A 13.03 g sample contains only ethylene glycol (C2H6O2) and propylene glycol (C3H8O2). When the sample is added to 100.0g of pure water, the resulting solution has a freezing point of -3.5C. What is the percent composition of ethylene glycol and propylene glycol in the original sample?

Answer 1

delta T = Kf*m
Solve for m

m = moles/kg solvent
Solve for moles.

moles = grams/molar mass
Solve for molar mass.

Then let X = fraction of C2H6O2
and 1-X = fraction of C3H8O2
--------------------------
X(molar mass C2H6O2) + (1-x)(molar mass C3H8O2) = molar mass of the mixture.
Then convert X to percent and 1-X to percent. I think the answer is about 48% and 52% respectively but these are approximations.Post your work if you get stuck.