THERMODYNAMICS OF IONIZATION AND COMPLEX-FORMATION OF PYROCATECHOL VIOLET WITH COPPER(II), NICKEL(II) AND ZINC(II) USING POTENTIOMETRIC TECHNIQUE

The complexation of copper, zinc and nickel with pyrocatechol violet ( PCV) was investigated using potentiometric method. The ionisation of p ure PCV and the formation constants of metal-PCV complexes are obtaine d from potentiometry at five temperatures ; 25, 30, 35, 40 and 45-degr ees in different aqueous solutions of fixed ionic strengths (I=0.04, 0 .07, 0.11 and 0.15 mol dm-3) using NaClO4. Thermodynamic equilibrium c onstants (at I=0) are also reported. The data are discussed in the lig ht of structural effects, proton transformation and hydrogen bonding e ffects. Thermodynamic parameters associated with the ionisation and th e complexation equlibria have been evaluated. Thermodynamic metal grad ient (B) was derived to discuss the thermodynamic characteristics of m etal ion complexes.