Jackson
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Tungsten compound
I was reacting a tungsten weight with 30% H2O2 and sulfuric acid to try and produce tungstinic acid. The photos of tungstinic acid shows it as a
yellow color. The solution so far is a cloudy gray. My question is, is tungstinic acid clear in solution?
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fusso
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Yes, both WO3 & H2WO4 are yellow. Gr(e/a)y means either the W hasn't done reacting or is unreactive towards H2O2. H2WO4 is insoluble.
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Jackson
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I was looking at the solution which is violently bubbling and it appears to be small pieces of metal.
There is also now a small amount of yellow precipitate on the bottom.
[Edited on 10/6/2018 by Jackson]
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diddi
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it take ages (weeks) to dissolve W. and i have found it is quicker in just H2O2. ie no acid
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Jackson
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The piece of tungsten has lost about half of its volume but there is nothing dropping out
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Jackson
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Does H2WO4 and WO3 disolve in H2O2 or H2SO4?
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fusso
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W(VI) is acidic. If they aren't soluble in H2O, I don't think
they'll dissolve in H2O2 or H2SO4 either.
[Edited on 07/10/18 by fusso]
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Jackson
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Ok its weird because the tungsten is around 1/3 of its size and the solution is clear so i dont know where it is going.
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fusso
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Quote: Originally posted by Jackson  | I was looking at the solution which is violently bubbling and it appears to be small pieces of metal.
There is also now a small amount of yellow precipitate on the bottom.
[Edited on 10/6/2018 by Jackson] |
The yellow ppt dissolved? Try boil down the solution to see if any tungstic
acid crystallized out. If yes then I think wiki is wrong. (wiki says tungstic acid is insoluble)
[Edited on 07/10/18 by fusso]
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diddi
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it is typically pale yellow solution even in 50% H2O2
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Foeskes
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I made tungstic acid by heating tungsten rods in a mix of NaNO3 and NaOH, once it starts it reacts violently and heats up all the way to over 600c.i
dissolved the mix in water.
After wards I filtered and added a bit of a reducing to remove the chromium(vi). Finally I added some hcl and filter.
[Edited on 8-10-2018 by Foeskes]
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phlogiston
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I dissolved tungsten rods in straight 10% H2O2. It took months, and yielded a yellow solution. It was perfectly clear at first, but a small amount of
bright yellow precipitate formed spontanously over time. This was only a very small fraction of the tungsten in the solution, however.
The precipitate redissolved when I added NaOH solution.
From the resulting clear, slightly yellow solution, tungstic acid was precipitated by adding hydrochloric acid. The precipitate was very voluminous
(consistency is a bit gel-like). It took ages to filter and dry.
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woelen
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Pure tungsten dissolves in 10% H2O2 fairly easily, no acid added. In one day you can dissolve a mm of metal from a rod. The resulting solution is
(nearly) colorless, not yellow. I have done this experiment myself, using small rods of very pure tungsten, I purchased on eBay.
The solid oxide, WO3 is yellow, looking very much like sulphur. Solutions of H2WO4 tend to be colloidal, but nearly colorless and clear (index of
refraction of the colloidal particles is very close to that of water), When the particles become larger, then the liquid becomes pale yellow.
Solid H2WO4 also is yellow, somewhat paler than WO3, but definitely yellow, not off-white.
If you get a turbid grey liquid, then most likely your tungsten is not really pure. A common impurity is carbon. The tungsten then dissolves and very
fine particles of carbon (or tungsten carbide? I do not know for sure) give the dark grey color. Just allow this to settle. This may take many hours,
or even days. Then carefully decant the clear liquid or use a pipette to carefully take it away from the layer of precipitated dark material.
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Mesa
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<---someone who has oodles and oodles of tungsten around and experimented with it quite a lot.
tungsten dissolves fairly well in H2O2 to yield a colorless H2WO4 soln which is unstable. soln slowly takes on yellowish tinge as WO3 precipitates
out.
eventually all dissolved tungsten precipitates as WO3.x2O.
edit: to not contradict woelen's comment above; i dont make a distinction between solid H2WO4 and WO3.(1)H2O and I'm not sure if such a distinction
exists. So we are kinda saying the same thing imo.
I think of H2WO4 as specifically the dissolved species.
[Edited on 8-10-2018 by Mesa]
[Edited on 8-10-2018 by Mesa]
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Jackson
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The solution is grey due to the color of acid I added to it. There is a dark grey precipitate at the bottom. The tungsten rod is around 1/3 to 1/4 of
its original size.
[Edited on 10/8/2018 by Jackson]
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Jackson
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Large White crystals have formed on the bottom of the container.
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Jackson
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Here are some photos of it
 
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Jackson
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What compound could it be?
Could it be sodium/potassium tungstate?
There maybe have been sodium or potassium salts in the cleaner.
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Fery
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| Quote: Originally posted by woelen | Pure tungsten dissolves in 10% H2O2 fairly easily, no acid added. In one day you can dissolve a mm of metal from a rod. The resulting solution is
(nearly) colorless, not yellow. I have done this experiment myself, using small rods of very pure tungsten, I purchased on eBay.
The solid oxide, WO3 is yellow, looking very much like sulphur. Solutions of H2WO4 tend to be colloidal, but nearly colorless and clear (index of
refraction of the colloidal particles is very close to that of water), When the particles become larger, then the liquid becomes pale yellow.
Solid H2WO4 also is yellow, somewhat paler than WO3, but definitely yellow, not off-white.
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I have to confirm that W dissolves in H2O2, just by my experiments not so easily (maybe too much stabiliser in my H2O2 ?).
Pertungstic acid forms while still excess of H2O2, only when H2O2 consumed near the end and there is still excess of W, then poorly soluble tungstic
acid starts to precipitate (pertungstic acid is then very likely source of some H2O2).
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