What this practice covers
These questions are drawn from past CIE 9701 Chemistry papers and filtered to atoms, molecules and stoichiometry. You answer, you find out immediately whether you were right, and you get the reasoning for the correct option and for each distractor. Wrong answers go to a mistakes locker so you can come back to exactly those.
Practice is free. You need an account only so your progress and your mistakes are still there next time.
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What examiners see students get wrong here
These are the errors that cost marks on atoms, molecules and stoichiometry, taken from our own topic notes. Read them before you practise and you will recognise the traps in the questions.
- Using 24.0 dm³ mol⁻¹ for a gas that is not at room conditions, or for a liquid or solid.
- Forgetting to divide cm³ by 1000 before using moles = c × V.
- Calculating theoretical yield from the reactant in excess rather than the limiting one.
- Rounding intermediate steps. Carry extra figures through and round only at the end.
- Leaving state symbols out of an ionic equation.
- Giving relative atomic mass a unit. It is a ratio and has none.
Revise it first
If any of the above is unfamiliar, work through the notes before practising: Atoms, molecules and stoichiometry revision notes.