mangoman667
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Need help determining identity of copper compund and precipitate
Hi all,
I have run into a very peculiar challenge. I was about to throw away an old lantern who's battery had leaked, when I noticed a layer of blue crystals
caking one of the contacts. The contacts appear to be brass covered, since there was only an iron color after washing off the caked substance. I
obtained a blue solution (obviously a copper compound), as well as what appears to be a very light blue precipitate. I can't be sure that it's not
simply contamination. I now have separated and dried the precipitate from the solution. Can anyone help me in determining the identity of these two
substances?
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The Chemistry Shack
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Is it a sulfuric acid battery? If so, the H2SO4 and air could have dissolved some of the copper metal in the brass into CuSO4.
There are a few tests you could do to determine the identity of these compounds.
1) For the solution:
Boil down to obtain a blue (or green, depending on what the solution actually is) powder, and heat the powder in a crucible to dehydrate it. If you
are left with a white powder, it might be CuSO4. (If the powder is another color, then it is another compound--if it is brownish, you most likely have
CuCl2.
If you end up with a white powder, test for CuSO4 by adding an excess of CaCl2 solution to the powder. You should get a white precipitate of CaSO4 and
a green solution of [CuCl4]-
2) For the precipitate
This might be CuCO3, as that is very light blue. Add a few drops of strong acid to the powder and, if gas is produced, it is most likely CuCO3. You
can test to make sure this is CO2 by bubbling the gas into a very dilute NaOH solution with phenolphthalein and observing a color change to clear, or
by bubbling the gas into a Ca(OH)2 solution and observing the formation of a white CaCO3 precipitate.
If these tests work, let me know. If you get different results than what I have mentioned, you likely have some different compounds and more testing
will be required.
[Edited on 27-6-2015 by The Chemistry Shack]
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blogfast25
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Quote: Originally posted by The Chemistry Shack  |
2) For the precipitate
This might be CuCO3, as that is very light blue. Add a few drops of strong acid to the powder and, if gas is produced, it is most likely CuCO3.
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As been pointed out before and for the UMPTEENTH time: there is no such thing as CuCO3. In the real world, only basic copper carbonate CuCO3.Cu(OH)2
(Malachite. aka Cu2CO3(OH)2) exists. A metastable 2CuCO3.Cu(OH)2 exists as a rare mineral (Azurite).
Malachite forms when cupric solutions are treated with carbonate or bicarbonate solution, with release of CO2.
Malachite would be hard to confuse with a 'white precipitate'.
[Edited on 27-6-2015 by blogfast25]
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aga
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For us Blind chemists they all feel much the same, apart from hydrofluoric acid - the Sizzler.
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violet sin
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mangoman667 : "I was about to throw away an old lantern who's battery had leaked"
leads me to believe it is a standard alkaline flashlight battery.
http://data.energizer.com/design_hints/catalog/designhints_c...
"The connectors used with conventional cylindrical cells are primarily Ni-plated "
nickel, nickel clad stainless, and nickel plated stainless were the main options, listed at bottom of first page ( of 2 pages).
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can't seem to find much more info on the external terminals, piles and piles of pages to look through for something that seems to matter the least in
dealing with battery spec's. not mentioned, but copper strike isn't too far fetched an idea. basically, just saying there may be copper and or
nickel on the terminals, and the residue may be from one or both of the metals. not just copper. the standard alkaline batter uses KOH, which after
exposure to air would make carbonate ( or basic carbonate for Cu  blogfast25).
also in several Ni searches for KOH oxidation, I came across some data about iron and copper leading to the oxidation of Ni, but in acidic conditions.
don't know if it would be the same in basic situations, or if after CO2 capture, it would be acidic enough to count. limited time. just a bit of
quick searching done. hope it helps.
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mangoman667
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I'm actually not sure what kind of battery it was since I found it somewhere without a battery, hence the conundrum. What leads me to believe it is
copper nitrate is that it does not seem to want to crystallize and evaporate properly like copper sulfate would. It just sits there in a darkish blue
solution and the liquid level does not seem to change from the meager 5 or 10mL that there is in the beaker. there are some small clear crystals
forming at the bottom that seem to be some kind of contaminant.
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violet sin
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ok, couple questions, you say the terminals were probably brass plated as only an iron color was left after washing off the corrosion. and now you
think it is copper nitrate?
-- we *are* talking about a standard house use flashlight run on disposable batts no? that would rule out sulfuric acid, and copper sulfate.
-- a super cheap flashlight, or a decent one? what size battery would you say fit into the flashlights case? lill AAA, AA, C, D or a big square
lantern battery.
--I take it you used nitric acid to wash off the crystals, if you assume to have found copper nitrate?
just because it's blue, and you are looking for physical properties of know substances, say from wiki, you can't assume that's what it is. one can
directly rule out a LOT of them, based on known battery components/chems. knowing which size batt would fit, could narrow down that list. knowing
how nice the flashlight was, could give one reasonable assumption as to the quality of the contact materials( was there nickel plate over the brass).
the solution in the battery that leaked, the spring composition and the battery terminal composition would give you a better starting list of
possibilities/things to cross off.
are you just leaving the solution in the window, or have you heated it at all to drive off water? it would be nice to get down to see if it will
crystallize out into separate colored crystals. or at least partition up the solid for a few tests, so you don't poison the whole solution in one go.
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mangoman667
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Well, for starters, I know that the terminal was brass plated, since the other one is still intact. I don't know whether or not there was any nickel
plating, I have only seen the brass layer on top, and the iron base metal below it. This is a lantern we're talking about, so it uses one of those
big, quad-cell carbon batteries, apparently alkaline. I used plain water to wash off the contact cake and ended up with the mixture of a blue solution
and a pale blue precipitate. I have not tried heating the solution, but there is a small blue crystal in there now, along with a bunch of small linear
crystals just lining the bottom of the beaker. The solution was just left outside to evaporate. It is now about a half of a milliliter, and has a
syrupy consistency. I just deem it really strange how a few drops of water haven't evaporated after being left in baking conditions for over a week
now.
Are there any concrete tests I could do to try and whittle down the composition of the mystery substances? It's not really important, I just thought
I'd sharpen my lab practice, and would enjoy the helpful tips.
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violet sin
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like this?
https://encrypted-tbn3.gstatic.com/images?q=tbn:ANd9GcSk4QdO...
forum members are from all over, not every region uses the same terminology. I have used lantern to mean flashlight on more than one occasion.
well regardless, if brass was present, you can assume that there is some Zn present.
depending on whether a carbon/Zn or alkaline batt, both come in that size. 50/50 availability at stores from my experience. the Carbon batt has
ammonium chloride/ZnCl2 paste in it. the alkaline has KOH.
the solubility of the crud, making crystals would on drying, would make me think it was the carbon type batt. with chloride salts,..
(look at the ammonium chloride pic here, is that what your crystals look like? https://en.wikipedia.org/wiki/Ammonium_chloride)
instead of a hydroxide sol which after reacting with Cu/Zn/Fe isn't soluble( other than the KOH itself), which would have also absorbed CO2
and made a largely insoluble residue. basic copper carbonate, zinc carbonate, etc.
flame test the sol? there are more chem based test you could do, but crystal color, shape and a flame test are a good start. they tell you a lot and
don't waste the material after its dry you could divvy it up for a couple tests
on each portion or test the individual crystals... have fun.
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