Darsh
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Copper peroxide complex?
So, I seem to have inadvertently synthesized a strange red/orange compound while trying to make a copper-ammonia complex.
I first made a solution of 200 mL of 5% acetic acid and 10 mL of household ammonia (to form NH4C2H3O2 in situ). I then put this solution under
electrolysis for about half an hour using 7 volts DC with a copper anode and cathode. After the half hour, a large amount of black material (Which I
presume is carbon) was observed on the cathode. At this point I attempted to bubble NH3 gas through the solution. No color change was noted after a
large amount of gas was bubbled through. I then used a pipette, which was apparently not very clean, to remove some of this liquid. The liquid inside
the pipette turned a very dark orange/red color. I realized that I had recently used the pipette with hydrogen peroxide and must not have cleaned it
thoroughly. I then repeated the above procedure, except without the bubbling of NH3 gas after electrolysis. After adding 3% H2O2, I still ended up
with a red solution.
So, after research, I have determined that a copper-peroxide complex may have been formed, but I haven't found any literature on this compound other
than passing mentions in a few health journals. Another possibility may be the formation of copper (III) ion. However, the CRC handbook's standard
reduction potentials table seems to indicate that this is very unlikely, which along with the instability of copper (III) in solution makes me doubt
this theory quite a bit.
So, I was wondering if anyone would have any insight or thoughts on what I may be observing?
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kclo4
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looks like all of the copper-peroxide complex articles talk about biological matterial. Perhaps the copper-peroxide complex is complexed with some
sort of protien?
* Copper(I) oxide (cuprous oxide, Cu2O), a red powder;
* Copper(II) oxide (cupric oxide, CuO), a black powder.
http://en.wikipedia.org/wiki/Copper_oxide
That sounds more reasonable to me.
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Darsh
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I've considered the oxides, but the product I have has remained completely in solution. The color of the solution is similar to the color of the
copper bromide/chloride complex on Woelen's website (which is incidentally how I found this website) in this
article:http://81.207.88.128/science/chem/exps/copper_halogenide/index.html.
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JohnWW
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To determine conclusively whether it is a peroxo complex of Cu(II), or a complex of Cu(III), which differ in the number of unpaired 3d electrons per
mole, you would need to do either a measurement of its paramagnetic susceptibility on a magnetometer, or take its ESR spectrum. In another thread,
someone prepared a Cu(III) compound which was an intense red color. However, there are qualitative chemical tests available for peroxide groups.
There are indicator strips available which change color on reaction with a peroxo compound.
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garage chemist
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The black substance could be finely divided copper, which is black.
As the black substance formed on the cathode, it is very likely to be copper.
I have seen black finely divided metals form at cathodes myself. Silver can do this. Platinum too, think of the "platinized platinum electrode" which
is cathodically coated with Pt black.
Copper(I)complexes can also have a dark color. There is also some kind of complex formed in solutions containing both Cu(I) and Cu(II)ions, which is
also strongly colored. Woelen can tell you more about this.
Maybe your solution contained mostly Cu(I)complex ions with ammonia as ligand, and then you created some Cu(II) with the H2O2.
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kmno4
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I have made few experiments (tests rather).
Effects:
Even solutions of copper(II) acetate or nitrate give dirty yellow-brown colour with 30% H2O2. This "colour" is stable up to boiling point - then O2
goes off and unchanged, blue Cu(II) solutions are obtained again.
So acetic anion or ammonium kation /ammonia have nothing to do with this colour.
BTW. carbonaceous material is often mentioned in the case of electrolysis of acetates
Edit:
This brown something is unstabe in acidic solutions and if H2O2 is introduced to acidic Cu(II) sol. then it does not appear at all.
Sol. Cu(II) acetate + H2O2 gives brown sol. and soon O2 bubbles appear. When citric acid is then added, brown colour slowly turns to green and with
short heating green turns to blue. O2 bubbles disappear.
Probably it is the same substance as in the case of acting of H2O2 on Cu(OH)2 or [Cu(OH)4](-) - "copper (hydro?)peroxide"
[Edited on 2-1-2009 by kmno4]
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Elawr
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Aqueous copper (II) will precipitate as Cu(OH)2 with small amounts of NH3, before any cuprammonium complex can form. In presence of H2O2, the light
blue precipitate turns olive green then dark reddish black or brown as the copper hydroxide turns into copper peroxide. This is unstable at low Ph,
however, and the peroxide will then give up O2 and dissolve as simple Cu II.
When I first encountered it, I mistook it for CuO! It was while playing around with some Cu(OH)2 freshly precipitated from dilute CuSO4 using NaOH,
that I observed it.
Several of the older textbooks of inorganic chemistry describe the copper peroxides in fair detail. Check Google books if you are interested in such.
[Edited on 10-4-2009 by Elawr]
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