Dissociation Constants of Perchloric and Sulfuric Acids in Aqueous Solution.

The experimental dissociation constants of strong acids are notoriously ill-defined, and it is necessary to rely on theoretical methods for their evaluation. We present a methodology for the theoretical evaluation of the dissociation constants, and the values of K for perchloric and sulfuric acids have been estimated. It has been shown that the acid dissociation constant K can be expressed as a product of two terms, K = K' × f, where K' is the apparent dissociation constant and f is the infinite dilution activity coefficient of undissociated molecule of acid in liquid solution. The values of K' can be computed from readily available reference data. The limiting activity coefficients f for strong acids can be determined by theoretical methods only. The following estimate for the limiting activity coefficients of perchloric and sulfuric acids has been obtained, -2.5 < log  f < -1.3. The ranges of values of the dissociation constants of HClO and HSO at 25 °C have been determined; log  K(HClO) = 10.8-12.3; log  K(HSO) = 4.5-8.6.