The molar mass (M) of a substance is the mass of one mole of its entities (atoms, molecules, ions, or other particles) in units of g/mol M H2O = 18.0 g/mol (one mole of H 2 O molecule weighs 18.0 g) M NO3- = 62.0 g/mol (one mole of NO 3 - ion weighs 62.0 g) M C = g/mol (one mole of C atom weighs g) Brown, T., E.
{}