Abstract:In the acidic aqueous Na2WO4solutions in a range ofZ(H⁺/WO^2-₄)=0~1.50, the chemical state of isopolytungstates has been studied using Raman spectroscopy. It was found that in the solution of Z≤1.25, the dominant polynuclear species at any time is paratungstate A, W₇O^6-₂₄, which also exists at Z=1.42. During the aging of solution, paratungstate A is slowly transformed to paratungstate B, H₂W₁₂O^10-₄₂, which is easily deposited as the crystal Na₁₀H₂W₁₂O₄₂·27H₂O, but the concentration of paratungstate B in the solution is too low to be detected. In the solution ofZ=1.42 and 1.50, there are probably metastable species, but metatungstate, H₂W₁₂O^6-₄₀, becomes the dominant species after long aging.

Key words: Raman spectra　isopolytungstate　paratungstate　metatungstate