Studies on the Citrate Complex of Cobalt (II)

The citrate complexes of Cobalt (II) has been studied by pH titration method within the pH range of 2.5 to 6.8. The results are confirmed qualitatively by measurement of specific conductance. Cobalt reacts with citric acid at lower pH forming a neutral complex C. liberating two protons simultaneously. The equili­brium constant of the reaction

                                 Co²+H₃Cit \(\rightleftharpoons\)C+ 2H⁺

is 8.40X10^-5. The neutral complex then dissociates at higher pH range in two steps to complexes \(C^-_1\) and \(C^{2-}_2\). The equilibrium constants of the reactions, C \(\rightleftharpoons\)\(C^-_1\)+H⁺ and \(C^-_1\)\(\rightleftharpoons\) \(C^{2-}_2\)+H⁺are 6.835 X 10^-5 and 1.05 X 10^-8 respectively. The formation constant of the complex C according to Co²⁺+ HCit^2- \(\rightleftharpoons\)C is determined to be 1.438 X 10³. The equilibrium constant of the reaction

                                          Co²⁺+Cit^3- \(\rightleftharpoons\)\(C^{2-}_2\) + H⁺

is determined to he 3.38 X 10^-6. The hydrolysis constant of th hydrolysis of Co²⁺according to Co²⁺+H₂O \(\rightleftharpoons\) CoOH⁺+H⁺ is calculated to be 4.285 X 10^-5.