# A student carries out a reaction to produce calcium carbonate as a precipitate. The theoretical yield is 25.0 g, but the student only collects 18.5 g of dry calcium carbonate. Explain why the actual yield is less than the theoretical yield, and describe TWO reasons that could account for this difference in this type of reaction.

> Edexcel GCSE Chemistry (1CH0) — 5.2 Quantitative analysis (Chem only) · Explain · 4 marks

> Calcium carbonate can be made by mixing solutions of calcium chloride and sodium carbonate. The white precipitate of calcium carbonate is then filtered, washed and dried.

## Mark scheme (4 marks)

1. The actual yield is less than the theoretical yield because the theoretical yield is the maximum possible mass of product that can be obtained from a reaction (and in practice this is rarely achieved).
2. Some product is lost during transfer, e.g. some precipitate remains stuck to the filter paper or glassware.
3. The reaction may be incomplete, meaning not all reactants have reacted to form product.
4. A side reaction may occur, producing a by-product instead of the desired calcium carbonate, reducing the amount of useful product formed.

## 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 Edexcel GCSE Chemistry (1CH0)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-carries-out-a-reaction-97cc720a) · Published by Druglandscape Ltd.