AQA GCSE Chemistry
AQA GCSE Chemistry 4.3.3 Yield and Atom Economy of Chemical Reactions Exam Questions
Free AQA GCSE Chemistry exam questions for 4.3.3 Yield and Atom Economy of Chemical Reactions, with a mark scheme for every pack. Covers percentage yield, reasons yield is below 100%, theoretical yield calculations and atom economy for choosing a reaction pathway.
4.3.3 Yield and Atom Economy of Chemical Reactions exam questions
1 question pack of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Chemistry 4.3.3 Yield and Atom Economy of Chemical Reactions
AQA GCSE Chemistry 4.3.3 is separate Chemistry only content that looks at how efficient a reaction really is. Percentage yield compares the product actually obtained with the maximum possible, while atom economy measures how much of the reactants' mass ends up in the useful product. Both are assessed on Paper 1 and link to industrial processes such as the Haber process in 4.10 and to sustainable development. Examiners commonly ask for both calculations, reasons why a yield is less than 100%, and an evaluation of which of two reaction pathways should be used industrially.
What you need to know
- Percentage yield percentage yield = (mass of product actually made / maximum theoretical mass of product) x 100.
- Why yield is less than 100% The reaction may be reversible and not go to completion; some product may be lost when it is separated from the mixture (for example during filtering or transferring); and some reactants may react in unexpected side reactions.
- Theoretical yield (Higher tier only) Calculate the theoretical mass of product from a balanced equation using moles, then use it in the percentage yield equation.
- Atom economy atom economy = (Mr of desired product from the equation / sum of Mr of all reactants) x 100. Use the balancing numbers in the equation.
- Choosing a pathway A high atom economy means less waste, which is better for sustainability and often cheaper. Industry also considers yield, rate, equilibrium position and the usefulness of by-products when choosing a reaction pathway.
Common mistakes in 4.3.3 Yield and Atom Economy of Chemical Reactions
- Confusing yield with atom economy. Yield is about how much product you actually get; atom economy is about how much of the reactant mass could, in theory, end up in the desired product.
- Forgetting the balancing numbers when calculating atom economy, for example using H2 instead of 3H2.
- Putting the actual and theoretical masses the wrong way round, giving a percentage over 100.
- Saying atom economy is low because 'product is lost'. Loss of product affects yield, not atom economy.
- Ignoring the value of by-products: a reaction with a low atom economy can still be worthwhile if the by-product can be sold.
Try three 4.3.3 Yield and Atom Economy of Chemical Reactions exam-style questions
1. A student expected to make 5.0 g of copper sulfate but obtained 3.8 g. Calculate the percentage yield. (2 marks)
Show the mark scheme answer
(3.8 / 5.0) x 100; = 76%.
2. Hydrogen can be made by the reaction CH4 + H2O → CO + 3H2. Calculate the atom economy for making hydrogen. (Mr: CH4 = 16, H2O = 18, H2 = 2) (3 marks)
Show the mark scheme answer
Total Mr of reactants = 16 + 18 = 34; Mr of desired product = 3 x 2 = 6; atom economy = (6 / 34) x 100 = 17.6%.
3. Give two reasons why the percentage yield of a reaction is less than 100%. (2 marks)
Show the mark scheme answer
Any two from: reaction is reversible so does not go to completion; product lost during separation or transfer; side reactions produce other products.
4.3.3 Yield and Atom Economy of Chemical Reactions FAQs
What does AQA GCSE Chemistry 4.3.3 cover?
It covers percentage yield, why yields are less than 100%, calculating theoretical yield from equations (Higher tier only), atom economy and why atom economy matters for industry.
Is yield and atom economy on the combined science course?
No. 4.3.3 is separate Chemistry only content and is assessed on Paper 1.
Which equations do I need for 4.3.3?
Learn percentage yield = actual mass / theoretical mass x 100, and atom economy = Mr of desired product / total Mr of reactants x 100. Both answers should be given as percentages.
