NaK
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Gallium + Aqua regia forms... What?
So I wanted to make some gallium chloride. So I started dissolving gallium metal in hot hydrochloric which was still very slow so I just thought I'd
add one third Nitric acid to it. This dissolved it pretty immediately under formation of nitrogen dioxide gas. I boiled it down but didn't get the
chloride but a very strange white compound. It isn't soluble in water or ethanol and reacts acidic (either it's an acid or there is even after
multiple hour heating at 200C still acid left). It dissolves in hydrochloric acid but boiling it down again afterwards doesn't lead to anything
dryable or usable anyway. Also no reaction with aluminum.
Now the strangest thing is that I heated a bit of it with a torch (inside a flask) hoping to decompose it and it actually formed a brownish black
chunk. The major brown gallium compound seems to be gallium(I) oxide but I have absolutely no clue how this could have formed.
So does anyone have any idea what I'm working with here?
[Edited on 14-9-2019 by NaK]
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12thealchemist
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Gallium and aluminium are very similiar in their chemistry. If you had treated aluminium in a similar manner, you would obtain hydrated aluminium
chloride, which behaves in a similar manner to your mystery white compound. I would guess therefore that you obtained hydrated gallium chloride, which
partially hydrolyses in water to hydrochloric acid and Ga(OH)xCly species. This mixture of oxychlorides is likely the residue
you ended up with, hence no reaction with aluminium - acidic but not that acidic.
The brownish-black material is probably mostly gallium hydroxychlorides and gallium(III) oxide - gallium(I) compounds are extremely difficult to
obtain and rapidly oxidise in air as a rule. The colouration I would put down to organic impurities that charred upon strong heating.
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NaK
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Thank you for your answer!
I can confirm that the black stuff was probably organic, it had a very distinct organic smell. But what I still don't understand is why the proposed
gallium chloride hydrate is not soluble in anything but acids. I think aluminum chloride hexahydrate is readily soluble. Maybe there was some
decomposition while crystallising though...
[Edited on 14-9-2019 by NaK]
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12thealchemist
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The issue, I believe, is the partial hydrolysis of the gallium "chloride" product. This forms gallium hydroxychlorides, which are insoluble in water.
In acid, the hydroxide ions are protonated and the solution is better described as an acidic solution of gallium chloride. A similar issue is present
with ferric chloride - a scum of iron hydroxides is formed when it is dissolved in DI water, and not acid.
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