What is Molecular Mass Molecular mass/Formula mass Molecular mass expresses as to how many times a molecule of a substance is heavier than th of the mass of an atom of carbon (carbon-12). Thus, Molecular mass = Molecular mass = 2 × vapour density Example: A molecule of water is 18 times heavier than th of the mass of carbon atom. Therefore, the molecular mass of water is … [Read more...] about What is Molecular Mass