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Na2SO2O5 vs. NaHSO3 for neutralizing hex chromium to trivalent

We have been sent sodium bisulfite in place of the sodium metabisulfite we had ordered. the company supplying the product informs us that is is the same chemical. In using the product to reduce hexa valent chromium to tri valent chromium the sodium bisulfite does not work like the sodium metasulfite compound. I need to have the basis for this problem so I will understand, or a source that will give me this information.

Thanks

Jim Graves
industrial chrome plating "bumpers" - Denver, CO, USA
2004

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2004

No, it is not the same thing. Sodium metabisulfite is also called 'sodium bisulfite anhydrous'. If you take one molecule of metabisulfite and add a water molecule, you get two molecules of bisulfite. It should do the same thing, but you need to use a little more of the bisulfite because about 9% of it is water, relative to the metabisulfite.

Dave Wichern
Consultant - The Bronx, New York