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Molar mass is defined as the mass of one mole of a substance. The molar mass of a compound is equal to the sum of the relative atomic masses of its constituents expressed in g mol-1.

The molecular weight is very commonly used as a synonym of molar mass, particularly for molecular compounds; however, the most authoritative sources define it differently (see molecular mass).

The formula weight is a synonym of molar mass that is frequently used for non-molecular compounds, such as ionic salts.


  •   relative atomic mass of one hydrogen atom = 1.008 u
  • molar mass  of hydrogen atom = 1.008 g mol-1
  •   relative  molecular mass  of glucose = 180 u
  •   molar mass of glucose = 180 g m

To find the molar mass of a compound:

  1. Use the chemical formula to determine the number of each type of atom present in the compound.
  2. Multiply the atomic weight (from the periodic table) of each element by the number of atoms of that element present in the compound.
  3. Add it all together and put units of grams/mole after the number.

Molar Mass Formula

Molar mass is the mass of one mole of a substance. The mass will be represented in grams while a mole of a substance is defined as 6.02 x 1023 representative particles (Avogadro’s number) of that substance.

Example :  Calculate the molar mass of a substance if 0.235 moles has a mass of 45.67 grams.




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