99chemicals
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Weird things happening to H2O2 catalysts
Today I was trying to test some catlysts on some ~10% hydrogen peroxide.
I first poured about 2.5 ml of peroxide into a test tube. I then added about .7 ml of some copper acetate solution into the tube. After 10 seconds a
very small amount of green precipitate showed up along with gentle bubbling of the peroxide decomposing. That is the test tube to the right. What
could the small amount of green be?
I then added around 3 ml of hydrogen peroxide to another test tube and added about 2 ml of copper acetate solution. The solution when black and
bubbled a lot more vigorously and over flowed a little. I assume that some how the copper acetate is being reduced/oxidixed to copper I/II oxide.
After that I took about a ml ferric chloride solution and added it to 2.5 ml of the 10% peroxide. That was a lot more vigorous than the copper
acetate reaction. It decomposed and the solution when red (seen on right in picture below) The ferric chloride was being made into ferrous chloride?
I then took the red solution and added around 3 ml of sodium thiosulfate solution to that and got the pumpkin orange precipitate which settled out. I
looks like iron III oxide but how could that be?
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Diablo
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Based on the wikipedia entry, "Basic copper acetate is prepared by neutralizing an aqueous solution of copper(II) acetate. The basic acetate is poorly
soluble. This material is a component of verdigris, the blue-green substance that forms on copper during long exposures to atmosphere." Perhaps what
you have now is this?
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AndersHoveland
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Quote: Originally posted by 99chemicals  | I first poured about 2.5 ml of peroxide into a test tube. I then added about .7 ml of some copper acetate solution into the tube. After 10 seconds a
very small amount of green precipitate showed up along with gentle bubbling of the peroxide decomposing. That is the test tube to the right. What
could the small amount of green be?
I then added around 3 ml of hydrogen peroxide to another test tube and added about 2 ml of copper acetate solution. The solution when black and
bubbled a lot more vigorously and over flowed a little. I assume that some how the copper acetate is being reduced/oxidixed to copper I/II oxide.
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I really do not see anything mysterious about these reactions. In the first reaction, the hydrogen peroxide, since it was catalyzed by copper ions,
was able to oxidize some of the acetate. That green precipitate was likely basic copper acetate or copper(II) carbonate. In the second reaction,
copper(II) oxide is a black color.
As for how copper ions are able to catalyze H2O2, I think that the copper ions are being transiently oxidized to a higher oxidation state (Cu+3), but
this higher oxidation state is immediately reduced back to Cu+2 by more H2O2, which can also act as a reducing agent, with the release of O2.
Actually, if I remember correctly, copper has its own uniqe way of decomposing H2O2, so this may be true of other transition metals but not copper. I
think I read that the a hydroperoxide of copper forms, and this is the oxidizing intermediate. I made a more detailed post about this, the ammonia
complex of copper hydroperoxide has been used as a selective oxidizing agent in organic chemistry, but frustratingly I cannot find any details now.
http://www.sciencemadness.org/talk/viewthread.php?tid=11623
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99chemicals
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I under stand the first reaction now but what is happening to the ferric chloride?
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I Like Dots
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While I was making copper acetate, I saw the same thing.
I used regular vinegar with 30% H2O2.
The reaction stopped and was a nice blue color..I added some more H2O2 because it still smelled like vinegar.
As I was pouring the Peroxide in, it immediately precipitated out copper. It was black, but started to look brownish, like old copper. I was pretty
ticked off because this took awhile, now I ruined it. >
I added some more vinegar and it rather quickly turned green. When I filtered it there was a lot of brown dust on the filter paper.
I evaporated a teaspoon of this liquid and it looks like regular copper acetate. But my regular copper acetate solution is blue, not green, what
happened?
The H2O2 turned the copper acetate into copper carbonate? So I should be able to purify by filtering the liquid because copper carbonate is not
soluble in water?
[Edited on 29-4-2013 by I Like Dots]
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