Quantitative Chemistry - AQA GCSE Chemistry Revision

Topic overview

What you need to know

Quantitative Chemistry is a key part of GCSE Chemistry. Link particles, structure and energy changes to the observations and calculations you may be given. The average mass of atoms of an element compared to 1/12 of a carbon-12 atom. Found on the periodic table. The sum of the relative atomic masses of all atoms in a formula. E.g. Mr of H₂O = (2×1) + 16 = 18. The amount of substance containing 6.02 × 10²³ particles (Avogadro's number). Moles = mass ÷ Mr.

Exam tip

Balance equations, show units in calculations and connect macroscopic observations to particles.

Revision notes

Core ideas

Secure these ideas first. Say each definition in your own words, then connect it to the topic overview.

Relative Atomic Mass (Ar): The average mass of atoms of an element compared to 1/12 of a carbon-12 atom. Found on the periodic table.
Relative Formula Mass (Mr): The sum of the relative atomic masses of all atoms in a formula. E.g. Mr of H₂O = (2×1) + 16 = 18.
Mole: The amount of substance containing 6.02 × 10²³ particles (Avogadro's number). Moles = mass ÷ Mr.
Conservation of Mass: In a chemical reaction, no atoms are lost or made — the total mass of reactants equals the total mass of products.

Revision notes

Apply it in the exam

The exam will rarely ask for an isolated definition. Practise selecting the right idea and using it as part of a complete explanation or method.

Balancing Equations: Adjusting coefficients so the number of each type of atom is equal on both sides of the equation.
Concentration (g/dm³): The amount of solute dissolved in a given volume of solution. Concentration = mass of solute ÷ volume of solution.
Concentration (mol/dm³): Concentration in moles per cubic decimetre. Concentration = moles ÷ volume (in dm³).
Atom Economy: A measure of efficiency: (Mr of desired product ÷ sum of Mr of all products) × 100%. Higher is better.

Core knowledge

Key facts for Quantitative Chemistry

8 essentials

Relative Atomic Mass (Ar)

The average mass of atoms of an element compared to 1/12 of a carbon-12 atom. Found on the periodic table.

Relative Formula Mass (Mr)

The sum of the relative atomic masses of all atoms in a formula. E.g. Mr of H₂O = (2×1) + 16 = 18.

Mole

The amount of substance containing 6.02 × 10²³ particles (Avogadro's number). Moles = mass ÷ Mr.

Conservation of Mass

In a chemical reaction, no atoms are lost or made — the total mass of reactants equals the total mass of products.

Balancing Equations

Adjusting coefficients so the number of each type of atom is equal on both sides of the equation.

Concentration (g/dm³)

The amount of solute dissolved in a given volume of solution. Concentration = mass of solute ÷ volume of solution.

Concentration (mol/dm³)

Concentration in moles per cubic decimetre. Concentration = moles ÷ volume (in dm³).

Atom Economy

A measure of efficiency: (Mr of desired product ÷ sum of Mr of all products) × 100%. Higher is better.

Active recall

Close the notes and answer these

1.Without looking, explain relative atomic mass (ar) and give one example or consequence.
2.Without looking, explain relative formula mass (mr) and give one example or consequence.
3.Without looking, explain mole and give one example or consequence.
4.Without looking, explain conservation of mass and give one example or consequence.

Content reviewed 23 July 2026 against the current linked specification.

Finished learning?

Mark the notes complete, then test what you can recall.

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