Post a New Question

chem- molar weight

posted by .

I worked this problem, I would like to know if I did it correctly, I think I missed something, I'm not sure.....


When a 20.0 gram sample of an unknown compound is dissolved in 500 grams of benzene, the freezing pointof the resulting solution was observed to be 3.77 degrees C. If the freezing point of pure benzene is 5.48 degrees C and the Kf fro benzene is 5.12 degrees C/m, calculate the molar mass of the unknown compound.

ÄTf = KfM
Kf for benzene = 5.12 degrees C/m
the normal freezing point = 5.480C
ÄT = (5.48-3.77) = 1.71

1.71 degrees = (5.12 degrees C/m)(20.0g/MW)(5kg of solvent)
MW = 20.48g/mol

Is this correct?

  • chem- molar weight -

    delta T is correct at 1.71 C.
    Then delta T = Kf*m and
    m = molality = 1.71/5.12 = 0.334 mols/kg
    mols = g/MW
    0.334 = 20/MW/0.5 kg or
    0.334 = (20/MW)*(1/0.5kg)
    MW = ??
    I have something like 120 or so. Check my thinking. Check my arithmetic.

  • chem- molar weight -

    ok got it!!!!


    Thanks for clearing it up for me!

Answer This Question

First Name:
School Subject:
Answer:

Related Questions

More Related Questions

Post a New Question