Exam Focus
This exam focus covers Exam Focus within Moles & Calculations for GCSE Chemistry. Revise Moles & Calculations in Quantitative Chemistry for GCSE Chemistry with 27 exam-style questions and 20 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 15 of 17 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
Topic position
Section 15 of 17
Practice
27 questions
Recall
20 flashcards
🎯 Exam Focus
Frequently Examined
Moles calculations appear in virtually every GCSE Chemistry paper. Examiners test this topic across multiple question types:
- 1-2 marks: Calculate Mr of a compound (e.g., "Calculate the Mr of CaCO₃")
- 3-4 marks: Multi-step moles calculation (mass → moles → ratio → mass)
- 2-3 marks: Percentage yield — given actual and theoretical mass, calculate %
- 2 marks: Atom economy — given equation, identify products and calculate
- 5-6 marks: Combined calculation involving conservation of mass, yield, and explanation
Command word alert: "Calculate" always requires a numerical answer with working shown. "Explain" requires you to state the conservation of mass principle. "Suggest" requires reasoning about why yield is less than 100%.
Edexcel 1CH0: Examined in Paper 1 (1CH0/1). Mole calculations, percentage yield, and atom economy are all tested — Edexcel includes Higher-tier questions on limiting reagents. In Edexcel-style questions, the command word "Suggest" appears frequently — use your chemistry knowledge to apply to an unfamiliar context.
Quick Check: Calculate the Mr of H₂SO₄. (Ar: H = 1, S = 32, O = 16)
Mr = (2 × 1) + 32 + (4 × 16) = 2 + 32 + 64 = 98. Remember: add the Ar of every atom in the formula.
Quick Check: How many moles are in 9g of water? (Mr of H₂O = 18)
n = m ÷ Mr = 9 ÷ 18 = 0.5 mol. Use the moles triangle: cover n, you see m over Mr.
Quick Check: A reaction has a theoretical yield of 20g but only produces 14g. What is the percentage yield?
% Yield = (actual ÷ theoretical) × 100 = (14 ÷ 20) × 100 = 70%. The yield is below 100% because some product was lost during purification or the reaction did not go to completion.
Keep building this topic
Read this section alongside the surrounding pages in Moles & Calculations. That gives you the full topic sequence instead of a single isolated revision point.
Practice Questions for Moles & Calculations
One mole of any substance contains how many particles?
Explain why the percentage yield of a reaction is never 100% in practice.
Quick Recall Flashcards
27 questions on Moles & Calculations — practise free
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