ldanielrosa
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copper bisulfate?
I was using some of the recycled copper from etching to make copper sulfate, and I may have overdone something.
I titrated the drain cleaner sulfuric acid at about 75%, but I wanted to have copper in excess since (I thought) I could filter the precipitate and
reuse that on the next batch. I kept adding copper carbonate to the liquid with the stirrer running, and it kept going clear.
I called it quits at enough copper to use 100% acid, and put it in the old crock pot/ sand bath to evaporate for a while. After I pulled out a few
nice blue copper sulfate crystals, the remainder of the solution is now green with green crystals forming. Did I make copper bisulfate? Is there a
fun use for this?
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blogfast25
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Copper bisulphate? Never heard of it but ‘theoretically’ it’s possible: Cu(HSO4)2.nH2O.
Are you sure your recycled copper isn't contaminated with iron? That would give greenish crystals of FeSO4...
One way of finding out is to isolate the green crystals and wash then carefully with cold water and dry them carefully (perhaps with a bit of acetone
or alcohol?)
Then dissolve them in water and test for acidity: HSO4(-) is quite a strong acid (pKa = 1.99). Titrating with NaOH should tell you just how much acid
is in your solution.
If you can’t titrate you can do something approximate with baking powder (NaHCO3 or Bicar):
HSO4(-)(aq) + NaHCO3(s) === > SO4(2-)(aq) + Na(+)(aq) + H2O(l) + CO2(g)
By weighing how much baking powder you need approximately for fizzing to stop and how much ‘copper bisulphate’ you started of with, you should be
able to confirm or infirm your hypothesis. But you’d have to know how much water your ‘green crystals) contained to begin with…
If no significant acidity is found, treat the dissolved green crystals with NaOH and allow any precipiate access to air: if it turns yellow/red/brown
that's Fe(OH)3 and your contaminant was Fe...
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ldanielrosa
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Thank you blogfast25. No, I'm not sure about Fe contamination. It is waste from copper etching with hardware store HCl, which may contain some iron.
This is one batch of many that I am reconstituting as copper sulfate from copper carbonate that I precipitated from the copper (II) chloride. The
difference is that instead of using the calculated quantity of CuCO3 for the drain cleaner sulfuric acid that I roughly titrated at 75%, I kept adding
the carbonate to the acid and waited for it to dissolve thinking maybe my titration was in error. I stopped when the amount of copper carbonate would
have been appropriate for 98% H2SO4.
The purity is not critical for the application I have in mind for this recycled waste, so I'll deal with it. If copper bisulfate isn't used for
anything interesting then I won't bother trying to repeat these results with better grade chemicals.
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aonomus
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Electrical grade copper from circuit boards is pretty darn pure, however hardware store HCl/technical grade is fairly high in iron content. Try taking
a sample of the HCl and neutralizing it with aqueous NaOH. If you do have iron content you should produce some highly insoluble iron hydroxides.
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