Obtain the relationship between freezing point depression of a solution containing nonvolatile-nonelectrolyte solute and its molar mass. - Chemistry

Exercise | Q 6 | Page 46

Obtain the relationship between freezing point depression of a solution containing nonvolatile-nonelectrolyte solute and its molar mass.

Solution:



1. The freezing point depression (ΔTf) is directly proportional to the molality of solution.

Thus, ΔTf = Kf m         ….(1)

2. Suppose we prepare a solution by dissolving W2 g of solute in W1 g of solvent.

Moles of solute in W1 g of solvent = W2M2

where, M2 is the molar mass of solute.

Mass of solvent = W1 g = W1g100g/kg=W11000 kg

3. The molality is expressed as,

m = Moles of soluteMass of solvent in kg

m = W2/M2 molW1/1000kg

m = 1000W2M2W1mol kg-1    ....(2)

4. Substituting equation (2) in equation (1), we get,

Tf=1000KfW2M2W1

Hence,

M2=1000KfW2TfW1