Question

The freezing point of 53.37 g of a pure solvent is measured to be 49.20 ºC. When 2.74 g of an unknown solute (assume the van 't Hoff factor = 1.0000) is added to the solvent the freezing point is measured to be 47.05 ºC. Answer the following questions ( the freezing point depression constant of the pure solvent is 7.83 ºC·kg solvent/mol solute). What is the molality of the solution? m

Answer 1

The molality of the solution can be calculated using the freezing point depression formula ΔTf = Kf x m. Given the freezing point depression constant (Kf) and the change in freezing point, we can calculate the molality of the solution.

Step-by-step explanation:

The molality of the solution can be calculated using the freezing point depression formula:

ΔTf = Kf x m

We are given that the freezing point depression constant (Kf) of the pure solvent is 7.83 ºC·kg solvent/mol solute. The freezing point of the pure solvent is 49.20 ºC and the freezing point when 2.74 g of the solute is added is 47.05 ºC.

Step 1: Calculate the change in freezing point (ΔTf) by subtracting the freezing point of the solution from the freezing point of the pure solvent: ΔTf = 49.20 ºC - 47.05 ºC = 2.15 ºC

Step 2: Use the freezing point depression formula to calculate the molality (m) of the solution: ΔTf = Kf x m, rearrange the formula to solve for m: m = ΔTf / Kf. Substituting the values: m = 2.15 ºC / (7.83 ºC·kg/mol) = 0.274 mol/kg.