Explain what is meant by the term 'mole' and state the significance of the Avogadro constant in chemistry.

Cambridge International IGCSE Chemistry (0620) — 3.3 The mole and the Avogadro constant · Explain · 4 marks · View as Markdown

Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).

Model answer (4 marks)

A mole is the amount of substance that contains the same number of particles as there are atoms in 12 g of carbon‑12.
The Avogadro constant is 6.02 × 10²³ mol⁻¹.
It gives the number of specified particles (atoms, molecules, ions or formula units) in one mole of a substance.
The mole allows chemists to count very large numbers of particles by weighing, linking mass to number of particles.

Examiner tips

  • Use the exact definition of a mole and the numeric value of Avogadro’s constant.
  • Explain both the counting function and the mass‑number link.
  • Mention the 12 g C‑12 reference.
  • Keep the answer concise to fit the 4 marks.

Common mistakes

  • Writing the Avogadro constant as 6.02×10²³ without units or as 6.02×10²³ per mole.
  • Confusing the mole with the molar mass or forgetting the 12 g C‑12 reference.

Mark scheme (4 marks)

  1. A mole is the amount of substance that contains the same number of particles as there are atoms in 12 g of carbon-12
  2. The Avogadro constant is 6.02 × 10²³ (per mole)
  3. The Avogadro constant gives the number of specified particles (atoms, molecules, ions, or formula units) in one mole of a substance
  4. The mole allows chemists to count very large numbers of particles by weighing, linking mass to number of particles

Key terms in this question

mole · Avogadro constant

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