Bleach and Chlorine Gas
Name: Stacie Y.
Date: 2001 - 2002
We are going to use full strength bleach (6%) to clean a
floor that has been stained from Tannin powder (Tannic Acid, C76H5O46).
There are concerns about the release of chlorine gas since it is known
that bleach mixed with acid can from chlorine gas and my chemistry is
rusty! I checked the archives which helped me a bit but I still have
questions:(a)Is the smell from a bottle of bleach (sodium hypochlorite)
actually chlorine gas or something else? (b)Since the sodium hypochlorite
in water forms a weak acid, hypochloris acid, why is the pH of bleach so
high (similar to a base)? (c)What is the chemical reaction between
bleach and an acid that makes the chlorine gas release (will this happen
with the tannin)? Thanks so much!
The odor of "household bleach" is chlorine, and should be used with adequate
ventilation. Chlorine poisoning by inhalation is a low risk because it is so
acrid one would evacuate the area unless trapped. Hypochlorous acid is a
"weak acid" because it only ionizes partially.
Household bleach is made by passing chlorine gas through sodium hydroxide.
The reaction is not run to stoichiometric completion so there is an excess
of sodium hydroxide in the final product rendering it alkaline. This
stabilizes the product and increases the concentration of
OCL(-1). The operative reaction is: OCL(-1) + H2O + 2e(-1) = Cl(-1) +
The two electrons are provided by what ever the bleach is oxidizing. The
residual odor of chlorine results from the equilibrium: 2ClO(-1) + H2O = Cl2
Now regarding the bleaching of tannin stains. You should test a small area
to be sure that household bleach is effective and does not attack the
flooring (You did not specify what it was.).
There are other options, e.g. hydrogen peroxide, calcium hypochlorite,
trichloroisocyanurate (both available from swimming pool chemicals
suppliers), citric acid (lemon juice), ascorbic acid (vitamin C). My point
is: You have assumed that oxidation of the tannins will de-colorlize them.
It probably is true because hypochlorite is used in the paper industry to
bleach paper, but I'm not sure that is necessarily true for your stains.
Tannins are a wide variety of chemical substances, and they may respond
I have some additional recommendations for you before you start your
project. Ask a professional dry cleaner how they remove tea stains (Those
are also tannin stains.). Ask a cabinet maker, if you can find one. They
"bleach" wood in the making of some cabinets. Find out what they use. You
could also consider using benzoyl peroxide which is used in the treatment of
acne, and is available at your local pharmacy, and is a strong oxidizing
There are also a class of stain removers that contain enzymes that are used
to bleach stains. They are used for grass and blood stains.
Hypochlorite will probably work, but it is not you only option.
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Update: June 2012