Chemistry
Mole calculations
GCSE & A-level
Choose AQA GCSE 8462 or A-level 7405 before revising. The GCSE view contains only GCSE equations; the A-level view adds the ideal-gas equation. Flip on Test yourself to check you can recall each one under pressure.
AQA GCSE Chemistry only — the ideal-gas equation is deliberately excluded.
| To find… | Use | Units / notes |
|---|---|---|
| Moles, from a massGCSE | Equationn =mM | Units / notesm in g; M = Mr in g mol−1 |
| Mass, from molesGCSE | Equationm = n × M | Units / notesrearrangement of the above |
| Moles, in a solutionGCSE | Equationn = c × V | Units / notesV in dm3; c in mol dm−3 |
| ConcentrationGCSE | Equationc =nV | Units / notesmol dm−3 (× M to get g dm−3) |
| Moles of a gas (at RTP)GCSE | Equationn =V24 | Units / notesV in dm3 at RTP (÷ 24000 if V in cm3) |
| Number of particlesGCSE | EquationN = n × L | Units / notesL = 6.02×1023 mol−1 (Avogadro) |
| Percentage yieldGCSE | Equationactualtheoretical× 100 | Units / notescompare moles (or mass) of product |
| Atom economyGCSE | EquationMr of desired productΣMr of reactants× 100 | Units / noteshow much of the reactant mass ends up wanted |
| % by mass of an elementGCSE | Equationn × ArMr× 100 | Units / notesn = number of that atom in the formula |
Unit conversions worth memorising
- 1 dm3 = 1000 cm3 — divide cm3 by 1000 to get dm3.
- For volume conversions: 1 m3 = 1000 dm3.
- 1 tonne = 1×10⁶ g; 1 kg = 1000 g.
The method examiners reward
- Work out moles of what you're given.
- Use the balanced equation's ratio to get moles of the target.
- Convert those moles to the quantity asked for.
Now put them to work
Reading the equations isn't the same as landing the marks — drill them until the method is automatic.
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