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shannon dove
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My explanation is a rotten egg smell coming from a lead acid battery.
but this might be caused by lead sulphate getting hot with reduced lead. Usually when my car battery starts making hydrogen sulphide smell, its going
bad.
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elementcollector1
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Empirical evidence is always a good start.
I couldn't find any evidence of car batteries emitting H2S, but perhaps I haven't been looking hard enough. It would be a useful method, however
(although my stomach turns at using my conc. sulfuric acid, when poor chemists in other states don't have any acid).
The only related thing I could find is "sulfation", when stable, crystallized lead sulfate collects in a car battery instead of turning back to lead
metal or oxides, leading to the loss of useable lead.
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shannon dove
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I can't find the book right now, but I can assure you that it said that both hydrogen sulphide and elemental sulphur can be made by electrolysis of
sulphuric acid. I read it over and over again just to make sure I was understanding correctly. If my memory is right, the sulphur and hydrogen
sulphide formed on the anode.
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elementcollector1
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I'll have to try that when I have the time! Incidentally, what if anything did it say about other sulfates?
Now is a great time for me to figure out a gas-capturing electrode...
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chornedsnorkack
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Quote: Originally posted by shannon dove  | I read in an old chemistry book that sulphuric acid can be electrolyticly reduced to elemental sulphur or hydrogen sulphide depending on acid
concentration, amp density and temperature. Unfortunately, after hundreds of hours of searching, I could not find a similar electrolytic reaction to
make elemental phosphorus from phosphoric acid. Can anyone explain why sulphuric acid can be electrolyticly reduced to elemental sulphur, but
phosphoric acid cannot be reduced to elemental phosphorus by electrolysis. ?
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Because phosphorus is a stronger reducer.
From:
http://www.webelements.com/sulfur/compounds.html
in acid solution, the electrode potential of HSO4/S is not expressly shown, but easily computes as +0,39 V. The electrode potential S/H2S is smaller
but also positive at +0,14 V.
From
http://www.webelements.com/phosphorus/compounds.html
in acid solution, the electrode potential of H3PO4/P is not expressly shown either but also easily computes, as -0,412 V. The highest reduction
potentials of H3PO4 are actually the expressly shown H3PO4/H3PO3 at -0,276 V and the not expressly shown but easily computed H3PO4/PH3 at -0,281 V.
So. In acid solution, cathode can reduce sulphate first to sulphur and then to hydrogen sulphide.
Under the same conditions, cathode cannot reduce phosphate because it reduces protons first, and ALL forms of phosphorus save phosphoric acid are
unstable against reducing hydrogen from acids.
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elementcollector1
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Can we get it to reduce just to sulfur and not H2S? This would probably require specific conditions, but give the end-product with less reactants
involved.
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AJKOER
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Note, the following reactions (see http://books.google.com/books?id=25qJbzc1wMEC&pg=PA83&am... ):
2 HI + H2SO4 --> SO2 (g) + I2 (s) + 2 H2O
6 HI(g) + SO2(g) --> H2S(g) + 3 I2(s) + 2 H2O
So heating an excess of Oxalic acid (or Tartaric or Citric acid) with an excess NaI with CaSO4, for example, may produce H2S which can be reacted
aqueous NaOCl (or SO2) to produce Sulfur.
[Edited on 2-12-2012 by AJKOER]
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elementcollector1
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I liked the electrolysis of sulfuric acid because it required so few reagents, just sulfuric acid, bleach and electricity. It would have been even
better to use a sulfate such as magnesium or calcium.
NaI is hard for me to procure, the closest analogue would be KI which I could probably extract from tincture of iodine.
Oxalic acid? I just ran out of that...
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shannon dove
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I have already said this before, but I will talk about it again because it pertains to this. Bacteria can reduce sulfates to hydrogen sulphide.
Landfill gas contains a little hydrogen sulphide. Some of it comes from decomposing plant and animal, but some of it comes from bacteria reducing
sulphates especially calcium sulphate wall board in construction debris.
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