Complexation and precipitation equilibria in the system NiII–CrVI–H2O

Abstract

A potentiometric and spectrophotometric study of the complexation equilibria between Cr^VII and Ni^II has been performed. Formation of the soluble NiCrO₄ complex has been found and the thermodynamic formation constant has been calculated (log β^°₁₁= 2.40 ± 0.03), as well as its molar absorptivity values at the different wavelengths studied. The precipitation equilibria in the system Ni^II–Cr^VI–H₂O have also been investigated. A mixed precipitate, NiCrO₄· 3Ni(OH)₂, has been found and its thermodynamic solubility constant has been determined (log K^°_so=–51.1 ± 0.2).