Thermodynamics of Ionisation and Complex Formation of Pyrocatechol Violet with Copper(II), Nickel(II) and Zinc(II) using Potentiometric Technique

Department of Chemistry, Faculty of Science, AI-Azhar University, Nasr City, Cairo-Egypt

Manuscript received 23 April 1991, revised 13 October 1992, accepted 7 January 1993

The complexation of copper, zinc and nickel with pyrocatechol violet (PCV) was investigated using potentiometric method. The ionisation of pure PCV and the formation constants of metal-PCV complexes are obtained from potentiometry at five temperatures ; 25, 30. 35, 40 and 45° in different aqueous solutions of fixed ionic strengths (I= 0.04. 0.07, 0.11 and 0.15 mol dm^-3 ) using NaCIO₄ Thermodynamic equilibrium constants (at I =0) are also reported. The data are discussed in the light of structural effects, proton transformation and hydrogen bonding effects. Thermodynamic parameters associated with the ionisation and the complexation equlibria have been evaluated. Thermodynamic metal gradient (B) was derived to discuss the thermodynamic characteristics of metal ion complexes.