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Daria

Bleach & Vinegar

Threads running on SCA-Garb & the Merry Rose have prompted this.  I will try to cross post.

The discussion started with bleach & bleaching agents (amminoa /urine) and the base/acidness of it and how to stop the bleaching action.  It

I'll try to make this as clear and untechnical as possible (yea right):
 

What is Bleach?

Sodium Hypochlorite, or bleach is commonly used as a household bleach. At stronger concentrations, it is used for bleaching paper pulp and textiles. It is used as an intermediate, in the manufacture of organic chemicals, in water purification, in medicine, in fungicides, in swimming pool disinfectants, as a reagent, and as a germicide.

The term hypochlorites refers to the salts of hypochlorous acid (HOCl). Since the acid is extremely unstable, most users handle the more stable hypochlorite solutions instead. These salts are prepared by reacting chlorine with an alkali or an alkaline earth hydroxide.

Preparation - The common method for making sodium hypochlorite is to react chlorine with a solution of caustic soda. The final concentration of the sodium hypochlorite solution depends on the initial concentration of the starting caustic soda solution. The following equation gives the chemical reaction involved, regardless of concentration:

(1) Cl2 + 2 NaOH NaOCl + NaCl + H20

A more active, but less stable, sodium hypochlorite can be produced by chlorinating a solution of soda ash according to the following equation:

(2) Cl2 + 2Na2CO3 + H2O NaOCl + NaCl + 2 NaHCO3

On further chlorination, hypochlorous acid will be produced:

(3) Cl2 + Na2CO3 + H2O HOCl + NaCl + NaHCO3

Most commercial production processes react chlorine with caustic soda as in equation (1).
 


So how do you stop bleach without killing yourself?

From http://www.getridofthings.com/get-rid-of-bleach-stains.htm:

If you're trying to remove or repair a bleach stain without the use of labratory grade chemicals, the first thing I would try is white vinegar.
Go get yourself some heinz white vinegar or even the generic stuff; it doesn't matter which. Soak a clean white cloth with the vinegar and start dabbing/blotting the stain. Keep doing this until the fabric won't hold anymore vinegar in the immediate vicinity of the bleach stain. Rinse with cold water and repeat. Vinegar has been used traditionally as a color restoration solution for a very long time. Not only does it immediate neutalize any bleach agents left in the fabric, but the acids in vinegar (acetic acid) will help to dissolve or peel away any damaged fabric that may be causing a bleach stain to stand out. Vinegar will eventually damage cotton fabrics with enough exposure, so use white vinegar conservatively when treating bleach stains.
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From http://www.newton.dep.anl.gov/askasci/chem00/chem00085.htm (Richard E. Barrans Jr., Ph.D.
Assistant Director,PG Research Foundation, Darien, Illinois)
 
"I have used vinegar to neutralize bleach and bleach to remove dye stains, etc. with no noticeable bad reactions. I realize that there is a hazard in mixing Hypochlorous Acid (bleach)and ammonia. Is there any reaction between bleach and any of these acids?

Bleach actually is sodium hypochlorite; hypochlorous acid itself is not a stable compound.  If sodium hypochlorite (bleach) is acidified, it generates chlorine gas.  This is hazardous, but it is also easily detectable.  It
smells bad, and causes asphyxiation.

Do any of these combinations produce Chlorine Gas or the toxic chloramines?

Yes.  Acid + bleach  = chlorine gas;  amminoa + bleach = chloramine."
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Now I have used Vinegar to stop bleach for a long time.  Although it does have its own problems...
You should NEVER add Vinegar directly to bleach.  Very bad things happen.  Toxic gases are produced.  When the bleach is reduced (you have rinsed your fabric in clear water) and then the vinegar is also reduced, the amount of gas produced is negligable.  I've never been able to smell it (which is the first sign it's a problem)

So what is the RIGHT way to stop bleach??
From "Ask A Scientist":
Bleach is a 3-5% solution of sodium hypochlorite [NaOCl]. It is rapidly reduced by reducing agents. One reducing agent that is fast,effective, available, and cheap is sodium sulfite [Na2SO3] -- not sulfate [Na2SO4].
It is available from any swimming pool chemicals retailer. It will be called something like "knock down", "de-chlor" or similar trade name. It is used to reduce the level of chlorination in swimming pools. I use it myself to de-chlorinate my bathing suit after swimming.

Sodium thiosulfate [Na2S2O3] will also work. It is used in developing photographic film and prints. Its common name is "Fixer". It is available in any photographic supply store, but is likely to be more expensive than sodium sulfite.

In principle, ascorbic acid [vitamin C tablets] should also work. It is a reducing agent, but I haven't tried it myself to neutralize bleach. I have used it to "bleach out" certain stains in clothing, because some dyes,
when reduced, become colorless. It works very well on certain stains."
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Products such as Bleach-Stop can be purchased that are safe to use as well.  Another person recommended Anti Chlor, also found in your local pet fish department for de-chlorinating tank water.

Very good info also found here (see below).  Paula Burch (a chemist & a pro dyer) recommends either Bleach-Stop, Anti Chlor, or Peroxide and gives cost/use estimates for each.

How much bleach neutralizer do I need to use?

Thiosulfate (Bleach Stop) is not as strong as Anti-chlor (sodium metabisulfite).

You need to use one whole ounce by weight (30 grams) of Bleach-Stop (sodium thiosulfate) per gallon of warm water, or a pound and a quarter for a twenty-gallon washing machine load — so, using your washing machine for this step would be very expensive and you'd better stick to a bucket, but you can do that. Cost per gallon of bleach neutralizing bath, 25¢. Not too expensive.

In contrast, you need only one teaspoon, or 2.2 grams, of Anti-chlor (sodium metabisulfite) per 2.5 gallons of water, or less than half a teaspoon per gallon of water. That works out to 18 grams per twenty-gallon washing machine load, if you like to use it there. Cost per gallon of bleach neutralizing bath, three-quarters of 1¢. Very, very inexpensive. Cheap enough even to use in the washer, if you're lazy about carrying buckets around, or if you want to use it as a regular laundry additive to reduce unwanted bleaching from chloramine in your water supply.

Buy whichever one your dye supplier sells, and be careful to use no less than their instructions say to. Rinse your garments in water quickly before neutralizing. ALWAYS fill your bucket or washing machine with rinse water to do this BEFORE you start to apply bleach to your fabric.

I'm not sure how much 3% hydrogen peroxide is absolutely required. I had good results by pouring half a bottle over my project; at $,79 per bottle, that was about 40¢ per use. Far less economical, but convenient for those times when you don't have any Anti-Chlor in the house and your next order isn't due to be delivered until next week. It works very well, too: although I had to leave that particular shirt in the bleach a long time to get my design, it never did develop any holes in the bleached part, over hundreds of washings. (There was no spandex or other synthetic fiber is the shirt, which helps a lot.) It eventually developed unrelated rips elsewhere on the shirt. I can certainly recommend 3% H2O2 as effective, even if not the most economical option.



I will probably switch to Peroxide after reading all of this....
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Daria

October 2010

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