The mole
Cambridge A-Level Physics (9702) · Unit 15: Ideal gases · 6 flashcards
The mole is topic 15.1 in the Cambridge A-Level Physics (9702) syllabus , positioned in Unit 15 — Ideal gases , alongside Equation of state and Kinetic theory of gases. In one line: The SI base unit for the amount of substance is the 'mole', symbol 'mol'. It quantifies the number of elementary entities (atoms, molecules, ions, etc.) of a substance.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 6 flashcards — 3 definitions, 1 key concept 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 SI base unit for amount of substance
The SI base unit for the amount of substance is the 'mole', symbol 'mol'. It quantifies the number of elementary entities (atoms, molecules, ions, etc.) of a substance.
What the Cambridge 9702 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- understand that amount of substance is an SI base quantity with the base unit mol
- use molar quantities where one mole of any substance is the amount containing a number of particles of that substance equal to the Avogadro constant NA
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9702 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in The mole
- › For ideal gases, state clearly that internal energy is the sum of only the kinetic energies of the atoms/molecules.
What is the SI base unit for amount of substance?
The SI base unit for the amount of substance is the 'mole', symbol 'mol'. It quantifies the number of elementary entities (atoms, molecules, ions, etc.) of a substance.
Define one mole in terms of the number of particles.
One mole of any substance contains the same number of particles as there are atoms in 12 grams of carbon-12. This number is defined as the Avogadro constant (Nₐ).
What is the approximate value of the Avogadro constant, and what are its units?
The Avogadro constant (Nₐ) is approximately 6.022 × 10²³ mol⁻¹. It represents the number of particles (atoms, molecules, ions, etc.) per mole of a substance.
How do you calculate the number of moles (n) of a substance given the number of particles (N) and the Avogadro constant (Nₐ)?
The number of moles (n) can be calculated using the formula: n = N / Nₐ, where N is the number of particles and Nₐ is the Avogadro constant.
A sample contains 3.011 × 10²³ molecules of water (H₂O). How many moles of water are present?
n = N / Nₐ = (3.011 × 10²³) / (6.022 × 10²³) = 0.5 mol. Therefore, there are 0.5 moles of water.
Describe how the concept of the mole is important in stoichiometry.
The mole allows us to relate macroscopic measurements of mass to the number of atoms/molecules involved in a chemical reaction. Stoichiometric calculations rely on the mole ratio from balanced equations to predict quantities of reactants and products.
Review the material
Read full revision notes on The mole — definitions, equations, common mistakes, and exam tips.
Read NotesMore topics in Unit 15 — Ideal gases
The mole sits alongside these A-Level Physics 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 deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
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