The molecular mass of a substance expressed in gram is called the gram-molecular mass of the substance.
or
It is also defined as mass of 6.022 x 1023 molecules.
or
It is also defined as the mass of 1 mole molecules.
For Examples for ‘O2’ molecule:
Molecular mass of ‘O2’ = mass of one ‘O2’ molecule
= 2 × mass of one ‘O’ atom = 2 × 16 amu = 32 amu
Gram molecular mass = mass of 6.022 × 1023 ‘O2’ molecules
= 32 amu × 6.022 × 1023
= 32 × 1.66 × 10-24 gm × 6.022 × 1023 = 32 gm/mole
