1. Calculation of Molecular Formula
May/Caiafa
Calculation of Molecular Formula
May/Caiafa’06
This calculation uses the molecular mass and
the empirical formula for a compound.
Determine the empirical mass.
Divide the molecular mass by the empirical mass. After this division you will have a number that:
Is the ratio of the molecular to empirical formula; for example if the # is 2 then the molecular formula would be double the empirical formula.
Will be multiplied by the subscripts of the empirical formula to get the true or molecular formula
Multiply all of the subscripts by the whole number from step 2.

2. Calculation of Molecular Formula
May/Caiafa
Calculation of Molecular Formula
A compound has an empirical formula of C4H4O
and a molar mass of 136 grams per mole.
What is the molecular formula.
Empirical Mass
C4H4O = 4(12.01) + 4(1.008) =
136/68.07 = 2
Ratio of molecular to empirical
C4x2 H4x2 O1x2
= C8 H8 O2
Molecular Formula