Ionization of Water in Concentrated Potassium Halide Media

Abstract

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, KBr and KI at 25˚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 increase smoothly and show systematic differences in the order KCl < KBr < KI, consistent with the decreasing H⁺-acceptor ability of the medium anions. Analogous behaviour is observed in MCl solutions, with pK_w values varying in the order NaCl < KCl < CsCl. Formation constants of MOH⁰ ion pairs derived from these data are consistent with literature values.