Many substances consist of Molecules. A molecule consists of a small number of atoms joined together by covalent bonds.
The Molecular Formula shows all the atoms of each element contained in one molecule.
Empirical Formula shows the simplest ratio of the different types of elements present in a molecule.
For example, Butane has Molecular Formula of C4H10 and Empirical Formula of C2H5.
As such, Molecular Formula is a simple multiple of the Empirical Formula:
Molecular Formula = n X Empirical Formula
where n = 1, 2, 3, etc
The molecular formula can be calculated from:
- Empirical Formula (we have discussed how to obtain it)
- Relative Molecular Mass, Mr of Compound
Let’s take a look at an example.
Glucose has empirical formula CH2O and relative molecular mass of 180. Find the molecular formula of glucose.
(given: H = 1.0; C = 12.0; O = 16.0)
Relative mass of Empirical Formula, CH2O = 12 + 2(1) + 16 = 30
Relative molecular mass = n X relative mass of the empirical formula
thus, n = Relative molecular mass / relative mass of the empirical formula
= 180 / 30 = 6
Therefore, Molecular Formula of Glucose = 6 X CH2O = C6H12O6
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