The Mole
The mole connects the number of particles to measurable mass. 1 mole of any substance contains 6.02 × 10²³ particles.
The mole is the SI unit for amount of substance.
Avogadro's number: 1 mole = 6.02 × 10²³ particles (atoms, molecules, ions, etc.)
Molar mass: the mass of one mole of a substance = Mr in grams per mole (g/mol).
- Molar mass of H₂O = 18 g/mol (so 1 mole of H₂O weighs 18 g)
- Molar mass of NaCl = 58.5 g/mol
The mole triangle:
n = m / Mr where:
- n = number of moles
- m = mass in grams
- Mr = relative formula mass
Examples:
- How many moles in 40 g of NaOH (Mr = 40)? n = 40/40 = 1 mol
- What mass is 0.5 mol of CO₂ (Mr = 44)? m = 0.5 × 44 = 22 g
- 1 mole = 6.02 × 10²³ particles. Molar mass = Mr in g/mol.
- n = m / Mr. m = n × Mr. Mr = m / n.