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Author: Subject: CuCO3 and CuAc2 for lead dissolution
chemoleo
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[*] posted on 25-8-2004 at 16:47


Well, when I did my 1.5 kg PbAc2 production via the CuSO4 + CaAc --> CuAc2 + CaSO4 (precip) route, and added the resultant CuAc2 ( in a 10 l bucket) to 5 kg blocks of Pb, it worked fine, the colour of the CuAc2 disappeared slowly.
I let this react for many weeks, so evaporation of course occurred. At the bucket walls, yellow/white insoluble stuff could be found (amorphous), and a fair amount of it. Some of it would resolubilise if strong HAc was added (always keeping the pH low), but some wouldnt resolubilise.
After many weeks I obtained massive & clean PbAc2 crystals, but a fair insoluble (in HAc) amount of yellow white stuff - which fortunately didnt interfere with PbAc2 crystallisation. In addition there were agglomerates of a dark red substance.
I have rationalised this as follows:
The white/yellowish stuff is mainly CaSO4, of which a fair amount must have dissolved in 10 l reaction volume. In fact, I subjected the white/yellowish stuff as pure solid directly to conc HAc, and I WAS able to crystallise some more PbAc2 from it. I am fairly certain that the yellow white stuff also contained various double salts of lead, i.e. hydroxy carbonates, mixed oxides, and hydroxy acetates. Some dissolve, some dont.
As to the red stuff - I still got it, and one day I will try and analyse it. I suspect its from some impurity of the lead. I wish I had made pictures then... being the 'originator' of this method :)

Anyway - I honestly wouldnt worry so much about insoluble precipitates. As long as your copper gets plated onto the lead, and the green/blue colour disappears, you are fine. Once it's done, you can filter, and then boil this down. Then allow this to crystallise - ensuring decent purity. If you start from pure CuAc2 (i.e. from CuCO3 or CuO), then by definition the only soluble substances can be PbAc2. Hydroxy acetates/carbonates are insoluble. So dont fret!

If you are really really worried about purity, subject your lead acetate solution to strong HCl.
This produces shiny glittery PbCl2 needles, so you can essentially purify the lead salts (not that many chlorides are insoluble).
Then, redissolve in a calculated amount of NaOH, filter & wash the Pb(OH)2, and subject yet again to a calculated amont of HAc.
Your final product should be nice and clean.

PS I changed the thread title slightly - to make it more appropriate

[Edited on 26-8-2004 by chemoleo]




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[*] posted on 25-8-2004 at 22:53


Quote:
Originally posted by chemoleo
Well, when I did my 1.5 kg PbAc2 production...
Thanks for the info. Found most of what you said in the PbO2 thread. The color _is_ starting to fade, however looks like it will take weeks as you say. I'm wondering if I could take some of the solution, crystallize the Pb(Ac)2 out, and return the unreacted Cu(Ac)2 crud back to reactions flask.

Dave
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[*] posted on 25-8-2004 at 23:21


BTW Anhydrous CaSO4 (the byproduct) is sparingly soluble in water, to the extent of 0.298 parts/100 parts at 20ºC, and 0.1619 parts/100 parts at 100ºC, which is a surprising decrease with temperature. However, gypsum, CaSO4.2H2O, is soluble at 0.223 parts/100 parts at 0ºC, and 0.257 parts/100 parts at 50ºC. It is also listed as being "soluble" in acids, glycerol, sodium thiosulfate, and ammonium salts.

John W.
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chemoleo
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[*] posted on 26-8-2004 at 17:03


Janger, to be honest I'd just wait. The colour will go in due time, and that way you will also ensure that there are no remaining soluble copper traces. I.e. wait until the solution is clear, then wait a few days more - just to make sure it is free of Cu2+.
People have been wondering this because of lead azide - i.e. if you were to prepare it, one would get copper azide (very sensitive) unless the lead acetate is clean. So, to be on the safe side, incubate as long as u can be bothered, and then work with your PbAc2!




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[*] posted on 26-8-2004 at 19:33


Well, I've stopped being so impatient about it :)
The blue color seemed not to be disappearing, even though there was heaps of lead. I added some more vinegar last night and this morning it's looking better. Need a damn lot of vinegar for this.

BTW, I'm using one of those coarse flat rasps to make my lead filings. Works a treat.
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[*] posted on 9-2-2005 at 15:51


What effect does the small amount of antimony present in most sources of lead (fishing sinkers, wheel weights, shotgun shot, etc) have on the resulting acetate? The MSDS for antimony acetate says that it decomposes with moisture.
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[*] posted on 10-2-2005 at 04:09


It probably therefore decomposes to the oxide/s, which is insoluble I suppose (at least antimony trioxide is at rtp), therefore on filtering the mixture it should be trapped with the copper. Little or no antimany is dissolved in the mixture and the lead acetate formed is reasonably pure. Hope this helps.

[Edited on 10-2-2005 by Esplosivo]




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chemoleo
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[*] posted on 10-2-2005 at 05:14


I made about 1.5 kg of lead acetate hydrate this way, and as it crystallises very nicely into big crystals (it takes time though of course) which can be separated easily from the rest of the basic lead acetates/antimony/tin etc salts, I am pretty confident that these crystals are free of major impurities.
But then again, I guess the lead acetate could be sort of doted with impurities.
Maybe you ought to find a different source of lead - which would be the easiest thing to do to fight potential impurities. Builders Supplies sell it too, in sheets.




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[*] posted on 11-3-2011 at 02:44


If I am going to use one lead wheel weight in the copper acetate solution, is copper going to deposit on lead and passivate it? Because that means it would stop it from reacting or it will continue reacting with solution even when copper is completely deposited on lead until all lead is gone?
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[*] posted on 7-5-2011 at 05:40


random did you ever find out if the reaction is complete when all the copper is gone? i want to make crystals and my solution is clear already.i threw away the precipitate as i think its lead sulfate. by complete i mean if it will still keep producing lead acetate.

[Edited on 7-5-2011 by cyanureeves]
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[*] posted on 7-5-2011 at 08:21


Well, if solution is not blue then you should have reduced every Cu2+ ion to Cu and lead goes into solution. So you can't make more lead acetate from that, or else you need to add more lead or copper acetate to that so the reaction continues.
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