THERMODYNAMICS OF AQUEOUS PHOSPHATE SOLUTIONS - APPARENT MOLAR HEAT-CAPACITIES AND VOLUMES OF THE SODIUM AND TETRAMETHYLAMMONIUM SALTS AT 25-DEGREES-C

Citation
H. Bianchi et Pr. Tremaine, THERMODYNAMICS OF AQUEOUS PHOSPHATE SOLUTIONS - APPARENT MOLAR HEAT-CAPACITIES AND VOLUMES OF THE SODIUM AND TETRAMETHYLAMMONIUM SALTS AT 25-DEGREES-C, Journal of solution chemistry, 24(5), 1995, pp. 439-463
Citations number
36
Categorie Soggetti
Chemistry Physical
ISSN journal
00959782
Volume
24
Issue
5
Year of publication
1995
Pages
439 - 463
Database
ISI
SICI code
0095-9782(1995)24:5<439:TOAPS->2.0.ZU;2-E
Abstract
A Picker flow microcalorimeter and a flow densimeter, were used to obt ain apparent molar heat capacities and apparent molar volumes of aqueo us solutions of Na3PO4 and mixtures of Na2HPO4 and NaH2PO4. Identical measurements were also made on solutions of tetramethylammonium salts to evaluate the importance of anion-cation interactions. The experimen tal apparent molar properties were analyzed in terms of a simple exten ded Debye-Huckel model and the Pitzer ion-interaction model, both with a suitable treatment for the effect of chemical relaxation on heat ca pacities, to derive the partial molar properties of H2PO4-(aq), HPO42- (aq) and PO43-(aq) at infinite dilution. The volume and hear capacity changes for the second and third ionization of H3PO4(aq) have been det ermined from the experimental data. The importance of ionic complexati on with sodium is discussed.