Calculate the freezing point of a solution containing 40.0 grams of KCl and 4400.0 grams of water. The molal- freezing- point- depression constant (K_f) for water is 1.86 ° C/m. A) +0.45 ^oC B) - 0.45 ^oC C) - 0.23 ^oC D) 1.23 ^oC E) +0.23 ^oC

Question

Quizplus · Accepted Answer

First, we need to calculate the molality of the solution:

molality = moles of solute / mass of solvent in kg
molality = (40.0 g KCl / 74.55 g/mol) / 4.4 kg water

molality = 0.0197 mol/kg

Next, we use the freezing point depression equation:

ΔTf = Kf * molality

where ΔTf is the change in freezing point, and Kf is the molal freezing point depression constant for water.

ΔTf = (1.86 °C/m) * 0.0197 mol/kg

ΔTf = 0.0367 °C

Since the solution is a KCl-water solution, the freezing point is lower than that of pure water.

freezing point = 0°C - ΔTf

freezing point = 0°C - 0.0367°C

freezing point = -0.0367°C ≈ -0.45°C

Therefore, the freezing point of the solution is about -0.45°C, so the best choice is B, -0.45°C.

Calculate the Freezing Point of a Solution Containing 40