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It's very difficult to get accurate information concerning household bleach residues. Imagine, for instance, that you pour pure (or diluted) bleach onto fabric or synthetic foam and let it dry without rinsing (as a scientific experiment). Some sources say: it will totally "vanish" (with air and/or light), leaving water and salt, and some others say it will leave some toxic compounds behind, such as sodium hydroxide (which is added to the bleach to slow its decomposition).

Question 1: Will the bleach only degrade into water and salt ($\ce{NaCl}$), or will it leave other substances? If so, which ones? If the first case is true (i.e., the degradation products are water and salt only), why does the solution still smell like bleach for a long time?

Question 2: If bleach (a base) does leave toxic residue(s), can we use vinegar (an acid) to neutralize it? $(~\ce{OH- + H+}$ should create $\ce{H2O}$)

  • White vinegar: I'm confused since there is contradictory information on Wikipedia. Some says vinegar will neutralize harmful residues from bleach, while another source says it "could result in much more caustic and dangerous chemicals, such as hypochlorous acid" being produced.

  • Will an antioxidant such as vitamin C work as neutralizer? (as suggested by Brian)

It seems that everybody agrees about the use of peroxide, bisulfite, metabisulfite or thiosulfite, and sodium thiosulfate to neutralize bleach residues, but I wonder if more common products such as vinegar or vitamin C can be used instead: What do you think about these two? Any other suggestions?

EDIT: I removed the washing example which was confusing since it implied rinsing + I updated my question since I thought bleach was an acid.

EDIT2:

Household bleach is, in general, a solution containing 3–8% sodium hypochlorite and 0.01–0.05% sodium hydroxide; the sodium hydroxide is used to slow the decomposition of sodium hypochlorite into sodium chloride and sodium chlorate. wiki

Brian and Drmoishe's answer suggest several ways to way to neutralized bleach but what about the sodium Hydroxide residues? (I check on a french bleach, it shows only on the composition: "3.7% of sodium hypochlorite", nothing else)

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Question 1

No. Bleach requires something to react with in order for it to be consumed. There will still be bleach residues on the material.

Question 2

I think this question is actually based on a misperception, likely due to the multiple senses of the English word 'neutralize':

neutralize, verb

: to stop (someone or something) from being effective or harmful

: to cause (a chemical) to be neither an acid nor a base

While you are completely correct that adding acid to sodium hypochlorite would neutralize it in the second sense, you would in fact be doing the opposite of neutralizing it in the first sense. Your 'other source' is correct -- adding any acid to sodium hypochlorite will shift the equilibrium toward hypochlorous acid ($\ce{HOCl}$), which in turn equilibrates with molecular chlorine ($\ce{Cl_2}$), which is a nasty character you don't want to mess with$\dagger$.

What you need in order to neutralize it in the first sense, since bleach is an oxidizer, is a reducing agent. My recommendation would be to, say, crush up a few dye-free vitamin C (ascorbic acid) tablets, dissolve in a bucket of water, and soak the article to be treated for half an hour or so. Note that I've not ever actually tried this, so I have no idea if it will work. It might also work to pour such a vitamin C solution into the 'liquid fabric softener' fill area of a washing machine, if it has one.

EDIT: I just came across this Chem.SE question from two years ago, which confirms that ascorbic acid is suitable for scrubbing of chlorine/hypochlorite.

$\dagger$ Note: Technically, since $\ce{Cl2}$ is volatile, soaking the material in an acid like vinegar would probably eventually result in all of the bleach/chlorine coming out of the material, making the actual answer to Question 1 a 'conditional yes.' However, this is a really bad idea from a health/safety perspective.

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  • $\begingroup$ 1/2 Thank you Brian to show me my misconceptions. I finally understood that bleach is a base, but not much more. I thought we could neutralized a base with an acid, but it seems unfortunately more complex than just a bath of OH- vs H+ swimming on it.Your Vitamin C suggest that introducing stuff that contain too much electrons (suc as VitC) would neutralized the bleach compounds which desperately need some. Is that (globally) correct? $\endgroup$ – JinSnow Jul 16 '15 at 10:17
  • $\begingroup$ 2/2 The thing I find weird is that since bleach is a base, (conntains OH-), we should provide more positive charge to neutralized it, and thus acid (which contain H+), but you suggest vitamin C which will provide more electrons... Why? $\endgroup$ – JinSnow Jul 16 '15 at 10:17
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    $\begingroup$ @GuillaumeCombot See my edit. Acid/base and too-many/too-few electrons are mostly unrelated in general, despite the fact that they both can involve charged species. You are generally correct -- bleach "has too few electrons" and thus wants to react with stuff that "has about the right number of electrons" or that "has too many electrons." That's what it means when I say that bleach is an oxidizing agent. $\endgroup$ – hBy2Py Jul 16 '15 at 13:32
  • $\begingroup$ Any idea about the sodium Hydroxide residues? (cf edit2) $\endgroup$ – JinSnow Jul 29 '15 at 14:39
  • $\begingroup$ @GuillaumeCombot There shouldn't be any $\ce{NaOH}$ residues, just $\ce{NaCl}$. The oxygen in $\ce{ClO-}$ will be transferred to the reducing agent in some fashion in the course of the 'neutralizing' reaction. $\endgroup$ – hBy2Py Jul 29 '15 at 14:41
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After a thorough wash, rinse and dry cycle, little or no bleach should be left in the fabric, but there is possible concern about the effect of chlorine bleach on organic compounds. However, if disinfection is needed, then the infinitesimally small risk of VOC* is outweighed by the elimination of microorganisms.

If any remaining smell of chlorine bothers you, an extra water rinse should be helpful. @Brian suggests a reducing agent, and $\ce{Na2S2O3}$, sodium thiosulfate, is inexpensive and is commonly used to remove residual chlorine for aquaria. However, leaving garments to air-dry or airing them for a day would be as effective.

(*) "Volatile organic compounds"

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    $\begingroup$ Ah, thiosulfate, good idea. $\endgroup$ – hBy2Py Jul 15 '15 at 18:42
  • $\begingroup$ EDIT: I removed the washing example which was confusing since it implied rinsing + I updated my question since I thought bleach was an acid. $\endgroup$ – JinSnow Jul 16 '15 at 8:58
  • $\begingroup$ @drMoishe Thanks for your edit! Any idea about the sodium Hydroxide residues? (cf edit2) $\endgroup$ – JinSnow Jul 29 '15 at 14:39
  • $\begingroup$ The concentration of any residue should be minimal, as only tiny amounts of chlorine or thiosulfate are present. There would probably be more trace minerals in tap water than the reaction products after a final rinse. $\endgroup$ – DrMoishe Pippik Jul 30 '15 at 0:57
  • $\begingroup$ @DrMoishePippik Ok, but the (edited) question specify "no rinsing"... $\endgroup$ – JinSnow Jul 30 '15 at 13:30

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