Sciencemadness Discussion Board

Separation of Cu(OAc)2 and Zn(OAc)2

Arsole - 7-9-2013 at 21:36

Lets say I have a mixture of 277g Cu(OAc)2 and 14g Zn(OAc)2 (both are hydrates). How would I go about separating them? (Purified copper acetate is the desired outcome)

My first thought was to look at solubilities. Wiki says that Zn(OAc)2 has a solubility of 43g/100cc in 20o C H2O. Wiki lists Cu(OAc)2 as having a solubility of 7g/100cc cold H2O and 20g/100cc hot H2O.

Would a good way to separate these compounds be to add the mixture to 200ml H2O at 20o C and stir for 15 minutes or so then filter off the solid followed by a cold water wash.

Due to the higher solubility of the Zn(OAc)2 would the undissolved solid product be relatively pure Cu(OAc)2?

Any other methods or advice?

elementcollector1 - 7-9-2013 at 21:55

Chill the solution to 0 degrees C - some copper acetate should drop out...

Arsole - 7-9-2013 at 21:58

Since they are salts and not in solution yet are you proposing just a simple recrystallization?

elementcollector1 - 7-9-2013 at 22:14

Pretty much. Make a saturated solution (carefully), and chill the solution: Crystals of pure copper acetate should drop out. Let us know how it goes! :)

Arsole - 7-9-2013 at 22:29

Great I will give that a try. I am going to read up on some zinc tests in order compliment a melting point.

I had thought about the recrystallization but it seems the losses would be quiet high. The reagents are cheap though I guess.

12AX7 - 7-9-2013 at 23:20


Toss in enough zinc to displace all the copper.

Dehydrate and crystallize.

After collecting the colorless crystals, realize something is wrong with this approach.

Buy copper acetate directly.

Open and consume beer.

:P Ok, yes I can be a little useful, from time to time.


Arsole - 8-9-2013 at 03:09


I'm not after the zinc acetate so displacement would not work.

I guess I could displace, then collect the copper precipitate, wash with HCl, and react that with acetic acid to yield the copper acetate. If I needed to go that far I would have to crack open a beer. :D

DJF90 - 8-9-2013 at 03:46

Copper should not react with acetic acid by itself. You'll need an oxidant in there. I've seen Pd(OAc)2 prepared from dissolution of Pd sponge (basically finely divided Pd metal) in AcOH, with a small amount of nitric acid added (6mL azeotropic acid in 250ml AcOH?)... Perhaps a similar approach could be used here. Almost certain I've seen AcOH and H2O2 used for copper specifically, actually.

unionised - 8-9-2013 at 04:26

I'm fairly sure that zinc hydroxide is amphoteric.

blogfast25 - 8-9-2013 at 05:22

Quote: Originally posted by unionised  
I'm fairly sure that zinc hydroxide is amphoteric.

Yes but so is Cu(OH)2! At high pH it forms cobalt blue cuprate anions: Cu(OH)42-.

Fractionated crystallisation will lead to incomplete separation and is tedious. You'll only obtain relatively zinc free copper acetate but the zinc acetate will always be soaked in copper acetate.

Separation by electroplating of the copper should be easy but requires redissolving of the obtained copper metal.

[Edited on 8-9-2013 by blogfast25]

AJKOER - 8-9-2013 at 11:08

I agree electroplating is a good path.

Here is another original idea, which you may wish to test. Treat the solution with NaI. Per Wikipedia on CuI2 (see ), it rapidly breaks down into the insoluble CuI and Iodine, whereas ZnI2 is more stable and highly soluble.

Then, separate out and wash the CuI with water and alcohol (I guess one could weigh the cost of the alcohol versus the loss of elemental iodine that may be recoverable (or not), in part, in the next step at the expense of introducing a dose of iodate). Next, treat with NaOH to form Cu(OH)2 (and the soluble NaI which can be recycled) and react with Acetic acid.

The introduction of NaI (or KI) is interesting here as it is rare that one that sees one salt becoming very insoluble and the other very soluble.

[Edited on 9-9-2013 by AJKOER]

Arsole - 8-9-2013 at 13:45

Quote: Originally posted by DJF90  
Copper should not react with acetic acid by itself. You'll need an oxidant in there.

Since the precipitated copper would be very fine could it not be oxidized in an oven using atmospheric O2 and a little heat. This should react with the acetic acid no problem. The first batch consists of zinc acetate and the second reaction yielding the pure copper acetate.

Yes, H2O2 will will provide the oxygen to drive the reaction to copper acetate.

I have never done electroplating and do not have the equipment to perform that currently though it sounds like an interesting project.

[Edited on 9-8-2013 by Arsole]

Arsole - 9-9-2013 at 13:17

I decided to run some simple experiments last night.

I took pennies between, years 1962 < X< 1982 as these contain 95% copper 5% zinc.

Experiment 1
The penny was placed in a small container and 10ml 5% acetic acid was added. The entire oxide layer was removed at room temperature in about 10 minutes. No apparent further reaction with the unoxidized copper was observed.

Experiment 2
The same procedure except the acetic acid was slightly heated. The oxide layer was removed in less than 2 minutes. The reaction was left to sit for 20 minutes the copper produced a few tiny bubbles that clung to the surface of the coin, but very slowly.

Experiments 3,4
The same procedures as above however this time 10ml of H2O2 was added to the solution. The oxide layers reacted and both pennies formed bubbles though the reactions were less than vigorous.

newer 022.JPG - 92kB
The penny to the left has a brown oxide layer. The penny to the right was the result of experiment 1.

Experiment 5
In order to see if the unoxidized pennies and acetic acid would react together. I removed the oxide layer from 4 pennies weighing 12.3g and added them to a 1L RBF. To the flask was added 600ml of 5% acetic acid this was then left to reflux for 4 hours. After 4 hours obvious bubbles had formed on the surface of the coins and the solution took on an extremely faint blue hue, indicating that a reaction had taken place although very very slowly.

Experiment 6
To a 1L RBF I added 250ml of 5% acetic acid, 250ml 3% H2O2 and 1 gram of copper turnings. At RT this mixture slowly formed very fine bubbles that clung to the copper's surface. After heating the mixture to about 80oC vigorous reaction took place.

newer 021.JPG - 95kB
Characteristic blue color.

newer 030.JPG - 64kB
View of reaction illuminated from below.

Experiment 7
About 30ml of solution from experiment 7 was added to a small glass container. A few tiny pieces of Zn were added to the solution. The zinc started to bubble immediately and after a few minutes the solution lost its blue coloring. After the zinc had stoped reacting the gray liquid (suspected zinc acetate) was discarded. Deposited on the glass appeared to be a small amount of copper metal. The glass was washed with dilute HCl and rinsed with tap water. To the glass containing the copper film was added 10ml acetic acid and 10ml hydrogen peroxide. After a few minutes of heating the characteristic blue hue of copper acetate was observed.

newer 039.JPG - 82kB
After washing, the copper deposits can be seen
on the bottom of the glass.

More experiments to come ;).

[Edited on 9-9-2013 by Arsole]

AndersHoveland - 9-9-2013 at 20:56

If the separation was for an industrial process, it might be possible they could add acetylacetone as a solvent that would complex with the metal ions. Then, with moderate heating and under reduced pressure these complexes can be relatively volatile. Under such conditions, fractional distillation may be possible.

blogfast25 - 11-9-2013 at 03:53

Quote: Originally posted by AndersHoveland  
Then, with moderate heating and under reduced pressure these complexes can be relatively volatile. Under such conditions, fractional distillation may be possible.

Selective solvent extraction would probably be easier.

But it all depends on what one wants to achieve: recovery of the copper for instance would be far easier by simple electroplating.

[Edited on 11-9-2013 by blogfast25]

DJF90 - 11-9-2013 at 06:26

Arsole: you seem like a nice guy and deserve a more suitable alias. Anyhow, you should ideally be using more concentrated acetic acid. Glacial is probably overkill, but 50-80% would be a good start.

gsd - 11-9-2013 at 06:50

5% acetic acid. Looks like you are using table vinegar. And after adding 250 ml of H2O2 (3% medicinal grade?) it gets further diluted. Like DJF90 said you need "home lab grade" chemicals not "kitchen grade".

Dilute AA (about 30 to 50 %) reacts fairly quickly with Cu under reflux and oxidizing conditions. You can even bubble air thru' the solution instead of using H2O2 to effect oxidizing atmosphere.


[Edited on 11-9-2013 by gsd]

Arsole - 11-9-2013 at 16:59


5% acetic acid. Looks like you are using table vinegar. And after adding 250 ml of H2O2 (3% medicinal grade?) it gets further diluted. Like DJF90 said you need "home lab grade" chemicals not "kitchen grade".

I have access to concentrated forms of these chemicals I used dilute because I am in a very small apartment and wanted to minimize the odor.

I am currently in the process of making my own vinegar from EtOH. I made and distilled the EtOH myself A few weeks ago. The acetic acid concentration should finish at roughly 20%. I plan on turning this into glacial through the reaction of copper acetate with concentrated sulfuric acid. This will provide me with a few weeks of simple yet fun experiments.

bismuthate - 28-9-2013 at 05:43

you sould probably just put zinc in the solution for a while, filter, and then wash the filtrate with hcl. then you have copper disolve this in H2O2 and acetic acid. this may take a long time unfortunatley.