Re: copper etching

From: Wilco Oelen (photo_at_woelen.nl)
Date: 12/28/04 

Date: 28 Dec 2004 12:06:59 -0800

I did the experiment.

Ambient temperature was just over 0 degrees (remember, my fumehood for
this kind of experiments is the great big outdoors), but the reactants
had a temp of appr. 15 degrees, which is the temp. of the storage
place.

I mixed approximately 2 ml of 37% reagent grade HCl (completely
colorless) with approximately 1 ml 30% H2O2. The 37% HCl was heavily
fuming, the mix with H2O2 did not fume anymore and had no choking
odour. After 1 minute, the liquid was light green. Two minutes later it
was clearly green. At that time it had a strong smell of Cl2.

Next, I heated the mix. When it was fairly warm (I think around 50 C, I
could just bear touching the outside of the test tube with the liquid
in it), the liquid started bubbling fairly strongly. The gas mixture
above the liquid became clearly green and a choking odour of chlorine
was produced! The liquid remained bubbling for a while and remained
warm (not so warm, that I could not bear touching the glass of the test
tube). The bubbles contain a considerable amount of Cl2, otherwise no
green gas mixture could be observed. Probably they also contain O2.

At a certain point, while the liquid was still bubbling, I added
another 1 ml of 30% H2O2. The liquid at once became colorless. Bubbling
continued. The green color of the Cl2 above the liquid now quickly
disappeared. So the last bubbles must be O2.

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

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