Molar mass is the mass of 1 mole of any specified chemical compounds. The molar mass of a chemical compound equals to the sum of the molar masses of all the atoms in one molecule of that compound.If there is any subscript in a chemical formula, then multiply the number of atoms of anything next to that subscript by the number of the subscript. Let's say if you are looking for molar mass of NaCO₃, you have one atom of Sodium (Na), one atom of Carbon (C) and 3 atoms of Oxygen (O) The molar mass of NaCO₃ will be equal to (1 x 22.99 g/mol Na) + (1 x 12.01 g/mol C) + (3 x 16.00 g/mol O) = 83.00 g/mol