Molar mass is defined as the
mass of a given substance (
chemical element or
chemical compound) divided by its
amount of substance. It is a physical property of a given substance. The base
SI unit for molar mass is
One mole of hydrogen atoms has a mass of 1.008 g and 1 mol of oxygen atoms has a mass of 16.00 g, so 1 mol of water has a mass of (2 x 1.008 g) + 16.00 g = 18.02 g. The molar mass of water is 18.02 g/mol.
In general, the molar mass of any molecular compound is the mass in grams numerically equivalent to the sum of the atomic masses of the atoms in the molecular formula:
The formula mass of methane, CH4, is 12.01 + (1.008 x 4) = 16.04 u and its molar mass is 16.04 g/mol.