Question

The freezing point of ethanol is –114.6 oC. The molal freezing point depression constant for ethanol is 2.00 oC/m. What is the freezing point (oC) of a solution prepared by dissolving 170.0 g of glycerin (C3H8O3, a nonelectrolyte) in 250 g of ethanol?

Answer 1

$∆T_f=K_fm$

Given : $K_f= 2°C/m; T_f=-114.6°C$ (actual freezing point)

m=moles of solute /mass of solvent

$m=170/(0.25*92)=7.3913molal$

$∆T_f=7.3913*2=14.7826°C$

Thus apparent freezing point is

$T_f'=T_f-14.7826=-128.8426°C$