The behavior of orthovanadate anions in acidified 10^-3-10^-2 mol/l solutions.

Abstract

In the master`s work the process of polycondensation in aqueousdimethylforamide solution of sodium orthovanadate at a temperature of 25⁰С was investigated in the acidity range Z = ν(H⁺)/ν(VO₄^3-) = 0÷3,5. The results of the pHpotentiometric titration were followed by mathematical modeling using the CLINP 2.1 program. According to the results of the titration, the models of equilibrium formation of the isopolyvanadate-anions, which satisfactorily describe processes in solution, are proposed. For complexformation reactions in the aqueous-dimethylforamide solution of the system Na₃VO₄ – HNO₃–(NaNO₃) – H₂O – DMFA with С(Na₃VO₄) = 10^-3-10^-2 mol·L^-1, the ionic strength µ(NaNO₃) = 0,1÷0,5 mol·L^-1 and φ DMFA=5vol.%, the concentration constants logarithms were first calculated by quazi-Newton method, and thermodynamic formation constants – by the Pitzer method. The standard Gibbs formation energies were determined and the possibility of reactions between the proposed forms of isopolyvanate-anions in the investigated solution was evaluated. For the first time the diagrams of isopolyvanate-anions distribution in aqueous-DMF solution depending on the medium acidity are constructed. The areas of dominance of individual ion-forms are determined, which allowes to synthesize their salts with sodium cation.