Vosoryx - 13-2-2018 at 21:32
I need some NaHSO3 for an upcoming project, and it needs to be relatively pure. I bought some "pH minus" from the local home depot, and the
MSDS says it contains NaHSO3 and Na2SO4. Because I want the sulphite to be relatively pure, my first question is:
1. The sulphate is insoluble in alcohol, and the bisulphite is slightly soluble. (According to pubchem, sites hyperlinked) Would it be practical to wash the mix in MeOH, filter off the sulphate, and then
evaporate the solvent off to obtain the bisulphite, or would the purity here be pretty shit? I don't care if there is a lot of loss due to the low
solubility, because the raw mix is very cheap, as is MeOH.
2. If that wouldn't work, i'd just do the simple:
SO2(g) + NaOH(aq) = NaHSO3 by bubbling SO2 through an aqueous solution of NaOH, until the pH is neutral.
I'd produce the SO2 by adding HCl to the raw mix of pool chemicals.
HCl + NaHSO3 = NaCl + H2O + SO2
Would the purity here be worse? (Perhaps due to the sulphate interfering...?)
Any other comments?
Sorry if the questions are amateur.
Thanks.
Bert - 13-2-2018 at 23:04
(Edit)
Saw the words "ph minus" and ass-U-Me-D that bisulfate was your interest- As noted, not what you're going to find in that package of swimming
pool chemical.
The home brew store has got your Sodium bisulphite.
--------------------
Take a read through this:
http://www.sciencemadness.org/smwiki/index.php/Sodium_bisulf...
.............
[Edited on 14-2-2018 by Bert]
woelen - 14-2-2018 at 00:13
pH minus does not contain NaHSO3. It contains NaHSO4 (and possibly some Na2SO4).
If you want NaHSO3, then you need to buy Campden tablets for wine making or beer brewing. These tablets can be Na2S2O5 or K2S2O5, which is sulfite
with an additional SO2 molecule added to it. In water these form HSO3(-) ions, but also free SO2 is produced. It actually is a complicated equilibrium
between S2O5(2-), SO3(2-), HSO3(-) and SO2.
I remember having read somewhere that in the solid phase the HSO3(-) ion does not exist and that on crystallization such solutions form the
metabisulfite:
2HSO3(-) --> S2O5(2-) + H2O
I, however, cannot find this written text anymore and other sources talk about sodiumbisulfite or sodium hydrogen sulfite. I myself only have sodium
metabisulfite and potassium metabisulfite, both at good purity.
[Edited on 14-2-18 by woelen]
unionised - 14-2-2018 at 01:41
Sodium metabisulphite is sold for home brewing use. It's food grade which implies pretty good purity.
Pool pH reducer is not a sulphite of any sort.
If you give us some details of the upcoming project, we might be able to help you further.
ninhydric1 - 14-2-2018 at 15:33
There is a brand of stump remover that isn't KNO3 but sodium metabisulfite, and I feel like sodium metabisulfite is more accessible IMO than NaHSO3.
Vosoryx - 14-2-2018 at 17:30
Thanks all - guess I have some more research to do.