SPECTROPHOTOMETRIC DETERMINATION OF THE STABILITY-CONSTANTS OF CO(II)AND DPKBH (DI-2-PYRIDYL KETONE BENZOYLHYDRAZONE)

In order to have more information about the thermodynamic properties o f the complexes formed by Cobalt(II) and DPKBH (di-2-pyridyl ketone be nzoylhydrazone) and for the development of speciation methods for coba lt, the respective stepwise formation constants were determined in eth anolic solution 50% (V/V), at pH 5.3 and 25.0 degrees C. The spectroph otometric method of corresponding solutions was used and the following overall formation constants were obtained: beta(1) = 5.305 x 10(6) M( -1) and beta(2) = 8.476 x 10(10) M(-2). The molar absorptivities of th e 1:1 (epsilon(1)) and 1:2 (epsilon(2)) complexes (Co(II):DPKBH) were determined to be 4.475 x 10(3) and 2.994 x 10(4) (M(-1).cm(-1)), respe ctively. The calculated distribution diagram shows the percentage of t he species at equilibrium as a function of the free DPKBH concentratio n.