[pure-silver] Re: sulfite in PMK working solution
- From: Ryuji Suzuki <rs@xxxxxxxxxxxxxxx>
- To: pure-silver@xxxxxxxxxxxxx
- Date: Tue, 28 Dec 2004 19:07:48 -0500 (EST)
From: Sandy King <sanking@xxxxxxxxxxx>
Subject: [pure-silver] Re: sulfite in PMK working solution
Date: Tue, 28 Dec 2004 18:04:14 -0500
> Would it be fair to say that one should substitute for the
> metabisulfite (assuming that the label is accurate) at the rate of
> one part metabisulfite to two parts sulfite?
Well, the precise answer is as I said:
> >1 mole of bisulfite makes 1 mole of sulfite when pH is adjusted well
> >above its pK. Similarly, 1 mole of metabisulfite makes 2 moles of
> >sulfite. (This is because 1 mole of metabisulfite makes 2 moles of
> >bisulfite when fully dissolved in water.) These are precise.
Perhaps you are not used to the unit mole. 1 mole of X is a quantity
where number of molecules of X equals the Avogadro's number. That is,
1 mole of anything has same number of molecules in it. It's sort of
like a foreign exchange of chemical quantities where the standard is
the Avogadro's number.
1 mole of sodium sulfite (anhydrous) has the mass of 126g.
1 mole of sodium metabisulfite (anhydrous) has the mass of 190g.
That is, (2 x 126)g of sodium sulfite and 190g of sodium metabisulfite
make same number of sulfite ions (dissociated molecules) when they are
fully dissolved and the pH adjusted. Similarly, 1.33g of sodium
sulfite and 1.00g sodium metabisulfite make equal amount of sulfite
ions.
> I would also conclude that it is probably not possible to know at
> this point exactly what Hutchings used in the original formulation,
> i.e. 1) pure sodium bisulfite, 2) a mixture of bisulfite and
> metabisulfite, or 3) pure metabisulfite sold as bisulfite?
I would also agree, but if I had to make one best assumption, I'd pick
3. Also note that the discrepancy is (only) 0.33.
--
Ryuji Suzuki
"Keep a good head and always carry a light camera."
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