UnintentionalChaos - 30-12-2006 at 15:10
Those of you that have made CuO by:
Cu(OH)2 -> CuO + H2O
What color does the powder generally end up? I thought it should be a dark black, but mine came out a brownish gray. I can think of no other compound
it could be/ be contaminated with. It is MUCH finer than another batch (made by roasting some as of yet unidentified copper compound (I suspect
oxychloride though)), though and suspends itself in water for up to an hour. The other batch is the expected pitch black, but is too large to suspend.
Aqua_Fortis_100% - 30-12-2006 at 15:21
mine has brown almost black..
i made mine from cupric sulphate and lye excess.. put in a 3 liter PET bottle and washed/decanted several times to remove any lye (which can
eat your metal pan ) or sodium sulphate... the suspension in a pan reduces extremely the original volume when heating to vaporizes the water...
[Editado em 30-12-2006 por Aqua_Fortis_100%]
12AX7 - 30-12-2006 at 18:35
Copper, Cu(I) or CuCl2(anh.) impurity?
Copper oxychloride smokes when I calcine it.
Tim
UnintentionalChaos - 30-12-2006 at 21:12
It was in a magnesium sulfate electrolyte 
Mg(OH)2 contamination? I tried
putting in vinegar because I figured any magnesium hydroxide would dissolve almost immediately to magnesium acetate while the CuO would take a while
to turn to copper acetate. No color change after filtering out the remaining CuO. 
I am aware of a small Cu2O impurity, but this does not explain the color. It's medium gray with a little brown tinge when dry. I did electrolysis of
pieces of copper scrap in a magnesium sulfate electrolyte, decanted the liquid, added a large volume of water, settled, decanted, and repeated this 4
more times before boiling the properly "light blue fluff" for an extended period of time in clean water.
PS: Calcined it way hotter than it should need for way longer than I thought necessary, and yet, no change.
[Edited on 12-31-06 by UnintentionalChaos]
12AX7 - 31-12-2006 at 03:19
Magnesium (as hydroxide) would ppt on the cathode. If it tends to fall off, then sure, it could be in there.
Did your electrolyte end up colored?
Tim
UnintentionalChaos - 31-12-2006 at 12:57
Solution was crystal clear. Anyway, I don't have much in the way of a current source, so it takes a really long time to produce even a small amount of
Cu(OH)2.
The_Davster - 2-1-2007 at 17:56
Ok...I posted this elsewhere but...
When electrolysing MgSO4 with copper electrodes, you do not get the expected Cu(OH)2. You get a whole mess of various Cu(x)(OH)(y)(SO4)(z) compounds
which ppt out in the cell. These basic sulfates do not decompose nicely to CuO like Cu(OH)2 does.
In my experience, one cannot use an electroylte with doubly charged ions in it, or such things happen. Best is a KNO3 solution, from which pure
Cu(OH)2 precipitates from. And if you run it long enough it gets hot enough to turn it into CuO
, if it gets to boiling temp you get nitrate reduced to ammonia as well.
UnintentionalChaos - 2-1-2007 at 18:48
And I just managed to get hold of some KNO3 as well as a much higher amperage power supply! Thanks a lot!
Ramiel - 3-1-2007 at 04:01
I know this is kind of off topic, but if I can just put in my two cents worth. 
I've only ever used electrolysis for chlorate prep. (since I can do it no other way) because electrolysis is expensive, time consuming, messy and
inefficient IMHO. Production of Sodium is another example of when electrolysis is a great method, but for the production of a metal oxide, I'd just go
with tried & true reaction of strong hydroxide solution with concentrated Cu(II) solution. Simple, one step reaction that has worked for me every
time giving a very fine (dust-like) precipitate which is as pure as your solutions (<i>i.e.</i> can be very pure indeed!).
So yea, sorry for the unsolicited advice 
- Ramiel
[edited a p.s. in just for kicks]
Relevant linkage:
<a href="http://www.sciencemadness.org/talk/viewthread.php?tid=271">Can't Make CuO</a> [by electrolysis] - old 4 page thread, many methods
discussed.
<a href="http://www.sciencemadness.org/talk/viewthread.php?tid=127">Exotic thermites and analogues</a> - even older thread, if you can
wade through all 9 pages, there's some interesting info there too.
[Edited on 3-1-2007 by Ramiel]
12AX7 - 3-1-2007 at 04:08
A shameful waste of hydroxide though...
Tim
Just a thought
Levi - 24-1-2007 at 04:42
Hi, I'm new here and not the most advanced chemist but I wonder if a -hot and concentrated- sol. of Sodium Carbonate would react with a solution of
Cu(x)Cl(y) to form a copper carbonate / copper hydroxide mix from which the desired CuO could then be obtained by heating.
??
12AX7 - 24-1-2007 at 08:13
Possible. Boiling with NaOH produces black material (CuO), but I don't know if carbonate is basic enough to attack the oxychloride.
Tim
YT2095 - 24-1-2007 at 09:54
I get a brown black with the hydroxide and the carbonate of copper, less brown with the carbonate though.
that`s in a 25 ml crucible at propane bunsen temps held for 20 mins with the lid on.
no gray material though?