madscientist - 11-12-2002 at 10:08
Yesterday, I dropped 10 US nickels (I believe that they're 25% nickel, 75% copper) into 60mL of ~35% hydrochloric acid. I was hoping that the nickel
would be dissolved out, leaving copper gause, and a solution of nickel chloride. But that did not happen. This morning, I checked on it. The coins did
not appear to have been corroded the slightest. The solution of hydrochloric acid had turned to the familiar and distinct yellow color of elemental
chlorine. This is what I think is happening: the hydrogen from the HCl is bonding to the surface of the coin, due to nickel's affinity for hydrogen,
causing elemental chlorine to form; and the copper causes the hydrogen to be gradually released from the nickel.
Very interesting. Perhaps this could be used to prepare elemental fluorine via non-electrolytic means from anhydrous hydrogen fluoride!
Blind Angel - 11-12-2002 at 17:59
just to know, nickel and copper doesn't oxydize on coins?
Polverone - 11-12-2002 at 22:22
I think your imagination is running ahead of your experiments again :-) First of all, nickel is more active than copper, so it is the nickel that
would be dissolved, leaving copper behind, if this reaction had worked how you had hoped.
I've tried dissolving nickels in HCl myself. The surface quickly acquired a sort of dull matte color - presumably from dissolution of the nickel - and
then didn't do much for a long time, since copper doesn't dissolve in pure HCl very well at all. You can speed up the reaction (as I'm sure you know)
with the addition of H2O2.
I think you are jumping to conclusions about the source of yellow in your HCl, as well. Technical grade acid contains considerable impurities. I have
often seen it turn yellow in various reactions, whether or not chlorine is being generated. Nickel is higher in the electromotive series than
hydrogen, so I'm sure it would react with HF to form nickel fluoride and hydrogen gas, assuming the surface did not become passivated.
[Edited on 6-30-2014 by Polverone]
[Edited on 6-30-2014 by Polverone]