Can an empirical formula ever be a molecular formula?

1 Answer
May 25, 2014

Yes, it can.

In chemistry, the empirical formula of a chemical compound is the simplest positive integer ratio of atoms present in a compound. A simple example of this concept is that the empirical formula of hydrogen peroxide, or H2O2, would simply be HO. An example of a molucule whose empirical formula is also its molecular formula is methane: #CH_4#.

In contrast to empirical formula the molecular formula identifies the number of each type of atom in a molecule, and the structural formula also shows the structure of the molecule. Different compounds can have the same empirical formula. Different compounds can even have the same molecular formula, but different structural formulas. In that case the two substances are said to be isomers.

An example is propanol and methoxyethane:
Propanol and methoxyethane from
These structural formulas all have the same molecular formula #C_3H_8O# ( or #C_3H_7OH#), and the same empirical formula, but different structural formulas. The first two are propan-1-ol and propan-2-ol (also called isopropyl alchohol, or rubbing alcohol), The third molecule is another arrangement of #C_3H_8O# called methoxyethane. This third molecule is not even an alcohol like the other two, it is an ether.