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Elemental Analysis. Percentages of carbon, hydrogen and oxygen from combustion. Combustion. Whenever a hydrocarbon burns, CO 2 and H 2 O are formed. CH 4 + O 2 g CO 2 + H 2 O All of the carbon was transferred to carbon dioxide All of the hydrogen was transferred to water.
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Elemental Analysis Percentages of carbon, hydrogen and oxygen from combustion
Combustion • Whenever a hydrocarbon burns, CO2 and H2O are formed. • CH4 + O2g CO2 + H2O • All of the carbon was transferred to carbon dioxide • All of the hydrogen was transferred to water
Using mass of products • Knowing how much CO2 and H2O was created, it is then possible to determine the mass of C and H in the hydrocarbon. • From mass, mass % may be found • Knowing %C and %H, the % of O may be determined by subtracting the others from 100%
Example • Acetic acid contains only C, H and O. A 4.24 mg sample of acetic acid is completely burned. It gives 6.21 mg of CO2 and 2.54 mg of H2O. What is the mass percentage of each element in acetic acid? • Do stoich to calculate mass of C. 6.21 mg CO2 | 1 mol CO2 | 1 mol C | 12 g C = 1.69mgC | 44 g CO2 | 1 mol CO2 | 1 mol C • Do stoich to calculate mass of H. 2.54 mg H2O | 1 mol H2O | 2 mol H | 1 g H = 0.285mgH | 44 g H2O | 1 mol H2O| 1 mol H • Find %. 1.69/4.24 = 39.9% C and 0.285/4.24 = 6.72% H Therefore 100 – 39.9 – 6.72 = 53.4% O
