A level Chemistry · Edexcel 9CH0 · Topic 5A
Moles and equations
Key points
- One mole contains 6.02 × 10²³ particles (the Avogadro constant, ). Number of particles = .
- where is molar mass in g mol⁻¹.
- Empirical formula: divide mass (or %) of each element by its , then divide by the smallest to get a whole-number ratio.
- Molecular formula = empirical formula × (relative molecular mass ÷ empirical formula mass).
- Water of crystallisation: heat a hydrated salt to constant mass to find in, e.g., CuSO₄·H₂O.
- Use the mole ratio from a balanced equation to find reacting masses; ionic equations show only the species that change.
- Include state symbols (s), (l), (g), (aq) when asked.
Topic notesPremium
The mole lets chemists count atoms, ions and molecules by weighing them. Once you can convert between mass and moles and read mole ratios from a balanced equation, you can predict how much of anything will react or form.
Unlock the full notes with Premium
Premium includes full topic notes, the paper generator, self-quizzes and progress tracking.
Practise this topicPremium
Premium members can generate an exam-style paper with a mark scheme, or take a quick quiz, on Moles and equations.