plumbandplumber
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Lead acetate making an acetate of me
Hi sciencemadness,
Long time lurker, first time poster - I really appreciate the great resource that this forum is, and I'm really hoping someone can help with my latest
bout of insanity. I'm trying to isolate tin from a solder that I'm fairly confident is 50/50 Pb/Sn. So far I have:
melted the solder bar and cast it into water to increase the surface area,
prepared a solution of peracetic acid by the addition of white vinegar to 3% hydrogen peroxide with the acetic acid in slight excess
boiled the spongy metal chunk in peracetic acid for several hours, during which the solution became cloudy and an off-white powder precipitated
So that's where I am now. From the few other resources I've seen on this route, the white precipitate is basic lead carbonate. A large chunk of
blue-gray metal remained undissolved by the peracetic acid, and I'm hoping this is pure(r) metallic tin; with lead acetate in solution.
Does the tin not also react to form tin (ii/iv?) acetate? I think this might be the first compound I've found without a wiki page. Sigma carries it
and I've seen it in literature, but why the dearth of information?
It's also my understanding that I can cement metallic lead from the acetate solution with any more electronegative metal, and I remember a
demonstration of this (Saturn's Tree) using zinc in high school. If there is in fact tin acetate also in solution, which metal would be preferred for
cementing in this way?
Am I approaching this from even the remotely right direction? Should I be thinking electrochemical? I have a 3amp 12v DC power supply I can use to
attempt some electroplating/purificating, but as it stands no pure tin or lead to use as the anode. I do have some carbon rods, but I'm not sure how
that would affect deposition if that is indeed the route I should be considering.
I'm sure I have a ton (tin?) more questions that I've not even considered yet or already forgotten, I really appreciate your help in advance
and I look forward to this discussion!
[Edited on 26-9-2014 by plumbandplumber]
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bbartlog
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I would expect tin acetate to also form (and it is soluble). In general, separating tin and lead is not trivial. In analytic chemistry, I think the
approach would be to dissolve the entire mass in nitric acid to form lead nitrate and tin (IV) nitrate, and then precipitate the sulfides, and then
add alkaline sulfide (which dissolves the tin (IV) sulfide but not the PbS). See http://www.web2.ridgewood.k12.nj.us/www/rhs/departments/scie... . But of course even if you did that you would not have elemental metals any more.
There are also processes for removing the tin by pumping chlorine or oxygen through molten lead and then removing the dross, but even if you wanted to
deal with molten metal, this is a way of isolating the lead rather than the tin.
The less you bet, the more you lose when you win.
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WGTR
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I've electrolyzed 60/40 tin/lead solder in sulfuric acid solution before. The solder is the anode, of course. Practically none of the lead goes
into either the solution or the plating on the cathode.
The cathode deposits in this case (straight DC, without pulse reversal) are dendritic in appearance.
Before the above experiment will work, however, take care to ensure that the anode current density is low relative to the cathode current density.
No oxygen evolution should occur at the anode. If it does, then the tin is becoming overly oxidized. The goal is to make soluble stannous sulfate,
not stannic sulfate.
Electrolysis with the same anode in sulfamic acid gives different results. Apparently the tin is overly oxidized to an insoluble form at
the anode, whereas the lead goes into solution, plating out onto the cathode.
Adding some of the stannous sulfate to the lead sulfamate precipitates out some lead sulfate. The resulting solution is one that I have used to
perform tin/lead electroplating with a solder anode.
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DraconicAcid
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If you're not worried about quantitative separation, tin(II) chloride is much more soluble in cold water than lead(II) chloride. The Merck Index says
that tin(II) chloride dihydrate is soluble in less than its own weight on water (as long as it's sufficiently acidic to avoid hydrolysis). Lead
chloride precipitates nicely from cold water (although it will dissolve much more in hot water).
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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plumbandplumber
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@WGTR, all I currently have at my disposal is that 12V power supply and a 120V variac.. I'm not sure if these can be used in tandem. I'm looking into
a digital bench power supply for all these exciting plating experiments but I just don't have the capability at the moment. I'll definitely look into
sulfamic acid electrolysis further though. Would graphite/carbon work as the cathode in this instance?
@Draconic, not going for quantitative at all, not yet at least. At this point I'm pretty much just trying not to poison myself. Even if I can get in
the ballpark of 90% purity, I can probably fudge the rest with fluxes upon melting and recasting. Seems like selective solubility of the chlorides is
the current contender.
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aga
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Get a PSU from a PC tower and use the 5V only.
12v will probably be too much volties.
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AJKOER
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If the reaction is actually electrochemical in the sense of creating electricity (a galvanic cell, the general topic is Metal–air electrochemical
cell), the proper procedure is to add H202 (dilute is OK, just serves as a better O2 source than exposure to air) to acetic acid containing the metals
also with a small amount of sea salt to serve as the electrolyte. Warm a bit ( microwave ) and then see if you can witness a reaction starting to
occur.
[Edited on 26-9-2014 by AJKOER]
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DraconicAcid
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Quote: Originally posted by AJKOER  | If the reaction is actually electrochemical in the sense of creating electricity (a galvanic cell, the general topic is Metal–air electrochemical
cell), the proper procedure is to add H202 (dilute is OK, just serves as a better O2 source than exposure to air) to acetic acid containing the metals
also with a small amount of sea salt to serve as the electrolyte. Warm a bit ( microwave ) and then see if you can witness a reaction starting to
occur.
[Edited on 26-9-2014 by AJKOER] |
It's a redox reaction, but it's not going to create electricity. And adding salt (sodium chloride) will passivate the lead because lead(II) chloride
isn't very soluble.
Please remember: "Filtrate" is not a verb.
Write up your lab reports the way your instructor wants them, not the way your ex-instructor wants them.
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AJKOER
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See the discussion by Carlos at http://www.researchgate.net/post/What_is_the_best_solvent_to...
If not working, try using NaNO3 in place of NaCl.
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phlogiston
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If you are doing this for the joy of the challenge, ignore this post.
Lead-free tin and compounds of it are readily available OTC, ingots of it are sold as a material for casting. SnO is sold for ceramic glazings.
Lead with impurites other than tin, from which it is much more easily purified, is available OTC from countless sources. Lead roofing, batteries,
fishing weights, wheel balancing weights.
-----
"If a rocket goes up, who cares where it comes down, that's not my concern said Wernher von Braun" - Tom Lehrer |
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plumbandplumber
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@AJKOER: I'm not sure I'm sure what you're suggesting? Carlos seems to be talking about using DMSO as a cosolvent but solubility of the PbCl hasn't
thus far been an issue. NaNO3 in place of NaCl at what point?
@phlogiston: let's definitely call it the "joy of the challenge" - although I wasn't quite expecting this much of the challenge for very little joy. I
appreciate your tips on sourcing them pure to begin with, which is likely what I'll do after I discover why nobody seems to have ever bothered to do
this. The short of the answer is this alloy is what I had, at no expense, with the intent to find a way to distill it. Definitely can't say I'm not
learning, though!
I stuck a small aliquot of the lead/tin acetate solution in a beaker between two graphite electrodes attached to a 9v battery. O2 I believe was
evolved on the anode, very small flakes of unknown metal reduced at the cathode, periodically falling to the bottom and I assume redissolving. Then I
realized all the preparations of dendritic tin I've seen used tin chloride and not tin acetate. I also learned that lead is used as a dopant to
suppress the growth of tin "whiskers" and suspect that the presence of lead may be slowing or at this current density at least preventing the
formation of metallic tin.
Treating the acetates with slight excess of HCl yielded a cloudy white precipitate. The solution was then heated with stirring until the chloride
salt had fully dissolved and the solution was again clear. Placed in an ice bath and allowed to cool, the resulting colorless needle-like crystals are
assumed to be relatively pure lead (ii) chloride while stannous chloride remains in solution, if it was there to begin with.
I melted the lump of undigested metal, it hissed and fouled a good deal and threw little molten spittle everywhere, occasionally puffing into a
green-yellow-black slag, from beneath which ran a small pearl of shiny molten silvery metal, which was cast into a small ingot. I've yet to try any QA
on this, I'm hoping it's at least slightly refined tin but it's entirely possible that all the tin was oxidized in the torch flame and burned off.
[Edited on 27-9-2014 by plumbandplumber]
[Edited on 27-9-2014 by plumbandplumber]
[Edited on 27-9-2014 by plumbandplumber]
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DrMario
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As I was reading this thread, I was going to suggest something along the lines of what phlogiston just wrote. I should add that the most commonly
available lead-free solder contains about 1 wt% of copper. There are other lead-free tin alloys available also - some with about 1 wt% of silver.
Silver chloride should be trivial to separate. That would be the option I'd try, if I were you: use HCl to etch the tin-silver eutectic and expose the
obtained solution to the sun or other source of UV.
EDIT: I see you're after SnCl2, which this process readily yields.
[Edited on 27-9-2014 by DrMario]
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blogfast25
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| Quote: Originally posted by phlogiston | If you are doing this for the joy of the challenge, ignore this post.
Lead-free tin and compounds of it are readily available OTC, ingots of it are sold as a material for casting. SnO is sold for ceramic glazings.
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I'm fairly sure it's SnO<sub>2</sub> (cassiterite) that is sold for pottery glazing.
High temperature (red heat) glowing with an excess of fine carbon yields the metal.
Alternatively, fuse with NaOH or KOH to convert to stannate. Hydrolysis of that gives freshly precipitated stannic hydroxide, which is soluble in
strong, hot HCl. Then plate out the Sn metal with electrolysis or Al, Mg, Zn or Fe.
[Edited on 27-9-2014 by blogfast25]
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Oxirane
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Why go through all this trouble?
Just get a car battery, charge it full, disassemble, crumble the PbO2 into SS pot and heat over 600C to turn it into lead oxide and then mix up that
oxide mass into vinegar, heat up to boil, filter all that did not react and boil or evaporate off the water. Done this many times and got a big lump
of white pure crystals every time.
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jock88
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http://www.sciencemadness.org/talk/viewthread.php?tid=5490
LEAD SALTS PREP. THREAD
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