# A chemist has two samples: 0.5 mol of sodium chloride (NaCl) and 0.5 mol of magnesium (Mg). Describe what is meant by the term 'mole' and explain why, although both samples contain the same number of moles, they have different masses.

> Cambridge International IGCSE Chemistry (0620) — 3.3 The mole and the Avogadro constant · Describe and Explain · 4 marks

## Mark scheme (4 marks)

1. A mole is the amount of substance that contains the Avogadro constant (6.02 × 10²³) number of particles
2. The relative formula mass / relative atomic mass of the two substances is different
3. Mass of one mole = relative formula/atomic mass expressed in grams, so different Mr values give different masses
4. Both samples contain the same number of particles (0.5 × 6.02 × 10²³), confirming moles measure amount not mass

## Key terms

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

## Related

- [Revision notes for Cambridge International IGCSE Chemistry (0620)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/a-chemist-has-two-samples-0-5-5f013467) · Published by Druglandscape Ltd.