Chemistry study notes
The Mole Concept and Stoichiometry
Turn masses, gas volumes and solution measurements into amounts, then let a balanced equation connect them.
A-Level 9476 (2026-2027)
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5 topicsRelative mass and the mole
Distinguish a relative mass, a molar mass and a number of particles.
Find an empirical or molecular formula
Convert composition or combustion products into atom ratios.
Balanced equations and limiting reagents
Use coefficients as mole ratios and identify what runs out first.
Gas volumes and hydrocarbon combustion
Use volume ratios only when temperature and pressure match.
Solutions, titrations and inferred ratios
Track dilution, aliquots and the reagent left over.
Scope and references
Learning outcomes and sources
6. The Mole Concept and Stoichiometry. Use the outcome map to find the explanation for a particular syllabus requirement.
See the learning outcome map
6(a) Define the four relative-mass quantities.
- Relative atomic, isotopic, molecular and formula mass
- Carbon-12 reference
- Relative formula mass for ionic compounds
6(b) Define and use the mole through the Avogadro constant.
- Specified entities
- Avogadro constant and particle-number conversion
6(c) Calculate weighted relative atomic mass.
- Relative isotope abundances
- Percent or relative-intensity weighting
6(d) Distinguish empirical and molecular formulae.
- Simplest whole-number ratio
- Actual atom numbers in a molecule
6(e) Calculate formulae from composition or combustion.
- Composition by mass
- Combustion data
- Independent molar mass for molecular multiplier
A formula records an atom ratio, not a mass ratioCombustion transfers carbon into carbon dioxide and hydrogen into water
6(f) Construct balanced chemical equations.
- Conservation of atoms and charge
- Correct formulae and coefficients
- Combustion equations
Combustion transfers carbon into carbon dioxide and hydrogen into waterThe balanced equation is the conversion between substancesAt the same temperature and pressure, gas volumes follow mole ratios
6(g) Calculate reacting amounts in solids, gases and solutions.
- (i) Reacting masses from formulae/equations
- (ii) Gas volumes, including hydrocarbon combustion
- (iii) Solution volumes and concentrations
- Appropriate significant figures
The balanced equation is the conversion between substancesAt the same temperature and pressure, gas volumes follow mole ratiosConcentration connects a measured volume with molesUse the measured difference to reveal an unknown ratio
6(h) Deduce stoichiometric relationships from measurements.
- Use calculated reacting amounts to infer ratios
- Gas-combustion and indirect mass/solution examples
- Check experimental assumptions
At the same temperature and pressure, gas volumes follow mole ratiosUse the measured difference to reveal an unknown ratio
- SEAB H2 Chemistry 9476, examination 2026
Topic 6, printed page 18. All eight outcomes, the three calculation categories and the significant-figure instruction inspected.