CALCULATIONS
BASED ON FORMULAE
7.9 - From Empirical Formula to Molecular Formula
Is the empirical formula of a compound
the same as the molecular formula?
For example,
- The molecular
formula of water is H2O. Since the ratio of H to O is 2:1,
it is also a simplest whole-number ratio. In
this case, the molecular formula is also the empircal formula of water.
- The molecular
formula of hydrogen peroxide is H2O2. The simplest
whole-number ratio of H to O is 1:1. Therefore, the empirical formula
of hydrogen peroxide is HO. In this case, the empirical formula is different
from the molecular formula.
- The molecular
formula of benzene is C6H6. The simplest
whole-number ratio of C to H is 1:1, therefore, the empirical formula
of hexane is CH. In this case, the empirical formula is different from the
molecular formula.
Summary:
- In example 1, the empirical formula of water is the
same as its true chemical formula or molecular formula.
- In example 2, the empirical formula of hydrogen peroxide is
NOT the same as its true chemical formula or molecular formula.
- In example 3, the empirical formula of benzene is
NOT the same as its true chemical formula or molecular formula.
From the three examples above, we see that:
- for water, the empirical formula IS
the molecular formula.
- for hydrogen peroxide and benzene,
the empirical formula is NOT the molecular formula.
