Hydrate-Anion Complex of Proton [H(H₂O)_n]^+- as the Basis of the Complex Acidity Function ₀^w of Aqueous Solutions of Strong Mineral Acids in Excess of Water

Based on the concept of the proton hydrate-anion complex [H(H2O)(n)](+)A(-), equations are proposed that characterize the catalytic activity of the proton in aqueous solutions of three acids: sulfuric, hydrochloric, and chloric. The equations are based on the linear dependence of the value of "excessive acidity" on the logarithm of the relative stoichiometric concentration of water & KHcy; = f(log C*(w)) in acid solutions with a predominance of water (& Ncy;(2)& Ocy;/& Ncy;& Acy; > 1). Using the directly proportional dependence of the Hammett function (-H-0) on the sum of parameters (log C*(H+) + mX), two-parameter equations were obtained for calculating the complex function of acidity -H-0(w) = log C*(H+) + Blog C*(w) (standard state-pure water, C-w(0)). The equations make it possible to calculate the function H-0(w) at a given acid concentration, having only data on the concentrations of the proton C-H+ and water H-0(w), i.e. avoiding the use of the ratio of the activity coefficients of the components included in parameter X. The function H-0(w) collectively reflects the participation of proton and water in the acidity of the medium, practically reproduces the experimental values of H-0 obtained by different authors in the concentration range from pure water to 68 wt % (H2SO4), 40% (HCl), 70% (HClO4), combines the pH and H-0 scales. It is concluded that the Blog H-0(w) contribution, which characterizes the participation of water in the hydration shells of ions, is determined by their nature and plays no less important role in characterizing the acidity of the medium than the proton itself. The final tables of the concentration dependence of the values H-0(w) for each of the acids are given. The paper represents a methodological review, since it is based on a critical analysis of experimental literature data.