Development of a Modified Bromley Methodology for the estimation of ionic media effects on solution equilibria: Part 5. The chemical model of boric acid in aqueous solution at 25 °C and comparison with arsenious acid

The chemical model of boric acid was built by means of the Modified Bromley Methodology using mean activity coefficient data and stoichiometric formation constant values in different ionic media at 25 °C. This study was performed considering the hydrolysis equilibrium of boric acid in aqueous solution, obtaining the thermodynamic equilibrium constant (log0 K=9.23±0.02) and the corresponding interaction parameters. Taking into account the chemical isomorphism between H2AsO3− and H2BO3−, the extension of the model to natural waters was compared with the chemical model of arsenite anion. The ionic radii for both species as well as all the ionic interaction parameters of these anions with the main cations in natural waters (Ca2+, Mg2+ and Sr2+) and Li+ were estimated. The model was validated against (logI K versus I) data in LiBr medium by using the predicted BLi+,H2BO3− value, obtaining a σ(logI K)=±0.02 with the four available logI K data.