High Temperature Aqueous Electrolyte Concentration Cells and the Ionization of Liquid Water to 200 °C

High temperature aqueous electrolyte concentration cells with and without liquid junction are described. These cells were used to measure the ionization constant of water in 0.1, 0.25,0.5, and]1.0 mol/kg KCl solutions at temperatures to 200 °C. Extrapolation to infinite dilution yielded the following functions for the temperature dependence of log K w 0 and the thermodynamic parameters for ionization: log K w 0 = −4046.16/T + 3.537 − 0.01323T; ΔG 0 = 77458.0 − 67.71T + 0.253187T 2 J/mol; ΔH 0 = 77458.0 − 0.253187T 2 J/mol; ΔS 0 = 67.71 − 0.5063T J/K mol; ΔC p 0 = −0.5063T J/K mol.