# A student adds excess marble chips (calcium carbonate) to dilute sulfuric acid. At first bubbles are produced, but the reaction soon stops even though marble chips are still present. Suggest why the reaction stops, and explain what the student could do to make the reaction continue.

> Eduqas GCSE Chemistry — 2.2 Acids, bases and salts · Explain · 4 marks

> Calcium carbonate reacts with dilute sulfuric acid: CaCO₃ + H₂SO₄ → CaSO₄ + H₂O + CO₂. Calcium sulfate is an insoluble solid.

## Mark scheme (4 marks)

1. Calcium sulfate (an insoluble solid/precipitate) forms on the surface of the marble chips
2. The insoluble calcium sulfate layer prevents the acid from reaching the calcium carbonate
3. The student could crush/grind the marble chips (to break up the coating and expose fresh surface)
4. This exposes fresh (unreacted) calcium carbonate surface so the acid can react again

## Key terms

- [calcium carbonate](https://www.gradenine.co.uk/glossary/calcium-carbonate)

## Related

- [Revision notes for Eduqas GCSE Chemistry](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-adds-excess-marble-chips-304a2140) · Published by Druglandscape Ltd.