Grebulocities
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Sn/Cu and peracetic acid: How to remove PAA without reducing Cu2+?
I'm reacting a tin/copper solder that is supposed to be 97/3 with peracetic acid to see if I can accurately determine how much copper there really is
in the alloy. This is just for fun of course.
I don't have any strong H2O2 but do have percarbonate, so I generated PAA by taking 3.6 g of sodium percarbonate and adding 9 mL of water and 11 mL of
glacial acetic acid, fairly slowly although a bit did bubble over. I also added 1.5 g of NaHSO4 because apparently sulfuric acid (and presumably
bisulfate too) catalyze the reaction of AcOH and H2O2. Then I added 1.33 g of tin/copper and let it react.
I grew impatient at the rate and added 5 mL of acetic anhydride, which I have a small quantity of from a "make aspirin from salicylic acid" kit. It's
reacting nicely now and I see a fair amount of what I believe to be SnO2.
But I realized I have a problem - potentially two problems. I want to use an excess of KI to reduce the Cu2+ and make I2, then do a thiosulfate
titration to calculate the Cu in the original alloy. But PAA, being an oxidizing agent, will also react with iodide. H2O2 does as well but in a
catalytic way, but as I understand it, PAA would actually just oxidize it to I2 without regenerating iodide. I could dilute it with water and reduce
the PAA concentration when I do my final titration but there will still be some error from whatever PAA is left.
Does anyone have any ideas for how to remove peracetic acid without also removing copper(II)?
The other thing is that I'm afraid I might have accidentally created the explosive diacetyl peroxide when I added acetic anhydride, as there wasn't
much water and perhaps some of the acetic anhydride might have reacted with PAA before hydrolyzing with water. Is this a serious concern? If so, will
the iodide take care of it or are there additional precautions I should take?
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Grebulocities
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I have an idea. If I catalytically decompose the H2O2, say with MnO2 or Pt foil, will I get rid of the PAA as well because PAA is always breaking
apart and coming back together into AcOH and H2O2?
Iodide still probably wouldn't be a good choice because in my experience,KI decomposition of H2O2 always leaves some unreduced iodine around in
solution after the reaction, which would still throw off my results.
Am I on the right track here?
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clearly_not_atara
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Peroxides are usually light-sensitive so I'd imagine you can just leave it out in the sun for a day or so.
[Edited on 04-20-1969 by clearly_not_atara]
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