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Author: Subject: Gallium Hydroxide to Gallium Hydrochloride (EDIT: GaCl3:NH3 complex)
Loptr
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[*] posted on 12-8-2017 at 19:12
Gallium Hydroxide to Gallium Hydrochloride (EDIT: GaCl3:NH3 complex)


Alright, so I dissolved about 20 grams of gallium into a HCl(aq) solution, but ended up having to use a large excess due to the reaction slowing down as it progressed due to decreasing concentration. I was left with a large volume of overly acidic solution that would have to be removed, so I decided to precipitate the gallium as the hydroxide with the addition of a 10% ammonia solution. This worked and I was able to filter the gallium hydroxide sludge slowly on a filter.

I then attempted to acidify the hydroxide with concentrated HCl(aq), and found that the hydroxide seems to either react very slowly with the acid, if at all. I ended up with a suspension of gallium hydroxide in the HCl(aq) solution.

What is going on here?

[Edited on 13-8-2017 by Loptr]

[Edited on 14-8-2017 by Loptr]




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[*] posted on 13-8-2017 at 05:25


I wouldn't rule out the possibility of gallium/ammonia complexes forming. At this point, your best bet is probably just to get it hot enough to drive off every possible gas that can form, leaving you with gallium oxide, which you can then figure out the stoichiometry for reacting with HCl.



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[*] posted on 13-8-2017 at 18:16


I should have just gone this route to begin by making the nitrate, and then thermally decomposing to the oxide.

One thing to note is that it does dissolve into very concentrated HCl solution, and rather slowly.

And yes, I have found some mention of GaCl3:NH3 complexes that decompose in the 300-500*C temperature range to GaCl3 and NH3.

Would this possibly be a way to anhydrous GaCl3? This complex is gelatinous when separated but dries pretty easily with heating well before 300*C. Or would the GaCl3 decompose around those temperatures as it formed? GaCl3 has a BP of 201.3*C, so it would be in a gaseous state at that time, too. Sounds problematic to say the least.

[Edited on 14-8-2017 by Loptr]




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[*] posted on 14-8-2017 at 02:56


I wouldn't use ammonia as a base for displacing hydroxides if I were you: as it was mentioned before, ammonia forms complexes a little too easily, and there's always a probability that you'll end up with some unwanted complex instead of your desired hydroxide.



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[*] posted on 14-8-2017 at 05:31


I am planning to redisolve this complex in conc. HCl, and then attempt to precipitate it with NaOH. I am not sure but I think the complex breaks down under low pH conditions, and might be the reason why it dissolves with a large excess of conc. HCl, or it could be some similar ion effect between GaCl3:NH3 and conc. HCl(aq).



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[*] posted on 14-8-2017 at 11:49


You probably have a mix of gallium oxides, hydroxides, and chlorides, if aluminum's behavior is any indication. You also can't rule out the possibility of the complex itself being soluble at low pH. Also, how do you plan to remove the ammonia, even if the complex breaks down at low pH? It'd just form again if you raised the pH in an attempt to remove the ammonia.

NaOH will form galliate salts, however sodium carbonate should precipitate oxides and/or hydroxides, if that's what you want. Gallium carbonate (like aluminum) won't form in aqueous solutions.




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[*] posted on 14-8-2017 at 12:01


Quote: Originally posted by Melgar  
You probably have a mix of gallium oxides, hydroxides, and chlorides, if aluminum's behavior is any indication. You also can't rule out the possibility of the complex itself being soluble at low pH. Also, how do you plan to remove the ammonia, even if the complex breaks down at low pH? It'd just form again if you raised the pH in an attempt to remove the ammonia.

NaOH will form galliate salts, however sodium carbonate should precipitate oxides and/or hydroxides, if that's what you want. Gallium carbonate (like aluminum) won't form in aqueous solutions.


I said that I was going to try using NaOH before I really thought about it, and you are right. Gallium is amphoteric and will act as an acid in that case. I recall reading that gallium hydroxide won't dissolve into a basic aqueous solution until around a pH of 9, so somewhere before that might be where my redemption will be found.

Any other suggestions?

[Edited on 14-8-2017 by Loptr]




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[*] posted on 22-8-2017 at 06:12


I still think you'd be best off to dry it, then heat the whole mess as hot as you feel comfortable getting it, at least for an hour, then reacting with HCl. The fewer elements are there, the simpler the reaction dynamics are.



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