Chapter summary
Chemical Calculations, at a glance
Turn formulae, measurements and equations into defensible numerical answers.
O-Level 5086 / 5088 (2026) / SEC G3 K326 / K328 (2027)
Quick revision
Revisit the essentials, then return to an explanation when you need it.
| Term | Definition to write |
|---|---|
| Relative atomic mass, Ar | The average mass of one atom of an element (taking its isotopes into account), compared with 1/12 of the mass of one atom of carbon-12. |
| Relative molecular mass, Mr | The average mass of one molecule of a substance, compared with 1/12 of the mass of one atom of carbon-12. It is the sum of the relative atomic masses of the atoms in the formula. |
| Term | Definition to write |
|---|---|
| Mole | The amount of substance that contains 6.02 × 1023 particles (the Avogadro constant). |
| Molar volume of a gas | One mole of any gas occupies 24 dm3 at room temperature and pressure. |
| Concentration | The amount of solute in 1 dm3 of solution, in mol/dm3 or g/dm3. |
- Formula and equation
Balance before calculating.
- Known quantity to moles
n = m/M; n = cV; n = V/24 at room conditions.
- Mole ratio
Use coefficients, including the limiting reactant.
- Requested quantity
Convert moles and include units.
Quick recall
Work out the formula of aluminium oxide.