The ionization constant of water over wide ranges of temperature and density

A semitheoretical approach for the ionization constant of water, K-W, is used to fit the available experimental data over wide ranges of density and temperature. Statistical thermodynamics is employed to formulate a number of contributions to the standard state chemical potential of the ionic hydration process. A sorption model is developed for calculating the inner-shell term, which accounts for the ion-water interactions in the immediate ion vicinity. A new analytical expression is derived using the Bragg-Williams approximation that reproduces the dependence of a mean ion solvation number on the solvent chemical potential. The proposed model was found to be correct at the zero-density limit. The final formulation has a simple analytical form, includes seven adjustable parameters, and provides good fitting of the collected K-W data, within experimental uncertainties, for a temperature range of 0-800 degrees C and densities of 0-1.2 g cm(-3). (c) 2006 American Institute of Physics.