This key facts covers Key Facts to Memorise within Moles & Calculations for GCSE Chemistry. Revise Moles & Calculations in Quantitative Chemistry for GCSE Chemistry with 27 exam-style questions and 20 flashcards. This topic shows up very often in GCSE exams, so students should be able to explain it clearly, not just recognise the term. It is section 7 of 17 in this topic. Use this key facts to connect the idea to the wider topic before moving on to questions and flashcards.
📌 Key Facts to Memorise
- Avogadro's constant = 6.02 × 10²³ particles per mole — this is the number of atoms in exactly 12g of carbon-12
- The golden equation: n = m ÷ Mr (moles = mass ÷ relative formula mass)
- Conservation of mass: atoms are rearranged, never created or destroyed — total mass in = total mass out
- Coefficients in equations give you the mole ratio (e.g., 2Mg + O₂ → 2MgO means 2 moles Mg : 1 mole O₂ : 2 moles MgO)
- Unit conversions: 1 dm³ = 1000 cm³ = 1 litre (CRUCIAL for concentration calculations!)
- Concentration: c = n ÷ V (mol/dm³) or c = m ÷ V (g/dm³)
- Percentage yield = (actual yield ÷ theoretical yield) × 100 — always less than 100% in practice
- Atom economy = (Mr of desired product ÷ total Mr of all products) × 100 — higher is greener!
Practice questions for Moles & Calculations
One mole of any substance contains how many particles?
Explain why the percentage yield of a reaction is never 100% in practice.
Quick recall flashcards
Define 'one mole'
The amount of substance containing 6.02 × 10²³ particles
One mole of any element weighs exactly its Ar in grams
What is Avogadro's constant?
6.02 × 10²³ particles per mole
This is the number of particles in one mole of any substance.