Analysis of the dependence of acid dissociation constants on temperature

Abstract

Analysis of the dependence on temperature of acid dissociation constants of weak acids in aqueous solution is considered from two standpoints. First, methods which assume a single-step reversible dissociation characterised by an acid dissociation constant K are examined with particular reference to the least-squares technique for deriving the required parameters. The importance is stressed of examining the structure of the model especially where high correlation factors are obtained between derived parameters. A method of analysis is proposed based on a polynomial in (T–θ) where θ is a reference temperature. The results of applying this technique to several sets of data are discussed with comparison, where possible, with thermochemical data. Second, the data are examined using a two-stage equilibrium process for the dissociation. The temperature dependence of K can be satisfactorily described by the final equation which contains two enthalpy terms, characterising the two reversible stages. The derived parameters indicate that the dissociation proceeds through an ion-pair intermediate.