Freezing-point depression describes the process in which adding a solute to a solvent decreases the freezing point of the solvent. freezing-point depression can be used to measure the degree of dissociation or the molar mass of the solute. This kind of measurement is called cryoscopy and relies on exact measurement of the freezing point. Cryoscopic constant relates molality to freezing point depression in a solvent. Through cryoscopy, a known constant can be used to calculate an unknown molar mass. Freezing point depression is a colligative property, so the change of the temperature depends only on the number of solute particles dissolved, not the nature of those particles. Cryoscopy is related to ebullioscopy, which determines the same value from the ebullioscopic constant (of boiling point elevation).
The Kf for water is 1.853 K·kg/mol.Related formulas
|Kf||Cryoscopic constant (K*kg/mol)|
|R||molar gas constant|
|Tf||Freezing point (K)|
|Lv||Enthalpy of fusion per gram (J/kg)|