How to Answer IGCSE Chemistry Exam Questions (And Stop Giving Marks Away)

Examiner reports for 0620 repeat the same complaint every session: candidates knew the chemistry and still failed to score, because they answered the question they expected instead of the question printed. Exam technique is not a soft skill bolted onto revision. In a subject where one word (“colourless” instead of “clear”) decides a mark, technique is content.

Read the stem like it’s part of the question, because it is

The stem is everything printed before the first sub-question: the scenario, the equation, the table, the diagram. Students skim it to “get to the question”. Examiners write it the other way round: the stem carries the information the answers need.

Three habits fix this:

1. Underline the substance names and states. If the stem says aqueous copper(II) sulfate, an answer about solid copper(II) sulfate is already off the scheme.
2. Circle the numbers and their units. A volume in cm³ that the calculation needs in dm³ is the most reliably planted trap in the paper.
3. Note what the question tells you that you didn’t have to know. If the stem hands you an equation, the examiners expect you to use it, usually for a mole ratio two parts later.

When part (c) feels impossible, the missing information is almost always sitting in the stem or in your answer to part (a). 0620 questions are built as chains; re-read the top of the chain before declaring defeat.

Command words decide what a “right” answer looks like

State, describe, explain, deduce, suggest. Each commands a different product, and the scheme marks the product, not the effort. The contrast that costs the most marks:

• Describe = say what happens or what is observed. “The grey solid dissolves and the solution turns blue.”
• Explain = say why, using chemistry. “Zinc is more reactive than copper, so it displaces copper ions from solution.”

Write a description under an explain command and you score zero, regardless of accuracy. Suggest signals that the situation is unfamiliar: apply known principles to a new case; nobody expects a memorised answer. Deduce means the evidence is in front of you; use it and show that you used it.

The full list, with what each word pays and how, is in our guide to 0620 command words. Learn them as vocabulary, the same way you learned the gas tests.

Data-extraction marks: the easiest marks on the paper

0620 theory papers and Paper 6 carry marks that require no recall at all: only careful reading of a table or graph. “From the table, state which metal reacted fastest.” “Use the graph to find the volume of gas at 60 seconds.” These are gift marks, and they get dropped two ways:

• Imprecision. Reading 38 cm³ off the graph when the gridline says 38.5. Take a ruler to the axes; quote the value the printed scale shows.
• Ignoring the instruction “use the data”. If the question says use the data, an answer from general knowledge scores nothing, even when it’s true. Quote the numbers: “Magnesium produced 40 cm³ in 20 s while iron produced 12 cm³, so magnesium is more reactive.”

Comparisons need both halves stated. “Magnesium is faster” earns the mark only if the paper can see faster than what, by what evidence.

Calculations: the working is the answer

A 0620 mole calculation worth 3 marks is usually structured as method mark, method mark, answer mark. The student who writes a single unexplained number is betting all three marks on perfect arithmetic under pressure. Bad bet.

Set out every calculation in labelled steps:

Mr of CaCO3 = 40 + 12 + (3 × 16) = 100 moles of CaCO3 = 5.0 ÷ 100 = 0.050 mol ratio CaCO3 : CO2 = 1 : 1, so moles of CO2 = 0.050 mol mass of CO2 = 0.050 × 44 = 2.2 g

If the last multiplication goes wrong, the first two marks survive. Three more rules: carry units through the working, keep unrounded values in the calculator until the final line, and give the answer to three significant figures unless told otherwise. The step-by-step framework is in the mole calculations technique.

Budget time by marks, not by difficulty

Every 0620 written paper prices its questions in plain sight: the mark allocation in brackets. Paper 4 runs at just under a minute a mark; Paper 6 (60 minutes, 80 marks) runs faster, at about 45 seconds a mark. The budgeting rules:

• A 2-mark question wants two points. Writing five sentences for 2 marks spends time the 6-mark question at the back needed.
• Set checkpoints. In Paper 4, you should be near question 4 of 6-7 at the 40-minute mark. Behind schedule means move faster on low-mark parts, not skip them.
• Never bleed time into a stuck question. Mark it, leave white space, move on. Questions later in the paper are not harder than the one you’re stuck on (0620 doesn’t ramp difficulty steeply), so the marks ahead are just as winnable.
• Bank the final five minutes for checking units, significant figures and any question left blank. A guessed MCQ answer has a 25% expected value; a blank has zero.

Train the technique, not just the content

Knowledge revision and technique revision are different activities. To train technique: sit questions timed, mark them against the genuine scheme, and write down why each lost mark was lost: wrong command word, missing working, vague phrasing, misread stem. Patterns appear within three papers. Our breakdown of the most common 0620 exam mistakes lists the patterns we see most, so you can check yours against them.

If your scores plateau even though the chemistry feels solid, technique is usually the ceiling, and it’s hard to diagnose your own habits. In a free 1-hour trial lesson, one of our Chemistry specialists marks your work live, shows you exactly which words earned and lost each mark, and gives you the phrasing fix on the spot. Most students find two or three repeated mark-losers in that first hour. Removing them is worth a full grade for most students.