Re: Sodium Bisulfite

From: Katharine Thayer ^lt;>
Date: 08/25/04-01:47:46 PM Z
Message-id: <>

Martin Angerman wrote:
> According to the Merck Index, tenth edition, "The bisulfite of commerce
> consists chiefly of sodium metabisulfite, Na2S2O3 (all numbers should be
> read as subscripts), and for all practical purposes possesses the same
> properties as the true bisulfite."
> The formula for metabisulfite is NaHSO3. One metabisulfite, plus one water
> equal two bisulfites. I think it rearranges when it is dissolved, kind of
> like dissolving chlorine gas into water gives hypochlorous acid (HClO).

Thanks, Martin,

So sodium bisulfite is essentially the same (for all practical purposes)
as sodium metabisulfite? Or at least sodium metabisulfite is for all
practical purposes, especially once it's in solution, the same as sodium
bisulfite? Well, okay, I can accept that in theory, except I can tell
you from my own experience that I can use sodium metabisulfite, even in
rather heavy concentration, indoors, but I can't use sodium bisulfite
even at 5%, indoors, because of the fumes. So something's different
about them.

But the problem is that it's sodium bisulfite and *potassium*
metabisulfite that are at issue in this discussion, so how similar are
they? My chemist consultant says that he doesn't see a role for the
potassium and sodium, so as far as he's concerned they are spectator
ions in the reduction. If this is correct, then it's only the sulfite
that matters, and metabisulfite should perform about the same regardless
of whether it came into solution along with potassium ions or sodium
ions. If that's so, then why would we expect big differences in how they
perform in the clearing and washing process? This is a lot of if's, but
if all this follows by the logic of chemistry, (BIG IF) then it seems to
me that potassium metabisulfite, which I've never used, should perform
about the same as sodium metabisulfite, which I have used. In my
experience sodium metabisulfite if anything is less soluble than sodium
bisulfite, (it tends to form plates that are harder to dissolve than the
bisulfite powder) and is much less effective as a clearing agent than
sodium bisulfite at the same concentration.

But if you are right that sodium bisulfite and sodium metabisulfite are
essentially the same thing, and if my other chemist friend is right that
the potassium and sodium are irrelevant, then logically it seems like
where this logic heads is toward the idea that you'd expect sodium
bisulfite and potassium metabisulfite to perform rather similarly? Tell
me where this logic isn't sound.

You can tell I have company coming; I'd always rather talk about gum
printing than clean house.
Received on Wed Aug 25 20:43:35 2004

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