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 =
where, M2 is the molar mass of solute.
Mass of solvent = W1 g =
3. The molality is expressed as,
4. Substituting equation (2) in equation (1), we get,