Question

A 12 gram mixture of methane, CH4, and ethane, C2H6, is completely conbusted in oxygen. If the total mass of CO2 produced is 34.2 grams, what was the approximate mass of the methane in the original mixture?

Answer 1

burning reaction of these alkanes:
CH4 + 2O2 -> CO2 + 2H2O
x mole ------> x mole => from this eq. mass of CH4 m(CH4) = 16x and m(CO2) = 44x
C2H6 + 7/2O2 -> 2CO2 + 3H2O
y mole--------> 2y mole ---> from this eq. m(C2H6) = 30x and m(CO2) = 44*2y = 88y
m(CH4) + m(C2H6) = 12
m1(CO2) + m2(CO2) = 34.2
16x + 30y = 12
44x + 88y = 34.2
solving this equation we find m(CH4) ~ 5.46 g