Class 9 Chemistry Atoms and Molecules Molar mass

Molar mass

In order to calculate the molar mass of a respective molecule keep the numerical value same as molecular mass but alter the units from u to g.

For instance, molecular mass of water is 18 u.


We know the atomic mass of hydrogen is 1u and that of oxygen is 16u.

  • Molecular mass of H2O containing two hydrogen atoms and single oxygen atom is

2 X 1 + 1 X 16 = 18u

i.e. 18 u of water has 1 molecule of water.

18u water = 18 g water

18g water = 1 mole molecules of water

Or 18g water = 6.022 X 1023 molecules of water

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