Papa Smurf's Chemistry Lessons

Calculation Of Empirical And Molecular Formulae :) 

 The empirical formula of a compound shows the simplest whole - number ratio of the elements present. For many simple compounds it is the same as the molecular formula. The molecular formula shows the total number of atoms of each element present in a molecule of the compund. Some examples are shown below:

Compund                    Empirical formula                 Molecular formula                                                                                                                           

Water                              H2O                                        H2O

Methane                           CH4                                        CH4

Butane                             C2H5                                      C4H10

Benzene                            CH                                        C6H6

Worked examples:

Write down the empirical formulae of the following:

a) hexane, C6H14

b) hydrogen peroxide, H2O2.

To work out the empirical formulae of hexane, you need to look at the number of each element that is present. There are 6 carbon atoms and 14 hydrogen atoms. You need to look for a number that the 6 and 14 can divide into. In this case, both number can be divided by 2. So when you divide both number by 2, you will get 3 and 7. This means that the empirical formula will be C3H7.

To work out the empirical formula of hydrogen peroxide, you need to do the exact same thing as you have done in the example above. In this case, there are two atoms of hydrogen and two atoms of oxygen. Because the two numbers are the same you can write the empirical formula as HO.