A spectrophotometric study of ionic association in aqueous solutions

Abstract

Measurements are reported of the extinction coefficients of aqueous solutions of potassium ferrocyanide, potassium ferricyanide, thallous perchlorate, thallous sulphate, thallous ferrocyanide and mixtures of lanthanum chloride and potassium ferrocyanide. Observed deviations from Beer's law in the last three cases have been interpreted in terms of the theory of incomplete dissociation, paying particular attention to assumptions about ionic activity coefficients. The formulae of the associated ions in ferrocyanide solutions have been determined by the method of continuous variations and thermodynamic dissociation constants have been obtained at 25, 35 and 50 degrees C for the TlFe(CN)$_{6}^{3-}$ ion and at 25 degrees C for the LaFe(CN)$_{6}^{-}$ ion. These dissociation constants are discussed in terms of Bjerrum's theory of ionic association.