Measurement of Stability Constant of Hymatomelanic Acid Metal Complexes

Department of Applied Chemistry, Calcutta University, Calcutta

Manuscript received 24 April 1972; revised 6 April 1973; accepted 24 July 1973

Log k values of Hymatomelanic acid metal complexes are evaluated at pH 4.0 and 5.5. Log k values for Ferric Hy.A. complex changes from 3.97 to 4.93 with change in pH from 4.0 to 5.5, same values for Al-Hy.A. complex are 3.81 at pH 4.0 and 3.88 at pH 5.5 which indicate that stabilities of Al-Hy.A. complex are not affected by change in pH. The Log k values for Cu-Hy.A., Ni-Hy.A. and Zn-Hy.A. complexes are 3:43, 2.75, 3.59 at pH 4.0 and 5.86, 5.42 and 4.82 at pH 5.5 an appreciable change in stabilities on change in pH. The result of this investigation indicate the following sequences Ni²⁺ < Cu²⁺ < Zn²⁺ < Al³⁺< Fe³⁺ at pH 4.0 and Al²⁺ < Zn²⁺ < Fe³⁺< Ni²⁺ < Cu²⁺ at pH 5.5.