Ionization of water in concentrated potassium halide media

The ionic product of water, pK(w) = -log[H+][OH-], has been determined as a function of ionic strength (I) in concentrated aqueous solutions of KCl, K Br and KI at 25 degrees C by high-precision glass electrode potentiometric titrations. The pK(w) values obtained are in excellent agreement with, but generally more precise than, literature data. At I > 1 M the pK(w) values i ncrease smoothly and show systematic differences in the order KCl < KBr < K I, consistent with the decreasing H+-acceptor ability of the medium anions. Analogous behaviour is observed in MCl solutions, with pK(w) values varyin g in the order NaCl < KCl < CsCl. Formation constants of MOH0 ion pairs der ived from these data are consistent with literature values.