Molmasse

Molmasse, or molar mass, is the mass of one mole of a substance. It is expressed in grams per mole (g/mol) and corresponds to the sum of the atomic masses of all atoms in the chemical formula, each multiplied by its number of occurrences in the formula.

Calculation is done by M = sum(n_i × M_i), where n_i is the number of atoms of element i in the formula and M_i is the atomic mass of that element. For example, water (H2O) has M = 2×1.008 + 15.999 ≈ 18.015 g/mol. Glucose (C6H12O6) has M ≈ 6×12.011 + 12×1.008 + 6×16.00 ≈ 180.156 g/mol.

Molarmass is distinct from the older concept molecular weight. Molecular weight is a dimensionless ratio relative to 1/12 of carbon-12, whereas molar mass is the mass per mole and is given in g/mol. In practice, standard atomic weights on the periodic table are used to obtain approximate molar masses for compounds; for precise work, isotopic masses or the exact isotopic composition may be required.

Hydrates and ionic compounds are treated by including all components in the formula. Water of crystallization increases the molar mass of a hydrate, and the mass of ions contributes to the molar mass of salts.

Applications include converting between mass and amount: m (grams) = n (moles) × M (g/mol). Molar mass is essential in stoichiometry, solution preparation, and various calculations in chemistry.