Thermodynamic parameters of interconversions of isopolyanions in solutions of tungsten(VI)

Interactions in the WO22- -H+-H2O system was studied by pH-potentiometric titration at 25 +/- 0.1 degrees C for c(W)(0) = 8 x 10(-3) to 2 x 10(-2) mol/l. An accurate mathematical model for polycondensation of tungsten(VI) anions in aqueous solution was proposed. The concentration constants of formation were calculated and the diagrams of distribution of isopolyanions of tungsten(VI) were plotted for pH from I to 8 with nitrate ions as a supporting electrolyte at different ionic strengths of the solution (I = 0.10 to 0.50). The dependences of the concentration equilibrium constants in solutions on the ionic strength were approximated by Pitzer's method. The thermodynamic constants of formation and standard Gibbs energies of formation of isopolytungstates from WO42- were calculated. The most probable scheme of interconversions of isopolyanions in solution at different pH values was proposed.