Densities and compressibilities of aqueous HCl and NaOH from 0 to 45°C. The effect of pressure on the ionization of water

The densities and sound speeds of aqueous HCl and NaOH solutions were measured from 0.1 to 1.0m and from 0 to 45°C. These data were combined with literature data and fitted to functions of molality and temperature. The apparent molal volumes V_φ{symbol} and compressibilities ΔK of these solutions were fitted to functions of molality and temperature. The partial molal volumes and compressibilities of HCl and NaOH solutions were used to calculate the partial molal volume ‡V and compressibility Δκ changes for the ionization of water. Combined with literature data these values of ΔV adn Δκ were used to calculated the effect of pressure on the ionization constant of water K_w from 0 to 200°C. The effect of pressure on K_w calculated from partial molal quantities are in reasonable agreement with that determined directly from high pressure measurements taken from the literature up to 1000 bar. It is necessary to use the pressure dependence of ΔK⁰ to extend the calculated pressure dependence of K_w up to 6000 bar.