A technician for the Ethanol-in-Octane fuel company was testing a mixture of ethanol and octane as a synthetic fuel. Combustion of a sample of this mixture of ethanol and octane (in the presence of excess oxygen) produced 208.09 g of water and 439.34 g of carbon dioxide. Determine the mass percent ethanol in the sample used for the analysis. (The technician forgot to record the mass of the sample used in the analysis. Because he knows the mass of water produced and the mass of CO2 produced he does not need the mass of the sample.) The balanced equations for the combustion of ethanol and octane are shown below.
ethanol 1C2H5OH + 3O2 → 2CO2 + 3H2O octane 2C8H18 +25O2 →16CO2 +18H2O
C2H5OH molar mass 46.07 C8H18 molar mass 114.22 H2O molar mass 18.02 CO2 molar mass 44.01