# Explain what is meant by the term 'amount of substance' and outline how the mole concept allows chemists to relate the mass of a sample of an element to the number of atoms it contains.

> IB DP Chemistry Higher Level (2023 syllabus) — S1.4 Counting particles by mass: The mole · Explain · 4 marks

## Mark scheme (4 marks)

1. Amount of substance is a base SI quantity (symbol n) that measures the number of specified particles (atoms, molecules, ions, etc.) in a sample.
2. One mole contains Avogadro's constant (Nₐ ≈ 6.02 × 10²³) particles / elementary entities.
3. The molar mass of an element (in g mol⁻¹) is numerically equal to its relative atomic mass (Ar), linking mass to amount.
4. The number of atoms in any sample can therefore be found by dividing the mass of the sample by the molar mass to obtain n (in mol), then multiplying by Avogadro's constant (N = n × Nₐ).

## Key terms

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

## Related

- [Revision notes for IB DP Chemistry Higher Level (2023 syllabus)](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/explain-what-is-meant-by-the-c6d50063) · Published by Druglandscape Ltd.