The temperature at which a solution freezes and boils depends on the freezing an

Question

The temperature at which a solution freezes and boils depends on the freezing and boiling points of the pure solvent as well as on the molal concentration of particles (molecules and ions) in the solution. For nonvolatile solutes, the boiling point of the solution is higher than that of the pure solvent and the freezing point is lower. The change in the boiling for a solution, Tb, can be calculated as

Tb=Kbm

in which m is the molality of the solution and Kb is the molal boiling-point-elevation constant for the solvent. The freezing-point depression, Tf, can be calculated in a similar manner:

Tf=Kfm

in which m is the molality of the solution and Kf is the molal freezing-point-depression constant for the solvent.

Part A

Cyclohexane has a freezing point of 6.50 C and a Kf of 20.0 C/m. What is the freezing point of a solution made by dissolving 0.463 g of biphenyl (C12H10) in 25.0 g of cyclohexane?

Part B

Paradichlorobenzene, C6H4Cl2, is a component of mothballs. A solution of 2.00 g in 22.5 g of cyclohexane boils at 82.39 C. The boiling point of pure cyclohexane is 80.70 C. Calculate Kb for cyclohexane.

Explanation / Answer

The temperature at which a solution freezes and boils depends on the freezing an

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