witekprytek
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copper chloride synthesis - any free HCl left in solution ?
Hi,
I needed to prepare some copper II chloride for future use, so done what I always did.
Placed some excess copper wire in a flask and poured hydrochloric acid in.
Its been sitting as that for quite while.
As usual nothing for while, then beautiful green of copper II chloride and then once more species of copper I chloride are being produced turns almost
black because of (CuCl4)2-.
I know that once diluted with RO water CuCl drops out and CuCl2 stays in solution.
Also, when drying CuCl2 I always could smell faint HCl aroma.
Thats as the background.
Question is, once I have the black mix mentioned before how do I know if there is any free HCl still remaining in solution ?
Basically, I don't want any (if possible) HCl vent into the atmosphere (health, environmental, corrosion and efficiency reasons).
If there is any free HCl still in there I don’t mind letting it react for another few weeks. I'm not in a rush, and will need CuCl2 in few months
time anyway.
[Edited on 31-8-2017 by witekprytek]
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Foeskes
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Once it's completely dry it shouldn't have any HCl. You should add H2O2 or bubbled oxygen into the black solution, since it would convert some CuCl to
CuCl2 and getting rid of some HCl in solution.
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witekprytek
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Once its dry it is obvious it wont have any HCl.
Problem is I don't want to dry it before I know there is no free HCl left.
If I add H2O2 then it will fizz oxidizing CuCl to CuCl2, but it will also fizz catalysing H2O2 decomposition without oxidising anything. Concentrated
CuCl2 solution look very similar to mix of chlorides of Cu(II) and Cu(I). And that is saying nothing about presence of excess HCl.
It is reacting with aerator present all the time. Don't want to waste H2O2 if I don't have to 
At some point the reaction it should consume all free HCl, but I don't know when it happens.
Was thinking to add Cu(OH)2 and see if dissolves, but I am not sure it will be definite test.
Right now I have only few long term reactions going on is separate containers but the Lab is taken down for refurb, so can't really run any tests.
[Edited on 31-8-2017 by witekprytek]
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DraconicAcid
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You can't get rid of all the excess HCl without risking hydrolysis of the copper(II) chloride to a basic copper(II) chloride.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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unionised
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Incidentally, if you have excess copper, the solution turns clear when all the Cu(II) has been reduced.
I suspect that the very dark colour you get is a mixed oxidation state material of some sort, giving rise to a charge transfer colour.
Adding a little copper carbonate or hydroxide seems like a sensible check.
Drying CuCl2 is likely to give rise to some hydrolysis anyway, even if you had removed the excess HCl.
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witekprytek
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Thanks for replies.
I'll do some testing in a week or two when some bits of lab are back in place
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