Copper Compound Conundrum, Part 1

If you've been following my blog, you've probably realized I like to write a lot. Well this one's no exception. I like to provide as much detail as possible so others can replicate my results and in reading it get the same enjoyment out of the experience as I did (hopefully). Enjoy!


In the process of filming a new video on copper compounds for my channel, I ran across a bit of a snag that ended up taking me down a different path that was both fun and instructive.

The scheme of reactions I had planned was the following:

1) CuSO4 + 2NaHCO3 == CuCO3 + Na2SO4 + CO2 + H2O
2) CuCO3 + 2HCl == CuCl2 + CO2 + H2O
3) CuCl2 + 2NaOH == Cu(OH)2 + 2NaCl
4) Cu(OH)2 + H2SO4 == CuSO4 + 2H2O

Each compound is a different color and exhibits different properties, and I thought it was nice to end back where I started at copper sulfate.

The reactions proceeded as planned, with each step working out smoothly.The following are still images from the video I was recording at the time, so they might not be as nice as some of my other shots.

Copper(II) sulfate solution:

Copper(II) carbonate, filtered and dried precipitate:

Copper(II) chloride solution (concentrated):

Copper(II) hydroxide thick, gooey precipitate:

Filtered and dried copper(II) hydroxide (?):

That last photo is where things went wrong. I filtered, washed, and dried my copper hydroxide and I ended up with this dark green powder instead of the turquoise blue that the hydroxide should be. I've had this problem before, and it's due to copper hydroxide's tendency to decompose and react with air readily, especially when wet. The two reactions I suspect occurred are:
Cu(OH)2 == CuO + H2O
Cu(OH)2 + CO2 == CuCO3 + H2O
Copper(II) oxide is black and copper(II) carbonate is green, yielding this dark green overall color. There were also bits of blue in there that aren't really visible - that was my surviving copper hydroxide.

This result was unfortunate, but I didn't think it would cause any problems. All three of these should react with sulfuric acid to form copper sulfate, as in step 4 above. However, this is where things really got strange. Stay tuned for Part 2, where I show what happened and perform some standard anion tests to test my hypotheses.

Part 2, Testing the Solution