Abstract: The present study reports the stability constants of complexes with fatty acids: Alpha Linolenic Acid (ALNA), Arachidonic Acid (AA) and Oleic acid (OA) with Co²⁺, Ni²⁺, Cu²⁺, Zn²⁺, Cd²⁺, Sn²⁺, Hg²⁺ and Pb²⁺ ions in water-ethanol medium 50% v/v at three different temperatures 25ºC, 35ºC and 450.1ºC keeping ionic strength constant (0.1 M KNO₃). Experiments were conducted in 1000 mL jacketed glass reaction vessel under nitrogen atmosphere. Hydrogen ion concentrations were measured and the stability constants were calculated from the potentiometric titration curves. The order of the stability constants of the formed complexes decreases in the sequence Cu²⁺, Cd²⁺, Co²⁺, Ni²⁺, Pb²⁺, Zn²⁺, Hg²⁺ Sn²⁺.  The effect of temperature was also studied and the corresponding thermodynamic functions (ΔG, ΔH and ΔS) were derived and discussed. The formation of metal complexes has been found to be spontaneous and entropically favourable. The method of Calvin and Bjerrum as adopted by Irving and Rossotti has been employed to determine log K₁ values. This order is in good agreement with Irving - Williams order of stability.
 

KEYWORDS: Stability constant; Fatty acids; Potentiometric titration; Thermodynamic functions.