theobromacacao - 20-3-2008 at 14:20
I wonder if any members may be able to shed some light on this, as I am stumped?! I was experimenting with ammonium paratungstate the other day, and
tried to dissolve some of it in a test tube with some ambient temperature distilled water to start off with. It did not readily dissolve and so I
added a dilute solution of HCl and shook the test tube for a while. At first the solution was clear and then suddenly a thick, white gelatinous
precipitate was formed. I filtered the solution, allowed the filter paper to dry out for a while at room temp and then placed it overnight in my
desiccator to dry out. The following day, I noticed that the ppt had turned a bright yellow colour. At first I thought it may be tungsten trioxide
but I doubt it can be? The yellow solid does not dissolve in water but does crackle a lot (similar to the sound made when lead nitrate is heated).
Does anyone have any ideas what this solid may be? Many thanks in advance!
not_important - 20-3-2008 at 14:35
tungstic acid
http://msds.chem.ox.ac.uk/TU/tungstic_acid.html
http://etd.caltech.edu/etd/available/etd-07202004-104651/unr...
woelen - 20-3-2008 at 14:35
I think it must be WO3, or some modification of H2WO4. Both are yellow insoluble solids.
How pure is your HCl? With certain reducing agents in the acid, there may be formation of a tiny amount of tungsten compounds in a lower oxidation
state. These can give a yellow color to the solution and the precipitate. When more reductor is present, then a deep blue color is obtained.
The_Davster - 20-3-2008 at 16:52
I concur that it is either WO3 or a hydrate therof. I prepared W(OiPr)6, a blue solid, but when I put it in the dessicator overnight, it was a yellow
crinkly lump the next day.