Re: Sodium Bisulfite

Alberto Novo wrote:
>
> Katharine Thayer wrote:
>
> > .... and if
> > it's basic chemistry, why not just spell it out simply, explain how it
> > works differently for sulfite vs bisulfite and metabisulfite.
>
> Solutions od sulphite (Na2SO3) are alkaline. From the chemical information
> you should have seen the pH value: 11 for a 20% solution.

Yes, but that didn't tell me why it would work differently than
bisulfite for clearing, which is what I was looking for an explanation
about. Thanks for spelling it out for us chemically-challenged. I have
another question below....

> Chromium(III) salts behave more or less as iron(III) salts: in neutral or
> alkaline solutions they form the insoluble tri-hydrate Me(OH)3 (Me is the
> metal).
> Solutions of bisulphite or metabisulphite (no matter which is the
> countercation) are all acidic, see for example -ever looking at the pH
> values-:
> www.basf.de/basf/img/produkte/schwefel/CAA-NBSLFG-E-REV7.pdf
> www.chemicalland21.com/arokorhi/industrialchem/inorganic/Sodium%20metabisulf
> ite.htm
> Both sulphite and bisulphite are able to reduce Cr(IV) to Cr(III), but only
> the latter has the capability to keep some reduced chromium in solution due
> to its acidity.
> Chromium hydrate and oxide-hydrates are all greenish.

You lost me again right there at the end. Not sure whether you're
saying here that the product of clearing with sulfite should be
greenish, or that both the product of clearing with sulfite and the
product of clearing with bisulfite should be greenish. If the latter,
then I must disagree on the basis of my own observations. The product of
clearing with bisulfites is a pure medium blue, with no greenish cast to
it at all, and the heavier the orginal stain, the bluer the product.
It's the color of chrome alum, not the color of the chromium oxides.
Katharine
Received on Fri Oct 8 09:50:47 2004