Question

calculate the freezing point of a solution having 257 grams of naphthalene (C10H8) dissolved in 500 grams of chloroform (CHCl3) Kf CHCl3= 4.70 C/m.

Answer 1

delta Tf = Kf x m

where m= molality

so first calculate the molality

molality m = weight / molar mass   x 1000/ weight of solvent n grams

= 257 / 128.17 x   1000 / 500

= 2 x 2

= 4 m

Kf = 4.7 ºC/m

now put these values in above equation

delta Tf = 4.7 x 4

= 18.8

freezing point of ChCL3 = -63.5 ºC

delta Tf = freezing point of pore chloroform - freezing point of the solution = 18.8

freezing point of the solution = -63.5 ºC -18.8 ºC

= -82.3 ºC