[science2000]

...can quickly dissolve copper in ammonia...however I'm curious if anyone knows why there's a rather violent release of gas, and what gas is it? What reaction is going on here? There's also a weird color change if Cu++ ions are present that quickly goes away.

[Mitch]

Color change is rather vague, be more specific.

[science2000]

I meant hydrogen peroxide, btw.
When the copper is first put in ammonia, and peroxide is added, no Cu++ ions are in solution, so only a fast then sustained release of gas takes place. If Cu++ ions are present in solution, and I added some peroxide, the area where I added turns a very dark color, blackish almost a greenish tinge. You could do this easily yourself, I used a copper screw. It very quickly goes away. Like something unstable forms then decomposes.

[jdurg]

Hydrogen Peroxide is a fairly unstable compound, and the presence of the copper will quickly decompose it into oxygen gas and water.