What is the freezing point of a 0.285 m solution of urea dissolved in Ethanol?
K_f(ethanol) = 1.99 ° C/ m and T_{f, ethanol} = - 117.3 ° C

Question

What is the freezing point of a 0.285 m solution of urea dissolved in Ethanol? K_f(ethanol) = 1.99 ° C/ m and T_{f, ethanol} = - 117.3 ° C

Quizplus · Accepted Answer

The freezing point depression (ΔTf) of a solution is given by the formula: ΔTf = Kf · m · i where Kf is the freezing point depression constant of the solvent, m is the molality of the solution (moles of solute per kilogram of solvent), and i is the van't Hoff factor, which represents the number of particles into which the solute dissociates (1 for urea in this case, because it does not dissociate in ethanol). Substituting the given values, we get: ΔTf = (1.99 °C/m) · (0.285 m) · (1) = 0.56655 °C (rounded to 5 decimal places) Therefore, the freezing point of the solution is: Tf = T_{f, ethanol} - ΔTf = (-117.3 °C) - (0.56655 °C) ≈ -117.87 °C The best choice is B because it is closest to this value. A is too low, C is too high, and D and E are not even negative, so they are clearly wrong.

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