Formation Constants and Partial Formation Constants of Some Metal Ions Coordinated with 8–Hydroxyquinoline by Potentiometric Titration

The association equilibria of HQ and HQ–coordinated with some transition metal cations such as: Al(III), Ca(II), Cd(II), Co(II), Cu(II), Fe(III), Mg(II), Ni(II), Pb(II) and Zn(II) ions were studied using potentiometric technique. The association constant (Ka) of HQ was calculated from the average number of protons attached per repeating unit in the HQ (nA) at different pH values. This value of pKa which formed was found to be 6.75.The titration curves revealed that the metal ion replaces protons and coordinates to HQ. In addition, the use of such titration curves could be computed of the formation constants (log β) of the different species exist at equilibrium. The formation constant (log β) for different molar ratios of species such as 1 : 2, 1 : 1 and 2 : 1 for metal : 8-quilonol, in solution were computed and the results were discussed. The value of ń and PL for the metal ions under investigation were calculated at different pH values. The Formation Constant (log β) of the coordinated 8-quilonol based on HQ–Metal ion were computed using ń– PL system. Mathematical calculations of differential change of ń (∆ń) gave a sharp signal for calculations of formation constant. From ń there are partial formation constant (log β2, log β3, log β4and log β5) which indicate to the protonation degree. The analyses of potentiometric data helped us to determine each value of the formation constant and/or partial formation constant for the metal ions such as: Al(III), Ca(II), Cd(II), Cu(II), Co(II), Fe(III), Mg(II), Ni(II), Pb(II) and Zn(II) coordinated with 8Hydroxyquinoline.