Molar mass is the mass of a substance that has 6.022 × 10 atoms (Avogadro's number). The mass number of an element is equal to the molar mass of the element . The molar mass of a chemical compound is the mass when the compound has 6.022 × 10 molecules. It can be found by adding the molar masses of all of its elements. Sodium hydroxide's (NaOH) molar mass can be found by adding the molar mass of sodium, oxygen, and hydrogen, which would be 39.997 g/mol.