chornedsnorkack
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Sulphurous acid as solvent
Which metal oxides do not dissolve in sulphurous acid?
It´s a fairly strong acid (pH about 1) as well as reducer.
Are there any insoluble sulphites?
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12thealchemist
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Apparently:
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The sulfites of Na+, K+, and NH4+ are soluble in water. Most other sulfites are insoluble in water. However, due to the basic nature of SO32-, all
sulfites dissolve in acidic solution. |
Reference, Arizona State University page
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chornedsnorkack
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Ah, I see.
Thus MnO2 should dissolve:
MnO2+H2SO3=MnSO4(aq)+H2O
but Fe2O3 should leave an iron sulphite residue:
Fe2O3+2H2SO3=FeSO4(aq)+FeSO3(s)+2H2O
Correct?
How refractory are sulphites to concentrated sulphurous acid? Would reaction
FeSO3(s)+H2SO3=Fe(HSO3)2(aq)
go ahead, or would the insolubility of FeSO3 prevent it?
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12thealchemist
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Certainly
MnO2 + H2SO3 = MnSO4(aq) + H2O
would take place, and I expect
Fe2O3 + 2 H2SO3 = FeSO4(aq) + FeSO3(s) + 2 H2O
to take place in limiting acid solution, while excess acid would lead to
FeSO3(s) + H2SO3 = Fe(HSO3)2(aq)
as is seen with carbonic acid - calcium carbonate is insoluble, but a molar equivalent of CO2 leads to dissolution via formation of the
hydrogencarbonate/bicarbonate. My understanding of this is based purely on the phrase "all sulfites dissolve in acidic solution."
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AJKOER
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Here is a link to a related SM thread "What can I do with Sulphur Dioxide gas ?" by Sulaiman at
https://www.sciencemadness.org/whisper/viewthread.php?tid=85... , which provides more background on SO2 which, in the presence of water/water
vapor, forms H2SO3.
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Note, the chemistry involving H2SO3 and sulfites can be quite advanced involving some radical based activity, especially in heterogeneous conditions,
rich in transition metals (in particular, iron and, in even trace amounts, cobalt) together with dissolved oxygen. See some references and my
comments at presented at https://www.sciencemadness.org/whisper/viewthread.php?tid=67... .
There are related commercial leaching of minerals involving sulfites, so the alluded to chemistry is not just theoretical in nature, see, for example,
https://www.sciencedirect.com/science/article/abs/pii/030438... .
There are also associated patents involving sulfites related mixtures for leaching purposes (see, for example, 'Separation of copper minerals from
pyrite using air-metabisulfite treatment' listed at https://patents.justia.com/patent/9051625 ).
[Edited on 2-9-2019 by AJKOER]
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