Sciencemadness Discussion Board
Not logged in [Login ]
Go To Bottom

Printable Version  
 Pages:  1  2    4
Author: Subject: Can't make CuO
12AX7
Post Harlot
*****




Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline

Mood: informative

[*] posted on 19-12-2005 at 12:01


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




Seven Transistor Labs LLC http://seventransistorlabs.com/
Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
View user's profile Visit user's homepage View All Posts By User This user has MSN Messenger
The_Davster
A pnictogen
*******




Posts: 2861
Registered: 18-11-2003
Member Is Offline

Mood: No Mood

[*] posted on 19-12-2005 at 17:35


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:o. 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]




View user's profile View All Posts By User
darkflame89
National Hazard
****




Posts: 255
Registered: 1-3-2004
Location: With probability 1, "somewhere" in this
Member Is Offline

Mood: No Mood

[*] posted on 19-12-2005 at 23:32


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.
View user's profile View All Posts By User
Magpie
lab constructor
*****




Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 25-5-2008 at 20:01


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?
View user's profile View All Posts By User
12AX7
Post Harlot
*****




Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline

Mood: informative

[*] posted on 25-5-2008 at 20:35


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




Seven Transistor Labs LLC http://seventransistorlabs.com/
Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
View user's profile Visit user's homepage View All Posts By User This user has MSN Messenger
Magpie
lab constructor
*****




Posts: 5939
Registered: 1-11-2003
Location: USA
Member Is Offline

Mood: Chemistry: the subtle science.

[*] posted on 25-5-2008 at 21:36


Quote:

Does the solution remain blue at all?


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


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]
View user's profile View All Posts By User
12AX7
Post Harlot
*****




Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline

Mood: informative

[*] posted on 26-5-2008 at 00:11


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




Seven Transistor Labs LLC http://seventransistorlabs.com/
Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
View user's profile Visit user's homepage View All Posts By User This user has MSN Messenger
ShadowWarrior4444
Hazard to Others
***




Posts: 226
Registered: 25-4-2008
Member Is Offline

Mood: Sunlight on a pure white wall.

[*] posted on 26-5-2008 at 09:22


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]




A bit of my photography (usually chemisty/physics inspired): ShadowWarrior4444.deviantart.com/gallery
View user's profile Visit user's homepage View All Posts By User
12AX7
Post Harlot
*****




Posts: 4803
Registered: 8-3-2005
Location: oscillating
Member Is Offline

Mood: informative

[*] posted on 26-5-2008 at 21:11


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




Seven Transistor Labs LLC http://seventransistorlabs.com/
Electronic Design, from Concept to Layout.
Need engineering assistance? Drop me a message!
View user's profile Visit user's homepage View All Posts By User This user has MSN Messenger
ShadowWarrior4444
Hazard to Others
***




Posts: 226
Registered: 25-4-2008
Member Is Offline

Mood: Sunlight on a pure white wall.

[*] posted on 27-5-2008 at 13:01


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.




A bit of my photography (usually chemisty/physics inspired): ShadowWarrior4444.deviantart.com/gallery
View user's profile Visit user's homepage View All Posts By User
 Pages:  1  2    4

  Go To Top