Video narration
Is a mole a mass, a volume, or something else? Think of a dozen: a counting unit. A mole works the same way, but counts 6.022×10^23 particles. These can be atoms, molecules, ions, or formula units. That count is the Avogadro number. The mole is not grams or litres. It bridges mass, particles, and gas volume. Start with mass: n equals given mass divided by molar mass. Then particles equal n times the Avogadro number. For a gas at STP, volume equals n times 22.4 litres per mole. Example: 18 grams of water. Water's molar mass is 18 grams per mole, so n equals 18 divided by 18: 1 mole. Molecules equal 1 times 6.022×10^23: 6.022×10^23 water molecules. So why is it called a mole? Because one mole is 6.022×10^23 particles; molar mass converts that count to grams, and 22.4 litres converts it to gas volume only at STP.