Kinetics of reduction, composition and the stability constants of the zinc–maleic acid complexes in aqueous medium

Polarographic reduction of the zinc-maleic acid complexes has been studied at the dropping mercury electrode (dme) in aqueous medium at 30° and ionic strength 2.0 Gelling's method is used for determining the reversible half-wave potentials and the kinetics parameters (α and K_s) for the quasireversible reduction of the complexes. The value of α and K_s varied from 0.41 to 0.35 and 2.58 × 10⁻³ to 2.21 × 10⁻³ cm/s respectively with the ligand concentration changing from 0.00 to 0.60 M. Analysis of the polarographic characteristics ,of the system by the DeFord and Hume method gave the following values of the overall stability constants: β₁ = 50±2; β₂ = 160± 10 and β₃ = 2250 ± 50. The overall stability constants of the zinc-maleic acid complexes have also been calculated using the recently developed method of Mihailov. The resulting values are: β₁ = 29.9, β₂ = 301.4 and β₃ = 2025. Percentage distribution of the complex species present in the system is shown as a function of log/ligand concentration.