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H1 Chemistry

Chemistry study notes

The Mole Concept and Stoichiometry

Turn mass, gas and solution evidence into amounts, formulae and balanced chemical relationships.

A-Level 8873, revised syllabus (2026-2027)

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3 topics

  1. Particles to formulae

    Separate mass ratios from atom ratios.

  2. Chemical accounting

    Balance atoms, charge and electron transfer.

  3. Reacting quantities

    Identify limiting amounts and infer unknown relationships.

Scope and references

Learning outcomes and sources

5. The Mole Concept and Stoichiometry (8873, 2026 revision; examinations 2026 and 2027). Use the outcome map to find the explanation for a particular syllabus requirement.

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  1. 5(a) Define the four relative masses.

    • Relative atomic, isotopic, molecular and formula masses; formula mass for ionic substances.

    Keep relative mass, molar mass and amount distinct

  2. 5(b) Define the mole through the Avogadro constant.

    • Specified entities and N = nNA.

    Keep relative mass, molar mass and amount distinct

  3. 5(c) Calculate isotope-weighted relative atomic mass.

    • Use relative abundances and isotope masses.

    Keep relative mass, molar mass and amount distinct

  4. 5(d) Distinguish empirical and molecular formulae.

    • Simplest ratio versus actual atom counts in a molecule.

    Turn mass evidence into an atom ratio

  5. 5(e) Calculate formulae from analytical evidence.

    • Combustion data and composition by mass; molecular-mass multiplier.

    Turn mass evidence into an atom ratio

  6. 5(f) Construct balanced equations.

    • Conserve atoms and charge; use correct formulae.

    Balance atoms and charge separately

  7. 5(g) Explain redox through electrons and oxidation numbers.

    • Fe3+/Fe2+ and MnO4-/Mn2+ examples.

    Balance atoms and charge separately

  8. 5(h) Combine relevant redox half-equations.

    • Balance electrons and cancel to obtain overall equation.

    Balance atoms and charge separately

  9. 5(i) Calculate reacting quantities.

    • (i) Reacting masses from formulae/equations.
    • (ii) Gas volumes including hydrocarbon combustion.
    • (iii) Solution volumes/concentrations; appropriate significant figures.

    Find the limiting reactant before the productA gas volume can reveal an unknown formulaMake dilution and titration steps explicit

  10. 5(j) Infer stoichiometric relationships.

    • Use quantity data rather than assuming the unknown ratio.

    Find the limiting reactant before the productA gas volume can reveal an unknown formulaMake dilution and titration steps explicit