Pure benzene, C₆H₆, freezes at 5.5° and boils at 80.1°C. What is the boiling point of a solution consisting of cyclohexane (C₆H₁₂)dissolved in benzene if the freezing point of this solution is 0.0°C? (For benzene, K_f = 5.12 °C/m, K_b = 2.53 °C/m; for cyclohexane, K_f = 20.0 °C/m, K_b = 2.79°C/m) A)82.8°C B)91.2°C C)80.9°C D)77.4°C E)83.1°C

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Quizplus · Accepted Answer

The freezing point depression is used to find the molality of the solution: ΔTf = Kf * m. With ΔTf = 5.5°C (5.5°C - 0.0°C) and Kf = 5.12°C/m for benzene, m = 5.5 / 5.12 = 1.074 m. The boiling point elevation is then calculated: ΔTb = Kb * m = 2.53°C/m * 1.074 m = 2.72°C. Adding this to the normal boiling point of benzene (80.1°C), the boiling point of the solution is 82.8°C.

Pure Benzene, C6H6, Freezes at 5

Pure Benzene, C₆H₆, Freezes at 5