Chemistry
posted by Matt on .
A mixture of C3H8 and C2H2 has a mass of 2.3g . It is burned in excess O2 to form a mixture of water and carbon dioxide that contains 1.6 times as many moles of CO2 as of water. What is the mass of C2H2 in the original mixture?

C3H8 + 5O2 ==> 3CO2 + 4H2O
2C2H2 + 3O2 ==> 4CO + 2H2O
Two equations and two unknowns. Solve simultaneously.
Let x = mass C3H8
and y = mass C2H2

The first equation is x + y = 2.3g
The second equation is more difficult to write on this board. In simple form equation 2 is
mols CO2 = 1.6*mols H2O
Substitute the below for mols CO2 and mols H2O
mols CO2 from C3H8 and C2H2 = [(3x/44) + (2y/26)] where 44 is molar mass C3H8 and 26 is molar mass C2H2.
mols H2O = [(4x/44) + (y/26)]
Post your work if you get stuck.