guy
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Precipatation Question
Would PbCl2 + HCO3 precipitate out PbCO3, and would most of it go into completion?
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12AX7
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Not H2CO3 (I presume your "HCO3" is a typo), because of two things:
1. PbCl2 + H2CO3 = PbCO3 + 2HCl, HCl is a much stronger acid.
2. H2CO3 = H2O + CO2 usually proceeds to the right, it dissociates weakly and would rather be out in the air than stuck in solution. (Exceptions are
club soda, or any soda for that matter, which you'll note are stored under pressure - the pressure builds up for this very reason.)
However, you can precipitate it with a strong base such as NaOH:
PbCl2 + 2NaOH = Pb(OH)2 + 2NaCl
Then filter and add to carbonic acid (..club soda..), which will dissolve it very slightly (not noticibly, unless bicarbonate happens to be
significantly soluble). On drying, it should be fully carbonate, or at least basic carbonate (which is what, Pb2CO3(OH)2?).
You can also precipitate with washing or baking soda directly:
PbCl2 + Na2CO3 = 2NaCl + PbCO3
or PbCl2 + 2NaHCO3 = 2NaCl + PbCO3 + (H2O + CO2 <--> H2CO3)
(Bicarb will probably release the extra CO2 content as bubbles as the carbonic acid decomposes in the neutral solution.)
Tim
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chemoleo
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| Quote: | You can also precipitate with washing or baking soda directly:
PbCl2 + Na2CO3 = 2NaCl + PbCO3 |
The only problem being, club soda (whatever that is) and all aside, is of course that PbCl2 is barely soluble, and PbCO3 not at all. So it might be
tricky bringing it into solution.
PbCl2 is pretty stable on air, and doesn't react with H2O/CO2, unlike PbAc2.
Never Stop to Begin, and Never Begin to Stop...
Tolerance is good. But not with the intolerant! (Wilhelm Busch)
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guy
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| Quote: |
Not H2CO3 (I presume your "HCO3" is a typo),
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sorry i meant HCO3-. What i really want to know though is will it go to completion or have a large Keq?
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12AX7
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PbCl2 isn't very soluble, but it is moreso than 'CO3 or OH, so it proceeds. I've done it before, it starts speckled with brown
(plumbite) then gradually levels out to white again in a day or three. Boiling would speed it up a lot since PbCl2 is somewhat soluble.
Club soda is CO2 in water, carbonic acid. I mentioned that.
Tim
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chloric1
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Digestion
Yes since of the limited solubilities in this situation, prolonged digestion would be the key. Rapid stirring with a magnetic stirrer and heat will
use the maximum surface area of the reagents to speed reaction.
Also, as I found out from practical experience, digestion can make precipitates easier to separate. In my production of tricalcium phosphate from
calcium chloride and TSP, I found an hour on the hot plate with rapid stirring cut my filtering time by at least 75%. Other difficult precipitates
like calcium sulfate may be able to be treated the same way. Make sure if none of your desired products are heat sensitive though.
Fellow molecular manipulator
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guy
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A similar Question
If I mix CuCO3 with PbSO4, I should be able to obtain CuSO4 and PbCO3 since the Ksp of CuCO3 is 2.5x10<sup>-10</sup> and PbCO3 is
1.5x10<sup>-13</sup> and PbSO4 is 1.8x10<sup>-8</sup>. Am I correct?
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12AX7
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Should be, though you'll have to boil for a good while due to the low solubility.
Tim
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