General equation for determining the dissociation constants of polyprotic acids and bases from additive properties. Part IV. Application to potentiometric titration

It is shown that acid-base titration can be treated, in general, as an additive property. This is based on the fact that the average charge on the undissociated and dissociated solute species at equilibrium is an additive property. This is also supported by the fact that the general equation for the acid-base titration curve can be written in the form of the general equation for additive properties as derived in Part I of this series of papers. The general equation is then used with the theory of statistical adjustment of data to derive an iterative procedure for extracting: the dissociation constants, the relative activity coefficients of the ionic species, the concentration of the analyte, and, at the same time, calculating the error in each parameter. The method yields a complete analysis of the error propagation resulting from the errors of measuring different variables. It is also shown that the equation of the titration curve can be transformed into an exact equation of a straight line whose slope is directly related to the equivalence volumes, thus providing an exact, simple method fbr determining end-points and equivalence volumes which is superior to Gran plots. (C) 2001 Elsevier Science B.V. All rights reserved.