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29 Nov 2019

A technician for the Ethanol-in-Octane fuel company was testing amixture of ethanol and octane as a synthetic fuel. Combustion of asample of this mixture of ethanol and octane (in the presence ofexcess oxygen) produced 208.09 g of water and 439.34 g of carbondioxide. Determine the mass percent ethanol in the sample used forthe analysis. (The technician forgot to record the mass of thesample used in the analysis. Because he knows the mass of waterproduced and the mass of CO2 produced he does not need the mass ofthe sample.) The balanced equations for the combustion of ethanoland octane are shown below.

ethanol: 1 C2H5OH + 3 O2 -> 2 CO2 + 3 H2O
octane: 2 C8H18 + 25 O2 -> 16 CO2 + 18 H2O

C2H5OH molar mass 46.07; C8H18 molar mass 114.22
H2O molar mass 18.02; CO2 molar mass 44.01

I guess I need to use system of equation to solve thisproblem, but I have no clue how to set up the equation.

P.S The answer is mass percent of ethanol = 13.1%, but I don'tknow why. Please show me the steps, thanks!

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