[BROe]

I am neutralizing a concentrated solution of copper, nickel, and excess HCl with sodium carbonate. I expected that after the excess HCl was neutralized, I would start to form basic nickel and copper carbonates which would precipitate as  blue-green solids, and could determine that I had dropped everything out of solution once the supernatant was colorless.

My starting solution was a very dark yellow-green, remaining so until I had added enough sodium carbonate to neutralize excess acid. The solution then started to turn green as a metal precipitates started to form, this continued until the solution was a light blue-green color. I then let the solution settle over several days. When I came back, the precipitate had settled to the bottom, but the supernatant was a light green which I took to mean that I still had metal-chlorides in solution. With heating and stirring I continued to add carbonate until the solution suddenly turned a light orange-brown color. I let the solution settle and the supernatant was clear, with a small amount of blue-green solid mixed with the orange-brown precipitate.

I think that the precipitate is copper (I) oxide and the blue-green solid is nickel(II) and copper(II) carbonate, but I don't understand why the oxide would form and if anyone has an explanation I would really appreciate it. Thanks.

[chenbeier]

So you have some reducing Agents, like formaldehyde, hypophosphite in the Solution?

[BROe]

I doubt that there were any reducing agents in the solution, I made it myself by dissolving a copper-nickel alloy in HCl with Cl₂ as an oxidizing agent. I have been looking around online for an explanation, and all that I have been able to find is a single sentence the Wikipedia page on copper(I) oxide that references a source I can't get access to.

"Copper(I) oxide may be produced by several methods.[3] ... Aqueous cuprous chloride solutions react with base to give the same material."

[3]  H. Wayne Richardson "Copper Compounds in Ullmann's Encyclopedia of Industrial Chemistry 2002, Wiley-VCH, Weinheim. doi:10.1002/14356007.a07_567

Wikipedia is far from ideal, but the reference to a source makes it seem more legitimate even if I can't get past its paywall. I'd really prefer to find an explanation from a more credible source.