Romix
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Grey copper hydroxide
I did electrolysis of pure copper in tap water.
First time I did it, I'v got blue copper hydroxide on anode, and hydrogen on cathode. also blue copper compound swimming on the top of cathode.
How I understand it,Cu = Cu2+ + e2 , Cu+2 + 2OH- = Cu(OH2)
2H+ + 2e = H2
Second and third electrolysis I did, grey hydroxide formed on anode. what is it? and why it changed colour? I used same electrodes, same
electrolyte(filtered).
[Edited on 27-6-2015 by Romix]
[Edited on 27-6-2015 by Romix]
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Volanschemia
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Was there a temperature difference the second time? Copper(II) Hydroxide decomposes pretty easily to Copper(II) Oxide (a black/grey insoluble
compound) and water:
Cu(OH)2 = CuO + H2O
"The chemists are a strange class of mortals, impelled by an almost insane impulse to seek their pleasures amid smoke and
vapor, soot and flame, poisons and poverty; yet among all these evils I seem to live so sweetly that may I die if I were to change places with the
Persian king" - Johann Joachim Becher, 1635 to 1682.
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Romix
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Quote: Originally posted by TheAustralianScientist  | Was there a temperature difference the second time? Copper(II) Hydroxide decomposes pretty easily to Copper(II) Oxide (a black/grey insoluble
compound) and water:
Cu(OH)2 = CuO + H2O
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Same temperature, not oxide, it's light grey.
[Edited on 27-6-2015 by Romix]
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DraconicAcid
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A bit of impurity might turn the light blue hydroxide grey. Iron, perhaps?
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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Romix
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Electrodes are pure copper, no impurities
[Edited on 27-6-2015 by Romix]
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99chemicals
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It most likely is copper II oxide being formed. The local heating of the solution around the electrode (if you were running enough current) could
have caused the oxide to be formed.
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Romix
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Yes you right, it is CuO.
I poured boiling water in a beaker with light blue copper hydroxide and it decomposed into same looking dark-grey oxide.
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AJKOER
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My guess actually is some Cu2O, Cuprous oxide, as well (hence the gray, not black per pure CuO). Here is a supporting source, to quote:
"Cuprous oxide is also formed at the anode in the electrolysis of a solution of cupric sulphate,12 and by heating cupric oxide in steam. "
Your boiling water/steam test is also supportive of the above statement.
Source link:
http://copper.atomistry.com/cuprous_oxide.html
[Edited on 1-7-2015 by AJKOER]
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Amos
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| Quote: Originally posted by AJKOER | My guess actually is Cu2O, Cuprous oxide. Here is a supporting source, to quote:
"Cuprous oxide is also formed at the anode in the electrolysis of a solution of cupric sulphate,12 and by heating cupric oxide in steam. "
Your boiling water/steam test is also supportive of the above statement.
Source link:
http://copper.atomistry.com/cuprous_oxide.html
[Edited on 1-7-2015 by AJKOER] |
This formed at the cathode according to the OP, and the color is neither red, brown, or yellow.
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AJKOER
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Amos, I since edited my comment (actually while you were forming your response) to be more inclusive (CuO + Cu2O) based on the coloration observed.
The CuO I once prepared by heating Cu(OH)2 was intensely black. One gets grey by mixing black with a light color.
[Edited on 1-7-2015 by AJKOER]
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