The Acidity Function, H0, in Aqueous Concentrated Acid and Salt Solutions

Some H0 measurements in concentrated LiCl solutions are reported. It is shown that the H0 values in 1–9 M LiCl, 1–9 M HClO4, and 1–11 M HCl solutions can be calculated using the equation[Formula: see text]where aw is the activity of water, C is either the molar or molal concentration, and n and B are least-squares constants. Values of n = 2 (molar equation) and n = 1 (molal equation) fit the experimental data better than does n = 4. With the molar equation a non-integral value of n for HClO4 is required to give reasonable H0 values. The adequacy and significance of integral and non-integral values of n are considered. The nature of the constant B is also discussed. A more general equation is developed which under certain conditions reduces to the simpler equation. The more general equation is based upon a model which assumes the existence of more than one hydrated form of the indicator base, its conjugate acid, and H3O+. Some of the implications of this more general equation are considered