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Author: Subject: Weird side product when making copper acetate
Jackson
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[*] posted on 22-5-2018 at 16:31
Weird side product when making copper acetate


So I tried making copper acetate by reacting copper wire with vinegar and 3% hydrogen peroxide. It made a blue solution that had a white powder at the bottom. I evaporated the water from the liquid and I got a turquoise powder. I added it back to water to try and grow crystals of the what I think is copper acetate but when I added it to water a lot of what looked to be copper and some green powder formed. I let it settle out and it wasn’t redisolving so I filtered it out. It is a green powder. Can anyone tell me what it might be?
Thanks
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DraconicAcid
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[*] posted on 22-5-2018 at 17:16


Copper(II) acetate will hydrolyze to give basic copper acetate in the absence of excess acetic acid.



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AJKOER
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[*] posted on 22-5-2018 at 18:49



My explanation is a bit different. First, I suspect you prepared a mix of cuprous and cupric acetate. Note, cupric acetate in the presence copper metal can form cuprous:

Cu(ll)L + Cu = 2 Cu(l)L

Second, an equilibrium reaction between water and the aqua cupric complex:

[Cu(H2O)6]2+ (aq) + H2O (l) = [Cu(H2O)5(OH)]+ (aq) + H3O+ (aq)

Lastly, an electrochemical reaction consuming the H+ created (moving the above equilibrium to the right) in the presence of oxygen and cuprous:

O2 (or H2O2) + 4 Cu+ + 2 H+ → 4 Cu2+ + 2 OH-

A related reaction also occurs with ferrous, oxygen and acid.

[Edited on 23-5-2018 by AJKOER]
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[*] posted on 22-5-2018 at 23:21


Yes, I think AJKOER is right (or close to it). These reactions finally lead to formation of basic products, e.g. basic acetate, and copper(I) oxide, which is brick red and looks a little bit like copper metal.



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Boffis
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[*] posted on 23-5-2018 at 04:57


I think DraconicAcid is correct. I have prepared a lot of copper, nickel, cobalt etc acetates and they all have a strong tendency to form basic salts which are surprisingly hard to redissolve even in strong acetic acid. Cu+ is not stable even in mildly acidic conditions and quickly disproportionates to Cu and Cu2+ unless there is something present to stabilize Cu+ and my experience is that acetate is not such a compound (they are usually nitrogen bearing ligands). Acetic acid has a modest tendency to complex with Cu2+ anyway, more so than water, that is why you don't see a much water of crystallisation in Cu II acetate as you do in say copper II sulphate. Even so if you boil a copper acetate solution it will still hydrolyse to a basic salt that then requires strong >30% acetic acid or a large excess of more dilute acid to get it back into solution and heating doesn't help as is increases the tendency to hydolyse. Don't use glacial acid undiluted as copper acetate is sparingly soluble in it.

I would recommend that you use an excess of acetic acid with your Cu + H2O2 mixture and allow it to spontaneously evaporate outside on a warm breezy day to get nice large crystals. Alternatively you can vacum evaporate it in a flask with a stirrer and this gives you a fine granular form.
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TheNerdyFarmer
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[*] posted on 23-5-2018 at 05:55


Pretty much the same thing happens if you leave copper wire in copper (ii) chloride solution. I observed this by testing ferric chloride by putting a piece of copper wire in the beaker. I came back a day later and the solution was green (expected). What I wasnt expecting was the white coating on the copper metal. The white coating eventually floated up and turned green. My theory was that somehow the CuCl2 was reduced to form CuCl. The CuCl then reacted with the oxygen to produce the oxychloride salt. My theory on how this is possible would be due to equilibrium shift. Since there was excess copper metal, the chloride ions were able to pick up a couple of the extra copper ions in solution. I'll see if I can recreate this experiment later, should be simple.
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[*] posted on 23-5-2018 at 19:04


I agree with AJKOER. As soon as reading your post about white powder I was reminded of preparing copper (I) chloride by the boiling of copper (II) chloride with copper metal.



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[*] posted on 23-5-2018 at 22:43


You can easily find out whether the product contains copper(I) or not. Add some of the material to a solution of CuSO4 in conc. HCl. If the liquid turns dark green/brown or even black you have copper(I) in it, if it becomes green/yellow and not really dark, then there is only copper(II).



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