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vano
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Phosphotungstic acid
Hi. Today I received 100 grams of the compound as a gift. I do not know exactly what it is, but something was written in Georgian on the jar, I read
three words, phosphorus or phosphate, tungsten and acid. Is white-gray in color. It is also heavy and that is why I think it is really a tungsten
compound. what do you think?
[Edited on 5-2-2021 by vano]
Edit by Texium: changed title
[Edited on 2-9-2021 by Texium (zts16)]
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vano
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It is also soluble in water. I mixed it with copper sulfate, but nothing did not precipitated(If it had been for tungstate). I added a concentrated
ammonia solution, suddenly a white precipitate formed and it also disappeared. I think that complex formed.
[Edited on 5-2-2021 by vano]
[Edited on 5-2-2021 by vano]
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vano
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vano
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I think it is a Phosphotungstic acid. Maybe it is anhydrous, because hydrate melts at 89°C.
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Bedlasky
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Phosphate, tugsten, acid - definitelly phosphotungstic acid. If you dissolve it in water, it will behave like a strong acid. Add some HCl and zinc -
it should form very dark blue solution (not a precipitate) of phosphotungsten blue.
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vano
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Thanks. Now I'm sure.I have read a lot now and it is quite an interesting compound, but what do you advise me to use it for?
 
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vano
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What is the phosphotungsten blue formula?
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vano
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It is unbelievable. Why it has this price?
https://www.amazon.com/HiMedia-GRM398-100G-Phosphotungstic-A...
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Bedlasky
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Vano: Structure of these W(VI)/W(V) and Mo(VI)/Mo(V) compounds can be quite complicated. Look at this, tungstem behaves similary as molybdenum (but tungsten have greater tendency to polymerize).
There is already several kinds of phosphotungstates, it is possible that your phosphotungstic acid is mixture of compounds (but it can be also one
particular kind of phosphotungstic acid).
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vano
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I think it is a H7[P(W2O7)6], Because I saw a jar on the internet that was identical to the one above. If it is considered an important substance,
then I will buy a lot.
[Edited on 5-2-2021 by vano]
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Bedlasky
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I don't think it is important reagent in homelab, but it have few interesting uses - catalyst in certain organic reactions, reagent for precipitation
of proteins and reagent for gravimetric determination of potassium. Look on wiki for more details.
There is also mention that this compound is super acid. I can test it in conc. sulfuric acid - I have plans for meassuring H0 for certain superacidic
systems using nitrobenzen as indicator, so I will tell you if it is superacid or not.
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vano
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I too am interested in using it in organic synthesis. I also think it is super acid and does not need a test. Its H0 is above 13.16. I can buy it very
cheaply, so if I can not use this compound often, i get tungstate anion above 8.3 pH.
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Fery
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Hi vano, I used H2WO4 as a catalyst in H2O2 cleavage of C=C double bond of oleic acid https://www.sciencemadness.org/whisper/viewthread.php?tid=15...
H2WO4 is poorly soluble in H2O but H2WO5 significantly better (somewhere it is referenced as WO3 . H2O2). I prepared it by direct dissolution of metal
W in 30% H2O2 (very slow process, I used welding W electrode, so low surface). You already have it in a soluble form. The original reference used 60%
H2O2 and I had only 30% H2O2 but it worked too (I observed that a lot of H2O evaporated during few hours of the reaction which concentrated the
unreacted H2O2) - it was just hard to manage the reaction to run at T 100 C, if the T rose few degrees higher than 100 C the H2O2 started to decompose
faster and faster which autocatalytically tried to destroy the peroxide - using a piece of old cloth wetted with cold water on the flask wall dropped
the T back quickly, using condenser would be contraproductive there as evaporating H2O helped to concentrate H2O2. When the T fall few degrees below
100 C the rate of exothermic oxidation slowed down and the T was falling faster and faster... 100 C was the optimal. H2WO4/H2WO5 seemed to inhibit
H2O2 decomposition significantly still at 100 C.
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Bedlasky
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Quote: Originally posted by vano  | | I too am interested in using it in organic synthesis. I also think it is super acid and does not need a test. Its H0 is above 13.16.
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Yes, but in the solid state. I don't know, how they determine H0 in solid state (this is mostly done by spectrophotomeric measurment of solutions with
some indicator). But its aqueous solution is deffinitely not a superacid. If you add oleum in to the water, you doesn't obtain superacidic solution
but just an ordinary acid. So I am interested if phosphotungstic acid behaves as superacid also in nonaqueous solution (and not just in solid state).
Fery: Higher stability of H2O2 solutions in the presence of H2WO4 have something to do with formation of peroxide complexes. H2MoO4 forms even more
stable complexes than H2WO4.
[Edited on 6-2-2021 by Bedlasky]
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vano
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Thanks.
I used 30g acid. I made Tungsten trioxide. But yeld was very low. Next I made only 1 gram copper tungstate and stored 2 gram trioxide. First I added
NaOH and pH was more than 8.3. Next when tungstate anion produced i added concentrated HCl. I want to make trioxide, but I don't like this method. Do
you have any ideas?
[Edited on 8-2-2021 by vano]
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vano
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I know it is a bad source, but i haven't choice. Otherwise, to get it, then I have to use tungsten carbide. It is quite difficult to find tungstate in
so many white compounds or trioxide in many yellow compounds.
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Bedlasky
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Thermal decomposition of ammonium dodecatungstate.
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vano
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Can i use sodium instead ammonium? Product will be sodium and Tungsten salt?
[Edited on 8-2-2021 by vano]
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DraconicAcid
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| Quote: Originally posted by vano |
Can i use sodium instead ammonium? Product will be sodium and Tungsten salt?
[Edited on 8-2-2021 by vano] |
If you thermally decompose an ammonium salt, you can get ammonia and water vapour. If you heat a sodium salt, nothing similar will happen.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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vano
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| Quote: Originally posted by DraconicAcid | | Quote: Originally posted by vano |
Can i use sodium instead ammonium? Product will be sodium and Tungsten salt?
[Edited on 8-2-2021 by vano] |
If you thermally decompose an ammonium salt, you can get ammonia and water vapour. If you heat a sodium salt, nothing similar will happen.
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Yes i know that. Reason is that ammonia solution cost more than alkaline hydroxide. Sodium and Tungsten salt is enough. I need eazy and cheap way to
make tungsten trioxide or tungstate from phosphotungstic acid. I can buy many of this acid, but yeld is very low.
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Bedlasky
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Vano: If you dissolve phosphotungstic acid in NaOH and your end solution is basic, than you get solution of Na2WO4 + Na2HPO4. You cannot separate
tungstic acid from this mixture, because after acidification you get phosphotungstic acid again.
If you heat Na2WO4.2H2O, you just evaporate water of crystallization. It deffinitely don't decompose in to sodium and tungsten trioxide - why would
this compound decompose in to very reactive sodium?
Wouldn't be easier to buy some sodium tungstate, instead making it from phosphotungstic acid (which is difficult). I think, that find WO3 or
Na2WO4.2H2O should be easier than find phosphotungstic acid, because these two compounds have many more uses than phosphotungstic acid. Na2WO4 can be
converted by HCl in to H2WO4 which can be dehydrate in to WO3.
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vano
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Thanks. When i said sodium, i meant sodium salt not metalic one. This is a method which i used. Phosphotungstic Acid + base, tungstate + hcl acid.
[Edited on 9-2-2021 by vano]
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vano
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Today I received more than 500 grams of the acid as a gift, I do not know how to use, because it is so much. so I will make oxide or tungstate.
[Edited on 9-2-2021 by vano]
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Bedlasky
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I have an idea. What I know, ammonium paratungstate have low solubility in water, so it will crystallize before phosphate. Paratungstates are formed
at pH 6, but ammonium paratungstates can form even from alkaline solution (ammonium orthotungstate can't be form by crystallization). Try dissolving
your phosphotungstic acid in ammonia, you should get ammonium paratungstate, which can be thermaly decomposed in to tungsten trioxide. If you want to
kept the ammonium salt, it have composition (NH4)10H2W12O42.4H2O.
[Edited on 10-2-2021 by Bedlasky]
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vano
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Bedlasky unfortunately I have now noticed this post. I will try that today.
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