Determination of dissociation and complex formation constants of nicotinic acid with Cd(II), Zn(II) and Hg(II)

ABSTRACT DETERMINATION OF DISSOCIATION AND COMPLEX FORMATION CONSTANTS OF NICOTINIC ACID WITH Cd(II), Zn(II) AND Hg(II) Ibrahim KANÎ Ph. D in Chemistry Adviser: Prof. Dr. Efraim AVŞAR May 1999, 145 pages In this study, determination of the acid dissociation constant of nicotinic acid (3-pyridine carboxylic acid) has been made potentiometrically in an aqueous medium of unit ionic strength at 20.0 °C, 25.0 °C and 30.0 °C. Besides, the complex formation constants with Cd(II), Zn(II) and Hg(II) have been studied at the prevailing conditions. Only the first ionization constant of nicotinic acid could be determined in the range of concenrations studied. The pKa values of the acid are found to be 4.95; 4.89 and 4.87 respectively. The complex formation equilibria of the nicotinate with Cd(II) and Zn(II) have been carried out via the central ion measurements by using amalgam electrodes. The Hg (II) -nicotinate system has been studied with glass electrode measurements. Calculations were done by graphical method. Cd(II) and Zn(II) form very weak complexes, while Hg(II) forms one very strong mononuclear complex. The stability constants of Cd(II) and Zn(II) were found to be 29±2 M"1 and 15±2 M"1 respectively, at each studied temperature. On the other hand, in the Hg (II) -system, 2.8xl04 M"1; 4.1xl04 M"1; 7.7xl04 M"1 values were found for pi at 20.0, 25.0 and 30.0 °C. respectively. KEY WORDS: Complexes, Stability Constant, Nicotinic Acid COMMITTEE: Prof. Dr. Efraim AVŞAR Prof. Dr. Erol AYRANCI Prof. Dr. Betül BAŞARAN