and mark the rest to come back to.
• Cover the options and work out your own answer first. Then look for it. The wrong options are built from common mistakes.
• For calculation questions, write the working on the question paper. A quick mole calculation beats guessing.
• Never leave a blank. There is no penalty for a wrong answer.

Stoichiometry is one of the biggest topics on the Extended papers. Nearly every calculation follows one chain: grams → moles → use the equation ratio → moles → grams (or volume).

• Moles = mass ÷ molar mass. Mass always goes on top.
• Gas volume at r.t.p. = moles × 24 dm³ (or 24 000 cm³).
• Concentration in mol/dm³ = moles ÷ volume in dm³. Divide cm³ by 1000 first.
• Percentage yield = actual ÷ predicted × 100. It can never be over 100%.

Free lessons: The mole and the Avogadro constant · Moles of gases and solutions · Reacting masses, yield and empirical formulae

Balance only by changing the big numbers in front of formulae, never the small numbers inside them. Then add state symbols if the question asks: (s), (l), (g), (aq).

Tip: Learn half-equations for electrolysis too. At the cathode electrons are gained (Pb²⁺ + 2e⁻ → Pb); at the anode they are lost (2Br⁻ → Br₂ + 2e⁻).

Free lessons: Formulae · Electrolysis

These are some of the easiest marks on the whole exam, and they appear on Paper 4 and Paper 6. Learn each test with its exact result.

• Hydrogen: lighted splint gives a squeaky pop. Oxygen: relights a glowing splint.
• Carbon dioxide: limewater turns milky. Ammonia: damp red litmus turns blue. Chlorine: bleaches damp litmus paper.
• Halides: add dilute nitric acid, then silver nitrate: white (Cl⁻), cream (Br⁻), yellow (I⁻).
• Metal ions with sodium hydroxide: Cu²⁺ light blue, Fe²⁺ green, Fe³⁺ red-brown.

Free lessons: Identification of ions and gases · Tests for gases

Paper 6 asks about experiments on paper. You need to plan, read apparatus, record results and judge them.

• Read a burette to the nearest 0.05 cm³ and record readings to two decimal places, such as 23.45 cm³.
• Table headings carry the unit after a slash: volume / cm³. No units inside the table.
• Plot with small crosses and draw one smooth best-fit line. Label both axes with units.
• Name the apparatus exactly: measuring cylinder, burette, volumetric pipette, gas syringe.
• Know how to improve an experiment: repeat it, control a named variable, or use more precise apparatus.

Free lessons: Experimental design · Acid-base titrations

1. Do one past paper section under timed conditions.
2. Mark it strictly with the mark scheme. Only give marks for the exact words it accepts.
3. Write every lost mark in a mistakes log: the question, what you wrote, and what earned the mark.
4. Re-learn that idea with a short lesson, then redo the question a week later.

Tip: Your mistakes log is worth more than any revision guide. By the exam, it is a list of the only things you still get wrong.