GCSE Chemistry calculations are one of the most common stumbling blocks for students — and one of the most rewarding areas to improve, because the marks are very achievable once you know the method.
This guide is useful whether you're studying AQA, Edexcel, or OCR GCSE Chemistry.
Key GCSE Chemistry Calculations You Need to Know
1. Moles The mole is the foundation of most Chemistry calculations.
Formula: Moles = Mass ÷ Relative Formula Mass (Mr)
Example: How many moles are in 18g of water (H₂O)?
- Mr of H₂O = (2 × 1) + 16 = 18
- Moles = 18 ÷ 18 = 1 mole
2. Concentration Formula: Concentration = Moles ÷ Volume (in dm³)
Example: What is the concentration of a solution containing 0.5 moles in 250cm³?
- Convert: 250cm³ = 0.25 dm³
- Concentration = 0.5 ÷ 0.25 = 2 mol/dm³
3. Percentage Yield Formula: % Yield = (Actual Yield ÷ Theoretical Yield) × 100
4. Atom Economy Formula: Atom Economy = (Mr of desired product ÷ Sum of Mr of all products) × 100
Tips for Tackling Calculation Questions
- Always show your working — you can pick up method marks even if your final answer is wrong.
- Learn your formulae — some are given, some aren't. Know which is which for your exam board.
- Practise under timed conditions — speed matters in the exam.
- Check your units — a correct answer in the wrong unit will lose marks.
Structured Calculation Practice
Our GCSE Chemistry calculation worksheets include worked examples, scaffolded questions, and exam-style practice — all created by a science teacher and aligned to the current spec. Check them out here👉 https://mrsfscience.com/collections/chemistry
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