AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Chemical amounts are measured in moles. The symbol for the unit mole is mol.
Full specification wording
Moles (HT only): Chemical amounts are measured in moles. The symbol for the unit mole is mol.
The mole is the chemist's counting unit for particles.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 1 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
The mole is the chemist's counting unit for particles. Because atoms and molecules are too small to count individually, chemists measure chemical amount in moles. One mole contains the Avogadro constant of particles, 6.02 × 10²³, just as a dozen contains 12. The unit is the mole and its symbol is mol, written after the number (e.g. 2 mol of carbon atoms). Chemical amount is a distinct quantity, measured in moles, not mass or volume. Always give the unit mol in answers. This concept, which is Higher Tier only, lets you compare reacting quantities directly using balanced equations.
For example: In 2H₂ + O₂ → 2H₂O, 2 mol of hydrogen molecules reacts with 1 mol of oxygen molecules.
What earns the marks
- States that chemical amount is measured in moles and gives the unit symbol as mol.
- Explains that one mole contains 6.02 × 10²³ particles, so the mole is a counting unit for atoms, molecules or ions.
- Uses the mole to compare reacting quantities from a balanced equation, for example 2 mol H₂ reacting with 1 mol O₂.
- Distinguishes amount in moles from mass in grams and volume in dm³.
- Applies the idea that equal numbers of moles of different substances contain equal numbers of particles.
Common mistakes and how to put them right
Writing the unit as 'mole' or 'moles' after a number instead of the symbol mol.
Put it right by writing 3 mol, not 3 moles as a unit label.
Confusing amount in moles with mass in grams.
Put it right by stating that moles count particles while grams measure mass, and the two are linked by relative formula mass.
Treating one mole as a fixed mass for every substance.
Put it right by explaining that one mole of carbon has a different mass from one mole of water because the particles differ.
Exam tips
- Always attach the unit mol to numerical answers about chemical amount, and never leave a bare number.
- When a question says 'amount of substance', expect moles; when it says 'mass', expect grams, so choose the matching quantity.
- Remember that mole calculations are Higher Tier only, so expect them in more challenging quantitative chemistry questions.
Try the lesson
The start of the Moles (HT only): Chemical amounts are measured in moles. The symbol for the unit mole is mol. lesson, made from checked teaching notes for this specification point.
Have a go first
Which symbol is used for the unit mole?
Listen
The mole is the chemist's counting unit for particles. Because atoms and molecules are too small to count individually, chemists measure chemical amount in moles. One mole contains the Avogadro constant of particles, 6.02 × 10²³, just as a dozen contains 12. The unit is the mole and its symbol is mol, written after the number (e.g. 2 mol of carbon atoms). Chemical amount is a distinct quantity, measured in moles, not mass or volume. Always give the unit mol in answers. This concept, which is Higher Tier only, lets you compare reacting quantities directly using balanced equations. For example, in 2H₂ + O₂ → 2H₂O, 2 mol of hydrogen molecules reacts with 1 mol of oxygen molecules. A strong answer earns marks for these points. States that chemical amount is measured in moles and gives the unit symbol as mol. Explains that one mole contains 6.02 × 10²³ particles, so the mole is a counting unit for atoms, molecules or ions. Uses the mole to compare reacting quantities from a balanced equation, for example 2 mol H₂ reacting with 1 mol O₂. Distinguishes amount in moles from mass in grams and volume in dm³. A common slip: Writing the unit as 'mole' or 'moles' after a number instead of the symbol mol. Instead, writing 3 mol, not 3 moles as a unit label. Exam tip: Always attach the unit mol to numerical answers about chemical amount, and never leave a bare number.
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Key words
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Measurement of chemical amount
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The mole as a counting unit
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Avogadro constant 6.02 × 10²³
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Mole ratios from balanced equations
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See every definition
- Measurement of chemical amount
- Chemical amounts are measured in moles, and the symbol for the unit mole is mol.
- The mole as a counting unit
- Because atoms and molecules are too small to count individually, chemists measure chemical amount in moles, the counting unit for particles.
- Avogadro constant 6.02 × 10²³
- One mole contains the Avogadro constant of particles, 6.02 × 10²³, just as a dozen contains 12.
- Mole ratios from balanced equations
- This concept lets you compare reacting quantities directly using balanced equations, for example 2 mol of hydrogen molecules reacts with 1 mol of oxygen molecules.
Label the diagram
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