Cryoscopy

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.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

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 Δt_c = E_c ⋅ n exists, where Δt_c is the lowering of the freezing point of the solution in degrees Celsius and n is the concentration of the solution. The coefficient E_c is called the cryoscopic constant of the solvent. The values of E_c 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 E_c is known, the molecular weight M of the substance may be calculated from the equation M = P₁ ⋅ E_c ⋅ 1,000/P₂ ⋅ Δt_c , where P₁ and P₂ are the weights of the solute and the solvent, respectively, in grams. The temperature difference Δt_c is usually measured with a metastatic thermometer or a thermocouple. The cryoscopic method may be used for the determination of the values of E_c 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.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.