Posted by Matt on Saturday, October 19, 2013 at 5:11pm.
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?

Chemistry  DrBob222, Saturday, October 19, 2013 at 8:43pm
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.