AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
One mole of a substance contains the same number of the stated particles,…
Full specification wording
Moles (HT only): One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance.
A mole is the chemist's counting unit: it is a fixed amount of particles, not a fixed mass.
Checked against the AQA 8464 specification (opens in a new tab) on .
- Point 3 of 6
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
A mole is the chemist's counting unit: it is a fixed amount of particles, not a fixed mass. One mole of any substance contains the same number of stated particles as one mole of any other substance, whether those particles are atoms, molecules or ions. For example, 1 mol of helium atoms, 1 mol of H₂ molecules and 1 mol of Na⁺ ions each contain the same number of particles, even though their masses differ. This Higher Tier only concept matters because balanced equations compare particles in fixed ratios, so moles let you convert between reacting masses and particle numbers. The identity of the particle must be stated: 1 mol of oxygen atoms, O, is not the same as 1 mol of oxygen molecules, O₂.
What earns the marks
- States that a mole is an amount of substance containing a fixed number of stated particles.
- Explains that one mole of any substance contains the same number of particles as one mole of any other substance.
- Identifies particles as atoms, molecules or ions, because the same substance can be described using different particles.
- Recalls that the number of particles in one mole is the Avogadro constant, 6.02 × 10²³ per mole.
- Applies the principle that equal numbers of moles of different substances contain equal numbers of particles but generally have different masses.
Common mistakes and how to put them right
Treating one mole as a fixed mass such as 1 g or 12 g.
Put it right: A mole is a fixed number of particles, and its mass depends on the substance.
Assuming 1 mol of oxygen atoms and 1 mol of oxygen molecules contain the same number of oxygen atoms.
Put it right: 1 mol of O₂ contains 2 mol of oxygen atoms.
Comparing moles of different substances by mass alone.
Put it right: Convert mass to moles using molar mass before comparing particle numbers.
Exam tips
- Underline the particle named in the question, such as atoms, molecules or ions, and keep that particle type throughout your working.
- Show the relationship you use, for example moles = mass ÷ molar mass, then substitute values with units.
- Remember this is Higher Tier only content, so expect to apply it in multi-step calculations involving the Avogadro constant.
Try the lesson
The start of the Moles (HT only): One mole of a substance contains the same number of the stated particles, atoms, molecules or ions as one mole of any other substance. lesson, made from checked teaching notes for this specification point.
Have a go first
Which statement about one mole of any substance is correct?
Listen
A mole is the chemist's counting unit: it is a fixed amount of particles, not a fixed mass. One mole of any substance contains the same number of stated particles as one mole of any other substance, whether those particles are atoms, molecules or ions. For example, 1 mol of helium atoms, 1 mol of H₂ molecules and 1 mol of Na⁺ ions each contain the same number of particles, even though their masses differ. This Higher Tier only concept matters because balanced equations compare particles in fixed ratios, so moles let you convert between reacting masses and particle numbers. The identity of the particle must be stated: 1 mol of oxygen atoms, O, is not the same as 1 mol of oxygen molecules, O₂. A strong answer earns marks for these points. States that a mole is an amount of substance containing a fixed number of stated particles. Explains that one mole of any substance contains the same number of particles as one mole of any other substance. Identifies particles as atoms, molecules or ions, because the same substance can be described using different particles. Recalls that the number of particles in one mole is the Avogadro constant, 6.02 × 10²³ per mole. A common slip: Treating one mole as a fixed mass such as 1 g or 12 g. Instead, a mole is a fixed number of particles, and its mass depends on the substance. Exam tip: Underline the particle named in the question, such as atoms, molecules or ions, and keep that particle type throughout your working.
See it
Key words
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Amount of substance and the mole
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Particle identity: atoms, molecules and ions
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Avogadro constant and particle number
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Molar mass and mass–mole calculations
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See every definition
- Amount of substance and the mole
- A mole is an amount of substance containing a fixed number of stated particles, not a fixed mass.
- Particle identity: atoms, molecules and ions
- The particle must be stated because the same substance can be described using atoms, molecules or ions.
- Avogadro constant and particle number
- The number of particles in one mole is the Avogadro constant, 6.02 × 10²³ per mole.
- Molar mass and mass–mole calculations
- Mass is converted to moles using molar mass, since equal numbers of moles of different substances generally have different masses.
Label the diagram
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1Box 1
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3Box 3
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