This is the topic where chemistry turns into calculation. It all rests on conservation of mass: because no atoms are lost or made during a reaction, the masses on both sides of an equation must add up. From there you can predict how much product a reaction will make, judge how efficient an industrial process is, or find the formula of an unknown compound. It’s also where careless working costs the most marks, so being methodical with your units and steps matters more here than almost anywhere else.
🧭 How this topic splits by tier
This is one of the most tier-dependent topics in the course, so check what your tier needs:
- Everyone — conservation of mass, balanced equations, relative formula mass, mass changes involving a gas, uncertainty, and concentration in g/dm³.
- Higher Tier H — the mole, reacting-mass calculations, balancing from masses, and limiting reactants.
- Triple (Chemistry only) T — percentage yield, atom economy, concentration in mol/dm³, titration calculations and gas volumes (these last two are also Higher Tier).
Mass, Equations & Measurement
Moles & Reacting MassesH
Concentration & Titrations
Yield & Atom EconomyT
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