Sciencemadness Discussion Board

Copper bicarbonate?

Draeger - 16-6-2020 at 14:36

So, yesterday I decided to use sodium bicarbonate to convert some copper waste into basic copper carbonate. What ended up happening after the bubbling stopped is it forming a grey solution of unknown composition. What could it be?

Texium - 16-6-2020 at 18:24

Not "copper bicarbonate" that's for sure. What else was in your waste solution? Since you mentioned bubbling, I presume there must have been some kind of acid present. Do you have litmus or universal indicator strips that you could use to check the pH of the solution?

woelen - 16-6-2020 at 23:21

Copper bicarbonate does not exist. When you mix copper(II) ions and bicarbonate in solution, you get copper carbonate, CO2 and water. I even doubt that you get pure copper carbonate, most likely it is somewhat basic copper carbonate, also containing hydroxide.

The copper carbonate you get has a blue/cyan color. If your material is grey, then probably it contains other metal cations as well. You write about 'copper waste', so I assume your material is not a pure copper salt.

If also chloride is present in the solution, then things get more complicated. Chloride ions keep coordinated to the copper metal ions as well. In that case, you'll get a complicated copper carbonate/chloride/hydroxide mix. This mix has a nice green color (provided, you only have copper metal cations in your mix).

A nice experiment is making a precipitate of a solution of copper sulfate with sodium hydroxide, and another with sodium (bi)carbonate. Then repeat the experiment with a solution of copper sulfate, to which some table salt is added as well. You'll see that you get completely differently colored precipitates, due to the coordinated chloride ions.

Draeger - 17-6-2020 at 09:01

Quote: Originally posted by woelen  
Copper bicarbonate does not exist. When you mix copper(II) ions and bicarbonate in solution, you get copper carbonate, CO2 and water. I even doubt that you get pure copper carbonate, most likely it is somewhat basic copper carbonate, also containing hydroxide.

The copper carbonate you get has a blue/cyan color. If your material is grey, then probably it contains other metal cations as well. You write about 'copper waste', so I assume your material is not a pure copper salt.

If also chloride is present in the solution, then things get more complicated. Chloride ions keep coordinated to the copper metal ions as well. In that case, you'll get a complicated copper carbonate/chloride/hydroxide mix. This mix has a nice green color (provided, you only have copper metal cations in your mix).

A nice experiment is making a precipitate of a solution of copper sulfate with sodium hydroxide, and another with sodium (bi)carbonate. Then repeat the experiment with a solution of copper sulfate, to which some table salt is added as well. You'll see that you get completely differently colored precipitates, due to the coordinated chloride ions.

Thank you. Yeah, I was just stupid. I wrote it at such a late hour that I just forgot that I label my waste bags after what hazardous substance is in it, not generally what is in it. It's probably contaminated with lots of sodium and chloride, and even probably lots of calcium.

Syn the Sizer - 17-6-2020 at 09:04

Quote: Originally posted by woelen  
If also chloride is present in the solution, then things get more complicated. Chloride ions keep coordinated to the copper metal ions as well. In that case, you'll get a complicated copper carbonate/chloride/hydroxide mix. This mix has a nice green color (provided, you only have copper metal cations in your mix).


If your copper waste has chloride ions in it, is it best just to crash the copper out with aluminum? I realize you will end up with copper metal instead of a easily usable basic carbonate. Is it possible to prevent the ion coordination?

chornedsnorkack - 18-6-2020 at 07:10

Quote: Originally posted by woelen  
Copper bicarbonate does not exist. When you mix copper(II) ions and bicarbonate in solution, you get copper carbonate, CO2 and water. I even doubt that you get pure copper carbonate, most likely it is somewhat basic copper carbonate, also containing hydroxide.

The copper carbonate you get has a blue/cyan color.


Pure copper carbonate stability field in room temperature water was found to be above 4,6 bar carbon dioxide. And judging by repeated failed attempts to produce it, probably not kinetically straightforward.

Copper has two basic carbonates - azurite Cu3(CO3)2(OH)2 and malachite Cu2CO3(OH)2. Different colours - one blue, one green. How do you reproducibly produce one or other?

Bezaleel - 19-6-2020 at 06:23

In case you are looking to purify you copper carbonate, Atomistry suggests to dissolve the hydroxide in ammonia solution, which leaves pure CuCO3 behind.

I think this will also help you get rid you the chloride, forming dissolved NH4Cl.

Bedlasky - 19-6-2020 at 06:25

Quote: Originally posted by Bezaleel  
In case you are looking to purify you copper carbonate, Atomistry suggests to dissolve the hydroxide in ammonia solution, which leaves pure CuCO3 behind.

I think this will also help you get rid you the chloride, forming dissolved NH4Cl.


Ammonia solution also dissolve copper carbonate.