AQA · GCSE · Chemistry
Course version: 8462 · 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 unit used to measure chemical amount.
Checked against the AQA 8462 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 unit used to measure chemical amount. Its symbol is mol. One mole contains the Avogadro number of particles, 6.02 × 10²³, where the particles may be atoms, molecules, ions or electrons. The mass of one mole of a substance is its molar mass, found by adding the relative atomic masses in the formula and expressed in g/mol. For example, the molar mass of water, H₂O, is 18 g/mol, so 36 g of water is 2 mol. The relationship amount in moles equals mass divided by molar mass allows you to convert between mass and chemical amount. Always write mol after the number, for example 2 mol, not 2 m.
What earns the marks
- State that the mole is the unit of chemical amount and its symbol is mol.
- State that one mole contains 6.02 × 10²³ particles.
- Calculate molar mass by adding relative atomic masses from the formula.
- Use the relationship amount in moles equals mass divided by molar mass.
- Give the unit mol with any calculated chemical amount.
Common mistakes and how to put them right
Writing m as the symbol for mole; correct this by writing mol.
Using relative atomic mass as a mass in grams without converting to molar mass.
Put it right by expressing molar mass in g/mol.
Forgetting to state the type of particle when using the Avogadro number.
Put it right by naming the particles, such as atoms or molecules.
Exam tips
- Write mol after every amount to secure the unit mark.
- Show the molar mass calculation before substituting into the moles equation.
- Check that mass is in grams and molar mass is in g/mol before dividing.
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 unit and symbol are used to measure the amount of a chemical substance?
Listen
The mole is the unit used to measure chemical amount. Its symbol is mol. One mole contains the Avogadro number of particles, 6.02 × 10²³, where the particles may be atoms, molecules, ions or electrons. The mass of one mole of a substance is its molar mass, found by adding the relative atomic masses in the formula and expressed in g/mol. For example, the molar mass of water, H₂O, is 18 g/mol, so 36 g of water is 2 mol. The relationship amount in moles equals mass divided by molar mass allows you to convert between mass and chemical amount. Always write mol after the number, for example 2 mol, not 2 m. A strong answer earns marks for these points. State that the mole is the unit of chemical amount and its symbol is mol. State that one mole contains 6.02 × 10²³ particles. Calculate molar mass by adding relative atomic masses from the formula. Use the relationship amount in moles equals mass divided by molar mass. A common slip: Using relative atomic mass as a mass in grams without converting to molar mass. Instead, expressing molar mass in g/mol. Exam tip: Write mol after every amount to secure the unit mark.
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Key words
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Chemical amount
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The mole and Avogadro number
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Molar mass
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Mass–mole calculations
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See every definition
- Chemical amount
- A quantity measured in moles, where the symbol for the unit mole is mol.
- The mole and Avogadro number
- The unit used to measure chemical amount, containing the Avogadro number of particles, 6.02 × 10²³, which may be atoms, molecules, ions or electrons.
- Molar mass
- The mass of one mole of a substance, found by adding the relative atomic masses in the formula and expressed in g/mol.
- Mass–mole calculations
- Converting between mass and chemical amount using the relationship amount in moles equals mass divided by molar mass.
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