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Saturday, September 27, 2014

Empirical and Molecular Formula Problems, 4

Category: Chemical Engineering Math

"Published in Vacaville, California, USA"

The tip of the head of a strike anywhere match contains a phosphorus-sulfur compound that readily ignites when drawn over a rough surface. What is the empirical formula of this ignitable compound given that a sample of the compound contains 0.5629 g of phosphorus and 0.4371 g of sulfur? 
(Molecular Weights: P = 31, and S = 32)

Solution:

Moles of each components:

         Moles of phosphorus is 



         Moles of sulfur is 


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



         Number of sulfur in a sample is


Since the number of atoms for phosphorus is a fraction which is 4/3, then we need to multiply all the atoms by 3 so that the number of atoms for empirical formula are all whole numbers. Therefore, the empirical formula for a strike anywhere match is