FIRST AND 2ND DISSOCIATION-CONSTANTS OF SOME DICARBOXYLIC-ACIDS AND RELATED THERMODYNAMIC FUNCTIONS

pK(1) and pK(2) values at zero ionic strength of six different dicarbo xylic acids (succinic, malic, tartaric, malonic, maleic and phthalic) in 20% ethylene glycol (by volume) at five different temperatures (30 to 50 degrees C) have been compiled from emf measurements of a glass e lectrode, HCl, buffer, calomel electrode cell. Dilute HCl was used to calibrate the cell and the pK's assessed after additions of stock buff er solution. The thermodynamic parameters Delta G degrees, Delta H deg rees and Delta S degrees for the first and the second dissociation rea ctions have been computed. A critical comparison with the published va lues in pure aqueous medium shows the importance of the electrostatic effect of the solvent. Analysis reveals that these dissociation reacti ons are entropy controlled reactions where the solute-solvent interact ion plays an important role.