Question

A chemistry student needs to determine the percent composition of nitrogen (N) in a sample of an unknown organic compound. Using elemental analysis, the student determines the mass of the sample to be 0.254 g and the mass of the products after combustion to be 0.727 g of CO2 and 0.298 g of H2O. What is the percent composition of nitrogen in the sample?

Answer 1

To determine the percent composition of nitrogen in the sample, we first need to find the mass of carbon  C  and hydrogen  H  in the sample. We can do this by using the masses of CO2 and H2O produced after combustion.1. Find the mass of carbon in the sample:The molecular weight of CO2 is 12.01 g/mol  C  + 2 * 16.00 g/mol  O  = 44.01 g/mol.The mass of carbon in the CO2 produced is  0.727 g CO2  *  12.01 g C / 44.01 g CO2  = 0.198 g C.2. Find the mass of hydrogen in the sample:The molecular weight of H2O is 2 * 1.01 g/mol  H  + 16.00 g/mol  O  = 18.02 g/mol.The mass of hydrogen in the H2O produced is  0.298 g H2O  *  2.02 g H / 18.02 g H2O  = 0.033 g H.3. Find the mass of nitrogen in the sample:The mass of the sample is the sum of the masses of carbon, hydrogen, and nitrogen.Mass of nitrogen = Mass of sample - Mass of carbon - Mass of hydrogenMass of nitrogen = 0.254 g - 0.198 g - 0.033 g = 0.023 g N.4. Calculate the percent composition of nitrogen in the sample:Percent composition of nitrogen =  Mass of nitrogen / Mass of sample  * 100%Percent composition of nitrogen =  0.023 g N / 0.254 g sample  * 100% = 9.06%The percent composition of nitrogen in the sample is 9.06%.