Determination of Stoichiometries and Stability Constants of Complexes of some Carboxylic Acids with Titanium, Chromium and Zirconium

Abstract

This investigation represents a comparative study of five methods for determination of stoichiomtries and overall stability constants estimation techniques, including; two algebraic methods; point-wise calculation method and Henderson-Hesselbalch’s equation, and other three graphical methods adopted were half integral method, linear plot method and least squares method, in purpose to select the most sensitive and accurate method, also The work aiming to determine the parameters affecting the precision of the methods under investigation, and steric effect of carbon chain length. For this purpose, the central metal ions chosen were titanium and chromium from first transition elements series of group four and six respectively of d-block, they have four valence bond electrons 3d24s2 in addition to zirconium second transition series, group four of d-block. The carboxylic acids, acetic acid, oxalic acid, oxalacetic acid, propanoic acid and citric acid have been selected as ligands. Metal-ligand stability constant and stoichiometries of above systems were determined by Calvin and Bjerrum pH-metric titration technique as adopted by Irving and Rossotti. The obtained results are in a good agreement with each other, with some restriction on least squares method for accumulation of error in Kn-1.