# A student prepares calcium chloride by reacting calcium carbonate with hydrochloric acid. The theoretical yield of calcium chloride is 50 g, but the student only collects 35 g. Give two reasons why the actual yield is less than the theoretical yield, and explain what is meant by the term 'theoretical yield'.

> AQA GCSE Chemistry (8462) — 4.3.3 Yield and atom economy of chemical reactions · Explain · 4 marks

## Mark scheme (4 marks)

1. Theoretical yield is the maximum amount of product that could be produced from the given reactants, assuming a complete reaction takes place.
2. First reason: product is lost during transfer/filtration/evaporation/collection (i.e. practical losses during the process).
3. Second reason: the reaction may not have gone to completion / some reactant was not fully used up.
4. Percentage yield is less than 100% because the actual yield (35 g) is less than the theoretical yield (50 g) — linking the two values to show the yield is not 100%.

## Key terms

- [actual yield](https://www.gradenine.co.uk/glossary/actual-yield)
- [theoretical yield](https://www.gradenine.co.uk/glossary/theoretical-yield)

## Related

- [Revision notes for AQA GCSE Chemistry (8462)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-prepares-calcium-chloride-by-8ab3c16f) · Published by Druglandscape Ltd.