On autoionization and pH of liquid water

Abstract

The ionization constant of water K_w (or pH) is currently determined on the proton conductivity σ₀ which is measured at frequencies lower than 10⁷ Hz. We develop the idea that the high frequency conductivity σ_∞ (~10¹¹ Hz), rather than σ₀ represents a net proton dynamics in water. We count the concentration c of the H₃O⁺ and OH^– ions from σ_∞ to find c to be not dependent on temperature. We conclude that spontaneous ionization of H₂O molecules is not essential in water electrodynamics; the common K_w reflects the thermoactivation of the H₃O⁺ and OH^– ions from the potential of their interaction; the lifetime of a target water molecule does not exceed parts of nanosecond.