Fantasma4500 - 18-7-2021 at 06:49
so as im trying to bulk dissolve copper in HCl i realized, the damn thing needs oxygen
so for fun i took a small amount of copper with HCl and added KClO4
it seemed to do something
a day later i find that it has turned brown?
i give it a whiff and theres still acid in there, CuO normally reacts very fast with HCl. i add some more HCl but it stays brown, swirling it around a
bit i can see a greenish tint to the brown color, it doesnt have any other smell than HCl
any guesses to what im looking at here? copper perchlorate is blue
CuCl is very light blue to faint tan
CuCl2 is green-bluish
CuCl2 complex with HCl is deep green
reaction was done at room temperature
RustyShackleford - 18-7-2021 at 08:39
Its due to a mixture of copper 1+ and copper 2+. If you bubble air through it (with HCl still in there) it will eventually turn to the green color you
expect.
In fact, air works perfectly fine for dissolving copper into HCl, no need to use perchlorate/other oxidizer, i was able to dissolve some 300g of 3mm
copper tubing in a week using that method.
Bedlasky - 18-7-2021 at 09:42
What concentration of HCl did you use? HCl >30% concentration pretty easily dissolves copper (especially powder). Complex formation lowers
potencial, so Cu(0) is oxidized to Cu(I) by concentrated HCl. And Cu(I) is very easily oxidized to Cu(II) by oxygen, so you obtained mixed
Cu(I)-Cu(II) chloro complex, which is brown.
Ordinary HClO4 or acidified perchlorates cannot dissolve copper. They don't have oxidizing properties in aqueous solution (this have just HClO4
>75%, but this stuff can be quite dangerous).
woelen - 19-7-2021 at 03:02
The KClO4 does nothing at all, as stated by Bedlasky. Ionic perchlorates have no oxidizing power at room temperature. Actually, they belong to one of
the most inert anions which are accessible for the home scientist (triflic acid and some fully fluorinated anionic species are even less reactive,
buit these are not easily obtained).
Copper(I) and copper(II) form very interesting deep brown mixed oxidation state complexes with chloride ion. Concentrated HCl and oxygen from air
oxidize some of the copper to copper(II), and the excess copper reduces copper(II) to copper(I) in the concentrated HCl and this copper(I), together
with copper(II) gives intensely colored complexes.
If you have some copper sulfate, dissolve a little in conc. HCl. You get a yellow solution (somewhat like piss, a little more intensely colored). To
this solution, add a little copper metal. You'll see that the solution turns nearly black! If you add excess copper metal and carefully seal the tube,
so that no oxygen from the air can get in, then you can get a (nearly) colorless solution of dichlorocuprate(I). As soon as you allow oxygen to get
in, the liquid will turn brown again. Liquid adhering to the glass and on the surface turns brown in seconds.
Fantasma4500 - 19-7-2021 at 13:06
a complex, huh? alright i guess that makes sense.
boiling CuCl in ammonia with excess ascorbic acid will also give you a completely colorless solution
i acquired an air bubbler but seems 78L/H is mainly good for gassing yourself with HCl so ill have to modify the air output with a volt limitor, last
resort is to get large pieces of copper and run electrolysis for all eternity
i might have to re-run the thing with KClO4 and HCl, it sure seemed to aid something and it doesnt produce any fumes without copper, so its not a
chlorate impurity. the flask was sealed up and was rather small but might not have been airtight