Parakeet
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HVO3 - Vanadic acid ?
I recently found this compound being sold while looking for my source of vanadium(V) and was wondering about its properties. I could find very little
information about this compound.
My questions are :
・Does anyone know about this stuff, or has anyone used it before?
・I want some sodium metavanadate. Will I get NaVO3 if I neutralized vanadic acid with sodium hydroxide?
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chornedsnorkack
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Quote: Originally posted by Parakeet  | I recently found this compound being sold while looking for my source of vanadium(V) and was wondering about its properties. I could find very little
information about this compound.
My questions are :
・Does anyone know about this stuff, or has anyone used it before? |
How does the seller demonstrate the stoichiometric purity? That is, that they have crystalline HVO3, rather than amorphous hydrate of
variable stoichiometry?
Possibly but how do you get it reliably? What might be easy to get is Na3VO4 - use excess NaOH. But at lower alkali excesses,
vanadates have the tendency to polymerize.
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Bedlasky
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Nothing like vanadic acid doesn't exist. There is only V2O5 and V2O5.H2O. Description of product as HVO3 is quite odd, who knows what the seller
actually sell.
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B(a)P
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Older (early nineteen hundreds) text books/papers refer to V2O5 as vanadic acid.
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teodor
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The general practic is treating V2O5 sold by different suppliers as V2O5 + nH2O + lower V oxides + other impurities.
If you need it pure it is better to convert it to NH4VO3 and decompose to V2O5 * H2O which is basically HVO3 but the problem it easily absorbs more
water from the air to form V2O5 * 2H2O, so there is no use of the formula HVO3 except for the salts.
NaVO3 and NH4VO3 can be easily converted to each other. The forms I have worked with have completely different crystal structures. NaVO3 is a
silk-like elastic threads looking like some organic polymer and NH4VO3 is just a snow-white powder, but probably it depends on the method of crystall
formation which would be different because of quite different solubility.
To test the purity of your V2O5 you can use this procedure.
1. Dissolve 17.5 g of Na2CO3 or 28 g of NaHCO3 in 125 ml of water in 400 ml beaker. NaOH or mix of NaOH and NaHCO3 could also be used.
2. Make it boiling and add 25 g your V2O5 (HVO3 or watever) in SMALL portions to the boiling solution (effervescence). Be careful to protect the place
from the spray, it's a bit toxic (not deadly).
3. If the color of the solution after the addition of V2O5 is blue or green, measure some volume of it in a test tube and add pink KMnO4 until it
becomes yellow. This is lower V oxides impurities. Add the calculated amount of permanganate to the solution to eliminate the lower oxides.
4. Filter it.
6. Put 75 g of NH4Cl into 125 ml of water and make the suspension boiling. It is hard to dissolve everything but try. The undissolved part should not
spoil the result.
7. To the near-boiling solution of NH4Cl add the first solution of NaVO3, the best when the last has temperature near 60C (effervescence!).
After several hours filter NH4VO3 and wash it one time with ice-cold water. Dry on the air.
If you V2O5 is pure the resulting NH4VO3 will be snow-white. If not, forget about V2O5 * H2O stoichiometry, it is not correct because it is not pure.
To purify it you can convert between NaVO3 and NH4VO3 several times. The difference between those 2 compounds is great difference in solubility. It is
possible to crystallize NaVO3 but with NH4VO3 you have lesser loss (in my experiments I've got yield from the first crystallization as 88% of
theoretical).
To convert NH4VO3 to NaVO3 solution add NaHCO3 or NaCO3 or NaOH and boil. NH3 and CO2 will leave the solution and you will get NaVO3 only.
To convert NaVO3 to NH4VO3 use the procedure described above.
NH4VO3 could be converted to V2O5 * H2O and further to V2O5 by heating and to other hydrates by adding acids to its water solution.
I can share more details about my experience with purification of V2O5 if you are interested.
[Edited on 25-5-2023 by teodor]
[Edited on 25-5-2023 by teodor]
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Parakeet
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@chornedsnorkack
I'm not sure. Here is the picture from the auction site where I found this.
It's grainy and hard to read, but I think this is the manufacturer's website.
https://chemcraft.su/node/23382
I'm not familiar with vanadium chemistry, but can't I just add the stoichiometric amount, assuming that it's 100% HVO3?
@Bedlasky, @B(a)P
Interesting point. So, maybe it's just 1/2V2O5・1/2H2O.
Judging from it's color, this might be a leading theory.
@teodor
Thanks for the detailed procedure. Unfortunately, KMnO4 is very difficult for me to get. Oh well.
I actually want vanadium for oxidation catalyst, as well as to enjoy colorful vanadium compounds. Since V2O5 is restricted in my country, I have to
buy something else, and found a website selling both NaVO3 and the said HVO3. At first I thought I'd buy the latter, because the former contained 250g
for about 40$, and I don't need that much. But considering the unreliability of purity, I might buy NaVO3, then convert it into NH4VO3 and then V2O5.
 
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teodor
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For your purpose I think it is better to use HVO3 (V2O5 * 1..2H2O) "as is". You don't need it pure for usage as a catalyst as well as test tube type
experiments.
But generally, the price for compound is dependent on its purity. So, if you have "pure for analysis" it can be used in wider types of reactions than
just "pure".
But NH4VO3 p.f.a. can cost something around 180 USD per 250g (e.g., LiMac Science), so for your case just buy what is afforded as cheapest price per 1
mole of V and purify it when you will need it more pure.
[Edited on 25-5-2023 by teodor]
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woelen
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In my experience, V2O5 can be obtained in quite a pure state from pottery suppliers. The latest sample I purchased does dissolve in NaOH and forms a
completely clear and colorless solution. If it would contain vanadium in lower oxidation state, then the solution would be brown (due to formation of
V4O9(2-) at high pH, hypovanadate). Other impurities most likely would cause turbidity of the solution, due to formation of insoluble
oxides/hydroxides.
The pure sample, I have is this: https://www.keramikos.nl/chemicalien/5957-vanadiumpentoxide-...
This material is really good, it has a nice yellow/orange color.
I don't know if they ship abroad.
I also have another sample from another shop (Creavisie in Surhuisterveen, close to Drachten, where I picked it up). This vanadium pentoxide has
noticeable impurities. It dissolves in a solution of NaOH, but the solution does not become clear and after some time, a thin layer of brown mud
settles at the bottom. This might be iron oxide, but I did not test it.
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teodor
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I can confirm that V2O5 from Keramikos is of relatively high purity.
It forms clear yellow solution with NaHCO3. On my experience Fe impurities becomes visible on prolonged standing. In this case I noticed some amount
of Fe3+ oxide-like flakes after few weeks (but it could be from NaHCO3 also).
The conversion to NH4VO3 gives a bit pinkish powder, something I would expect from Mn presence. I would like to test it for Mn but didn't find a test
yet which will definitely separate V and Mn ions in the case of low concentration of Mn.
The second crystallization (NH4VO3 -> NaVO3 -> NH4VO3) improves the purity.
On this foto there is the starting material, the result of the first crystallization is on the left and the second crystallization is on the right.
Each crystallization cause 12-14% loss of the material, not so many, so it can be repeated multiple times.
[Edited on 26-5-2023 by teodor]
[Edited on 26-5-2023 by teodor]
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Parakeet
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Keramikos seems like a good shop, but it's risky to import restricted items. I'd rather buy NaVO3 and purify it. (HVO3 is actually expensive for V per
gram)
Thank you for your advices and suggestions.
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