CHAP. 7: PHASE EQUILIBRIA [CONTENTS] 214
s
s
A B
C
C 1
E
F
D
Obr.7.10:Isobaric-isothermal diagram of three component system.
This relation makes it clear that the distribution coefficient generally depends on tem-
perature, pressure and composition; at the critical point (point C 1 in Figure7.10), the
distribution coefficients are equal to 1.
- Extraction, Nernst’s distribution law
Let us have two immiscible liquids, components 1 and 2. In liquid 1, another substance,
component 3, is dissolved. If we add substance 2 to a mixture of substances 1 and 3,
then the transfer of part of the dissolved substance from liquid 1 to liquid 2 is called
extraction. If we choosen 0 to denote the initial amount of the extracted substance,
which is contained in volumeV 1 of solvent 1, andnpto denote the amount of substance
which during extraction passes to solvent 2, whose volume isV 2 , we write
np=n 0
Kc, 3 V 2
V 1 +Kc, 3 V 2
. (7.60)
If the extraction is performedk−times with the same volumeV 2 of pure solvent 2, we
