GCSE Chemistry · AQA 8462 · Topic 4.3
Quantitative chemistry
Key points
- Mass is conserved in a reaction: the total mass of products equals the total mass of reactants. Apparent changes happen when a gas escapes or is gained.
- Relative formula mass () is the sum of the relative atomic masses in a formula.
- (Higher) The mole is the amount of substance; one mole contains particles (the Avogadro constant). .
- Balanced equations give the ratio in which substances react; the reactant used up first is the limiting reactant.
- Concentration in g/dm³ = mass ÷ volume in dm³ (Higher: also mol/dm³).
- Percentage yield and atom economy (chemistry only) measure how efficient a process is.
- (Higher, chemistry only) Titrations find unknown concentrations, and one mole of any gas occupies 24 dm³ at room temperature and pressure.
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Quantitative chemistry is about numbers: how much of each substance reacts and how much product forms. It turns balanced equations into recipes, and it carries a large share of the calculation marks on Paper 1.
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Sub-topics
- 4.3.1Chemical measurements, conservation of mass and the quantitative interpretation of chemical equations
- 4.3.2Use of amount of substance in relation to masses of pure substances
- 4.3.3Yield and atom economy of chemical reactions
- 4.3.4Using concentrations of solutions in mol/dm³
- 4.3.5Use of amount of substance in relation to volumes of gases
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