Moles and molar mass

The mole connects particle counts with laboratory masses. Molar mass tells you the mass of one mole of a substance. To find an amount in moles, divide mass by molar mass, using consistent units. Water has a molar mass of approximately 18 grams per mole. A 36-gram sample therefore contains about two moles of water. This does not mean two molecules: each mole contains an enormous number of molecules.