What is the freezing point of 0.200 m lactose in ethanol?
K_f(ethanol) = 1.99 ° C/ m and freezing temperature of ethanol = - 117.3 ° C

Question

What is the freezing point of 0.200 m lactose in ethanol? K_f(ethanol) = 1.99 ° C/ m and freezing temperature of ethanol = - 117.3 ° C

Quizplus · Accepted Answer

The freezing point depression is calculated using the formula ΔTf = i * Kf * m, where ΔTf is the change in freezing point, i is the van't Hoff factor (which is 1 for non-electrolytes like lactose), Kf is the cryoscopic constant of the solvent (1.99 °C/m for ethanol), and m is the molality of the solution (0.200 m). Thus, ΔTf = 1 * 1.99 °C/m * 0.200 m = 0.398 °C. The freezing point of the solution is then the freezing point of pure ethanol (-117.3 °C) minus ΔTf, which equals -117.3 °C - 0.398 °C = -117.698 °C, rounded to -117.7 °C.

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