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Author: Subject: Questions about CuCl/HCl solution
bbartlog
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[*] posted on 9-3-2010 at 09:22
Questions about CuCl/HCl solution


I've been producing some cuprous chloride, using old (all-copper) pennies and hardware store HCl (31%). In my latest run this involved
- adding 880g of HCl solution (~8 moles) to 254g of copper coins (~4 moles copper)
- adding 440g of water to reduce the concentration of the HCl
- adding 35g of mixed CuCl/CuCl2 from a previous run (theoretically, the CuCl2 should help start the reaction, since HCl + Cu + CuCl2 -> HCl + 2CuCl, at least when boiling)
- boiled a while, let cool, added some 3% H2O2 (~300g)
- boiled again until almost clear (slightly yellowish), let cool, bubbled air through with an aquarium pump until dark green / nearly opaque
- boiled again and cooled. Lots of white crystals formed. The solution is now brown (dark but not entirely opaque).

At this point I filtered out what was left of the pennies, along with the crystals. However, much of the CuCl is still in solution (pennies are far from totally dissolved; I still have to weight them though).
My questions though relate to the saturated CuCl/HCl solution. First, why is it brown? When hot (boiling) this solution is nearly clear with a faint yellow color, but it darkens on cooling (even if not exposed to air).
Second, I notice on bubbling air through this solution that it doesn't oxidize the CuCl any longer. This seems a little odd in that wet, solid CuCl (the white precipitate) is very readily oxidized by exposure to air; further, the more dilute solution I had earlier also was oxidized by atmospheric oxygen. But this solution seems resistant: after half an hour of bubbling air through, I took out a small sample (~10ml) and diluted it with 10x the volume of water. White CuCl precipitated as expected but only a very faint tint of green CuCl2 was seen.
Anyway - any ideas why this would be? My guess is that, when highly concentrated, the CuCl forms some kind of complex with the HCl, resulting in both the brown color and the resistance to oxidation. In general (from what I understand) the dissolution of the CuCl already involves the formation of HCuCl+ and Cl-, so this would presumably be something else. But what?
Any suggestions for further tests welcome; I still have about 3/4 liter of the solution.
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watson.fawkes
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[*] posted on 9-3-2010 at 14:58


Quote: Originally posted by bbartlog  
I've been producing some cuprous chloride, using old (all-copper) pennies and hardware store HCl (31%).
I can heartily recommend reading through this page on etching copper with copper chloride, which has a quite a lot of information on the Cu(0), Cu(1+), Cu(2+), Cl(-) system.
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bbartlog
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[*] posted on 10-3-2010 at 07:35


Thanks! That is some good information; even though I'm not interested in etching specifically it still provides guidance on how to turn copper into CuCl more quickly. It turns out I was wrong about the oxidation too (or at the least, it's still possible to air oxidize it, it just takes a while). Twelve hours with an aquarium air bubbler finally turned the brown solution into nice green CuCl2.
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Siconic
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[*] posted on 11-3-2010 at 07:38


Quote: Originally posted by bbartlog  
I've been producing some cuprous chloride, using old (all-copper) pennies and hardware store HCl (31%). In my latest run this involved
- adding 880g of HCl solution (~8 moles) to 254g of copper coins (~4 moles copper)


Just to let you know(in case you didn`t already) modern copper coins are primarily zinc, with a thin copper jacket.

1909 - 1942, 1944-1962
Composition: 95% copper, 5% tin & zinc
Weight: 3.11g
Diameter: 19mm
Edge: plain

1943 - 1943
Composition: Steel coated with zinc
Weight: 2.7g

1962 to 1982
Composition: 95% copper, 5% zinc
Weight: 3.11g

1982 to date
Composition: 99.2% zinc, 0.8% copper - coated with a pure copper.
Weight: 2.5g

Figured this might come in handy if anyone needs zinc, or has some supper old pennies laying around that aren`t valuable. :)

Quote: Originally posted by bbartlog  
-boiled again and cooled. Lots of white crystals formed.


Thats zinc chloride from the 95% zinc in the pennies. Just so you know. :) Copper chloride (dihydrate) is blue to bluegreen. Anhydrous is brown(no H20).

[Edited on 11-3-2010 by Siconic]
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bquirky
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[*] posted on 11-3-2010 at 07:55


I like copper pipe. :)

and australian 20 cent coins (if im after some nickel aswell)

allso i have found desolving metals in hcl or h2so4is much easer if you make them anodes in a electrolitic cell. boiling acid vats have never relly thrilled me.

or if conveniance suits create the metal hydroxide or oxide in a NaOH electrolitic cell and desolve the percipitate in whatever acid as required.

Iorn Chloride crystals are allways fun to try to make.. man ive wasted sometime on that :)
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watson.fawkes
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[*] posted on 11-3-2010 at 12:51


Quote: Originally posted by bbartlog  
Twelve hours with an aquarium air bubbler finally turned the brown solution into nice green CuCl2.
Hydrogen peroxide also works, if you'd rather spend money on chemicals than spend a bit of money on electricity and wait.
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12AX7
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[*] posted on 11-3-2010 at 14:28


No worries about coins, he specifically noted "old pennies".

I guess the moral of the story is, the brown complex is very soluble in concentrated solution. If you want CuCl out, dilute the hell out of it (or find a ligand that sticks to Cu(2+) better than the mixed ion?), or keep adding copper, using the brown solution as catalyst.

Tim




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