Stoichiometry

Worked examples (12)extended set

• 1Molecular and empirical formulae from a displayed formula
• 2Formulae with polyatomic ions (multiple choice)
• 3Roman numerals, oxidation numbers and ionic formulae
• 4Formula of an ionic compound from a lattice diagram
• 5Formula from positions in the Periodic Table (multiple choice)
• 6Balancing three symbol equations
• 7Equations with state symbols from descriptions
• 8Deducing an equation from a particle diagram
• 9Ionic equation for a precipitation test
• 10Ionic equations for two displacement reactions
• 11Deducing the formula of an unfamiliar ion
• 12Equations for the ammonium ion test

Model answers (6)

• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Adapted from 0620/42 May/Jun 2023 Q3
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 (Extended) structured style

Worked examples (12)extended set

• 1Relative atomic mass and the carbon-12 standard
• 2Relative formula mass with brackets (multiple choice)
• 3Relative molecular mass from a displayed formula
• 4Relative atomic mass from isotope percentages
• 5Relative atomic mass from an abundance ratio
• 6What a whole-number relative atomic mass tells you
• 7Identifying elements from relative formula masses
• 8Diffusion and relative molecular mass
• 9Reacting masses in simple proportion from a graph
• 10Finding isotope abundance from the relative atomic mass
• 11Maximum mass of iron from an ore
• 12How many different chlorine molecules? (multiple choice)

Model answers (6)

• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 (Extended) structured style

Worked examples (12)extended set

• 1The mole and concentration in two units
• 2Counting atoms, not molecules (multiple choice)
• 3Mass, amount and molar mass — identifying a metal
• 4From a gas volume to a mass of product
• 5Gas volume from a solution, collected in a gas syringe
• 6Limiting reactant from a gas-volume graph
• 7Titration: burette readings to concentration
• 8Empirical and molecular formula from percentages
• 9Empirical formula of an oxide from a crucible experiment
• 10Percentage purity and percentage yield
• 11Volume of alkali to neutralise a diprotic acid
• 12Thermite: limiting reactant and percentage yield

Model answers (6)

• ✓Model answer — Paper 4 short-answer style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 structured style
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 (Extended) structured style
• ✓Model answer — Paper 4 (Extended) structured style