Re: NANFA-L-- Chlorine Bleach

dlmcneely-in-lunet.edu
Thu, 09 Jun 2005 16:47:02 -0500

OK, I think I've got it. Bleach (5% sodium hypochlorite or
hypochlorous acid) is made by bubbling chlorine gas through a solution
of sodium hydroxide (caustic soda). An excess of sodium hydroxide is
included in the final product to provide additional bleaching power,
and to keep the ph around 10 or 11. Sodium hypochlorite is a highly
hygroscopic solid (it adsorbs water from the air), and so is always
stored and shipped in solution, but the pure compound is a white
powder. If evaporated to dryness, bleach leaves a solid white powder
that is a mixture of sodium hypochlorite, sodium chloride (table salt)
and sodium hydroxide. The last two are also hygroscopic, but less so
than the sodium hypochlorite itself. There are other chlorine bleaches
besides sodium hypochlorite. Though sodium hypochlorite spontaneously
breaks down to release chlorine gas as the pH in the solution drops
when used, and chlorine itself is a strong oxidizing agent,-in-the pH
used (usually above 8), it is the hypochlorite itself that oxidizes the
coloring agents, along with any residual (or purposely added in excess)
sodium hydroxide.

Source; local chemist, after consulting an industrial chemistry text.

Since the white residue left on drying includes sodium hydroxide, it
would be undesirable in aquaria, and so a bleach solution should not be
allowed simply to evaporate to dryness if used to disinfect tanks.

David L. McNeely, Ph.D., Professor of Biology
Langston University; P.O. Box 1500
Langston, OK 73050; email: dlmcneely-in-lunet.edu
telephone: (405) 466-6025; fax: 405) 466-3307
home page http://www.lunet.edu/mcneely/index.htm

"Where are we going?" "I don't know, are we there yet?"

----- Original Message -----
From: "Welaka T. Phishhed" <welaka75-in-yahoo.com>
Date: Thursday, June 9, 2005 3:10 pm
Subject: Re: NANFA-L-- Chlorine Bleach

> I found this . . .
> "To say that chlorine bleach does not contain chlorine is true,
> but somewhat
> misleading. True, it does not contain diatomic chlorine gas, CL2.
> It does
> contain sodium hypochlorite, NaOCl, which is one of the products
> producedwhen aqueous sodium hydroxide (caustic soda) reacts with
> Cl2. (The other
> product is sodium chloride, NaCl.) It is a very strong oxidizing
> agent.Some non-chlorine bleaches contain slightly weaker oxidizing
> agents, which
> will oxidize the colored molecules in many common stains, but not the
> robust pigments of commercial textile dyes. That's what makes them
> "color-safe." It's a trade-off: if the stain is a tough molecule
> (such as
> turmeric, the vegetable dye used to make mustard bright yellow), the
> strength of bleach required to oxidize it will also destroy the
> textile'scolor."
>
> WARREN
>
> dlmcneely-in-lunet.edu wrote:
> You're right about the calcium hypochlorite. My mistake there. But
> I
> found this
>
> http://www.inchem.org/documents/pims/chemical/pim495.htm
>
> "IPCS INCHEM is a means of rapid access to internationally peer
> reviewed information on chemicals commonly used throughout the
> world,
> which may also occur as contaminants in the environment and food.
> It
> consolidates information from a number of intergovernmental
> organizations whose goal it is to assist in the sound management
> of
> chemicals.
>
> Sodium hypochlorite
>
> Composition/Purity: Usually sold in solutions
> containing 5 to 15% sodium hypochlorite in water,
> with
> 0.25 to 0.35% free alkali (usually NaOH) and 0.5 to
> 1.5% NaCl. Solutions of up to 40% sodium
> hypochlorite
> in water are available. Solid sodium hypochlorite
> (NaOCl.5H2O) is not commercially used."
>
> All data I could find on the web discussed as liquid sodium
> hypochlorite the water solution used as bleach, not the pure
> material.
> And I found nothing that indicated that commercially available
> bleach,
> including 'Purex" brand, was prepared by mixing washing soda
> (sodium
> bicarbonate) with a chlorine source, though they might be. If so,
> then
> the white residue that bleach leaves on evaporation would be
> sodium
> bicarbonate -- which would be relatviely harmless in an aquarium.
> But,
> the labels on bottles indicate that it is "hypochlorous acid," --
> that
> is a water solution of sodium hypochlorite.
>
> So, I remain confused about solid sodium hypochlorite.
>
> David L. McNeely, Ph.D., Professor of Biology
> Langston University; P.O. Box 1500
> Langston, OK 73050; email: dlmcneely-in-lunet.edu
> telephone: (405) 466-6025; fax: 405) 466-3307
> home page http://www.lunet.edu/mcneely/index.htm
>
> "Where are we going?" "I don't know, are we there yet?"
>
> ----- Original Message -----
> From: geoffrey kimber
> Date: Thursday, June 9, 2005 2:24 pm
> Subject: Re: NANFA-L-- Chlorine Bleach
>
> > the pool stuff I have seen is calcium hypochlorite.
> >
> > I wonder if the white residue is buffers, or maybe salt?
> >
> > I searched the web and found several sites that stated that sodium
> > hypochlorite is a liquid, so I'm pretty sure it's true but not 100%
> > because who can trust the web?
> > /----------------------------------------------------------------
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> Best Wishes !
>
> WARREN
> *?-::-?:*'''''*:?-::-?*
> (Welaka T. Phishhed)
> WELAKA CREATIONS
> (E-BAY...photoguy6900)
> welaka75-in-yahoo.com
>
>
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