A-Level Chemistry: Amount of Substance

Amount of substance is the calculation engine of A-Level Chemistry: nearly every quantitative mark in the qualification routes through moles. This quiz drills the full toolkit with concrete numbers, and every answer has been independently recomputed during verification.

The mole itself is tested conceptually through its relationship to the Avogadro constant, then put to work immediately. The ideal gas equation question is a full pV = nRT calculation with the unit conversions that decide the mark — cm³ to m³, Celsius to Kelvin — where most errors are actually made. Empirical formula determination works from percentage composition through the divide-by-Ar, find-the-ratio routine, and a molecular formula question pins down the relationship between empirical formula and molar mass.

The titration question is exam-standard: sodium hydroxide against sulfuric acid with a 2:1 stoichiometry that must be applied, not just noticed. A dilution question exercises C₁V₁ = C₂V₂, and the atom economy question computes a deliberately unglamorous 1.46% for hydrogen production — making the point that atom economy is about the equation, not the effort.

Percentage yield appears twice: once conceptually (which factors genuinely lower yield — reversibility, losses on transfer, side reactions) and once numerically, in a calcium carbonate decomposition worked through theoretical mass to a clean 80.0% (this question was rebuilt during verification after the original numbers implied a physically impossible yield above 100% — the kind of error the pipeline exists to catch).

Explanations show every step of every calculation, making the set equally useful as diagnosis or as worked-example study.

• Use the mole and the Avogadro constant fluently
• Apply pV = nRT with correct unit conversions
• Determine empirical and molecular formulae from composition data
• Perform titration and dilution calculations with non-1:1 stoichiometry
• Calculate atom economy and percentage yield and explain what lowers yield

Aligned to the quantitative chemistry core of the DfE A level science subject content: the mole, the ideal gas equation, empirical and molecular formulae, volumetric analysis, atom economy and percentage yield.