The freezing point of pure chloroform is -63.5°c, and its freezing point depression constant is 4.07°c•kg/mol. if the freezing point of a solution of benzoic acid in chloroform is -70.55°c, what is the molality of this solution? a.0.58 m b.1.7 m c.16 m d.17 m

Data:

Tf = - 63.5 °C
Kf = 4.07 °C .kg /mol
ΔTf = -63.5°C - (-70.55°C) = 7.05

Formula:

ΔTf = Kf * m => m = ΔTf / Kf

Solution:

m = 7.05°C / 4.07 °C . kg/mol = 1.7 mol / kg = 1.7 m

Comments: the depression point of a solution is a colligative property which means that it depends on the number of particles disolved, which is measured by the molality. A more general formula for the depression point includes the ionization factor i: ΔTf = i * kf * m. For non-electrolitic solutes i = 1 and ΔTf = kf * m, which is the formula used.

option b. 1.7m