woelen
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Chlorine dioxide, production and ignition of this colorful gas
I did some experiments with chlorine dioxide. This gas can be made at high purity from sodium chlorite and hydrochloric acid. In this reaction no
chlorine is produced (I did not smell any, and the smell of chlorine is very strong, so it hardly can be missed).
The chlorine dioxide can be ignited and 'burns' with a pale grey flame and at higher concentration it explodes, when ignited (it sometimes even
self-ignites, for no apparent reason).
http://woelen.homescience.net/science/chem/exps/ClO2_propert...
I liked this experiment quite much. It is nice to see such a strongly colored gas disappear. Most beautiful results are obtained if one can make the
gas in such a low concentration that it slowly decomposes and one can see the decomposition move through the gas.
Don't scale up the experiment, only make small test tubes full of gas and do not confine the gas!
[Edited on 6-1-13 by woelen]
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Fleaker
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Excellent, as usual. I can't wait to try this out as a demo. Your experiments make perfect demonstrations for general chemistry classes!!
Neither flask nor beaker.
"Kid, you don't even know just what you don't know. "
--The Dark Lord Sauron
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chloric1
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sodium chlorite is exotic for some. I suggest mixing solid potassium chlorate and solid oxalic acid and adding dilute sulfuric acid. No reaction
occurs at room temp but put the reaction vessel in some hot water a controllable evolution of chlorine dioxide ensues with a diluent of carbon
dioxide. Simply cooling the flask in cold water will stop the reaction and it can be restarted with GENTLE heating to 60 or 80 degrees Celsius. I
wouldn't store this mix though but it sure is nice to have a controllable reaction.
Fellow molecular manipulator
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Magpie
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Very nice work woelen. This brings back memories of one of my first jobs out of college at a pulp mill. IIRC the bleaching sequence for the pulp out
of the digester was: NaOH/Cl2/NaOCl/ClO2. I remember that the mill used a chlorate salt to generate the ClO2.
ClO2 is an excellent bleaching agent and that is one reason it is on the end of the above sequence, ie, to get the maximum brightness (whiteness) for
the pulp. You might enjoy an experiment with some ClO2 bleaching. Take some brown paper bag or such, slurry it up in water, and then expose it for a
few minutes to an aqueous solution of ClO2. You should gain quite a few points of brightness. 
[Edited on 24-3-2008 by Magpie]
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The_Davster
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As always, very nice!
Even the solid chlorite works as a bleaching agent. I have observed a few grains of chlorite bleach a paper bag in spots just by sitting on it
overnight. It even bleaches cork, which is odd to observe.
Some camping/hiking stores sell solutions of chlorite for emergency disinfectation of ground water. I can purchase 15% sodium chlorite for this
reason at a local shop. The reagent grade chlorite I came into was just luck, and it is very hard to find anywhere.
[Edited on 24-3-2008 by The_Davster]
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MagicJigPipe
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Well, then I suppose that means that he chlorite ion (ClO2-) is responsible for the bleaching effect. So, of course chlorite salts in solution should
accomplish this as well (ClO2 shouldn't bleach without H2O present to ionize). Is this correct?
[Edited on 24-3-2008 by MagicJigPipe]
"There must be no barriers to freedom of inquiry ... There is no place for dogma in science. The scientist is free, and must be free to ask any
question, to doubt any assertion, to seek for any evidence, to correct any errors. ... We know that the only way to avoid error is to detect it and
that the only way to detect it is to be free to inquire. And we know that as long as men are free to ask what they must, free to say what they think,
free to think what they will, freedom can never be lost, and science can never regress." -J. Robert Oppenheimer
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7he3ngineer
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Up to your usual standard of experiments and write-ups woelen!
Is that a spirits burner made from an old ink bottle? ...engenuity
Josh
Engineers aren\'t boring people, we\'re just interested in boring things!
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woelen
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Its an alcohol burner from a chemistry set. I use this thing quite a lot and you can see it on many of my webpages
The suggestion of trying a bleaching experiment also sounds good. I called this webpage "properties of ClO2", so that would nicely fit in the webpage.
I know the method of CO2/ClO2 production in a 1 : 1 ratio. For this particular experiment it is less suitable, because for the explosion demo with the
grey flame you want the gas in an almost pure state.
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AndersHoveland
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I think that chlorine dioxide can be prepared by reacting a solution of sodium chlorate with a limited quantity of hydrochloric acid:
2 NaClO3 + 4 HCl --> 2 NaCl + 2 H2O + 2 ClO2 + Cl2
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woelen
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Yes, that is indeed the reaction which occurs, but the ratio of chlorine to chlorine dioxide is not fixed. There are two reactions, one which produces
ClO2 and the other produces Cl2 and any linear combination of these reactions is possible. So, in practice there is not a precise stoichiometric ratio
between the amounts of Cl2 and ClO2.
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Endimion17
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This is awesome. Most people are scared to work with this gas.
Just wondering... did you have any failed videos where your hand would jerk because of stress?
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woelen
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Why should I have stress if I only have test tube amounts of gas, unconfined? Keep in mind that a test tube full of gas only is milligrams of
material, spread over a relatively large amount of space.
I would feel more stressed if I had around 100 ml of the gas in a spherical flask with a narrow opening. An explosion then may shatter the glass.
I routinely ignite open test tubes with gas mixes to test their flammability. I many times had loud pops and whoosh sounds, but if you are prepared
for that, then it is not that scary. The geometry of the test tube also helps. The open end is as wide as the tube itself and in such cases the
chance of shattering is very low.
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Heuteufel
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If you heat the bottom of the test tube with the bunsen burner, the chlorine dioxide is confined by its own explosion, and a very loud bang occurs
(the glass may also shatter, and there are lots of projections) (my own experience).
A similar thing occurs, when you cause the decomposition by an incandescent wire: http://lp.uni-goettingen.de/get/text/2036
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Endimion17
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Quote: Originally posted by woelen  | Why should I have stress if I only have test tube amounts of gas, unconfined? Keep in mind that a test tube full of gas only is milligrams of
material, spread over a relatively large amount of space.
I would feel more stressed if I had around 100 ml of the gas in a spherical flask with a narrow opening. An explosion then may shatter the glass.
I routinely ignite open test tubes with gas mixes to test their flammability. I many times had loud pops and whoosh sounds, but if you are prepared
for that, then it is not that scary. The geometry of the test tube also helps. The open end is as wide as the tube itself and in such cases the
chance of shattering is very low. |
Because it's a reflex. Most people can't get used to such bangs. I know that how much I try to light up a small test tube filled with knallgas, I
always get startled. It's obvious nothing bad can happen, but...
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woelen
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| Quote: Originally posted by Heuteufel | If you heat the bottom of the test tube with the bunsen burner, the chlorine dioxide is confined by its own explosion, and a very loud bang occurs
(the glass may also shatter, and there are lots of projections) (my own experience).
A similar thing occurs, when you cause the decomposition by an incandescent wire: http://lp.uni-goettingen.de/get/text/2036 |
I never heat test tubes with such explosive gases at the
bottom, I always ignite at the open end.
The link you provided describes a very dangerous experiment which I would never do myself. This indeed may lead to nasty explosions. In my
experiments, pure ClO2 is produced from aqueous solutions and no heat is involved at all (the reaction is not exothermic nor is it necessary to heat
up things in order to speed up the reaction).
[Edited on 8-1-13 by woelen]
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AndersHoveland
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That is an understatement. Explosions usually occur with this reaction. Often it is several small popping/splattering explosions in
quick consecutive sequence. And this is just when an eye dropper is used to drop a few drops of the sulfuric acid onto the chlorate. I shudder to
think what would happen if one emptied a whole test tube of the acid into a beaker containing some chlorate! Probably a big explosion shooting out the
acid everywhere. I just cannot think of any reaction more dangerous (at least one that does not involve extremely toxic chemicals).
However, there are a few mentions in the old literature about this reaction being successfully used to disproportionate chlorate into perchlorate:
"When finely powdered KClO3 is gradually added (over several small additions) into a dish containing conc.
H2SO4, using 1 part H2SO4 and 1 part KClO3, the solution warms, and ClO2, KHSO4 and KClO4 form, the latter two can easily be separated by
crystallization."
(Mitscherlich. Pogg. Ann. 25 [1832] 298)
Another interesting thing about this reaction is that it turns a deep red color, I suspect because of chloryl cations, ClO2+,
that transiently form in the concentrated sulfuric acid solution. As soon as it is diluted with water, the color dissappears.
[Edited on 8-1-2013 by AndersHoveland]
I'm not saying let's go kill all the stupid people...I'm just saying lets remove all the warning labels and let the problem sort itself out.
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Heuteufel
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In qualitative inorganic analysis you can consider yourself very lucky, if you see a green gas being evolved during the preliminary test with
concentrated sulfuric acid, followed by a loud bang. It means, you have identified at least one anion without any doubt (chlorate - chlorite is too
exotical). 
| Quote: |
The link you provided describes a very dangerous experiment which I would never do myself. |
I would rather call it an impressive demonstration of the dangers of chlorine dioxide. When performed in a fume hood or behind a safety screen you
risk nothing.
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AndersHoveland
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Perhaps with a robotic arm and extra thick plexiglass  .
But seriously, even if you are using just an eye dropper, I would strongly suggest wearing a chemically resistant long sleave glove, and have your
entire body (including shoes) covered with splash-proof wear. You should also wear a face shield, I would still suggest one, rather than just goggles,
even if you are behind a safety screen. The reason being because the screen may be partially raised while you are working at it, at if there is a big
explosion the acid that shoots out might have a chance of bouncing/splattering off the surface, or possibly even shooting out in all directions out of
the opening by a pressure wave inside. Eye dropper ammounts should be reasonably safe, but anyhting more (like a test tube)... that mix of
concentrated sulfuric acid and chlorate is going to be very corrosive, might want to be sure to use the right chemically resistant gloves, possibly
double glove. If the explosion is big enough, the glass fragments could potentially rip through the gloves, which would also be drenched in acid, and
then you would be in trouble. Perhaps I am being overly cautious here, but better safe than sorry.
Woelen's experiment with chlorite and hydrochloric acid is much safer in comparison.
Preparing Chlorine Dioxide from Chlorite
Chlorine (1.36v) is also a stronger oxidizing agent than chlorine dioxide (0.96v) (at least under alkaline/neutral conditions), so chlorine dioxide is
often prepared by passing chlorine gas into sodium chlorite solutions.
2 NaClO2 + Cl2 --> 2 NaCl + 2 ClO2
[Edited on 9-1-2013 by AndersHoveland]
I'm not saying let's go kill all the stupid people...I'm just saying lets remove all the warning labels and let the problem sort itself out.
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AndersHoveland
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In another common process used in water treatment, chlorine dioxide is made by reacting a mixture of sulfuric acid (dilute) and hydrogen peroxide with
sodium chlorate:
2 NaClO3 + H2O2 + H2SO4 --> Na2SO4 + 2 H2O + 2 ClO2 + O2
(In this reaction, hydrogen peroxide is acting as reducing agent towards the chloric acid.)
[Edited on 27-1-2013 by AndersHoveland]
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Traveller
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Is it not also possible to make up a solution of chlorite and water and apply electrolysis to it to make chlorine dioxide?
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