The Mole
Year 9 ⚛️ Particles & Structure Use n = m/M; understand Avogadro's number 6.022 × 10²³.
🧮 The Mole
The mole is the SI unit for amount of substance. 1 mole = 6.022 × 10²³ particles (Avogadro's number).
Mole Triangle
$$n = \frac{m}{M_r} \qquad m = n \times M_r \qquad M_r = \frac{m}{n}$$ n = moles (mol), m = mass (g), Mr = relative formula mass (g/mol).
⚖️ Calculating Mr
Mr(H₂O) = 2(1) + 16 = 18 g/mol
Mr(NaCl) = 23 + 35.5 = 58.5 g/mol
Mr(H₂SO₄) = 2 + 32 + 64 = 98 g/mol
Mr(CaCO₃) = 40 + 12 + 48 = 100 g/mol
Mr(NaCl) = 23 + 35.5 = 58.5 g/mol
Mr(H₂SO₄) = 2 + 32 + 64 = 98 g/mol
Mr(CaCO₃) = 40 + 12 + 48 = 100 g/mol
🔬 Worked Examples
Example 1: Moles in 44 g CO₂ (Mr = 44)?
n = 44 ÷ 44 = 1 mol
Example 2: Mass of 0.5 mol NaCl (Mr = 58.5)?
m = 0.5 × 58.5 = 29.25 g
Example 3: Particles in 2 mol CO₂?
= 2 × 6.022 × 10²³ = 1.204 × 10²⁴ molecules
n = 44 ÷ 44 = 1 mol
Example 2: Mass of 0.5 mol NaCl (Mr = 58.5)?
m = 0.5 × 58.5 = 29.25 g
Example 3: Particles in 2 mol CO₂?
= 2 × 6.022 × 10²³ = 1.204 × 10²⁴ molecules
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Interactive Demonstration — The Mole
🧮 Mole Calculator