Query Regarding the Production of CuO

[amphibole]

I am attempting to prepare some CuO for various experiments and am running into a bit of a sore problem. I have, on hand, an excess of Copper (II) Sulfate pentahydrate and baking soda, and decided to employ them as precursors to CuO. To my best knowledge, the reaction should resemble this:

 2(CuSO₄.5H₂O) + 4NaHCO₃ -> Cu₂(OH)₂CO₃ + 2Na₂SO₄ + 3CO₂ + 11H₂O

After the reaction was complete (i.e. no more fizzing) , I was left with the precipitate of the basic copper carbonate (Cu₂(OH)₂CO₃). I then washed this precipitate several times and then heated it up to decompose it to CuO, H₂O and carbon dioxide. I believe the reaction should go:

Cu₂(OH)₂CO₃ + heat -> 2CuO + H₂O + CO₂ 

However, upon heating, I was left with a powder visually similar to the one in the attached picture. It is a sickly sort of yellowy/grey-ish color instead of the presupposed black. What kind of errors or impurities might I be encountering here? Did some of the Na₂SO₄ contaminate it? Or am I missing something?

Thanks. 

Edited January 16, 2018 by amphibole

[John Cuthber]

One possibility is the so called "basic copper sulphate"  A sort of mixed sulphate/ oxide.

Did you wash the copper carbonate with plain water, or with solution of bicarbonate?
You may find that leaching  the powder with a solution of bicarbonate, then water and then heating it again gets you a better sample of copper oxide.

[amphibole]

I think the error was a combination of "not leaching the powder" and "I didn't heat it at a high enough temperature". I ran two more trials today, one following the same steps as before, except I heated it at a greater temperature (approx. 260C), as well as a second run where I repeated the first trial (same temperature as the first go - around 200C), but I leached it with the bicarbonate solution before heating. Both trials resulted in a darker product. Thanks. 

[AJKOER2]

Save your CuSO4 and try dissolving a small amount of  Cu powder (copper sources include electric wires, copper pipe,..) into a mix of excess ammonia water, O2  (from an air pump or H2O2),  optionally NH4HCO3, and a required small amount of sea salt to serve as an electrolyte.  Reactions and source:

2 Cu + 4 NH3 + 1/2 O2 (or H2O2) + H2O --> 2 [Cu(NH3)2]OH  (see https://onlinelibrary.wiley.com/doi/abs/10.1002/bbpc.19630670412 )

 2 [Cu(NH3)2]OH + 4 NH3 (aq) + 1/2 O2 + H2O --> 2 [Cu(NH3)4](OH)2 

 Cu + [Cu(NH3)4](OH)2 <---> 2 [Cu(NH3)2]OH

CO2 + H2O = H2CO3 = H+  + HCO3-

[Cu(NH3)4](OH)2 + H+ + HCO3- -->  [Cu(NH3)4]CO3 + 2 H2O

If employing H2O2 + NH3 + HCO3- + electrolyte, one can jump start the reaction for a minute in a microwave in an open vessel, which I usually place in a plastic bag with expansion room to control ammonia fumes. In a few hours, the solution will approach royal blue in color, at which point, remove unreacted copper metal. Then, boil down the solution, in a fume hood or outdoors, releasing steam, NH3, CO2  creating a precipitate of copper oxides, predominantly CuO if an excess of ammonia /oxygen source was used. See comments at US Patent 5,492,681 https://patents.google.com/patent/US5492681 especially, to quote:

"(IVb)  Cu(NH₃)₄ (OH)₂ + HEAT → CuO + 4 NH₃ + H₂O "

Note, an advantage of this method is that one can pass the above formed NH3/CO2 back into fresh water (or dilute H2O2) to make another batch upon adding copper. Also, the suggested path outlined above differs from the patent in the expressed use of sea salt or plain NaCl as an electrolyte given the underlying electrochemical aspects of the dissolution reaction of copper with ammonia and oxygen. The cited patent preference for the addition  of ammonium sulfate may stem for its added benefit in acting as an electrolyte, in my opinion.

Edited March 30, 2018 by AJKOER2
Recycle comment, patent comment

[John Cuthber]

Or you can just heat copper in air.

[amphibole]

On 3/30/2018 at 9:59 AM, AJKOER2 said:

Save your CuSO4 and try dissolving a small amount of  Cu powder (copper sources include electric wires, copper pipe,..) into a mix of excess ammonia water, O2  (from an air pump or H2O2),  optionally NH4HCO3, and a required small amount of sea salt to serve as an electrolyte.  

At this point, I already have everything I need. For future batches, I'm just going to stick with heating up and decomposing the copper (II) carbonate. It's a quick and easy process that leaves me with a pretty pure product. 

[Sensei]

On 16.01.2018 at 3:42 PM, amphibole said:

I am attempting to prepare some CuO for various experiments and am running into a bit of a sore problem.

I would do it using electrolysis of copper electrodes. It'll produce bluish color Cu(OH)₂, if there is used low/medium voltage. But after overheating it, or using higher voltage, there will be created black CuO and it'll gather at the bottom of tank, as it's insoluble in water. It could also produce traces of Cu₂O (especially when there is used high voltage). I made it couple times. But it's easy to spot them and filter as they have reddish color.

On 16.01.2018 at 3:42 PM, amphibole said:

Did some of the Na₂SO₄ contaminate it? Or am I missing something?

If something contains Sodium you can check using flame test for Sodium..

https://en.wikipedia.org/wiki/Flame_test

 

 

[AJKOER2]

On 3/30/2018 at 3:53 PM, John Cuthber said:

Or you can just heat copper in air.

My experience with heating a copper penny was disappointing. As I was using a methane flame, I eventually realized that inserting the hot CuO / Cu2O in CH4 is like heating the oxide in hydrogen, with a reduction of the hot copper oxide back to Cu/Cu2O by CH4!

If one somehow heats copper powder in air till it is black, is that just a CuO coating on possibly Cu/Cu2O? Not exactly a preparation of pure CuO it seems to me.

Also, no heat needed. Just pour chlorine bleach (NaOCl) onto room temperature copper powder, and at least the surface looks like CuO!  Here is a reference: https://www.hunker.com/13401530/what-does-bleach-do-to-copper .

Edited April 3, 2018 by AJKOER2
Added link

[John Cuthber]

13 hours ago, AJKOER2 said:

onto room temperature copper powder,

OK, so you complain that oxidation in hot air only gives a surface coating of oxide (clever people will realise that bending the copper makes this flake off, so you can repeat the process- but that's another story). Reheating the flakes ensure they are fully oxidised.

Then you assume that people have powdered copper available

If they do then heating it in air will provide copper oxide- without needing to mess about with bleach and also without adding any other elements.