Use of Padé approximants in the processing of pH titration data. Determination of the parameters involved in the titration of acetic acid

Abstract

The proposed method is founded on the idea of titration in a titrand + titrant isomolar system. The method enables concentrations of the weak monoprotic acid and strong acid or base species in the sample tested to be found. It is also possible to evaluate the activity coefficient of hydrogen ions and equilibrium constants [protolysis constant (K₁) of the weak acid HL and the ionic product of water (K_w)]. All these values are found from only one titration curve by use of an iteration procedure. The regression functions applied have the form of the Padé approximant W=g₁(h)/g₂(h), where W is the total volume of the solution at a given point of titration and g₁(h) and g₂(h) are the polynomials of hydrogen ion activity (h). The method is illustrated by the determination of acetic acid, the iteration procedure being performed according to the MINUITS computer program.