kyro8008
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Sodium Metabisulphite
When Sodium metabisulphite is dissolved in water, I am under the impression that the following occurs:
Na2S2O5 + H2O --> 2NaHSO3
What I dont know is if this reaction goes to completion and the speed of it, does it happen as it dissolves or should it be left in solution for some
time, etc?
Reason: I want to make some Sodium Sulphite:
NaHSO3 + NaOH --> Na2SO3 + H2O
Thankyou.
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unionised
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The reaction is fast and adding NaOH will make it faster.
What do you want Na2SO3 for?
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Vitus_Verdegast
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It is useful in the Sandmeyer reaction: production of phenylhydrazine from aniline
http://www.orgsyn.org/orgsyn/orgsyn/prepContent.asp?prep=cv1...
and in the preparation of cuprous halides from copper sulfate
http://www.orgsyn.org/orgsyn/prep.asp?prep=cv3p0185
[Edited on 11-6-2006 by Vitus_Verdegast]
Sic transit gloria mundi
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garage chemist
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Yes, adding NaOH to a solution of sodium bisulfite will immediately give a solution of sodium sulfite. You will be able to tell by the pH (it will
stay more or less acidic until the stochiometric amount of NaOH has been added).
Na2S2O5 is an acidic salt.
Heating Na2S2O5 also gives sodium sulfite (and SO2), and its already dry. But you will get only half as much as you get when using NaOH.
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kyro8008
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Thanks for all the replies, thats what I was hoping to hear.
Nothing too exciting im afraid, I wanted to make some sodium thiosulphate (Boil sulphur with solution of sodium sulphite), its also good for a easy
quick source of sulphur dioxide (acid + sulphite).
Also, an interesting reaction I read about involving just the hydrogen sulphite and mixing with acetone: (NaHSO3 + CH3COCH3 --> (CH3)2C(OH)SO3-Na+)
- a bisulphite adduct or something I think it was called.
Also Vitus_Verdegast, thats interesting about preparing copper(I) salts; another reason I want sulphite is as it is generally a good reducing agent.
Thanks all 
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garage chemist
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For thiosulfate, you need either very finely divided sulfur, or heat under pressure (beyond 100°C), or heat really long. You have to have a means of
testing for unreacted sulfite.
As a quick source of SO2, sodium metabisulfite is actually much better, as it releases the same amount of SO2 with only half the amount of acid used.
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kyro8008
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I didnt realise sodium metabisulfite could be used directly for SO2 production; thanks garage chemist, although it makes alot more sence now.
I have very fine powdered sulphur but I have the feeling that it will not be as easy as it looks on paper...
Thanks.
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AllanD
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Sodium Meta-bisulfite is most commonly used to clean winemaking equipment (most commonly cleaning wooden barrels)
Potassium metabisulfite is used as a source of direct addition of SO2 to Wine primarily to inhibit several different bacteria and fungus species Until
the yeast (winemaking yeast strains are specifically selected to tolerate SO2) can "defend" itself by it's own antibiotic and fungus toxin
production... I.E. Ethanol.
AllanD
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YT2095
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I use the stuff in tablet form for homebrew, these: http://www.homebrewers.com/product/800145
they dissolve entirely and crush up very easily too, and if there IS a binder it`s in insignificant quanties as to be completely ignorable for the
most part.
\"In a world full of wonders mankind has managed to invent boredom\" - Death
Twinkies don\'t have a shelf life. They have a half-life! -Caine (a friend of mine)
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AllanD
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In tablet form it is generally refered to with the british name of "Campden Tablets" and the usual binder is (which should be unsuprising) Corn
Starch.
I use it in the pure (USP-Food Grade) powdered form and I buy it in 1 kilo bags, the same way I buy Food Grade Malic Acid and Tartaric Acid, though
obviously I use it far more slowly than I use the acids...
I make my own "Acid Blend" omitting the Citric Acid that is usually included in commercial acid mixtures, as I have family members that have a
chemical sensitivity to Citric Acid.
And No, I don't use Ascorbic Acid instead of Citric, because a few of my prefered yeast strains have a tendency to produce H2S and will do it with far
greater efficiency if Ascorbic Acid is present in the fermenting "Must".
Though I must add that beer/ale yeast strains are NOT specifically bred to tolerate SO2 like wine yeasts are, so you should proceed with extreem
caution lets you get a "stuck"
or failed fermentation.
AllanD
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