GCSE Chemistry · Edexcel 1CH0 · Topic 1D
Calculations involving masses
Key points
- Relative formula mass () is the sum of the values in a formula, e.g. of CO₂ = 12 + 2 × 16 = 44.
- Empirical formula is the simplest whole-number ratio of atoms: divide each mass by , then by the smallest answer.
- Conservation of mass: total mass of reactants = total mass of products. An apparent change happens when a gas escapes or is taken in.
- Concentration (g dm⁻³) = mass of solute ÷ volume of solution in dm³ (1 dm³ = 1000 cm³).
- Higher tier: one mole contains particles (the Avogadro constant). .
- Higher tier: use moles to balance equations from masses, and find the limiting reactant (the one that is used up first and limits the product).
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Chemists need to know how much of each substance reacts and how much product forms. These notes cover relative formula mass, conservation of mass, empirical formulae, concentration and, for Higher tier, moles and limiting reactants.
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