Subject: Re: wierd hunger

From: Remco Vietor <[email-masked]>
Date: Tue, 03 Dec 1996 09:57:52 +0000

H. Wayne Richardson wrote:
> 
> >In article <[email-masked]> Eric Lovett ...
> >I know that acid + metal, yield hydrogen gas.
> True for zinc but not for copper metal.

Sorry, true for copper as well, just requires more time and/or stronger acid.
Using the proper acid (aqua regia, or hydrochloric + nitric acid), 
even gold dissolves.

Regards,

Remco.
[email-masked]
 
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From: "Eric Lucas" <[email-masked]>
Date: 3 Dec 1996 23:27:39 GMT

Remco Vietor <[email-masked]> wrote in article
<[email-masked]>...
> Using the proper acid (aqua regia, or hydrochloric + nitric acid), 

Yes, but in aqua regia, it's the nitric acid (high-oxidation state N) that
does the oxidizing.  Those copious red fumes are NO2 (or is it N2O4, I can
never remember) from reduction of the nitric acid.  No H2 is generated. 
Cu, Ag and Au are all above H2 in the electrochemical series.  It is
thermodynamically impossible for H+ alone to oxidize any of them.  However,
in the presence of NH3, CN-, or other strongly stabilizing ligands, Cu can
be oxidized by protons in aqueous media.  Dissolution of water pipes
dissolve slowly in acidic water can be explained by reduction of dissolved
O2 in the water.  The acidic water probably just dissolves the surface
layer of Cu2O (or whatever) that would otherwise (under non-acidic
conditions) prevent further oxidation of the pipe.

	Eric Lucas