Is your tungsten powder pure? With H2O2 you get colorless compounds, based on tungsten(VI), such as H2WO4. With certain metals, these tungstate
compounds can be pale yellow, as is WO3.
Tungsten in lower oxidation state (+5, +4) only forms a few well-defined stoichiometric compounds. In water, these oxidation states can exist, but
only in ill-defined compounds with variable composition. These compounds have a blue color. It might be that you obtained these compounds transiently,
but it would surprise me. These compounds of tungsten with oxidation state lower than +6 are quite strong reductors and i would not expect them to be
formed at all in the presence of H2O2.
One way to make these compounds is adding zinc to an acidified solution of a tungstate. With molybdenum (the lighter congener of tungsten) the
production of these blue compounds works much better. |