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Squall
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[*] posted on 12-6-2010 at 11:11
Copper Hydroxide


I am trying to synthesize some copper hydroxide by method of electrolysis of copper. So far i have made two attempt both seemed to produce hydroxide at first, but as the reaction continued a yellow cloudiness appeared in the electrolyte solution. The first time i though it might be a result from using a steel cathode but my second try i am using two copper electrodes and the yellowish substance has again appeared in the solution after about an hour of running the cell. Can anyone tell me what this yellow substance can be and if it will ruin my yield of copper hydroxide thanks.
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jokull
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[*] posted on 12-6-2010 at 11:54


That yellowish substance could be copper chloride complexes. Perhaps the problem is in the quality of water used for your electrolysis.
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Squall
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[*] posted on 12-6-2010 at 11:57


I guess i can try distilled water next and see if that helps right now I am trying a salt bridge but its seems painstakingly slow and i am not sure what that will yield and i am using distilled water this time



[Edited on 12-6-2010 by Squall]
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12AX7
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[*] posted on 12-6-2010 at 13:54


What electrolyte?

The yellow to brick-orange precipitate is Cu2O, generally the result when chloride is present.

Tim




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[*] posted on 12-6-2010 at 13:58


Quote: Originally posted by Squall  
I am trying to synthesize some copper hydroxide by method of electrolysis of copper.




If I were King - people who post questions like this
would have to state why they choose their method
rather than the standard method — which for
copper (II) hydroxide is chemical simplicity.


Byda - what is your electrolyte?
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Squall
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[*] posted on 12-6-2010 at 15:49


My electrolyte consists of distilled water and NaCl, i chose this method because it seemed to be a simple way of making copper hydroxide, my actual goal is to make CuO.
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[*] posted on 12-6-2010 at 16:57


Quote: Originally posted by entropy51  
If you were King, would Your Royal High Ass also stop idiots from spamming every thread?



------------
Prey tell .... what spam?

How is noting that NO chemist would make copper hydroxide
by electrolysis. They would simply mix sodium hydroxide
and copper sulphate - spam?

Dobe it a crime among the fussbudget/pedants here in
SciMad to suggest simple ways of doing things?!

If I were King — no one could post here unless they certified that
they had read and understood —

Laurence J. Peter and Raymond Hull
The Peter Principle
1969

You people measure input but not output.

Now thanks to my question we now know what Squall
is interested in synthesizing — CuO.

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entropy51
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[*] posted on 12-6-2010 at 17:23


Quote: Originally posted by The WiZard is Insane  
You people measure input but not output.
By "you people" you mean those of us less worthy than your esteemed self? What a great entertainment you are! We love you old fahrts.
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[*] posted on 13-6-2010 at 00:37


If copper oxide is what Squall is after and he uses NaCl in the eletrolyte it means he is not concerned at all about possible Na contamination (thus he doesn't need the CuO for pyro use I'd say).
Having that, why he doesn't just use the "first grade studied" reaction Wiz is proposing and instead farts around with electrolysis it's beyond my comprehension. Some people just like fly over to cook an egg into a volcano crater for the breakfast it seems.

While I enjoy entropy51's posts and he's knowledge I guess he is in no position of saying anything about Wiz. If I were to say who's the spammer on this thread, it's entropy51. No contribution at all here.

[Edited on 13-6-2010 by a_bab]
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Squall
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[*] posted on 13-6-2010 at 04:53


I know one could go and mix sodium hydroxide with copper sulfate and be done with it, but why not explore the other possibility of electrolysis. I know that this is probably not the best or even a cost effective method but my reasons for performing this is more for the knowledge gained then for the end product. As I am performing these trials I am learning about different electrolytes and their products, and I would like to thank you for your advice and criticism it has been helpful in pointing me in the right direction. Maybe someday I'll Learn how to post like the pro's but that's in the future.

Anyway I have switched electrolytes, because several of you made the comment about the presence of chloride in the electrolyte, I will now use sodium bicarbonate and see what happens. Thanks again
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12AX7
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[*] posted on 13-6-2010 at 05:03


Hah, copper tends to form a carbonate complex. You will eventually have a deeply blue solution (and some copper plating over, and not much copper carbonate!). This is also a poor way to generate copper hydroxide.

Your best bet is an anion which doesn't reduce easily and doesn't complex with copper significantly. Nitrate and chlorate do, so they are out. Acetate forms a complex, so it's out. Perchlorate and most accessible of all, sulfate, come to mind.

Tim




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Squall
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[*] posted on 13-6-2010 at 05:12


Sulfate is accessible, but what I am not sure of is how much sulfate contamination will be present in the hydroxide, if it is minimal then that's the way I should go.

Thanks Tim
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not_important
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[*] posted on 13-6-2010 at 05:36


Might try the following:

copper electrodes

low voltage AC - not DC

whatever electrolyte

brisk stirring

running hot, near 90 C

Let's say you use NaCl. At the (momentary) anode Cu(I) and Cu(II) are formed. At the (momentary) cathode H2 and OH(-) are formed. The mixing insures the copper ions and hydroxide meet, forming copper hydroxides. On reversal of polarity some copper ions will plate out onto the cathode, but will be stripped off on the following polarity reversal. With NaCl some hypochlorite and chlorate are formed, the OCl isn't stable under the conditions both oxidising Cu(I) and disproportionating to chloride and chlorate. The hot conditions encourage Cu(OH)2 to convert to CuO, but there's still be a mix in the precipitate; that can be taken care of later.

If you use NaHCO3 electrolyte, you'll get a mixture of copper hydroxides and basic carbonates. Ammonium sulfate will give mostly CuO with some basic salts, the electrolyte will lose some ammonia so you may have to add aqueous ammonia to keep the pH from going too acid. Yes, some copper will remain in solution, how much depends on the electrolyte salt used, but it's kind of a 'who cares'; you can save and reuse the electrolyte if you want.

In all of those cases, after you stop the electrolysis let the rig cool and precipitate settle. Decant the electrolyte off, wash with a little water, add a fair amount of water then boil for some minutes. Cool and settle, decant through a filter, wash several times by decantation - again pouring off the water through the filter to catch bits of escaping oxide. Finally wash the rest of the oxide into the filter and give a final rinse. Let the oxide air dry, crushing big lumps as it does so. Put the oxide in a glass or ceramic dish or bowl style container, evaporating dish if you have one of proper size. Slowly heat it with stirring, and lump crushing, to at least 120 C for non-carbonate electrolytes, for carbonates and preferably for others to at least 300 C to insure full decomposition to CuO.

Note that technical CuSO4, such as 'root killer', may contain appreciable amounts of iron. If you wish to go the CuSO4 + NaOH route to the hydroxide, you best first test for iron and if found purify the CuSO4; you can't do this by recrystallising, chemical means must be used.
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[*] posted on 13-6-2010 at 06:08


Quote: Originally posted by Squall  
Sulfate is accessible, but what I am not sure of is how much sulfate contamination will be present in the hydroxide, if it is minimal then that's the way I should go.

Thanks Tim


---------
Try ammonia water (ammonium hydroxide).

Active Nature of Copper Proved in Your Laboratory
Popular Science
June. 1934

http://tinyurl.com/27fvog5


From copper carbonate

Popular Science
Copper the Ageless Metal
December, 1943

http://tinyurl.com/3762q2m

&c., &c.
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[*] posted on 13-6-2010 at 06:36


If i was to pursue the copper sulfate + a hydroxide , my only source at the moment of copper sulfate is root killer, my question is how do I test it for iron content and if it is contaminated by what chemical processes do I remove it.
And thanks for the links Tim.
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not_important
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[*] posted on 13-6-2010 at 07:28


One way -
Make a fairly strong solution of a bit of the root killer, just a crystal or two in 1 or 2 ml water. Add several ml of hydrogen peroxide %3 or a few drops of a higher concentration H2O2. Put a drop or two of this on a piece of filter paper, or even plain paper toweling. Drop concentrated aqueous ammonia onto that drop, slowly adding several more drops right on top. Copper hydroxide forms at first, then the excess ammonia complexes with it and dissolves the copper away, forming an expanding circle of blue becoming paler and paler as additional ammonia water dilutes it. Iron will form the hydrated oxide, and remain as a rusty spot where the drop of root killer solution was originally placed.

The clean-up is related. Make a solution of root killer, add H2O2 and heat to near boiling for 10 to 15 minutes, adding a few ml of H2O2 every minute or so; the set aside to cool. When it's lukewarm measure out about 10% into a second container.

Take that 1/10 and add aqueous ammonia to get Cu(OH)2, slowing down the addition as the solution appears to get colourless (let a couple of drops drip through filter paper if you need to. It's not real critical to get it exactly right on balanced, a bit to little NH3 or a bit over isn't going to hurt, but not a whole lot too little or much. Filter and wash the Cu(OH)2 with distilled water.

Add the washed Cu(OH) to the main solution of root killer, and stir it for awhile. Fe(III) hydroxide/hydrated oxide is very insoluble, Fe(III) salts in solution will exchange with the Cu(OH)2 to give a precipitate of "ferric hydroxide" with the copper going into solution as whatever the iron salt was - sulfate in this case.

After stirring for at least 15 minutes to a half hour, you can take let it settle for awhile and then test a drop of the solution - free from precipitates - for iron as before. If it still tests positive, repeat the H2O2-boil steps, but only use about 5% for making the Cu(OH)2.

Filter the solution if the precipitate looks to be easy to filter. If the ppt is sort of floaty then try bringing the solution to a boil again to convert the excess Cu(OH)2 to the oxide, which generally is easier to filter. The iron is mixed in with the excess copper hydroxide/oxide.

You can just let the filtrate, covered with a cloth to keep out dust, evaporate slowly until it's mostly crystals with a cm or so of solution above it. Or you can heat it to near boil, until crystals start to form, add enough hot distilled water to dissolve those then let the hot solution get cold. This will give you about 3/4 of the copper sulfate as crystals, after filtering off the mother liquor you can take that and concentrate it to et a second batch of crystals. Don't evaporate to dryness, expect to leave 5% to 10% of the CuSO4 in solution along with whatever impurities; iron sulfate would have formed mixed crystals so that's why it needed to be removed chemically.

If all you want the CuSO4 for is making CuO, you can skip crystallisation and just used the filtered solution as is.



[Edited on 13-6-2010 by not_important]
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[*] posted on 13-6-2010 at 09:11


Quote: Originally posted by 12AX7  
Hah, copper tends to form a carbonate complex. You will eventually have a deeply blue solution (and some copper plating over, and not much copper carbonate!). This is also a poor way to generate copper hydroxide.

Tim




---------
Poor way? Actually it is THE way. Brauer add's a detail to the
process - ammonia water is added first.

La Book is in the SicMad library.
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[*] posted on 13-6-2010 at 11:44


i use to make pound of CuO straight by electrolysing Cu metal in pool calcium hypochlorite or simple bleach. The content of cuO over Cu2O was about 40:1 in weight. another way is to electrolyse chlorate solution with cu metal, but then the ratio of CuO to Cu2O is 15:1 or even worst.

You can easily separate the two with some acetic acid as only CuO dissolve. Then if you still wan CuO instead of CuAc then you are screwed ;-). but CuAc is like CuO if you intend to reac the CuO with strong acid like HCl of H2SO4...

it seem you can convert Cu(I) to Cu(II) by dissolving it in excess HCl but i don't know why, it just look like because it create a green solution ressembling CuCl2.

used to have a blog about my copper experiments but it got corrupted when the host broke his computer
[Edited on 13-6-2010 by Hamilton]

[Edited on 13-6-2010 by Hamilton]
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[*] posted on 13-6-2010 at 13:07


I can imagine that making copper hydroxide in this way is an interesting option. Copper wire is something which is available everywhere. Copper sulfate more and more becomes a less common chemical, although of course it still is available through eBay and other online sources.

A nice method of making Cu(OH)2 is electrolysing a solution of baking soda (NaHCO3) with copper electrodes. Quite some precipitate of light blue Cu(OH)2 is formed. This precipitate also may contain some CuCO3. If you filter the precipitate and heat it, then it becomes black and CuO is formed. Even the wet suspension in water can be boiled to make a black precipitate of CuO. Any carbonate then is destroyed and expelled as CO2. The CuO, prepared in this way is not suitable for pyrotechnical purposes, due to sodium-remains (the orange/yellow light if sodium overwhelms the cyan color of copper in pyrotechnic flame compositions). For many other chemical experiments (e.g. making CuCl2 by dissolving it in dilute HCl) it is perfectly suitable.

[Edited on 13-6-10 by woelen]




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[*] posted on 13-6-2010 at 15:38


'it seem you can convert Cu(I) to Cu(II) by dissolving it in excess HCl but i don't know why'

I don't think this works. HCl alone will not oxidize CuCl to CuCl2 (though it will dissolve it by forming complexes). Now, in the presence of air, oxygen will gradually oxidize Cu(I) to Cu(II), which will immediately be converted to CuCl2.
I've made Cu(OH)2 by first dissolving copper in HCl to make CuCl2 (air has to be bubbled through for this to work), then reacting the CuCl2 solution with NaOH. CuCO3 is also easily produced via similar neutralization with Na2CO3.

So far as the yellowish substance mentioned in the first post is concerned, it sounds like cuprous hydroxide (see: http://pubs.acs.org/doi/abs/10.1021/j150103a002). For what it's worth, cuprous carbonate (or whatever you get when neutralizing a solution of CuCl and HCl with Na2CO3) is an orange insoluble precipitate. Exposure to air turns it green.

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