Re: copper etching

farooq_w_at_hotmail.com
Date: 12/29/04 

Date: 28 Dec 2004 21:44:25 -0800

Wilco Oelen wrote:
> I did the experiment.
[snipped the experimentals details for brevity]
>
> Conclusion from this is that H2O2 and HCl definitely can produce Cl2,
> even at a high rate, but HCl should be at excess. With excess H2O2 no
> Cl2 is formed.
>
> Wilco

That is surprising (though the electrode potentials suggested so). Have
you come up with another complex riddle which has never been thought
of. The color change to green is a clear indication of a chemical
reaction between HCl and H2O2; ofcourse assuming no metallic traces
were present in both. Note that often hydrogen peroxide contains
stabilizing agents.
I have analytical grade HCl and H2O2 (extra pure), and would like to
repeat it; but that will be after two or three days.
The reaction mechanism is most likely not as simple as we are thinking.
There could be species which might have been formed containing chlorine
in higher oxidation state say chlorite, etc which is immediately
decomposed by acidinc medium to chlorine...or chlorine dioxide being
reduced to chlorine by HCl...possibilities are countless.

What is even more surprising is that H2O2 can behave as an oxidizing
agent as a reducing agent towards the same species under different
conditions. That is agreed upon that gaseous chlorine is immediately
reduced to chloride by H2O2 (written in the literature), but H2O2 is
oxidizing chloride ion to chlorine in not mentioned!!

Secondly, even concentrated nitric acid can not oxidize chloride to
chlorine as far as I know. What you could do, in spare time is to use
another highly acidic medium (say from sulfuric acid -6M, which would
be equivalent to 12 M conc. HCl) and use sodium chloride under same
experimental conditions. Do you notice chlorine gas now or any color
change?

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