Sciencemadness Discussion Board

Getting rid of acetic acid in copper acetate solution?

Draeger - 16-6-2020 at 14:40

I made some copper acetate. Problem is that there's still some acetic acid in solution. I don't have any sort of ventilation so boiling it is not an option. Is there any other way I could get rid of it?

UC235 - 16-6-2020 at 16:13

What's the end goal here? It crystallizes just fine from solution with an excess of acetic acid. In fact, it's probably preferred so as not to get basic copper acetate.

Draeger - 16-6-2020 at 17:14

Quote: Originally posted by UC235  
What's the end goal here? It crystallizes just fine from solution with an excess of acetic acid. In fact, it's probably preferred so as not to get basic copper acetate.

Can't crystallize most of the product without concentrating the solution, as far as I know at least, and to concentrate it I'd have to boil it, which I can't since the smell would likely be unbearable because I have no ventilation. I could also wait for it to evaporate, but that would take a long time, so I am looking for a different way to get rid of the acetic acid, provided it exists.

Ubya - 16-6-2020 at 17:49

i also had your issue, i overestimated the amount of acid i needed so instead of wasting the excess acid (cheap for many but i made this myself, i was emotionally involved) i added more copper and instead of using H2O2 (i only have 3%, the volume would have been excessive) i used a ceramic airstone and a small air pump on the lowest setting to oxidize the copper in solution (it took maybe 2 days).
Lucky for me the solution got to saturation and i begun seeing copper acetate crystals growing, soi just filtered the copper metal and evaporated the solution (without boiling) for an evening unitil i got my powder :)

if this is not an option for you, maybe solvent extraction can work as acetic acid is a weak acid. you could try with a non miscible alcohol or maybe ethylacetate (more apolar solvents could be used but i'm not sure about their efficacy)

Bedlasky - 16-6-2020 at 19:42

What acid you used? GAA or vinegar? If you have excess of vinegar or only slightly excess of GAA, just boil it down with open window. People normally boils infusions containing lots of vinegar. Yes, it smells horrible but it can be done inside.

woelen - 16-6-2020 at 23:14

It really is important to crystallize the copper acetate from the acidic solution, otherwise you will get basic copper acetate. Copper acetate tends to hydrolyse in water and forms insoluble compounds. If a little acid is present, then this hydrolysis does not occur.

I myself made copper propionate recently in a similar way (from unknown eBay-quality CuO and high grade propionic acid) and I just let the solution evaporate slowly, in our garden shed. There was a strong smell of propionic acid in the shed (it smells much like vinegar, albeit a little more musky), that's why I did not do this inside. The vapor is not really toxic (just like acetic acid vapor is not toxic), but having that smell inside is not fun. It took more than a week, before solid crystalline material settled at the bottom. I also did not allow all of the liquid to evaporate to dryness, when 90% or so was gone, I decanted the remaining part and press-dried the crystals in filter paper (coffee filter with tissue wrapped around it) and then allowed the crystals to dry. Impurioties remain mostly dissolved in the liquid and by sacificing 10% or so of your yield you end up with a much purer product.

Chemorg42 - 17-6-2020 at 08:55

According to wikipedia, sodium acetate has a solubility of about 32 g / 100 mL in cold water, while copper (II) acetate has a solubility of about 7 g / 100 mL in cold water. Therefore, couldn't you just neutralize the acid with sodium bicarbonate, then boil off the excess liquid, and finally chill the solution to cause most of the dark green copper acetate to crash out of solution?
Others have said that you want a somewhat acidic environment, so maybe this is not the best option, though I think it would theoretically work.

DraconicAcid - 17-6-2020 at 09:15

Quote: Originally posted by Chemorg42  
According to wikipedia, sodium acetate has a solubility of about 32 g / 100 mL in cold water, while copper (II) acetate has a solubility of about 7 g / 100 mL in cold water. Therefore, couldn't you just neutralize the acid with sodium bicarbonate, then boil off the excess liquid, and finally chill the solution to cause most of the dark green copper acetate to crash out of solution?
Others have said that you want a somewhat acidic environment, so maybe this is not the best option, though I think it would theoretically work.


Mo, that won't work at all- you'll precipitate basic copper acetate.

unionised - 17-6-2020 at 10:55

It won't really work- because you will precipitate basic acetates when you crystallize it but... if you insist.

Take a little of the solution (maybe 5 or 10%) and add an excess of sodium bicarbonate to it in a separate container.
That will give you a precipitate of copper carbonate.
Filter that off and wash it with water.
Then add the clean copper carbonate to the remaining copper acetate / acetic acid solution and leave it to react with the acid.

hat should get rid of the smell of acetic acid.
But I still think you will get poor crystals when you let the water evaporate.

RogueRose - 17-6-2020 at 19:28

I would also really suggest crystalizing with an excess acid and the acetate does the best with slow evaporation. If you don't need it ASAP then just let it sit out and forget about it for awhile. If you want to make it go a little faster, put a fan to blow across it and it should speed it up by 2-6x faster (depends on the humidity where you are).