Arthur Dent
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Copper Carbonate
Filtering Copper Carbonate sucks!!!
Literally!  I've had a pint of concentrated Copper Chloride solution that I've
made last year, so I decided to make myself a bit of copper carbonate...
I put the copper chloride solution in a large beaker and slowly added sodium bicarbonate intil it stopped fizzing. Success!
My beautiful emerald green solution turned into a lovely vert-de-gris insoluble precipitate. Now to the next step: I thought it would be faster to use
a buchner funnel under vacuum. Not! After 10 minutes at maximum warp on the water aspirator, barely a few drops had fallen. At that rate it would take
an eternity!
So I went to the next logical step since the pores of the buchner funnel were too fine and clogged, I decided to use a plain old coffee paper filter
and an ordinary glass funnel... Failure again!
The paper filter clogged up and the solution wouldn't budge. So I dunked the whole mess back in the beaker and added distilled water. I'll let the
precipitate settle completely and i'll discard the excess water. I'll have to do this a few times to get rid completely of the sodium impurities.
Would heat help? How many times should I "wash" my precipitate before declaring that I have relatively pure CuCO<sub>3</sub> ? I guess the
last step to remove the last bit of water will be to gently heat the paste until it's completely dry?
Bah, what a mess! After 2 hours the precipitate has settled well so i'll proceed
to the first "wash"...
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EDIT: I've been at it for 4 cycles now, adding water, stir, let settle and discard the water right down to the precipitate. I'll do it a few times
more to make sure it's clean.
How would I go about testing if there are traces of sodium salts left in my precipitate?
Robert
[Edited on 27-5-2011 by Arthur Dent]
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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not_important
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Yeah, decanting - letting a ppt settle and pouring off most of the liquid - often is the best way to go. Wash the same way, after the last wash then
transfer to the filter with minimal amount of wash liquid - sometimes using alcohol instead of water.
Warming the basic copper carbonates, which are what you get when adding a soluble carbonate or bicarbonate to a solution of a copper salt, decomposes
fairly easily; better to dry by washing with alcohol and then acetone and let air dry.
By controlling the conditions of precipitation you can get more larger ppt grains which filter more easily. And by heating the wet basic carbonate in
CO2 at 45 to 50 bar you can get true CaCO3.
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Arthur Dent
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Good idea, after a few more washing cycles, i'll pour some acetone on it and let it dry on a paper filter. I won't use heat as you suggested.
Unfortunately, I do not have a pressure cooker. Yet another gismo to acquire evenually...
As for traces of sodium left, I was thinking a flame test, using a bit of the precipitate on a small platinum wire loop and see if there's some yellow
in the flame. If there is, is there a way to remove the impurities?
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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mr.crow
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Sodium gives a very strong color even in trace amounts. If you don't have platinum wire just use a clean copper wire, it wont color the flame that
much if at all (needs to be a salt).
Same thing happened to me when I tried to make CuO using NaOH. The precipitate didn't even settle. What a mess.
Once you get rid of the sodium you can blast your carbonate with heat to decompose it and get some nice dry CuO. I have always though carbonates were
pretty worthless
Double, double toil and trouble; Fire burn, and caldron bubble
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not_important
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An ordinary pressure cooking will get you no where near 45 bar, most culinary cooker top at at around one bar.
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Arthur Dent
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I do have Platinum wire, i've melted a few glass capillaries with a tiny loop of platinum wire so i can do some flame tests, but i've never used them
yet. The Platinum wire comes from spools of "Corotron wire" from Xerox.
I've synthetized the carbonate because it's simple and does not require heat, and it's a good precursor to many copper salts, including the acetate,
that I have succesfully produced a few moments ago with a little spatula of CuCO<sub>3</sub> goop on a test tube and a few drops of GAA,
giving a lovely deep blue/green solution.
There's this pottery store I've discovered recently that sells some CuO so i'll investigate that source. For now, I've ordered some Strontium and
Cobalt salts from them.
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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blogfast25
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Mr Crow is right though: sodium is extremely easy to find in just about anything because of the intensity of its Na D doublet (which is why we use
sodium streetlights).
Firstly you'll need to check anything you use for washing your carbonate for Na. Secondly, occlusion means that almost certainly some sodium will be
'locked into' the carbonate's crystal lattice, from which washing it out is almost impossible.
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AJKOER
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Mr.Crow say: "Same thing happened to me when I tried to make CuO using NaOH. The precipitate didn't even settle. What a mess."
Actually not getting the suspension to settles means that you may have created a nano-particle size suspension of CuO!
Congratulations! This is actually a topic of interest and research.
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m1tanker78
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Hey Robert,
Amen.
I've often wondered if fine particles in suspension can be poured though clean sand of a specific grain size. Dry and 'shake out' only the fine
particles through a filter that will hold back the sand grains.
Thinking out loud. 
Tank
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Arthur Dent
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Did a quick fire test, and nothing but green/blue flame, so I think I'm good!
I dropped the copper carbonate paste in a large glass cooking pan and i'll let the stuff dry out for a few days.
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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blogfast25
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Yet if you looked with even the most primitive spectroscope that sodium would probably stare you in the face!
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Arthur Dent
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So what you're saying is that the flame test isn't really conclusive?
Is there a way to clean-off the carbonate even further? I checked the pH of the wet slurry and it's about 7 / 7.5. It's been a whole day in a glass
pan slowly drying off.
Robert
--- Art is making something out of nothing and selling it. - Frank Zappa ---
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m1tanker78
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I think he means that the flame test as seen through a spectroscope is more conclusive than by naked eye. Traces of sodium show up very
strongly (yellow-orange). Some colors are easily washed out or perceived as a combination by the human eye. A diffraction grating will separate the
incident light by wavelength, making it easier for us to discern (resolution depends on the grating and scope).
Your carbonate is probably reasonably sodium free but a 'primitive' spectroscope can be made with a CD and a cereal box. 
Tank
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blogfast25
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Tanker’s right: the detection limit of Na is lower with a spectroscope than with a naked eye flame test. But the fact that your flame test is
negative for Na does show that there can’t be much in it.
Further cleaning up the carbonate after precipitation and washing is difficult. Best to start from quite pure materials and carry out the
precipitation in quite dilute circumstances and quite slow with good stirring.
For home made spectroscopes (a hobby horse of mine) there’s a ton of resources on the web. ALWAYS use DVD-R instead of a CD, the resolution is much
higher with the former (more data tracks per mm). Mine just about splits the Na D doublet. Not bad for a modified cardboard cookie box…
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