Physico-chemical Studies on the Composition and Stability Constants of Zn(II), Cd(II) and Hg(ll) DL-Valine Complexes

Department of Chemistry, Alalaviya Regional Engineering College, Jaipur-802 017 Manuscript received 30 May 1981, revised 4 Januairy 1982, accepted 2 February 1982 DL-Valine [(CH3)2CH.CH(NH2).COOH] complexes of divalent Zn, Cd and Hg have been investigated potentiometrically in aqueous 0.1 M NaCIO4 solution using Bjerrum-Calvin technique as modified by Irving and Rossotti at 20,30 and 40°. The refinement of stability constants was made by the method of least square. The trend in the stability of these 1 : 1 metal complexes has been found to be : Zn(II)>Hg(II)>Cd(II). Cd(II) forms only 1 : 1 complex at pH 3.35-8.55 and Zn(II) and Hg(II) 1 : 1 and 1 : 2 complexes at pH 2.90-8.20 and 3.40-7.75, respectively. The overall changes in thermo­dynamic parameters, ∆G, ∆H and ∆S, accompanying the complex formation have been determined