I was trying to recover copper from a failed attempt at using ammonia as a purification step.

I theorized that if I neutralized all of the ammonia using sulfuric acid, I'd have a mixture of copper and ammonium sulfate, then I could add sodium hydroxide to knock the copper out as CuO, then filter, wash and recover the pureish CuO for further experiments.

Everything went pretty much as I theorized, I got a decent yield of black copper oxide powder and a ton of ammonia fumes (why is it so hard to get rid of‽).

Weighed it out, added an appropriate quantity of sulfuric acid, observed a cheerfully exothermic reaction, everything going exactly as I expect.

The bubbles clear up, I add a couple squirts of water to dilute the solution a bit, and it's a greenish colour I'd expect from a chloride rather than a sulfite.

On resting, tiny, light blue sulfite crystals began to snow out, so I know it kinda worked, but why would it be green?