AQA · Chemistry · 8462
GCSE Chemistry: Percentage yield
Quantitative chemistry · AQA GCSE Chemistry (8462), specification point 4.3.3.1. Cards are generated from the exam board's own specification for "Percentage yield", and every card links back to the page it came from. Separate science only. Specification © AQA — used with attribution.
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What is the equation for percentage yield?
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% Yield = (mass of product actually made ÷ maximum theoretical mass of product) × 100
In chemistry, what is meant by the yield of a reaction?
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The amount of a product obtained from the reaction.
Define percentage yield.
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The amount of product actually obtained, expressed as a percentage of the maximum theoretical amount.
Why might a reversible reaction give a lower yield than calculated?
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Because the reaction may not go to completion, so not all the reactants are converted into product.
How can separating a product from the reaction mixture reduce the yield?
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Some of the product may be lost during separation (e.g. filtering, transferring or purifying).
How can unexpected side reactions lower the yield of a product?
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Some of the reactants react in ways different to the expected reaction, so less of the intended product is formed.
Is the percentage yield of a reaction ever greater than 100%? Why?
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No — no atoms are gained in a chemical reaction, so the actual mass can never exceed the maximum theoretical mass.
A reaction that does not go to completion because it is ? gives less than the calculated amount of product.
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reversible
A reaction has a theoretical yield of 20 g but only 15 g is obtained. What is the percentage yield?
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75% — (15 ÷ 20) × 100 = 75%.
What two pieces of information are needed to calculate the theoretical mass of a product? (HT)
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The mass of the reactant and the balanced equation for the reaction.
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