GCSE & IGCSE chemistry practice

Percentage yield questions and answers

Percentage yield compares the mass of product you actually made with the maximum possible (the theoretical yield): % yield $= \dfrac{\text{actual mass}}{\text{theoretical mass}} \times 100$ . Yields are almost always under 100% because of incomplete reactions, side reactions and losses when separating the product.

8 questions · Foundation and Higher tier · Every answer is checked as you type it, with a full worked solution. Updated 27 Oct 2026.

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Where percentage yield comes up

GCSE (AQA)	GCSE Chemistry only (not Combined Science), Foundation and Higher: calculate percentage yield. Higher: calculate the theoretical mass of product from the equation.
Cambridge IGCSE (0620)	Supplement (Extended): calculate percentage yield, percentage composition by mass and percentage purity from data.

The method

% yield = actual ÷ theoretical × 100.
Theoretical yield: use moles and the balanced equation (reacting masses).
Actual = % yield ÷ 100 × theoretical.

Percentage yield questions

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Warm-up

Question 1Warm-upFoundation

A reaction could make 20 g of product but only 15 g is made. What is the percentage yield?

Question 2Warm-upFoundation

The theoretical yield is 8.0 g and 6.4 g is collected. Calculate the percentage yield.

Exam-style

Question 3Exam-styleFoundation

A reaction has a 60% yield. The theoretical yield is 50 g. What mass of product is actually made?

Question 4Exam-styleHigher

50 g of calcium carbonate is heated: $\text{CaCO}_3 \rightarrow \text{CaO} + \text{CO}_2$ . 22.4 g of calcium oxide is collected. Calculate the percentage yield. ( $M_r$ : CaCO₃ = 100, CaO = 56)

Question 5Exam-styleHigher

12 g of magnesium burns: $2\text{Mg} + \text{O}_2 \rightarrow 2\text{MgO}$ . 16 g of magnesium oxide is collected. Calculate the percentage yield. (Mg = 24, O = 16)

Question 6Exam-styleFoundation

Which of these is NOT a reason a percentage yield is below 100%?

Challenge

Question 7ChallengeHigher

$\text{N}_2 + 3\text{H}_2 \rightleftharpoons 2\text{NH}_3$ . 28 kg of nitrogen gives 6.8 kg of ammonia. Calculate the percentage yield. (N = 14, H = 1)

Question 8ChallengeHigher

A reaction has an 85% yield. What theoretical yield is needed to actually collect 34 g of product?

Common mistakes

Dividing theoretical by actual.
Using the mass of a reactant as the theoretical yield.
Confusing percentage yield with atom economy.

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Sources

The questions are our own. The “where it comes up” notes are from each board's published specification, checked on 27 October 2026:

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