IGCSE Extended Chemistry Cheat Sheet

STOICHIOMETRY

Key Definitions

• Mole: Amount of substance with 6.02 × 10²³ particles.

• Relative atomic mass (Ar): Average mass of an atom compared to 1/12 of carbon-12.

• Relative molecular mass (Mr): Sum of atomic masses in a molecule.

• Empirical formula: Simplest ratio of atoms in a compound.

• Molecular formula: Actual number of atoms in a molecule.

• Concentration: Amount of solute per unit volume.

• Molar volume of a gas: 1 mole occupies 24 dm³ at RTP.

Conversions & Formulas

• Moles (solid): Use relative mass to convert.

• Moles (solution): Concentration and volume relation.

• Moles (gas at RTP): Same ratio as in balanced equation.

• Percentage Composition: Divide by Ar and simplify.

• Empirical Formula Calculation: Divide, find smallest number, multiply for whole numbers.

• Reacting Mass Calculation: Use mole ratios from balanced equations.

• Gas Volume Ratio (at RTP): Same ratio as moles in balanced equation.

Example Question

Q: Calculate mass of CO₂ from 10g of CaCO₃ decomposition.A: 4.4g CO₂ produced.