Empirical and Molecular Formula Problems, 3

Category: Chemical Engineering Math

"Published in Vacaville, California, USA"

Analysis of a sample of ibuprofen, the active ingredient of Advil, shows that the sample contains 7.568 g of carbon, 0.881 g of hydrogen, and 1.551 g of oxygen. Use these data to calculate the empirical formula of ibuprofen.

Solution:

Moles of each components:

         Moles of carbon is

         Moles of hydrogen is
 

         
         Moles of oxygen is
 

 

From the number of moles of each component, we need to divide all of them by their least number of moles which is oxygen in order to get the number of atoms in a sample.
  
         Number of carbon in a sample is

         Number of hydrogen in a sample is

         Number of oxygen in a sample is
 

Since the number of atoms for carbon is a fraction which is 6.5, then we need to multiply all the atoms by 2 so that the number of atoms for empirical formula are all whole numbers. Therefore, the empirical formula for ibuprofen is