Cryoscopic constant
The cryoscopic constant (from cryoscopy , see below) is a measured variable from physical chemistry . It indicates the temperature (in Kelvin ) by which the melting point of a solution is reduced compared to that of the pure solvent (melting point or freezing point lowering ) when 1 mol of a non- volatile substance is dissolved in 1 kg of the pure solvent.
The cryoscopic constant can be calculated using the following formula:
- : molar mass of the solvent
- : universal gas constant
- : Melting temperature at a given pressure
- : molar enthalpy of fusion
Some values
solvent | Freezing point in ° C | Cryoscopic constant in K kg / mol |
---|---|---|
water | 0 | −1.853 |
naphthalene | 80.2 | −6.80 |
chloroform | −63.5 | −4.68 |
benzene | 5.5 | −5.12 |
Camphor | 179 | −39.7 |
Ethanol | −114.6 | −1.99 |
Cyclohexane | 6.4 | −20.2 |
Carbon tetrachloride | −23 | −30 |
application
The cryoscopic constant can be used to determine the molar mass of a soluble substance from the depression of the freezing point by cryoscopy (for example according to Beckmann using a Beckmann thermometer ).
See also
Individual evidence
- ^ Gordon Aylward, Tristan Findlay: SI Chemical Data , Sweden, John Wiley & Sons, 2002, 5th edition, ISBN 0-470-80044-5 .
- ↑ Otto-Albrecht Neumüller (Ed.): Römpps Chemie-Lexikon. Volume 4: M-Pk. 8th revised and expanded edition. Franckh'sche Verlagshandlung, Stuttgart 1985, ISBN 3-440-04514-5 , pp. 2650-2651.