What is the molecular weight of water?

Molecular mass – the sum of the masses of the atoms that make up a molecule, expressed in atomic mass units. To determine the molecular weight of a molecule (Mr), add the atomic masses of the Ar elements (indicated in the periodic table) that make up the molecule, having previously multiplied them by the number of corresponding atoms.

Mr (H2O) = 2 * Ar (H) + Ar (O) = 2 * 1 + 16 = 18 amu. eat.

It should be remembered: the molecular mass is numerically equal to the molar mass, however, they differ in dimension (a.u. and g / mol).