Calculate the freezing point of a solution made by dissolving 3.50 g of potassium chloride (ℳ = 74.55 g/mol) in 100.0 g of water. Assume ideal behavior for the solution; K_f = 1.86°C/m. A)−1.7°C B)−0.9°C C)0.0°C D)0.9°C E)1.7°C

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Quizplus · Accepted Answer

The freezing point depression of the solution can be calculated using the formula ΔTf = i * Kf * m, where ΔTf is the freezing point depression, i is the van't Hoff factor (which is 2 for KCl, since it dissociates into K+ and Cl-), Kf is the molal freezing point depression constant for water (1.86°C/m), and m is the molality of the solution. First, calculate the moles of KCl: moles = 3.50 g / 74.55 g/mol = 0.0469 mol. Then, calculate the molality: molality = moles of solute / kg of solvent = 0.0469 mol / 0.100 kg = 0.469 m. Finally, calculate ΔTf: ΔTf = 2 * 1.86°C/m * 0.469 m = 1.746°C, which rounds to −1.7°C, indicating the freezing point of the solution is −1.7°C.

Calculate the Freezing Point of a Solution Made by Dissolving