Question

Hydrocarbon mixtures are used as fuels. What mass of CO₂ gas is produced by the combustion of 281.5 g of a mixture that is 18.4 % CH₄ and 81.6% C₃H₈ by mass?

Answer 1

Mass of CH₄ in 281.5 g of the mixture = 18.4*281.5/100 = 51.796 g

Molar mass of CH₄ = 16 g/mole

thus, moles of CH₄ in 51.796 g of it = 51.796/16 = 3.24 moles

Now, CH₄  + 2O₂  -----------> CO₂ + 2H₂O

Clearly moles of CO₂ produced = moles of CH₄ = 3.24 ................(1)

Now, mass of C₃H₈ in 281.6 g of the mixture = 81.6*281.6 = 229.79 g

Molar mass of C₃H₈ = 44 g/mole

thus, moles of 229.79 g of C₃H₈ = 229.79/44 = 5.2224

Now, C₃H₈ + 5O₂  -------------> 3CO₂  + 4H₂O

Clearly moles of CO₂ produced = 3*moles of C₃H₈ = 15.6672............(2)

Hence total moles of CO₂ proiduced = 3.24 + 15.6672 = 18.9072

molar mass of CO₂ = 44 g/mole

thus, mass of CO₂ produced = 44*18.9072 = 831.92 g