Benzene freezing point depression constant

Pure benzene freezes at 5.50°C and has a density of 0.876 g/mL. A solution of 1.7 g of nitrobenzene in 250 mL benzene freezes at 5.18°C. What is the molality-based freezing-point depression constant of benzene and at what temperature does a solution containing 3.2 g of bromobenzene in 250 mL of benzene freeze (You may make the ideally dilute approximation for both these solutions.)... 

The freezing point depression constant for cyclohexane is 20.3, which is very high when compared to the 1.86 for water. You need 20-30 mL of pure material in order to make several measurements, and all you have available is some technical-grade material that was prepared by catalytic hydrogenation. You are to do an extractive distillation to remove the benzene impurity. 

Here Ky is the freezing-point-depression constant and depends only on the solvent. Table 12.3 gives values of Ky for some solvents. The freezing-point-depression constant for benzene is 5.07°C/m. Thus a 0.100 m solution freezes at 0.507°C below the freezing point of pure benzene. Pure benzene freezes at 5.46°C the freezing point of the solution is 5.46°C - 0.507°C = 4.95°C. 

---