Interaction of the Ni2+ ion with citric acid in an aqueous solution

The formation of nickel citrate complexes was studied at ionic strength values of 0.1 and 0.3 mol/l (Et4NCl) and 298.15 K by potentiometric titration. The NiCit−, NiHCit, and NiH2Cit+ complexes were formed in a Ni2+ ion-citric acid (H3Cit) system. The thermodynamic formation constants of the nickel(II) citrate complexes were calculated in an aqueous solution at $$I = 0:\log \beta _{NiCit^ - }^0 $$ = 6.86 ± 0.12 (Ni2+ + Cit3− ai NiCit−), logK 1 0 = 4.18 ± 0.10 (Ni2+ + HCit2− ai NiHCit), and logK 2 0 = 2.24 ± 0.11 (Ni2+ + H2Cit− ai NiH2Cit+). The spectral properties of the Ni2+-H3Cit system were studied by spectrometry. The conditions of calorimetric determination of the thermal effects of formation of the nickel citrate complexes in an aqueous solution were optimized on the basis of the calculated stability constants of the Ni(II) complexes with H3Cit.