Calculation Technique

Chemistry calculations carry significant marks across all three papers. A clear, systematic approach to calculations will earn you method marks even when you make arithmetic errors — and prevent errors in the first place.

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The Golden Rules

1. Show Every Step

Chemistry mark schemes award method marks (M marks) and answer marks (A marks) separately. If you show your method clearly and make an arithmetic error, you lose only the final answer mark. If you show no working and get the answer wrong, you lose everything.

Always write:

• The formula you are using
• The substitution of values
• The calculation
• The answer with units

2. Units at Every Step

Include units throughout your calculation, not just at the end. This helps you check that your answer makes sense and shows the examiner your reasoning.

3. Significant Figures

Give your final answer to the same number of significant figures as the data in the question (or as specified). If the question says "give your answer to 3 significant figures," do exactly that. If no guidance is given, use 3 significant figures as a default.