Exercise 1 — IGCSE 0653 May/Jun 2024 Paper 31 Q2
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(molecule containing) two atoms (chemically combined)
Cambridge IGCSE·Combined Sciences 0653·Chemistry
Stoichiometry
Key knowledge — Stoichiometry
Formulas & equations
Moles = mass (g) ÷ molar mass (g/mol)Moles = volume (dm³) × concentration (mol/dm³)Moles of gas at RTP = volume (dm³) ÷ 24 (at room temperature and pressure)% yield = (actual yield ÷ theoretical yield) × 100% purity = (mass of pure substance ÷ total mass) × 100Empirical formula: simplest whole-number ratio of atoms. Molecular formula: actual ratio.
Key facts & rules
- Avogadro's number: 1 mole contains 6.02 × 10²³ particles.
- Molar mass: sum of Ar values from the periodic table for one formula unit.
- Balancing equations: atoms must be equal on both sides — only coefficients can change, not formulae.
- Limiting reagent: the reactant that runs out first, determining the maximum yield.
- Excess reagent: the reactant that is not used up.
IGCSE Chemistry — Stoichiometry
1 Cambridge IGCSE 0653 Combined Sciences past paper questions on stoichiometry, across Theory, Multiple Choice and Alternative to Practical.
About Stoichiometry on IGCSE 0653
Stoichiometry uses the mole concept to calculate the quantities of reactants and products in chemical reactions. Students must be able to calculate percentage composition, empirical formulae and reacting masses.
What's covered:
- Relative atomic and molecular mass
- The mole and Avogadro's number
- Empirical and molecular formulae
- Reacting masses from equations
- Percentage yield
- Concentration of solutions in mol/dm³
Theory
Stoichiometry — Core1 · Paper 3
All Stoichiometry questions in this collection
| Type | Level | Paper | Session | Q# | Marks | Answer / key |
|---|---|---|---|---|---|---|
| Theory | Core | Paper 31 | May/Jun 2024 | Q2 | 11 marks | (molecule containing) two atoms (chemically combined) |