The mole and the Avogadro constant
Cambridge A-Level Chemistry (9701) · Unit 2: Atoms, molecules and stoichiometry · 7 flashcards
The mole and the Avogadro constant is topic 2.2 in the Cambridge A-Level Chemistry (9701) syllabus , positioned in Unit 2 — Atoms, molecules and stoichiometry , alongside Relative masses of atoms and molecules and Formulas. In one line: One mole is the amount of substance that contains 6.02 × 10²³ particles (atoms, molecules, ions or electrons). This number is the Avogadro constant, L or Nₐ = 6.02 × 10²³ mol⁻¹. The mole is the chemist's counting unit.
Marked as AS Level: examined at AS Level in Paper 1 (Multiple Choice), Paper 2 (AS Structured Questions) and Paper 3 (Advanced Practical Skills). The same content may also be assumed in Paper 4 (A Level Structured Questions).
The deck below contains 7 flashcards — 3 definitions, 2 key concepts and 2 calculations — covering the precise wording mark schemes reward. Use the 3 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
The term 'mole'
One mole is the amount of substance that contains 6.02 × 10²³ particles (atoms, molecules, ions or electrons). This number is the Avogadro constant, L or Nₐ = 6.02 × 10²³ mol⁻¹. The mole is the chemist's counting unit.
What the Cambridge 9701 syllabus says
2025-2027 syllabus, in our words · AS LevelWhat the syllabus expects you to be able to do in this topic, in plain English. For the exact wording, see the official syllabus (PDF).
- Define the mole by reference to the Avogadro constant, and use the term.
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9701 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Define the term 'mole'.
One mole is the amount of substance that contains 6.02 × 10²³ particles (atoms, molecules, ions or electrons). This number is the Avogadro constant, L or Nₐ = 6.02 × 10²³ mol⁻¹. The mole is the chemist's counting unit.
What is the Avogadro constant (NA), and what is its value?
The Avogadro constant (Nₐ) is the number of constituent particles (usually atoms or molecules) that are contained in the amount of substance given by one mole. Its value is approximately 6.022 x 10²³ mol⁻¹.
How do you calculate the number of moles in a given mass of a substance?
Number of moles (n) = mass (m) / molar mass (M).
What is the relationship between the number of particles, the number of moles, and the Avogadro constant?
Number of Particles = Number of Moles x Avogadro Constant (N = n x Nₐ). This equation allows conversion between the number of moles of a substance and the number of individual particles it contains.
A sample contains 3.011 x 10²³ molecules of a compound. How many moles of the compound are present?
Moles = Number of particles / Avogadro's constant. Therefore, moles = (3.011 x 10²³) / (6.022 x 10²³) = 0.5 moles.
Explain why the mole is a useful concept in chemistry.
The mole provides a convenient way to relate masses of substances to the number of atoms, molecules, or ions present. It bridges the macroscopic world (grams) to the microscopic world (atoms).
Define molar mass.
Molar mass (M) is the mass of one mole of a substance, usually expressed in grams per mole (g/mol). It is numerically equal to the substance's atomic or molecular weight in atomic mass units (amu).
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The mole and the Avogadro constant sits alongside these A-Level Chemistry decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this The mole and the Avogadro constant deck
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