Applying the Extended Helgeson–Kirkham–Flowers Equation of State to Strongly Polar Undissociated Substances: Properties of Arsenous Acid and Orthophosphoric Acids at Infinite Dilution

An improvement is proposed for the Helgeson–Kirkham–Flowers (HKF) equation of state for polar undissociated substances at infinite dilution. It is used to describe the properties of aqueous solutions of As(OH) 3 and H 3 PO 4 at infinite dilution, along with equilibria with their participation. Parameters of the equation of state are clarified for the anion. The proposed equation of state allows theoretically consistent descriptions of polar noncharged species with accuracy on a par with the classical HKF equation.