Question

Determine the freezing point depression of a solution that contains 30.7 g glycerin (C3H8O3, molar mass = 92.09 g/mol) in 376 mL of water. Some possibly useful constants for water are Kf = 1.86°C/m and Kb = 0.512°C/m.

A) -3.33°C

B) 0.887°C

C) -1.65°C

D) 3.33°C

E) 0.654°C

Answer 1

number of moles ofglycerin = 30.7 g / 92.09 g/mol
= 0.333
density of water = 1 g /cc
? mass of solvent(water) = 36 g
molality of solution = 0.333 * 1000 /376g
= 0.885 m

freezingpoint of water = 0oC
let thefreezing point of solution = Tf
? depression in freezing point ?Tf =0oC -Tf
?Tf = Kf * molality
0oC -Tf = 1.86 oC /m * 0.885m

? freezing point of solution = Tf = - 1.65oC