woelen
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Explosion of ClO2 in presence of bromate.
I discovered a rather interesting phenomenon, and did two experiments. Use SMALL amounts of chemicals for these experiments if you wish to repeat
them, and use thick-walled test tubes, or use a test tube wrapped in a towel. DO NOT SCALE UP!
Experiment 1
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Take a small amount (at most 100 mg!) of solid sodium chlorite (80% NaClO2/20% NaCl, e.g. MMS powder from eBay) and add 2 ml or so of concentrated HCl
(35%). When this is done, then there is vigorous bubbling and a lot of intensely colored yellow gas is produced. This yellow gas is pure ClO2. This
gas can be ignited with a flame at the open end of the test tube. This gives an impressive WHOOP sound.
I repeated this experiment many times and always I obtained the yellow gas and never had an explosion.
Experiment 2
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This is like experiment 1, but instead of only NaClO2 a mix of NaClO2 and NaBrO3 (sodium bromate) is used. Not more than 100 mg total sum of weight of
both chemicals! When conc. HCl is added, then again there is vigorous bubbling and a golden yellow gas mix is produced. The somewhat golden color
probably is due to the presence of some BrCl besides ClO2. Just a few seconds after adding the acid, suddenly the gas above the liquid explodes with
an impressive BOOM. I tried the experiment two times and both times resulted in an explosion. The explosion starts at the liquid.
What surprises me in these experiments is that the presence of bromate causes certain explosion of ClO2. When bromate is added to HCl alone, then
mainly Cl2 is produced, but also some BrCl. The resulting gas mix then is yellow (Cl2, contaminated with the fairly intensely colored golden yellow
BrCl). I see no reason why ClO2 would explode in the presence of BrCl.
ClO2 does not explode in the presence of Cl2. When sodium chlorate is added to HCl, then you get a mix of appr. 2 parts of ClO2 and 1 part of Cl2 and
this mix is actually less prone to explosion than pure ClO2.
Any ideas of what kind of reaction could trigger the explosion in this little experiment?
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deltaH
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Fascinating, perhaps this kinetic study might be useful?
Kinetics and Mechanism of the Initial Phase of the Bromine−Chlorite Ion Reaction in Aqueous Solution, Zsuzsanna Tóth and István Fábián,
Inorg. Chem., 2000, 39 (20), pp 4608–4614
Theres more here in the thesis overview of Zsuzsanna Tóth as well as her other publications on the topic.
http://www.chem.science.unideb.hu/DoktIsk/Ertekezesek/KDI007...
I see there is mention of a reactive 'BrClO2' specie in those kinetics. Maybe this species is responsible?
[Edited on 17-5-2014 by deltaH]
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The_Davster
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As ClO2 can det simply from light, this implies a radical mech. It could be that ClBr is more easily able to form radicals as a result of
illumination, and said radicals trigger ClO2 explosion.
Try it in total darkness maybe?
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feacetech
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the roll of conc, temperature and pressure, apperantly its well studied and very predictable for ClO2.
Well so I was told by an expert from a company I worked for, they used it to decontaminate the building in the US during the anthrax scare.
They had to prove they werent going to blow the buildings up.
What if you generate the ClO2 with Citric acid or a different acid do you still get the same result?
On a side note, it was one of the only chemicals that actualy killed the annthrax spores on the control cards
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woelen
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Just to see what is responsible for the explosions, I tried the experiment with KBr instead of NaBrO3. I also did the experiment in near dark. With
KBr you also get an explosion. I did one experiment and the first experiment gave a (small) explosion. This is quite convincing.
Both bromate and bromide lead to formation of Br2 (or BrCl). With bromate, it is the HCl, which causes the formation of BrCl. With bromide, it is the
acidified chlorite and/or chlorine dioxide, which causes formation of BrCl.
So, apparently the presence of bromine (most likely in the form of BrCl) causes explosion of ClO2.
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AJKOER
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I suspect that a possible caustive initiator in the explosion comes not from ClO2 itself, or BrCl, but the formation of a very small amount of BrO2
(or Br2O) from the reduction of the bromate in the presence of water vapor, a chloride (including HCl from HClO2/HClO3 breakdown ) or bromide (from
the decomposition of the bromate), and a some amount of acid from the hydrolysis of ClO2 (that is, paralleling preparatory paths for ClO2).
Apparently, Bromine dioxide is much more unstable than ClO2 and just as explosive. In essence, it would be acting as the explosive primer for ClO2.
This hypothesis is stronger, in my opinion, in accounting for the change in the explosive behavior of ClO2 than postulating radical formations with
respect to BrCl (exactly how is BrCl formed here?) that some how initiates a detonation of the ClO2.
Note, the argument that Br2 is responsible is not in disagreement necessarily as the action of ClO2 and water vapor on Bromine could form an oxide of
Bromine. As these oxides are stable only at low temperatures, iimmediate decomposition/detonation would follow.
[Edited on 26-5-2014 by AJKOER]
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Zyklon-A
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Interesting theory, BrO2, is generally made by reacting bromine with ozone at -50 degrees C in freon, or passing an electric current
through bromine and oxygen at low temperatures and reduced pressure.
Is it just a guess, or do you have a ref. that says BrO2 can be made the way you suggested?
[Edited on 26-5-2014 by Zyklonb]
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AJKOER
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Actual, the standard of a preparatory path may be too strong here as we need only a transitory formation. In other words, aqueous reactions cannot be
too cold (solution will freeze) for a stable formation of BrO2.
Wikipedia on BrO2 does remark that its properties are similar to those of ClO2.
[Edited on 26-5-2014 by AJKOER]
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