indigofuzzy
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Separating Hydroxides
Does anyone know of an effective way to separate Copper(II) Hydroxide form Magnesium Hydroxide?
I've gotten a good deal (sorry, I don't have a scale to weigh it) of these two compounds as a by-product from some electrochemistry experiments. If
there's a way to remove the Mg(OH)<sub>2</sub>, I could add acetic acid to make Copper(II) acetate (which works quite well for
electroplating, when mixed with a small amount of Tarn-X™).
On a side note, after removing the Mg(OH)<sub>2</sub>, is there a way to get elemental magnesium out of this? Actually, I should ask, "Is
there an easy and/or cheap way to get magnesium metal out of Magnesium Hydroxide?"
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UnintentionalChaos
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Yes, there is a somewhat easy way to get the copper out, but it may not be exceedingly easy to get the copper hydroxide back, if that is what you want
(it decomposes at below boiling water temperatures anyway). Add aqueous ammonia to make tetraammine copper hydroxide [Cu(NH3)4](OH)2, which is
soluble. If you filter out the Mg(OH)2, which does not make complexes and boil the solution, you should (I have never done this exactly, but I don't
see why it shouldn't work) ppt CuO, which can be filtered out. You will also reek the place up with ammonia, so do it outside or in a fume hood.
Edit: I assume that there is not too much copper here, or this would be very impractical. There is effectively no chance at changing this stuff to
elemental Mg easily. It is very useful for making Mg salts though.
Option 2: Roast the hell out of it and add vinegar. CuO is mind-bendingly slow to react with vinegar, while any hydroxide should react very quickly.
The remaining CuO can be left to dissolve in vinegar if you want Cu2(OAc)4, but it takes a while depending on how fine the particles are.
[Edited on 3-26-07 by UnintentionalChaos]
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'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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Nicodem
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It depends on how pure Cu(OH)2 you need?
If you know the composition of the mixture and do not need very pure Cu(OH)2, you can just dissolve the mixture in just enough diluted HCl to
selectively dissolve the Mg(OH)2, filter the remaining Cu(OH)2, wash a couple of times and air dry (do not use any heat while drying or else it will
dehydrate to CuO!). This is the cheapest method I can think of. You can use some other acids instead of HCl, but I doubt you can get anything cheaper
than HCl. Acetic acid would be better since the chlorides form a soluble complex with Cu(II) ions, but that complex is not stable enough to dissolve
Cu(OH)2 in my opinion. If you want to prepare copper(II) acetate you can use this crude Cu(OH)2 for its preparation and purify the resulting acetate
by recrystallization (if purity is important, which I doubt since you want to use it for electroplating anyway).
If you do not know the composition of the mixture you can first titrate a sample with diluted HCl to the point where the green-blue color of the
solution intensifies rapidly (drop the suspension on apiece of filter paper to separate the color of the solution from the blue of the suspended
particles when these refuse to precipitate fast enough; you can also intensify the color by waving such wetted filter paper above ammonia vapors). The
green-blue color should at one point start to intensify much more rapidly and you can take that as the point where most of the Mg(OH)2 dissolves.
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indigofuzzy
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@unintentionalChaos: 1) stupid question: Is aqueous ammonia the same "Ammonia" sold in grocery stores? Or will that not be pure enough?
2) Ending up with CuO is just fine, as long as the magnesium is out of the way. I could substitute Sulfuric acid for acetic, and convert CuO into
CuSO<sub>4</sub> which should be just as useful.
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UnintentionalChaos
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Yes, aqueous ammonia is just storebought ammonia. The problem is that if Cu(OH)2 is your major product, it will require a lot of ammonia since each
atom of Cu needs 4 ammonia. The second method would probably be much faster, if not as efficient. The tetraamminecopper complex is a lovely intense
cobalt blue if you haven't seen it before.
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'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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indigofuzzy
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| Quote: |
The tetraamminecopper complex is a lovely intense cobalt blue if you haven't seen it before.
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That sparked my curiosity. For that reason alone I'll have to try the ammonia method at least once  too bad it'll smell nasty 
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UnintentionalChaos
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If you want to see an even bluer one, pour a saturated solution of a copper salt into a (excess of) saturated solution of sodium carbonate, and I mean
really saturated. You will ppt a bunch of CuCO3 (and Cu(OH)2, since its near-impossible to escape the basic copper carbonate), but the solution should
turn intensely dark blue due to formation of an unstable copper complex, most likely dicarbonatocuprate, [Cu(CO3)2] (+2). Overnight, this will
decompose into copper carbonate and copper hydroxide, however. I've only done it once, and it was sort of an accident while making a whole bunch of
copper carbonate to convert to CuO for an experiment at school using copper sulfate and sodium carbonate.
You can try out these complexes with any copper salt, just dissolve it in some household ammonia and a similar amount in water. The normal
tetraaquacopper complex pales in comparison to the tetraammine or dicarbonatocuprate.
[Edited on 3-26-07 by UnintentionalChaos]
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'In organic synthesis, we call decomposition products "crap", however this is not a IUPAC approved nomenclature.' -Nicodem
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indigofuzzy
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| Quote: |
The tetraamminecopper complex is a lovely intense cobalt blue if you haven't seen it before.
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My roommate and I went down to the basement tonight, filtered the hydroxides from the MgSO<sub>4</sub> soln that they were made in (see my
post about making CuSo<sub>4</sub> electrolyticly), then added the filtrate to some aqueous ammonia, as suggested. WOW! I'll post pictures
tomorrow, but that's an amazingly cool shade of blue.
Upon running a small sample of the ammonia soln through more filter paper, the Mg(OH)<sub>2</sub> was easily removed, yielding a
beautiful, transparent, dark blue liquid.
Now, I just have to find a way to dry the solution without stinking up the house! (crowded neighborhood, so outdoors is a no-go, and I don't have a
fume hood) Any ideas?
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not_important
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If you just evaporate it, the ammonia will escape and the complex break up. I believe the method used to obtain the complex as a solid is to add
alcohol or acetone to the solution...
ah, yes, like this
http://www.creative-chemistry.org.uk/alevel/module5/document...
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UnintentionalChaos
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If you have tubing, you can just lead the gas from the boiling solution into ice water which will regenerate your ammonia. You will still lose some of
it though. If you run it into a cold acid bath instead, you'll trap the ammonia as salts and a decent setup will keep nearly all the fumes in.
EDIT: Avoid my stupid mistakes and keep any copper salts out of anything metal (except more copper) You do it once, dissolve the inside of a pot out
and never make the same mistake again (although I made related ones).
EDIT No2: Just a thought. I dont think that the complex is stable at boiling temperatures and neither is hydroxide, so boiling for a few minutes
should produce (most likely) a suspension of very fine CuO particles, which can be filtered out. The rest of the solution will just be ammonia
solution again, though depending on the amount, I'd probably just dump it since its pretty cheap.
EDIT No3: Surfing around on the web, nobody seems to be able to agree about the solubility of CuO in aqueous ammonia (also, this thread shows up
halfway down the first page of google for "CuO ammonia complex") If I was home, I'd give it a shot, since I still have some tetraammine salt lying
around. Give a small sample of the solution a boiling test to see if it does ppt the CuO.
Beat this shade of blue. That is about two inches (5cm) of very concentrated tetraamminecopper sulfate solution from when I did the CuSO4 synth that
is in prepublication (never got put into member publications though). All the tubes are a fishtank bubbler used to make the copper metal dissolve
faster.
[Edited on 3-28-07 by UnintentionalChaos]
[Edited on 3-28-07 by UnintentionalChaos]
[Edited on 3-28-07 by UnintentionalChaos]
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Levi
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| Quote: | Originally posted by indigofuzzy
@unintentionalChaos: 1) stupid question: Is aqueous ammonia the same "Ammonia" sold in grocery stores? Or will that not be pure enough?
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Make sure you use clear ammonia. Grocery stores will often sell "cloudy" ammonia which contains detergents. If your ammonia isn't as clear as water
it's no good.
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indigofuzzy
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Very good advice. Glad to know I got the right stuff
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