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woelen
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I made a web page of the experiments. It contains two videos with the explosions and the sound of the bangs.
http://woelen.homescience.net/science/chem/exps/explosive_ch...
Edit: Made link to web page work again.
[Edited on 21-2-18 by woelen]
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not_important
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It does give a nice little 'snap', doesn't it.
Would be interesting to scale it up a bit. I'd try it, having a few kg of dichromate, but I too live in a dense urban area.
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YT2095
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if it`s of any use to anyone, it doesn`t seem to form using 9% H2O2.
it`ll go from the lemon yellow to NO2 brown then darker to bromine brown, but there will be no PPT.
Bubbles are formed though and liberate regularly (probably O2).
I guess you can count me out as a tester for this, 9% is the best I have.
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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woelen
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The brown material you have, indeed is from the CrO8(3-) ion. Were your solutions really ice cold and very concentrated (except the H2O2)? I indeed
did the synth with 30% H2O2. You also did not get any crystals after longer standing in the freezer? The crystals do not appear immediately, they only
appear after a longer time of standing.
You can concentrate your H2O2 quite well, by partially freezing it, such that half of it is frozen. The ice will be low in H2O2 and the remaining
liquid will have higher concentration. Separate the ice from the liquid. In this way you can easily go to 30%, repeat the procedure 2 times. Don't
discard the ice, it still contains a few percents of H2O2 and can be useful for other experiments.
You can make another peroxo compound of chromium with your 9% H2O2, that is Cr(O2)2(NH3)3. Dissolve some potassium dichromate (or better: ammonium
dichromate) in household ammonia, such that you obtain a yellow solution (it must really be yellow, not orange or gold-colored). Then add the hydrogen
peroxide. Assure liquids are cold. The liquid will darken and crystals will settle. I do not know, however, how stable this Cr(O2)2(NH3) is, so only
make very small amounts.
[Edited on 12-2-07 by woelen]
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12AX7
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Seems like a worse idea than ammonium dichromate! 
Tim
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YT2095
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I`ve left it in the fridge overnight (it`s still giving off bubbles) and there`s a Very slight ppt at the bottom, I`ll leave it another 24 hours and
see what happens, it`s unlikely to break down the existing ppt in that time I should imagine.
meanwhile I`ll get a PP bottle and conc some H2O2.
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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YT2095
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well it seems my patience paid off, the liquid became less Bromine brown and went very much lighter and there was a crop of crystals along the bottom
side of the test tube and at the base of it also, not a fantastic yield but a good milligram or 2, and certainly enough to experiment with 
I entirely forgot to conc some of the H2O2, but that can wait until the morning.
currently this compound is still in the test tube after a good rinse and is drying on its side under the lamp heater (I dry all my glassware that
way).
I`m looking forwards to tomorrow, I have plenty work and projects to complete, also my copper acetate should be ready for drying, already the
crystals are large and almost black looking, truly beautiful! I shall take some pics if the cam will do it justice.
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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Toran
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Some research on peroxchromates
Hello everyone!
I did some experiments with KPC's and just want to put some down her to prevent some accidents.
a) The formation of K3CrO8 in an alkaline solution is UV-light sensitive. Use only conventional light bulbs and avoid the sun. With neon light I got
no brown salt, evey time the solution got dark it decomposed. Somtimes very quick. Took me some time till I saw a light...
Proper cooling is essential as well. Lot of ice and salt will do.
Crystallisation will take place in the freezer at -10°C within 12 hours. In a dark freezer, that is.
Make the solution with H2O2 3-5% (maybe with the ice from the concentration). This will ease the addition of the concentrated H2O2 an you will see if
your raw materials are dirty with some catalyst.
b) CrO5 cannot be obtained in pure form, the compound is only temporarily stable in solutions like in ether. Decomposition to CrO3 is not possible as
far as I know. The structure of CrO5 is not totally clear. For more details read Gmelins Handbook of inorganic chemistry.
c) The mixture with P detonates. Comparable to Ag2C2. Pressure, friction, heat, hitting ...and base drums!!! I made small throwing crackers (cup of Al
around the finger, 0,05g mixture in, 1 grain lead and twisting tight - carefully!!!!) which exploded by dropping them. And deflagrated in my pocket
(in a small container with cotton filling which saved me) when I came near a ghetto blaster. Hitting the mixture with a hammer makes a loud, very
short bang, harder than heating it. I think that compresing should be tried very carefully. If compressed to a hard pill with less than 10% free space
there may be no detonation by heating. Somebody to try it?
d) Mixing : Don't stir! Not even with a feather! Put the two compounds in a small glass beaker (20ml) in amounts of max 25mg each. Shake slightly to
mix it.
e) Compressing : Possible up to approx. 3 bar without ignition. Keep care to reduce the friction in the process to a minimum.
f) Mixing wet : Possible. Do not use CCl4, CHCl3 or other alkali sensitive organic compounds. Cyclohexan, Pyridine or Toluene will go fine.
g)Storage : 21 years up to now. Very dry and nearly free of KOH. Slightly yellow color on the outside of the glass (K2CrO4 most probably). Will get
wet and decompose when not sealed airtight due to KOH traces.
h) ..and last for now : Keep care! Cr(VI) is cancerogenic! No maybe, it is. And if you burn yourself with Phosphorus (as I did, real black finger) put
CuSO4-Solution on it which will avoid a poisoning with white P.
That enough for now. Have fun.
sometimes you loose, sometimes the other win
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woelen
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| Quote: | Originally posted by garage chemist
Woelen, would it be possible that the green color you observed upon standing of the blue extract was caused by a mixture of yellow (from dilute CrO3)
and blue (from remaining peroxide)?
Or did green Cr2O3 precipitate from the solution? |
Sorry for the late response on this. I missed this post between the others.
The green color is not from a mixture of peroxide and chromate. After a much longer time of standing, the ether layer becomes clear and colorless
again, and some green slurry settles at the bottom. That green slurry most likely is a mix, containing chromium (III) and all kind of adducts from
water and ether.
@Toran: From your post I draw the conclusion that you have done quite a few nice things with the peroxo chromates. Do you also have experience with
the blue Cr2O12(2-) ion or the dark brown Cr(NH3)3(O2)2?
[Edited on 16-2-07 by woelen]
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woelen
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After some private communications with someone, who also wants to do some experiments with peroxo chromates, I decided to do a little experiment with
my K3CrO8. The result is good enough to dig up this old thread again.
I took approximately 25 mg of the solid and put this in a dry test tube.
I heated the test tube above a flame.
For quite some time nothing special happened, but suddenly I had a nice loud and dark bang. The bottom half of the test tube immediately was filled
with a bright lemon yellow smoke. This yellow smoke must be due to chromate:
Unbalanced pseudo equation: K3CrO8 --> K2CrO4 + K2O + K2O2 + O2.
When the test tube was allowed to cool down, some water was added. The yellow smoke at once dissolved and a bright yellow solution was obtained, the
well known color of a solution of a chromate.
So, potassium tetraperoxochromate (V) can explode, even without any reductor present. Not as violent as the mix with red P, but still quite
impressive. So, when someone is making this compound, please be careful. I have 15 grams or so of this compound, but I must not think of getting the
vial with this stuff in a fire, that certainly will give a very loud bang.
I made a small webpage about this explosive property of K3CrO8:
http://woelen.homescience.net/science/chem/exps/raw_material...
The videos on this webpage nicely show the explosion of K3CrO8.
Edit: Made link to web page work again.
[Edited on 21-2-18 by woelen]
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