Potentiometric and conductometric studies on the composition and stability of zinc complexes of thiomalic acid

Abstract

The precise nature of the reaction between zinc and thiomalic acid in aqueous 0.1 M KNO3 has been investigated potentiometrically and conductometrically. The formation of two complexes, one predominating at pH 5.5–7 and another at pH 8–9.5, was found. The stability constants of the complexes formed have been determined by applying Calvin and Melchior's extension of Bjerrum's method at three different temperatures. The log K values for 1:1 and 1:2 complexes computed by alternative methods at 25, 30, and 35 °C have been found to be 8.75, 8.85, 8.86, and 6.82, 6.75, 6.93, respectively. The values of the overall changes in ΔG, ΔH, and ΔS accompanying the reaction have also been evaluated at 30 °C and found to be −21.61 kcal/mole, −5.3 kcal/mole, and +53.8 cal/deg respectively.