# Calcium carbonate reacts with hydrochloric acid according to the equation: CaCO₃ + 2HCl → CaCl₂ + H₂O + CO₂. A student carries out this reaction using an excess of hydrochloric acid and a limited amount of calcium carbonate. Explain what is meant by the term 'limiting reactant' and explain how the law of conservation of mass applies to this reaction, even though a gas is produced.

> WJEC A-Level Chemistry (Wales) — 3.6 Amines and polymers (A-Level only) · Explain · 5 marks

## Mark scheme (5 marks)

1. The limiting reactant is the reactant that is completely used up during the reaction
2. The limiting reactant (calcium carbonate) limits the amount of product(s) formed
3. The law of conservation of mass states that no atoms are lost or made during a chemical reaction
4. The mass of the products equals the mass of the reactants
5. The carbon dioxide gas produced still has mass, so if it is collected and included, the total mass of all products (CaCl₂ + H₂O + CO₂) equals the total mass of the reactants

## Key terms

- [limiting reactant](https://www.gradenine.co.uk/glossary/limiting-reactant)
- [conservation of mass](https://www.gradenine.co.uk/glossary/conservation-of-mass)
- [excess](https://www.gradenine.co.uk/glossary/excess)

## Related

- [Revision notes for WJEC A-Level Chemistry (Wales)](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/calcium-carbonate-reacts-with-hydrochloric-acid-339600fa) · Published by Druglandscape Ltd.