Question

The molal freezing point constant(Kf) for acetic acid is 3.90 C/m. When 31.5 grams of unknown solute is dissolved in 650 grams of acid the freezing point is lowered by 0.79 what is the molar mass
We must assume this is a non-volatile, non-ionizable solute.
delta T = Kf*m
Substitute and solve for m

m = mols/kg solvent
Substitute and solve for mols.

Then mols = grams/molar mass. You know grams and mols; solve for molar mass.

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