Calculating the Empirical Formula of Organic Compound

Today we've learned how to calculating the empirical formula of organic compound, well, it is sort of complicated, but if you follow step by step you will find out it is not hard at all !!

So, to get started, lets know what is an organic compound.
-An organic compound is any member of a large class of gaseous, liquid, or solid chemical compounds whose molecules contain carbon.

The empirical formula of an organic compound can be found by:
-Burning the compound
-Collecting and weighing the products
-From the mass of the products, the moles of each element in the original organic compound can be calculated


Ex. What is the empirical formula of a compound that when a 5.00 g sample is burned produces 15.0 g of CO2 and 8.18 g of H2O?

First let the empirical formula of the compound be CxHy
CxHy  +  z  O2  =  x  CO2  + y/2  H2O

We want to find x and y (the simplest ration of the atoms or moles of the elements).
From the equation above, we can see that ALL of the C and the H in CxHy went into making x CO2 and y/2 H2O

mol CO2  = 15.0 g CO2  x 1 mol CO2 / 44.0 g CO2 = 0.341 mol
mol H2O =8.18 g H2O x 1 mol H2O / 18.02 g H2O = 0.454 mol

0.454 moles of water and 0.341 moles of Carbon dioxide were produced

mol C = 0.341 mol CO2 x 1 mol C / 1 mol CO2 = 0.341 mol  C
mol H = 0.454 mol H2O x 2 mol H / 1 mol H2O = 0.908 mol H 

Divide both by the smallest molar amount 

Carbon  0.341 / 0.341 = 1
Hydrogen  0.908 / 0.341 = 2.66


Scale ratio to whole numbers


2.66 x 3 = 8  H
0.341 x 3 = 3  C


   C3H8