[johnoxide]

Hello everyone! First post here, go easy on me!

Ok so recently I placed a few euro cent coins (some 10-cent and some 5-cent) in a plastic cup and covered them with ethanol 70%. I was hoping to clean them but I kind of forgot them there.
So today, some weeks later, I remembered them and checked them and I was surprised to see the coins covered in a bluish/greenish substance as well as some redish substance in the bottom (I'm guessing from the smaller coins).

At first I was surprised by this but I'm guessing it was some kind of reaction? What happened exactly? I know that copper is present in the coins and is probably responsible for the blue but I didn't expect this much and the red has me beaten...

[Borek]

If you can spare another few coins put them in the same place but in water. At least you will know if the ethanol was an important part of the experiment.

[curiouscat]

To use Borek's approach further keep 5 cent and 10 cent coins separately in water and ethanol. That way you will know which causes which color.

[Borek]

You can also put the together but one pair touching and one pair not touching.

But it becomes costly 

[Enthalpy]

I expect the 70% ethanol to be little corrosive to metals, but the remaining 30% are essentially water...

http://en.wikipedia.org/wiki/Euro_coins
5 cent is iron coated with copper, 10 cent is copper, alu, zinc and tin.

My guess (chemists must have better ideas):
- You have obtained a mix of oxides and hydroxides
- Green and blue are from Cu⁺ and Cu²⁺
- Clean metallic copper can be strikingly red, especially by electrolysis. Might happen if copper is reduced by the oxidation of an other metal?
- Among the many iron oxides, some are red, like the soil of Brazil, or bricks, or a tennis court.
http://en.wikipedia.org/wiki/Iron_oxide

More sources of red, I feel less likely:
- Traces of chromium make aluminium oxide red. But the hydroxide?
- Traces of manganese make zinc oxide red
- Tin (II) oxide can be red

[ajkoer]

I agree with the advice on separating the coins. Also, add a little H2O2 and perhaps H2CO3 to speed the reaction up to test whether it is oxygen or CO2 or both responsible for the products.

Now, per recent research on the reaction between NH3, Cu and air, the reaction as of 1962 was speculated to procedure via several paths (see http://www.academia.edu/292096/Kinetics_and_Mechanism_of_Copper_Dissolution_In_Aqueous_Ammonia ). The best theory is apparently the oxidation of metals in an electrolyte procedures along the lines of galvanic corrosion (basically an electrochemical reaction process).

I would guess, assuming the presence of O2 and CO2, a similar process forming, in part,  Basic copper carbonate, Cu2(OH)2CO3. Its color per Wikipedia (http://en.wikipedia.org/wiki/Basic_copper_carbonate ) to quote:

"The colour can vary from bright blue to green, because there may be a mixture of both copper carbonate and basic copper carbonate in various stages of hydration. "

Also, some Cuprous oxide, Cu2O, could be formed as per Wikipedia (http://en.wikipedia.org/wiki/Cu2O ), it forms a "bright red precipitate" assuming insufficient CO2 as else Cu2(OH)2CO3.

Now, normally hot copper (CuO) reacts with Ethanol as follows (see http://www.google.com/url?sa=t&rct=j&q=reaction%20between%20copper%20oxide%20and%20ethanol&source=web&cd=4&ved=0CD4QFjAD&url=http%3A%2F%2Fwww.nistepkscience.com%2FChemistry%2F14RedoxReaction.pdf&ei=i_S5UfQ6hbfgA93PgfgO&usg=AFQjCNF-amrv9PW1UlgL1FyL5NP6s5rHIA ) to quote:

"Copper oxide oxidizes ethyl alcohol to acetaldehyde, copper oxide is reduced to copper.

C2H5OH + CuO --> CH3CHO + Cu + H2O "

So, the bright red could also be the copper per the reduction of the copper oxide occurring slowly with time. To those who insist on a water free environment for this reaction to proceed, the formation of the Basic copper carbonate may sufficiently remove the water.