Ion Trios: Cause of Ion Specific Interactions in Aqueous Solutions and Path to a Better pH Definition

Many important thermodynamic calculations for aqueous systems are profoundly limited because ion specific interactions have not been understood. Here an alternative modeling paradigm with compelling advantages is presented based on fundamental insights regarding ion–ion interactions at higher electrolyte concentrations. We also show how an intense ongoing controversy regarding single ion activity coefficients (SIACs) can be resolved and how SIACs can be quantified in full thermodynamic compliance using an overlooked convention. SIAC values can in fact be determined unequivocally and compatibly from two independent types of measurement at trace concentrations. These developments promise important advances, especially in defining pH and modeling multicomponent aqueous systems.