# A student prepares two solutions of hydrochloric acid. Solution A has a concentration of 2.0 mol/dm³ and Solution B has a concentration of 0.5 mol/dm³. Explain what is meant by the term concentration and describe how the student could change Solution A into Solution B without making a fresh solution.

> AQA GCSE Chemistry (8462) — 4.3.4 Using concentrations of solutions in mol/dm³ (Chem only) · Explain · 4 marks

## Mark scheme (4 marks)

1. Concentration is the amount of substance (in moles) dissolved in a given volume of solution
2. The student should add more water / solvent to Solution A (dilution)
3. The number of moles of solute stays the same / is unchanged when water is added
4. The volume of the solution increases, which decreases the concentration

## Key terms

- [concentration](https://www.gradenine.co.uk/glossary/concentration)
- [mol/dm³](https://www.gradenine.co.uk/glossary/mol-dm)

## 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)
- [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-prepares-two-solutions-of-6dc9ebf9) · Published by Druglandscape Ltd.