[science2000]

When I place zinc or aluminum in a copper solution, a gas is released as the metal reduces copper. Anyone know offhand what gas that is and why it's produced?

[constant thinker]

You would need to know what was in the "copper solution". Metals coming in contact with metals don't just start bubbleing gas. It would have to be a contaniment in there.

State what's in that "copper solution" so when someone more knowlegable than I reads this will know what's going on in this reaction. Otherwise all anybody reading this knows is that Zinc, Aluminum, and Copper are coming in contact which shouldn't produce any reaction as far as I'm aware of.

[billnotgatez]

does it get warm enough to produce steam?
is the copper solution really hydrochloric acid with copper
what is the copper solution really

[science2000]

Two solutions, actually. One is a cobalt(II) acetate solution gone wrong, it's contaminated with the +3 state, so rather than wasting it I decided to put zinc in it, to displace the cobalt out of solution. Zinc is +2 so I wonder if that has anything to do with it.

The other solution is copper acetate (some peroxide is present in it), and I'm reducing it with aluminum. There's also a difference in oxidation numbers, Al=+3, Cu=+2.

I don't really know how hot it is on the reducing metal, cobalt and copper solutions are too poisonous to put my finger in.  

*there's probably still acid in these salt solutions, if that's a factor.

[billnotgatez]

During the American Civil War hydrogen gas for balloons was generated by combining hydrochloric acid and zinc.

[P-man]

Yeah, it's probably hydrogen coming off, as billnotgatez said. But are the bubbles accumilating around the metal or are they floating to the surface and going into the atmosphere?

[Borek]

I don't really know how hot it is on the reducing metal, cobalt and copper solutions are too poisonous to put my finger in.

Don't worry. Not that I will drink them, but these are not so dangerous. Although rinsing hands after using your finger to mix the solution will not hurt

*there's probably still acid in these salt solutions, if that's a factor.

Ah, so you are putting Zn or Al into acidic solution and you wonder what gas evolves?

[science2000]

I was kinda thinking since when metals are reduced, it creates electricity, like in a zinc-copper sulfate battery. Maybe these metals were causing water to decompose or something. There's not enough acid in these solutions to cause the serious bubbling.
Even when I put zinc in vinegar, it doesn't bubble so much. The bubbling even propels the small piece of metal through the solution, it's quite strange. My hypothesis is that it's related to the reducing process.

**Unless, the reducing sort of "activates" the zinc and aluminum, enabling them to react faster with what little acid is present in these solutions.

I heard cobalt salts are carcinogenic, so I don't want to push my luck.

[mike]

Zinc in copper sulfate solution should not bubble.

Cu²⁺ + Zn_(s) ---> Cu_(s) + Zn²⁺ E = 1.1V

It will only really "make electricity" if you can separate the half reactions.

Do you see copper metal depositing on the zinc?

[science2000]

I've observed two reactions. The cobalt is deposited on the zinc, and eventually it becomes a black powder spread throughout the bottom of the vial.

The aluminum is in the copper acetate solution, and yes it turns reddish.
I've tried to dissolve aluminum in vinegar before, but it's hard. It's oxide layer is very strong. too strong for the weak diluted acid to break. How can it's oxide layer break so easily when put in a copper solution?

[jdurg]

Remember that copper acetate salts form a basic solution due to the fact that acetic acid is a weak acid.  (Therefore salts of its conjugate base would form a basic solution).  Aluminum oxide is amphoteric, and in fact aluminum metal reacts with a base pretty readily to give off hydrogen gas.  Chances are, your acetate ion is forming hydroxide ions in solution which is attacking the aluminum oxide coating.  Aluminum is a VERY reactive metal, so as the Al2O3 is being removed by the OH- ions, the Al(s) is able to immediately react with the water and give off hydrogen gas.

[Borek]

Chances are, your acetate ion is forming hydroxide ions in solution which is attacking the aluminum oxide coating.

Good idea, once he wrote about remnants of acetic acid I have forgot about hydrolysis completely.

science2000 - try universal indicator paper to check pH of the solutions.

[science2000]

That's very interesting, jdurg. I never knew that. Do you suppose the situation is the same with zinc in the cobalt acetate solution? I'm kinda sure Zinc reacts faster with bases then diluted acetic acid.
When I get home this weekend I'll test the pH of these solutions.

[jdurg]

That could be possible with zinc, as zinc reacts with OH- to form the complex zincate ion.  Therefore, there is a chance that it could be occurring.