[Anthony]

To me this is complicated and I don't know all the right words so bare with me please.


I made malachite (copper carbonate) by neutralizing copper sulfate with sodium bicarbonate.  The first batch proceeded as expected with the expected result.  In turn, I reduced the copper carbonate with charcoal in a graphite crucible in a kiln and that yielded copper metal.

To the second batch of copper sulfate I added a moderate amount of hydrochloric acid.  I didn't mean to.  I meant to add sulfuric acid. Mistakes were made.  Nevertheless I proceeded as before adding sodium bicarbonate until the solution was neutralized.  After decanting I found that the precipitate was not the color of malachite but rather the color of azurite.
I've read about and tried to understand what happened but I don't know how or if azurite formed.  I can confirm that upon reduction as before, copper was yielded.

There were several hot days and cold nights with the solution in an open bucket outside between the addition of HCl and the neutralization.  The copper sulfate was derived by "pickling" copper in a hot bath of sodium bisulfate to which 3% hydrogen peroxide was added.  There may well have been residual sodium bisulfate in solution.

I've read the addition of HCl to copper sulfate should have created cupric chloride along with sulfuric acid.
CuSO4 + HCl => CuCl2 + H2SO4

The addition of sodium bicarbonate to cupric chloride would have created copper carbonate, sodium chloride, carbon dioxide, and water.
2 NaHCO3 + CuCl2 => Cu(HCO3)2 + 2 NaCl
Cu(HCO3)2 + 2 NaCl =>  CuCO3 + 2 NaCl + CO2 + H2O

The addition of sodium bicarbonate to sulfuric acid would result in
sodium bicarbonate + sulfuric acid =>  sodium bisulfate + carbon dioxide + water
NaHCO3 + H2SO4 => NaHSO4 + CO2 + H2O   

Azurite is
Cu3(CO3)2(OH)2
which I read described as copper carbonate hydroxide

Viewing YouTubes I've learned that the addition of a strong acid may change reaction products.  I am thinking this must be what happened.  I do not know how or why.  I'm hoping someone here will explain it to me.

A second attempt to create the same product by the same means is in works.