Cryoscopy

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cryoscopy

[krī′äs·kə‚pē]
(analytical chemistry)
A phase-equilibrium technique to determine molecular weight and other properties of a solute by dissolving it in a liquid solvent and then ascertaining the solvent's freezing point.

Cryoscopy

 

a physicochemical research method based on measurement of the lowering of the freezing point of a solution relative to the freezing point of the pure solvent. Raoult’s law states that, for infinitely dilute solutions (in the absence of electrolytic dissociation), the dependence Δtc = Ecn exists, where Δtc is the lowering of the freezing point of the solution in degrees Celsius and n is the concentration of the solution. The coefficient Ec is called the cryoscopic constant of the solvent. The values of Ec are different for various liquids (for water, 1.86; for benzene, 5.07; for acetic acid, 3.90; for dioxane, 4.63; and for phenol, 7.27 ). If Ec is known, the molecular weight M of the substance may be calculated from the equation M = P1Ec ⋅ 1,000/P2 ⋅ Δtc , where P1 and P2 are the weights of the solute and the solvent, respectively, in grams. The temperature difference Δtc is usually measured with a metastatic thermometer or a thermocouple. The cryoscopic method may be used for the determination of the values of Ec for substances with known molecular weights, as well as concentrations of substances in solution.

REFERENCES

Kireev, V. A. Kratkii kurs fizicheskoi khimii, 4th ed. Moscow, 1969.
Spravochnik khimika, 2nd ed., vol. 3. Moscow-Leningrad, 1964. Page 485.