DORI
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Copper acetate and residue
Hello All
I Have prepared copper acetate (to be used as an ingredient in a brass patination process), following the procedure described here(short brief if you don't have patience to watch it - making copper carbonate from copper sulfate and sodium bicarbonate, and making copper
acetate from the copper carbonate and 5% acetic acid).
However, I know nothing about stoichiometry, so I just multiplied the amounts to fit my yield of copper carbonate.
The guy in the video calculated 230ml AA for 12.36 grams of copper carbonate, but used 250ml of 5% acetic acid for 12.36 grams of copper carbonate to
be on the safe side and make sure all the CC reacted. I figured the ratio as 18AA/1g CC, and since I used 27g of copper carbonate, I mixed in 510ml of
acetic acid (5% ofcourse).
Now I have a jar with a nice dark blue liquid, just like in the video, but on the bottom of the jar there is a light verdigris sediment, that looks
very thin.
What is this sediment? is the reaction over? what is the most efficient way to extract my copper acetate (since this is what I needed in the first
place...)?
wow, that was a lot to read...sorry about this guys 
Thanks for your time reading and even more if you can help!
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I Like Dots
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You don't need to be exact with this.
Just make a solution of copper sulfate, and add sodium bicarbonate solution. Add until copper carbonate stops precipitating.
Add vinegar until everything is dissolved. simple.
As for the sediment who knows, by the color it might be left over copper carbonate.
Just filter the solution through a coffee filter, and save the liquid. Then you could just toss it on the stove to concentrate it.
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Metacelsus
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You need to be careful about boiling down solutions of copper acetate to dryness - too much heating and the copper acetate will decompose. Also, it's
best if you wash you precipitate of basic copper carbonate with water several times before adding acetic acid in order to remove all sodium sulfate
and unreacted sodium bicarbonate. This way you can be sure about how much acetic acid to use.
Note: Make sure your calculations are for basic copper carbonate (Cu2(CO3)(OH)2), not copper carbonate. If you don't use enough acetic acid, you will
have unreacted basic copper carbonate, which could be your sediment.
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woelen
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Just use enough acetic acid. If the procedure asks for a certain amount, multiply by 1.5 and add this. The excess acetic acid evaporates and assures
that you get real copper acetate and not some basic copper acetate.
Obtaining the salt is easy, but requires patience. Pour the liquid in a plastic or glass dish and put this on a warm and dry place, free of dust. A
nice place is on top of a heater radiator, but in summer, a nice warm place near a window with sunshine is suitable as well. The larger the surface of
the dish, the better. After a few days all water and acetic acid will have evaporated and crystals of copper acetate remain behind. I would not
strongly heat the liquid, this may lead to decomposition. Copper acetate is not that stable, it easily looses acetic acid and becomes a mixed
oxide/acetate (so-called basic copper acetate), which is insoluble in water.
Another important issue is the purity of the acetic acid. Some brands of vinegar contain extractions from spices, salt and sometimes even some sugar
besides acetic acid and water. Even the colorless vinegar may have quite a lot of impurities. You could check that by boiling down a little amount of
vinegar and see if a residue remains behind. Maybe you can find cleaning vinegar in a supermarket? This cleaning vinegar usually just contains acetic
acid and water and in most countries it also has a higher concentration (10% or so).
[Edited on 18-6-13 by woelen]
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DORI
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Thanks for all your answers! I will follow Your advice and see what happens.
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DORI
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OK, I started the procedure again, trying to avoid previous mistakes. I now have a vessel with that nice looking deep blue liquid, and some crystals
have already formed on the bottom. I would like to speed up the process - currently I'm just waiting for the liquid to evaporate. I read in the
comments above that heating can cause the copper (II) acetate to decompose, so I'd rather not risk it (this is not just a fun experiment, I actually
need the copper acetate...). my question is - can I speed things up by electrolysis? it may sound like I'm rushing it, but I'd really hate to just
wait for it to evaporate.
I have copper electrodes and a power source, but so far I haven't found any explanations on the web.
Many thanks for your help!
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