Question

The freezing point of pure benzene is 5.49 °C. The freezing point of a solution made using toluene in benzene is determined to be - 13.0 °C, What is the molality of the toluene? (Kf benzene = 5.12 °C/m)

a) 1.42 mol/kg
b) 0.98 mol/kg
c) 2.31 mol/kg
d) 1.05 mol/kg

Answer 1

The molality of the toluene in the solution is 2.54 mol/kg.

Step-by-step explanation:

To find the molality of toluene in the solution, we need to use the freezing point depression formula:

ΔTf = Kf · m

Where ΔTf is the change in freezing point, Kf is the freezing point depression constant for benzene, and m is the molality of the toluene.

Given ΔTf = -13.0 °C and Kf = 5.12 °C/m, we can solve for m:

m = ΔTf / Kf = -13.0 °C / 5.12 °C/m = -2.54 m

Since molality cannot be negative, the value of m is actually 2.54 m (the negative sign is not used in molality).

Therefore, the molality of the toluene in the solution is 2.54 mol/kg, which is closest to the answer choice c) 2.31 mol/kg.