Evaluation of Stability constant of Binary complex of Tannic Acid with Fe(II) in Aqueous Solution: Potentiometric Study

In this study, the protonation equilibria of the tannic acid was determined and used for determining the stability constants of the binary complexes formed with iron (II) ions in the aqueous medium under the experimental conditions by potentiometric method using Irving and Rossotti equation, where Stability constant was 3.205 for Fe(II)–tannic acid complex, while Fe(II) was formed complexes with tannic acid of various stoichiometries, which in the 1:1 molar ratio at pH = 11.24. Furthermore, the ionic strength and the influence of temperature on the stability of the complexes is investigated, where stability constant in presence 0.1 M NaCl (ionic strength) of binary iron-Tan complex equal 3.254, and at different temperatures were log K1= 3.156 at 298.15 K, log K1 = 3.205 at 310.15 K, and log K1 = 3.256 at 313.15 K.