From Big Medical Encyclopedia

KRIOMETRIYA (grech, kryos cold + metreo to measure, measure; synonym krioskopiya) — definition of a difference between temperature of freezing of pure solvent and temperature of freezing of solution of any substance in this solvent. Determination of size, on to-ruyu increases temperature of boiling of solutions in comparison with temperature of boiling of pure solvent, is called ebulliometriya (see). To. the pier is used for definition. scales of nonelectrolytes, extent of dissociation of weak electrolytes (see) and osmotic pressure (see) solutions. In a wedge, diagnostic testings To. it was applied in nefrol, to practice, however now the method lost the diagnostic value and is used generally in medical - biol, researches during the studying physical. - chemical properties biol, liquids (e.g., their concentration), and also for definition of purity of pharmaceuticals.

The size of observed temperature difference of freezing is called a depression and designated grech, a letter Δ; Δ = t0 — t, where t0 — temperature of freezing of pure solvent, a t — temperature of freezing of solution. The size of a depression is connected with concentration of molecules of solute (in the absence of electrolytic dissociation):

Δ = k • m,

where m — the molal concentration, i.e. the concentration expressed by number of moths of solute in 1000 of solvent, and k — the coefficient of proportionality called by a molar depression or the cryoscopic constant. Dependence of a depression on the molal concentration of solution carries the name of the Raoult's law. Each solvent is characterized by a certain size k. E.g., for water k it is equal — 1,853 °; therefore, the solution containing 1 mol of a nonelectrolyte in 1000 ml of water will freeze at — 1,853 ° (pure water freezes, as we know, at 0 °). The size of a depression depends only on number of the dissolved particles, but not on their nature therefore at equal molal concentration the depression of solution of electrolyte (Δэ) owing to dissociation will be more, than a depression of solution of a nonelectrolyte (Δ):

Δэ = Δ [α (n — 1) + 1],

where α — extent of electrolytic dissociation, n — number of the ions which are formed at dissociation. Between a depression of the diluted solution and its osmotic pressure there is a ratio

of p= (Δ/k) RT

where p — osmotic pressure in atm, R — the universal gas constant equal 82,05•10 - 3 atm/hail • mol; T — absolute temperature.

The device for cryometric researches was offered it. chemist Bekmann (E. O. Beckmann).

Bibliography Galinker I. S. and Medvedev P. I. Physical and colloid chemistry, M., 1972.

L. M. Ginodman.