Ask A Scientist Chemistry Archive

name         Martin R.
status       other
age          40s


Question -   I am attempting to bleach Walnut lumber. The basic method
that I am using requires that I wash coat the wood with a solution of
potassium permanganate then sodium bisulfite solution. I did not have any
soduim bisulfite and so I substituted sodium hydrosulfite[laundry
bleach]. This method works well.The soduim bisulfite is on its way and I
was wondering if the sodium hydrosulfite was  generally similar to soduim
bisulfite?
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My main concern is that what ever I use I need to be able to stop the
reaction so that the wood does not continue to bleach.What would you
suggest that I use to halt the bleaching?
Sodium bisulfite is an old name for sodium hydrogen sulfite -- the "bi" in
the older literature standing for "hydrogen". I'm a bit confused by your
equating this substance with "laundry bleach" which is typically sodium
hypochlorite (an oxidizing agent, as is potassium permanganate). The purpose
of the sodium hydrogen sulfite is to neutralize any excess permanganate, as
you point out. You could also use sodium sulfite, which is a chemical used
in swimming pools to lower the level of "chlorine" when the pool is
"shocked" to kill off an algae growth.

You will be able to judge when the neutralization treatment is done when the
deep blue-purple of the permanganate disappears.

Vince Calder
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