What formulas do I need to memorise for IGCSE Chemistry maths questions?
Talimat Academic Team
Education Specialist · 22 May 2026
Seven formulas cover the vast majority of calculation marks in IGCSE Chemistry exams.
The mole equation sits at the centre of everything. Moles equals mass divided by relative formula mass (Mr). Rearrange it to find mass by multiplying moles by Mr. Every stoichiometry question traces back to this relationship.
For gas volumes at room temperature and pressure, use: Volume (dm³) equals moles multiplied by 24. One mole of any gas occupies 24 dm³ at RTP, regardless of identity.
The molarity equation links concentration, moles, and volume. Concentration (mol/dm³) equals moles divided by volume in dm³. Always convert cm³ to dm³ by dividing by 1,000 before applying this formula. Exam questions almost always give volumes in cm³ to catch students who skip this step.
The remaining formulas appear in Higher Tier papers. These four are the ones students most often forget under pressure:
- Percentage yield: (actual yield / theoretical yield) × 100
- Atom economy: (Mr of desired product / sum of Mr of all products) × 100
- Energy change: mass × specific heat capacity × temperature change
- Bond enthalpy: energy in (bonds broken) minus energy out (bonds formed)
A common mistake across all of these is mismatched units. Check the unit on the answer line before you calculate, and show every conversion step. Examiners award method marks even when the final answer is wrong.
Students doing Cambridge IGCSE chemistry, Edexcel, or AQA all face the same set of calculation types. The formulas do not change between boards, though the context and phrasing of questions varies. Practising past papers from your specific board is the most reliable way to build speed and accuracy.
If you want the full reference table with units for each formula, plus worked examples for gas volumes and titration questions, our blog has a complete revision guide. You can also contact us to be matched with an IGCSE tutoring specialist who can work through calculation questions with you in a live 1:1 session.