Abstract
The work presented here is divided into two parts, In the first part, the extraction of phosphoric acid with solutions of tri-n-octylamine in benzene has been studied. The distribution data have been quantitatively explained by the formation in the organic phase of two amine phosphate species with, stoichiometries R3N:H3PO4 (amine:phosphoric acid) of 1:1 and 1:2. The apparent equilibrium constants for the formation of organic phase species R3NHH2PO4 and R3NHH2PO4.H3PO4 have been calculated. Linear relationships have been obtained between ln K11and in K12, the apparent equilibrium constants for the formation of a series of salt species with amine:acid ratios 1:1 and 1:2, and In Ka, the dissociation constants of the corresponding acids. The constants obtained in this work successfully fit onto the above straight lines. In the second part, a statistical thermodynamic treatment originally developed for solid ion exchangers has been successfully applied to several uni-univalent anion exchange reactions with tri-n-octylamine hydrochloride, a liquid ion exchanger. From the equilibrium experiments, the thermodynamic equilibrium contstants (ln KTAB ) and hence the standard free energies of exchange (?G° ) have been evaluated. For some uni-univalent reactions, where data were available, a linear correlation has been obtained between the thermodynamic equilibrium constants, for the exchange of different anions with chloride ion, and the difference in the free energies of hydration of chloride ion and the corresponding anion, The aggregation of the amine salts involved has been studied by the vapour pressure lowering method for a, limited range of concentration, and the interaction energy w obtained from selectivity plots has been attributed to possible formation of micelles in the organic phase.