chemtag - 28-12-2017 at 08:28
I have a white powder that I suspect is copper(I) chloride (CuCl) given where this material came from. Unfortunately I do not have access to XRD or
other analytical instruments that can easily discern between CuCl and CuCl2. I was hoping to find some qualitative test that could identify the
existence of CuCl. The best I could come up with is to oxidize the material to CuCl2 (with HCl + H2O2 perhaps?) and then hope to see the
characteristic color of CuCl2.
That seems crude, and with too many potential sources of false positives.
Pok - 28-12-2017 at 09:34
If it is pure white, it's probably not CuCl. CuCl gets oxidized in air to copper oxychloride. Crush some of the material to powder and let it remain
in air for some time. If it stays white, it's not CuCl. If it becomes yellowish green: add a few drops HCl. A dark brown/black complex should form.
DraconicAcid - 28-12-2017 at 12:43
It's really easy to tell the difference between CuCl and CuCl2. The former is white and insoluble in water; the latter is brown (or green if
hydrated) and readily dissolved to give a green solution (blue when dilute). CuCl is usually contaminated with green copper(II) compounds, so it's
rarely white, as Pok says (although I don't think it will readily oxidize when dry). Do Pok's test with the HCl- pure CuCl will dissolve to give a
yellowish solution, which will turn brown-black upon exposure to air. Impure CuCl will give a brown-black solution immediately.
chemtag - 28-12-2017 at 14:39
The material was off white but delivered to me in a green supernatant. I mixed the solids + supernatant in a large excess of water, then filtered.
This gave me faintly yellow solids and a bright green (kelly-green) filtrate.
I took a small portion of the yellow solids and added to 36% HCl. After several minutes of mixing/shaking at room temperature, there was no evidence
of a reaction. Adding a small amount of 30% H2O2 started a reaction that quickly dissolved all of the solids and gave a darker green solution.
Analysis of that solution showed >99.9% copper (essentially all Cu).
Finally, the yellow solids were left to stand out on the lab bench for ~1 hour and have already taken on a noticeably green color.
At this point my assumption is that its CuCl, as that fits best of what I have seen. Do you two agree?
[Edited on 28-12-2017 by chemtag]
DraconicAcid - 28-12-2017 at 14:51
So it seems like CuCl, except for it not reacting with HCl. Weird. CuI and CuBr are also white, but CuI would give iodine with hydrogen peroxide
instead of copper(II).
chemtag - 29-12-2017 at 13:54
I took some of the material - now green from standing in the air overnight - and mixed it with 36% HCl. This time the material dissolved (probably
completely consumed after ~1 hour) and gave a very dark green/yellow (so dark it looked black/dark brown upon casual inspection) solution. I believe
this is inline with what was originally expected to happen?
Now the greater mystery: how the hell is a process run in HCl with H2O2 producing CuCl, even if in small amounts?
[Edited on 29-12-2017 by chemtag]
DraconicAcid - 29-12-2017 at 17:22
Why shouldn't it? If you have excess hydrogen peroxide, you would get CuCl2, but with excess copper, you'd get CuCl.