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12AX7
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If it does, and the salt doesn't break down on boiling, then nevermind.
It should work better than MgSO4 at the very least because Mg(OH)2 will want to plate on the cathode...
Tim
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The_Davster
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Well I did a longer bigger test of producing CuO in KNO3 solution. About 9 copper wires 4" long were suspended over a 600mL beaker filled with KNO3
solution as the anodes. The same number of the same lenght of copper wires were used as the cathodes. 12V(max 7A) was applied for aproximatly 4h-5h.
for the first 2h, Cu(OH)2 was flaking off the anode, but around the fourth hour, the cell had heated up enough to be producing CuO right away. Around
the 4.5h mark, ammonia(or at least what smelled to be ammonia) began to be given off . I must have reduced nitrate to ammonia somehow. Seeing as this was running indoors, I turned off the power. Interesting. Perhaps if
the temp was kept lower, ammonia formation could be avoided.
EDIT: The CuO produced this way is not as pure as CuO produced the usual way of NaOH + CuSO4 while heating, there was a bit of Cu2O and Cu particles
in there as well, Cu likely from electrode corrosion.
[Edited on 20-12-2005 by rogue chemist]
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darkflame89
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The ammonia would come from the cathode side. At the temp. that your cell encountered during electrolysis, nascent hydrogen produced from the cathode
would reduce nitrates to ammonia. I only wonder if the electrolysis setup was run long enough, might the copper(II) oxide redissolve to form the
ammonia complex. Provided that the setup is stirred that is.
Ignis ubique latet, naturam amplectitur omnem.
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Magpie
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Although my current work with CuO is not electrolytic I thought this a good thread in which to continue a discussion of its preparation.
My original goal was to prepare cupric acetate monohydrate, Cu(OAC)2*H2O. However, as often occurs when you don't have a proven method, problems
popped up along the way. My approach was to use CuO as the precursor for the cupric acetate. My preparation of CuO would be with the readily
available root killer, CuSO4*5H2O.
Experiment 1
CuSO4*5H2O was dissolved in deionized water and warmed to around 50C. A stoichiometric amount of NaOH crystals was then added. This first formed
the light blue ppt of Cu(OH)2 which upon heating to near boiling produced very dark chocolate brown suspended solids, which I took as
CuO. This was Buchner filtered, washed, dried, and weighed. The weight indicated a CuO yield over 100%. Upon reading some reference for making
verdigris I suspected sulfate contamination of my product. Dissolution of a small sample in 6N HCl and adding a few drops of BaCl2 confirmed the
presence of sulfate.
Experiment 2
Several references specified the addition of NH4OH until the initial light blue Cu(OH)2 turns to a deep blue from the complex [Cu(NH3)4]++, prior to
the addition of the stoichiometric amount of NaOH. By doing this an almost perfectly black ppt of CuO was formed and the test for sulfate was
negative. Also, the yield was just slightly less than theoretical 100%.
I wanted to share these results and give enough detail so that those more versed in copper chemistry could comment. Can anyone tell me exactly what
chemistry is taking place here? I.e., why did I get contaminated CuO wo/ammonia addition and apparently good CuO w/ammonia addition?
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12AX7
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Hmm... ya know, I have:
Cu(2+) + SO4(2-) <---> CuSO4(aq) pKf = -2.36
So maybe you have a 0.1~1% sulfate impurity complexed in. CuSO4 is soluble, so I don't really know how the complex would precipitate. If it is a
complex, displacing it with a stronger ligand (NH3) would get rid of it, but that begs the question, how does CuO precipitate from that solution? I
thought Cu(NH3)4(OH)2 was soluble. Does the solution remain blue at all?
Heating it to 500-800C should cook off most anything anyway (including CuCl2, incidentially), although some CuO may decompose to Cu2O, which is more
stable at very high temperatures (by a hundred C, near the melting point).
Tim
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Magpie
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| Quote: |
Does the solution remain blue at all?
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After addition of the NaOH the solution goes to light blue as is Cu(OH)2. Then as this is heated the suspension goes black as CuO is formed. When
Buchner filtered the filtrate shows some clear blue characteristic of [Cu(NH3)4]++. This is a source of a slight loss of Cu, but not much.
| Quote: |
Heating it to 500-800C should cook off most anything anyway
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I wanted to avoid calcination as a reference says that this makes the CuO insoluble except in boiling strong acid. It would be interesting to calcine
a sample to determine purity, however.
[Edited on 25-5-2008 by Magpie]
[Edited on 25-5-2008 by Magpie]
[Edited on 25-5-2008 by Magpie]
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12AX7
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So only a small amount of ammonia is needed, enough to produce a catalytic amount of Cu(NH3)4 you might say?
Hmm, that implies Cu(NH3)4 (or some n-ammine species) coexisting with Cu(2+) or CuOH+ species, but not Cu(OH)2 as that would precipitate. So I guess
the question is, what pH can it reach, without precipitating, but while retaining some NH3 in solution? I guess it can't be too horrible, I have
CuOH+ <---> Cu(OH)2(aq) pKa = 8.7, not far from NH3. It should suffice to add any ammonium salt before adding NaOH, no?
Tim
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ShadowWarrior4444
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Preparing CuO by electrolytic processes is as simple as electrolyzing a copper metal anode using an NaOH electrolyte. I have recently tested this as
part of another project--when given 13.8v at 25A the anode will be quickly eroded with the evolution of a black insoluble powder.
>99% pure copper can be had in the form of uncoated high-gauge copper wire at most local hardware stores (in the electrical wire section.) Copper
nails are also sold, however they are likely an alloy.
[Edited on 5-26-2008 by ShadowWarrior4444]
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12AX7
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What strength NaOH? Cu(2+) is soluble in alkali.
Electrolysis of a Na2SO4 solution with copper anode gives Cu(OH)2, which decomposes on heating to CuO, especially convienient if the cell is run hot.
NaCl complexes Cu(I) giving Cu2O which would need to be roasted to CuO. A nitrate or chlorate solution probably serves as well, but the cathode would
need to be protected to prevent reduction. Perchlorate probably works as well as sulfate (say, I have a bunch of sodium perchlorate, I can easily try
that).
Tim
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ShadowWarrior4444
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| Quote: | Originally posted by 12AX7
What strength NaOH? Cu(2+) is soluble in alkali.
Electrolysis of a Na2SO4 solution with copper anode gives Cu(OH)2, which decomposes on heating to CuO, especially convienient if the cell is run hot.
NaCl complexes Cu(I) giving Cu2O which would need to be roasted to CuO. A nitrate or chlorate solution probably serves as well, but the cathode would
need to be protected to prevent reduction. Perchlorate probably works as well as sulfate (say, I have a bunch of sodium perchlorate, I can easily try
that).
Tim |
The NaOH concentration need not be very high. It would simply be a matter of powering up the cell, then adding small portions of electrolyte until a
black precipitate is visible from the anode.
My favorite method for producing copper hydroxide is to use an MgSO4 (Epsom salt) electrolyte; though, it should be noted that running the cell hot
will not appreciably decompose the hydroxide. Dry copper hydroxide will need to be roasted in air at 185C to produce CuO, and while wet copper
hydroxide will decompose over time, it will not be satisfactorily fast nor will it provide a relatively pure product.
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Texium
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Thread Moved
19-11-2023 at 12:29 |
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