How would you find the molecular formula from the empirical formula?

1 Answer


You will need to know the empirical formula and the molar mass in order to do this.


Let's say you have a compound which contains nitrogen and oxygen.

Experimental evidence reveals that the ratio of nitrogen to oxygen is 1:2, so the empirical formula would be #NO_2#.

The mass of #NO_2# would be 14 + 16 + 16 = 46g/mol. I'm using the molar mass of nitrogen (14g/mol) and oxygen (16g/mol) to figure this out.

If additional experimental evidence reveals that the molar mass of the same compound is 92g/mol you would need to multiply the empirical formula by 2 to get the molar mass of the compound.

2(14 + 16 + 16) = 92

Doubling the empirical formula will give a molecular formula of #N_2O_4#.

Here is another example:

Video from: Noel Pauller

Hope this helps!