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Topic: Copper etching using HCl and H202 : What is the reaction?  (Read 6400 times)

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Offline obones

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Copper etching using HCl and H202 : What is the reaction?
« on: May 21, 2008, 03:32:22 AM »
Hi all,

I regularly etch copper plates using a mix of hydrochloric acid (23% concentration), hydrogen peroxide (35% concentration) and some tap water. When the copper plate is dipped into the mix, gassing occurs and the mix gets a blue/green color which intensity depends on the quantities of the various components of the mix.
I don't know the exact nature of the gas that gets out and the various websites that describe this method do not agree on what it is. Some say it's pure oxygen (O2), some others say it's pure chlorine (Cl2), some just say it's "toxic gas".
I have been given this equation :

Cu + H2O2 + 2HCl -->  2H2O + CuCl2

This one explains the "etching" of the copper and the color of the mix. As to the gas, it would thus only be the consequence of a parasitic reaction of hydrogen peroxide :

2H2O2 --> 2H2O + O2

Does this look correct to you?
Personally, I came up with the following double reaction:

H202 + 2Cu --> 2CuO + H2
CuO + 2HCl --> CuCl2 + H2O

My last chemistry lessons are about ten years old, and I unfortunately lost some of the basics so it may well be that I'm writing obvious errors. That's why I would appreciate if you could help me with this.

Regards
Olivier

Offline Borek

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Re: Copper etching using HCl and H202 : What is the reaction?
« Reply #1 on: May 21, 2008, 04:11:36 AM »
Cu + H2O2 + 2HCl -->  2H2O + CuCl2

2H2O2 --> 2H2O + O2

Looks reasonable. That'll be my bet, although reality can be more complex.
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