Modeling of equilibria in an acidified solution of sodium orthotungstate in the presence of barium(II) ions

Abstract

Interactions in the Ba2+–WO42––H+–H2O system, that was acidified to the molar ratio (acidity) Z=(H+)/(WO42–)=1.00, in the range of Z=0.60–2.00 at 2980.1 K with NaNO3 as the background electrolyte (I=0.1–0.3 mol•l–1), were studied by the methods of pH-potentiometry, mathematical modeling and conductometry. Logarithms of concentration constants of equilibrium were calculated by Newton's method. Previously unknown logarithms of thermodynamic constants and Gibbs energies of formation reactions for some ion pairs (BaOH+,[W12O40(OH)2]10–; Ba2+,[W12O40(OH)2]10–; Ba2+,H2[W12O40(OH)2]8–; Ba2+,H3[W12O40(OH)2]5–; Ba2+,[W12O18(OH)2]6–; and Ba2+,H[W12O18(OH)2]5–) were calculated by Pitzer's method. The formation of particles with a Ba2+:[W12O40(OH)2]10–=1:1 ratio in solutions was established by conductometric titration method. A scheme of interconversions between ion pairs in an aqueous solution was proposed. From acidified to different Z values aqueous solutions of Na2WO4, the normal and double barium(II) paratungstates B Ba5[W12O40(OH)2]30H2O (Z=1.17), Na4Ba2[W12O40(ОН)2]28Н2О (Z=1.25), and Na2Ba4[W12O40(ОН)2]25Н2О (Z=1.33) were synthesized. The data of FTIR spectroscopy showed that the isopoly anion in the salts' composition belongs to the paratungstate B structural type.