plante1999
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H2O2 + Cr2O3
5minute a go i was ading Cr2O3 on 30% sol. of H2O2 to check if it act like a Catalisor ( for HNO3 production) but , when i ad it it disolve to an dark
red oil that make an huge ammont of buble (GAS) that is not oxigen but , when i make the test the wood match accidentaly fall in the solution , and a
very uge rocket of fire was made. All the solution returned to green , i suspect an Cr VI species but witch one ? Do you think it be CrO3?
Thanks!
I never asked for this.
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AJKOER
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See the attached reference that uses Sodium Peroxide, Na2O2, in place of H2O2 on Cr2O3.
http://www.ajcn.org/content/49/5/901.full.pdf+html
Note, Sodium Peroxide in water yields H2O2:
Na2O2 + 2 H2O → 2 NaOH + H2O2
so you are performing a hydrated form of the reaction addressed in the article (just my opinion).
[Edited on 29-5-2011 by AJKOER]
[Edited on 29-5-2011 by AJKOER]
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symboom
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Quote: Originally posted by AJKOER  | See the attached reference that uses Sodium Peroxide, Na2O2, in place of H2O2 on Cr2O3.
http://www.ajcn.org/content/49/5/901.full.pdf+html
Note, Sodium Peroxide in water yields H2O2:
Na2O2 + 2 H2O → 2 NaOH + H2O2
so you are performing a hydrated form of the reaction addressed in the article (just my opinion).
[Edited on 29-5-2011 by AJKOER]
[Edited on 29-5-2011 by AJKOER] |
yes but that decomposes to O2 with evolution of heat because peroxide is unstable in high ph.
how concetreated is your peroxide i guessing it oxidized (burned) forming a higher oxidation state
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froot
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Your description matches that for Cr2OCl2, any chance there is a chloride in there somewhere?
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blogfast25
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| Quote: Originally posted by plante1999 | 5minute a go i was ading Cr2O3 on 30% sol. of H2O2 to check if it act like a Catalisor ( for HNO3 production) but , when i ad it it disolve to an dark
red oil that make an huge ammont of buble (GAS) that is not oxigen but , when i make the test the wood match accidentaly fall in the solution , and a
very uge rocket of fire was made. All the solution returned to green , i suspect an Cr VI species but witch one ? Do you think it be CrO3?
Thanks! |
You claim the gas wasn’t oxygen, yet claim a huge fire occurred when you approach it with a test match!
In alkaline conditions, CrO<sub>2</sub><sup>-</sup> (+III) is oxidised by HO<sub>2</sub><sup>-</sup>
to chromate: CrO<sub>4</sub><sup>2-</sup> (+VI)
Dichromate (Cr<sub>2</sub>O<sub>7</sub><sup>2-</sup> , however, is capable of oxidising H2O2 to oxygen, the chromium being reduced back to green Cr<sup>3+</sup> (consistent with
your green colour).
This is in all likelihood what you saw, due to the high peroxide concentration…
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plante1999
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I think the solution is more oxidizing thant the 30% H2O2.
Likelihood you said... I will repeat this experiment this week , with a procedure adapted for examination of this reaction and not experimentation
about catalist.
[Edited on 6-6-2011 by plante1999]
I never asked for this.
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blogfast25
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I have seen something very similar happen in quite dilute solutions (less than 0.1 M Cr, 6 % H2O2) when using the peroxide to oxidise chromite (III)
to chromate (VI) with H2O2. On acidifying to convert the chromate to dichromate, oxygen was then released: that was the formed dichromate oxidising
the excess H2O2 to O2. Of course I was deliberately manipulating pH, whereas you weren’t. But the in the much more concentrated solutions you were
using, this explanation remains the most likely one… Remember that most of the laws, rules and recipes in inorganic chemistry are ‘designed’ for
quite dilute solutions.
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woelen
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| Quote: Originally posted by plante1999 | | 5minute a go i was ading Cr2O3 on 30% sol. of H2O2 to check if it act like a Catalisor ( for HNO3 production) but , when i ad it it disolve to an dark
red oil that make an huge ammont of buble (GAS) that is not oxigen but , when i make the test the wood match accidentaly fall in the solution , and a
very uge rocket of fire was made. All the solution returned to green , i suspect an Cr VI species but witch one ? Do you think it be CrO3?
|
What did you do in this experiment? I really cannot reproduce any of these results. I am inclined to think that you did not have Cr2O3. Cr2O3 is very
inert.
I tried the following:
- Take Cr2O3 and add 30% H2O2 --> Nothing happens
- Take Cr2O3 and add 50% H2O2 --> Nothing happens
So, with real anhydrous (calcined) Cr2O3 there is no reaction, nothing at all. Not even a gentle catalytic action on the decomposition of the H2O2.
Next I did an experiment with home-made hydrous Cr2O3 (also written as Cr(OH)3). Making this is not difficult:
- Dissolve a lot of chrome alum in water.
- Add excess ammonia. A green precipitate is formed.
- Shake such that all chromium(III) is allowed to react.
- Add a lot of water and shake again.
- Let precipitate settle (this takes a day)
- Decant as much of the water as possible
- Shake again
- Let precipitate settle again
- Decant almost all water and collect the rest of the green slurry on a coffee filter.
- Scrape off the green mud (do not allow it to dry)
Making Cr(OH)3 with NaOH is not easily done. If excess NaOH is added, then the precipitate redissolves, giving chromite in solution. Chromium(III)
hydroxide is amphoteric.
This green mud was added to 30% H2O2. Again nothing happened. There was faint production of oxygen, but only very slowly and in small quantities.
Similar experience with 50% H2O2.
Finally, I added some NaOH. When this is done, then production of oxygen becomes faster, but not violent. The precipitate dissolves and the liquid
becomes yellow/brown. Only in the presence of NaOH there is formation of chromium(VI) and subsequent formation of a peroxo complex of chromium(VI).
The addition of NaOH causes the hydrous Cr2O3 to dissolve and then this is oxidized by the H2O2.
When the brown solution is added to dilute H2SO4, then a nice blue solution is obtained, which quickly looses its deep blue color and becomes pale
green/grey.
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plante1999
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The Cr2O3 was from decomposition of ammonium dichromate.
I will made some experiment and I will show the results.
I never asked for this.
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blogfast25
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That makes me think your results may have been caused by undecomposed (NH4)2Cr2O7 but let's see your experiment first...
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woelen
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I have done my experiment with two kinds of Cr2O3. One kind is the green powder from a pottery supplier, the other part is Cr2O3 from decomposition of
ammonium dichromate. In order to remove unreacted ammonium dichromate I left it standing in distilled water for a few days, decanted the water and
repeated that process three times. At the third time no yellow color was given to the water anymore.
So, indeed I think that the Cr2O3 used by plante1999 was strongly contaminated with unreacted ammonium dichromate. That decomposition reaction is far
from clean, more than 10% of the ammonium dichromate may remain, especially if the material is put in an open pile and that pile is ignited.
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plante1999
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I am compiling the results , the rapport will be finish in 1 day.
I never asked for this.
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plante1999
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Different type of Cr2O3 , and result of 0.5g of the Cr2O3 with 5ml of 30% H2O2 ( outch , Befor I made the test I have 25ml of it , now i have 10ml) at
RT approx 18 degree C :
Ammonium dichromate , decomposition in a pile Temperature : Unknow : Disovle readily , make a dark red precipitate ( probably CrO3) all the Cr2O3
disolve , make bubble that do not religth a glowing splint.
Ammonium dichromate , decomposition in a test tube approx 550 degree C , this is the one that I use: Disolve slowly do not make precipitate , red sol
make buble that do not religth a glowing splint.
Ammonium dichromate , decomosition in my tiny metal fondry (100ml of metal) approx 1300 degree C (copper is very liquid in it copper meting point:1084
degree C) : Nothing seem to happen.
Conclusion : It seem that the presence of Dichromate is nessecary for acelerating the disolution and that no oxygen seem to be produce , I do not know
if it is that not enoug oxygen is produce or another gas is produce , I think the first one is more probable.
[Edited on 1-7-2011 by plante1999]
I never asked for this.
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woelen
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Your experiments confirm my observations. When heated at 1300 C then no dichromate remains left and you only have chromium(III). Nothing happens in
that case.
In the other two cases, unreacted dichromate remains and this dissolves, giving a red solution (which is due to formation of a peroxo complex of
chromium(VI) in weakly alkaline solution).
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