Abstract:
Identification of the role of metals, ligands and their complexes in chemical speciation needs
understanding of their equilibria. The stabilization /destabilization of the complex is a function of
the magnitudes of stability constant. A computer assisted pH metric investigation has been
carried out on the chemical speciation of the binary complex of Ca(II) and Mg(II) with 1,10-
phenanthroline. The titrationswere carried out with sodium hydroxide in varying concentrations
of 0.0-2.5% SDS-water mixture at an ionic strength of 0.12mol L-1 and at a temperature of 298.0
k. The stability constant and best fit models for metal-ligand complex were obtained from
MINIQUAD75 computer program with important statistical parameters by refining the
experimental or alkalimetric titration data. The formation and distributions of different species
with varying pH were represented in the form of species distribution diagram. The model
speciesare detected within the pH range of 1.0-5.0 (ML), 1.0-3.2 (ML2) and 3.5-7.0 (ML3) for
Ca(II) and 0.5-3.2 (ML),0.5-3.5 (ML2) and 2.0-4.5 (ML3) for Mg(II) metals. The rejections of
some species and the variation of standard deviationand stability constant in the introductions of
purposive errors confirm the suitability or appropriateness of experimental conditions,
correctness of ingredient concentrations and choice of the best fit models. The magnitude of the
stability constant of the species are affected in the order of alkali > mineral acid > ligand
