When 0.030 mol HCl dissolves in 100.0 g benzene, the solution freezes at 4.04 °C. When 0.030 mol HCl dissolves in 100.0 g water, the solution freezes at -1.07 °C. Use the data in Table 12.4 to complete the following exercises.

Table 12.4

(a) From the freezing point, calculate the molality of HCl in the benzene solution.

(b) Use the freezing point of the aqueous solution to find the molality of HCl in the water.

(c) Offer an explanation for the different values found in parts a and b.

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TABLE 12.4 Boiling-Point Increases and Freezing-Point Depression Constants for Solvents kb (C/m) 3.07 2.53 Solvent Acetic acid Benzene Naphthalene Water Boiling Point (C) 117.90 80.10 100.00 0.512 Freezing Point (C) 16.60 5.51 80.2 0.00 k (C/m) 3.90 4.90 6.8 1.86