Sciencemadness Discussion Board

Sodium Bisulphite

technologist - 20-7-2006 at 01:49

Can I make Sodium Bisulfite as below

Na2CO3 + 2 SO2 + H2O ----> 2NaHSO3 + CO2

What are the conditions required to make this reaction happen.

hodges - 20-7-2006 at 02:54

I would think this would work given that H2SO3 is a stronger acid than H2CO3. You would simply bubble SO2 through a Na2CO3 solution until no more was absorbed then evaporate the solution to get the NaHSO3.

Hodges

woelen - 20-7-2006 at 03:09

This reaction indeed works, first you get sodium sulfite, then you'll get bisulfite. You can't, however, make NaHSO3 as a solid. When the solution is evaporated then the solid Na2S2O5 remains (sodium metabisulfite). The bisulfite ion only exists in solution, in solid form, it looses water and metabisulfite is formed.

technologist - 20-7-2006 at 20:07

Thanks to all.
Can I request any specific condition to me maintained during this reaction e.g. Temp & pH especially.

woelen - 21-7-2006 at 11:46

Do as hodges suggested. Temp & pH not really important, just add SO2 until no more dissolves and heat, and you'll get Na2S2O5.

metabisulfite

chloric1 - 22-7-2006 at 10:32

I read that sodium metabisulfite heated gives dry sulfur dioxide gas. Unfortunately, this is not correct. You actually get an auto redux reaction forming sulfate and sulfide. The sulfide was strongly alkaline and at the high temperature, the test tube cracked:(. This is just FYI.

cral - 27-7-2006 at 06:07

Is there a feasible route to produce Sodium Bisulphite through reduction of, for instance, Sodium Bisulphate?

woelen - 27-7-2006 at 06:35

Doing that in an economical way is very difficult. Sulfate (and bisulfate) ion is very inert with respect to reduction. ALthough it has sulphur in its highest oxidation state, fairly extreme conditions are needed for its reduction (e.g. very high temperature, as part of concentrated sulphuric acid, or in combination with really strong reductors). Under these conditions, the reaction is not clean at all. Besides formation of (bi)sulfite and/or SO2, which is desired, you also get all kinds of side reactions, which result in formation of sulfides (or H2S) and free sulphur or even other more complicated oxo-sulphur ions. The result will be crap.

garage chemist - 28-7-2006 at 06:00

When sodium or calcium sulfate is heated with an excess of charcoal powder to 800- 1000°C under exclusion of air, it is reduced quantitatively to the sulfide. This is an industrial method fr the production of sodium sulfide. The Na2S is separated from the excess charcoal by leaching with water and the Na2S is crystallized as the nonahydrate.

However, sulfite can not be made that way.

bbartlog - 2-11-2009 at 18:53

Quote: Originally posted by woelen  
Doing that in an economical way is very difficult. Sulfate (and bisulfate) ion is very inert with respect to reduction. ALthough it has sulphur in its highest oxidation state, fairly extreme conditions are needed for its reduction (e.g. very high temperature, as part of concentrated sulphuric acid, or in combination with really strong reductors). Under these conditions, the reaction is not clean at all. Besides formation of (bi)sulfite and/or SO2, which is desired, you also get all kinds of side reactions, which result in formation of sulfides (or H2S) and free sulphur or even other more complicated oxo-sulphur ions. The result will be crap.


Mostly, I think you're right. Especially with respect to sodium sulfate/bisulfate. However, I did find this interesting patent while looking for other information on ammonium bisulfate: http://www.freepatentsonline.com/3835218.html

Basically, it claims that with 1-5% weight of one of a wide range of catalysts (e.g. CuSO4), you can get the net reaction
3NH4HSO4 ➝ N2 ↑ + 5H2O + 2SO2 ↑ + NH4HSO3
at temperatures of 350-450C. Actually temperatures as low as 140C are mentioned but I'm thinking the reaction probably doesn't proceed at any appreciable rate at temperatures that low; anyway, while 350C is not *terribly* kitchen-friendly it's not much worse than the melting point of lead.
The main problem I see with this is that you're not getting a lot of sulfite for your sulfate; unless I had something useful I could do with the SO2 being given off I don't think I'd find this interesting. However, as already pointed out, you could use the SO2 to make sulfite via a different path.

And of course the patent could be BS.

starman - 16-2-2011 at 21:40

Is there a simple method for producing sodium sulfite from the metabisulfite?(without using the metabisulfite as a source of SO2)

woelen - 17-2-2011 at 01:48

Simply add some NaOH to a solution of Na2S2O5. Do this until the solution becomes slightly alkaline. At that point you will have fairly pure Na2SO3 in solution with just a little bisulfite left.

starman - 17-2-2011 at 21:32

Thanks Woelen,I think I recall a sulfite solution is somewhere near pH 9.