Re: Sodium Bisulfite

Here is the basic chemistry reminder. My apologies if it is too basic, but
it's better not to leave too much for granted. Sodium sulfite has two
sodiums and no hydrogen ions. Sodium bisulfite has one of each. Kind of
like sodium carbonate (washing soda) and sodium bicarbonate (baking soda).
In solution the difference is pH. pH is related to the negative log of the
hydrogen ion concentration. for example pH7 has 10^-7 hydrogen ions per
liter (neutral). pH3 has 10^-3 (acid), and ph10 is 10^-7 (basic). Working
from this, you can make the solution one, the other, or a mixture by
adjusting the pH.

The smell comes from the hydrogen compound being volatile, when the sodium
salt is not. Also, the sodium comes off completely when it is dissolved,
whereas the hydrogen does not completely dissociate. This is the same
principle as free basing, in order to volatilize (and inhale) alkaloid
drugs. They all exist in a kind of equilibrium:

"acidic" "basic"
SO2 + H2O <>H2SO3 <> HSO3- <> SO3--

(Sorry about the lack of subscripts)

As one goes from right to left, the smell goes down, and one moves toward
sulfite. If one takes a sulfite solution, and adds one half of the MOLAR
concentration in HCl, one will get a bisulfite solution, plus salt (and some
smell). The opposite would work with adding carbonate or hydroxide to a
bisulfite solution.

Clear as mud???

----- Original Message -----
From: <gdimase@hotmail.com>
To: <alt-photo-process-l@sask.usask.ca>
Sent: Thursday, August 26, 2004 6:43 AM
Subject: Re: Sodium Bisulfite

> Hi Martin,
> If so, where does it stand the sodium sulfite?
> Christopher James book says it can be used as a replacement of sodium
> bisulfite, also photformulary.
> Thanks,
> Giovanni
>
>
> ----- Original Message -----
> Wrom: NNYCGPKYLEJGDGVCJVTLBXFGGMEPYOQKEDOTWFAOBUZ
> To: <alt-photo-process-l@sask.usask.ca>
> Sent: Thursday, August 26, 2004 12:32 AM
> Subject: Re: Sodium Bisulfite
>
>
> > Here's the math:
> >
> > Formula weights are potassium metabisulfite=222, sodium
metabisulfite=190,
> > sodium bisulfite=104. Remember that you get two bisulfites from every
> > metabisulfite. There was no listing for potassium bisulfite.
> >
> > A 5% solution of sodium bisulfite=0.48M The equivalent molar
> concentrations
> > are 5.33% potassium metabisulfite and 4.56% bisulfite. All are close
> enough
> > for 5% to work in clearing baths for most situations.
> >
> > The potassium salts are listed as pharmaceutical antioxidants, and the
> > potassium salt as the food additive, and wine preservative (there may be
a
> > cost-effective opportunity for bulk purchases here). The metabisulfites
> are
> > listed as "freely soluble" in water. The sodium bisulfite is listed as
> > soluble in 3.5 parts water (~30% solution). pH may affect the ability
to
> > dissolve.
> >
> > All are listed as giving off a sulfur dioxide odor. They pick up water
> from
> > the air, and oxidize to sulfate (and are then ineffective). Keep them
dry
> > and tightly closed. As far as the smell of a solution goes, check the
pH.
> > A solution is acidic. The acid form is volatile, and therefore smelly.
> Get
> > some test strips or an inexpensive meter. I don't know the ideal pH.
> With
> > bulk and technical grades, this may be the source for differences from
> type
> > and batch differences. Remember, the difference between a bisulfite
> > solution, and a sulfite solution (as in developer) is just the pH.
> >
> >
> > ----- Original Message -----
> > Wrom: XUWLSZLKBRNVWWCUFPEGAUTFJMVRESKPNKMBIPBAR
> > To: <alt-photo-process-l@sask.usask.ca>
> > Sent: Wednesday, August 25, 2004 1:51 PM
> > Subject: Re: Sodium Bisulfite
> >
> >
> > > Katharine Thayer wrote:
> > > >
> > >
> > > >
> > > > 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?
> > > >
> > >
> > > I just re-read my chemist's message, and found that the conclusion I
> > > came to by reasoning my way through a logical sequence, he actually
> > > said straight out to start with: "I wouldn't think there would be any
> > > difference between sodium and potassium
> > > metabisulfites at the same molar concentration." So maybe I should
just
> > > read my mail more carefully and give my brain a rest. Any chemists
> > > disagree with this, please say so, and support your answer. Thanks,
> > >
> > > kt
> > >
> >
> >
Received on Thu Aug 26 20:44:11 2004