Salt effects on the proton transfer equilibria in the 3,5‐dinitro‐2‐hydroxybenzoic acid/ammonia system: A T‐jump study

A thermodynamic study of the proton transfer equilibria involved in the system 3,5-dinitro-2-hydroxybenzoic acid/ammonia has been undertaken in LiClO4 and NaClO4 aqueous solutions at different ionic strengths. The enthalpy for the different equilibria involved was measured by T-jump techniques, while the free energies were determined spectrophotometrically. The different thermodynamic magnitudes, ΔG, ΔH and TΔS, are functions of the nature and concentration of the salt. However, the MSA provides a reasonable explanation for the experimental trends in most of the cases, although in this model only one parameter, the radii of the ions, is used to reproduce the mean ionic activity coefficients of electrolyte solutions at high ionic strengths. The extrapolated values at infinite dilution were also compared with the MSA prediction, and a good agreement was found.