Four comparative methods for determination of stoichiometries and stability constants of chromium and zirconium complexes with citric and propanoic acids were studies, in purpose to select the most accurate and sensitive method, and to compare the formation of complexes of these two transition metals. (Cr 1st transition series group 6B, Zr 2nd transition series group 4B)Metal-ligand stability constants and stoichiometries of the above systems were determined by Calvin & Bjerrum pH-metric titration technique as adopted by Irving & Rossotti.Four methods employed were point-wise calculation method, half integral method, linear plot method and least squares method. The result seems in a good agreement with each other and any method can represents the other.

This investigation represents a comparative study of four graphical methods for overall stability constant estimation techniques, included point wise calculation method, half integral method, linear plot method and least squares method, in purpose to select the most sensitive and accurate method, the paper aiming also to determine the parameters that affect the precision of these methods under investigation. Metal-ligand stability constant and stoichiometries of above systems are to be determined by Calvin and Bjerrum pHmetric titration technique as adopted by Irving and Rossotti. For this purpose titanium has been chosen as a central metal ion. Titanium element from first transition series of d-block and has four valence bond electrons 3d24s2. Acetic acid, oxalic acid and oxalacetic acid have been selected as ligands. The obtained results seem in a good agreement with each other, with some restriction on least squares method for accumulation of error in Kn-1. These suggestions have been introduced in conclusion for treatment of data by least squares method and Henderson's Hasselbalch's equation and other modifications have been done.

<p>The present work, deals with the study of proton-ligand (pK) and metal-ligand (logK) of acetic acid, oxalic acid, and oxalacetic acid with Cr (Ⅲ) and Zr (IV) by potentiometric titration technique. The stoichiometries and stability constants of these complexes were evaluated, usingCalvin-Bjerrum pH-titration technique as adopted by Irriving and Rossotti.</p><p>Graphic and algebraic methods have been employed, for determination of the stability constants, in purpose to select the most accurate and sensitive method. Furthermore, aiming to determine, the factor that effectingthe precision of those methods under investigation, and to compare the complexes of these ligands with first and second series transition elements of D-block Cr and Zr taken as an example. The obtained results were in a good agreement with each other.</p>