In thermodynamics, the cryoscopic constant, Kf, relates molality to freezing point depression. It is the ratio of the latter to the former:
i is the van 't Hoff factor, the number of particles the solute splits into or forms when dissolved. b is the molality of the solution.
Through cryoscopy, a known constant can be used to calculate an unknown molar mass. The term "cryoscopy" comes from Greek and means "freezing measurement." Freezing point depression is a colligative property, so
The Kf for water is 1.853 K·kg/mol.