Calculate the freezing ?

Question

Calculate the freezing depresion constant if foming a 0.445 m solution fo para-dichlorobenzene in cyclohexane provokes the FP of cyclohexane to change from 6.65 to -2.13 deg. C. Remember to use absolute value of the freezing temperature difference. Units: deg.C/m

Answer 1

Freezing point depression is given by:

ΔTf = Kf ∙ i ∙ m

with

Kf cryoscopic constant of solvent, i van't Hoff factor of solute, m molality of solute. In non-polar solutes like this one solute doe not dissociate, hence van't Hoff factor is equal to one.

Solve for the cryoscopic constant of cyclohexane is:

Kf = ΔTf / ( i ∙ m)

= (6.65°C - (2.13°C) / ( 1 ∙ 0.445m)

= 19.73°C/m