molar mass is the mass of a substance that has 6.022 × 1023 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 × 1023 molecules. molar mass of chlorine is 35.45 due to consideration of avg molar mass by including mass of its all isotopes.