Lab and analysis
Molecular weight (molar mass)
Definition
The mass of one mole of a substance in grams per mole, calculated from its formula and standard atomic weights.
Molecular weight is used to convert between mass and moles, for example when preparing solutions or calculating yields. Water is about 18.02 g/mol and sodium chloride about 58.44 g/mol.
Hydrates have a higher molecular weight than the anhydrous form, so always check which form a price or recipe refers to.