An Interpretation of the Acidity Function in Glacial Acetic Acid

The “acidity function” in dilute glacial acetic acid solutions is a linear function of the logarithm ot the equilibrium concentration of undissociated acid present. Expressions are derived relating the apparent acidity function in glacial acetic acid to thermodynamic equilibrium constants in water and glacial acetic acid for a solution of a pure acid or salt, a mixture of an acid and its salt, and a mixture of a base and its salt. It is demonstrated that the acidity function in acetic acid depends upon the choice of reference indicator base. The effect of small concentrations of water on the acidity function in acetic acid is quantitatively explained in terms of the reaction H₂O + HX ⇄ H₃O⁺X⁻.