STUDIES ON THE DISSOCIATION-CONSTANTS OF PHTHALIC-ACID IN AQUO-ETHANOLIC MIXTURES

As in aqueous solutions, potassium hydrogen phthalate solution (0.05 M ) may be used as a suitable buffer in mixed solvents also, provided th e first and second dissociation constants bf phthalic acid in mixed so lvents are known, The first dissociation constants have been determine d using solubility and conductometric measurements and the second ones have been determined pH-metrically. The quantitative measure of the i on-solvent or solute-solvent interactions have been obtained from the values of Gibbs energy of transfer of phthalic acid, biphthalate ion a nd phthalate ion by coupling solubility values of H(2)Ph and. the diss ociation constant values using appropriate relations, Delta G(t)(o)(HP h(-)) and Delta G(t)(o)(Ph(-2)) have been found to be increasingly unf avourable in going from water to non-aqueous solvents. The Lambda(o) v alues of H(2)Ph and KHPh also decrease continuously in going from wate r to mixed solvents.