Bleach Potency

Posted by: Susan

Bleach Potency - 01/26/06 02:01 AM

I do understand that chlorine bleach loses its potency over time. But is that in reference to sealed or unsealed (partly used) bottles, or both?

Sue
Posted by: JohnN

Re: Bleach Potency - 01/26/06 06:48 AM


Take a look at this thread on eGullet.

I get the impression that the main issue is evaporation, so it seems that uncapped bleach would be useless pretty quick.

-john
Posted by: lazermonkey

Re: Bleach Potency - 01/26/06 07:41 AM

thanks for the link. Very informitive.
Posted by: benjammin

Re: Bleach Potency - 01/26/06 02:28 PM

Wow, that thread was chock full of nonsense.

As far as bleach losing it's effectiveness, let me put it this way. All bleach solutions (a combination of Sodium Hypochlorite and water) contain water right off the shelf. To say that water has some adverse effect on the solution is not supported by the facts. Contaminants in the water can react with the chemical to liberate some of the chlorine and weaken the effectiveness, and it will off gas and lose its concentration in an open environment, but if it is in a closed container mixed with clean water, it will not diminish any more than the initial dilution when it was put in the container. If you have it in a spray bottle, it will remain approximately as effective over nominal time usage as long as the seal is reasonably good and no contaminants are introduced.

Heating the solution doesn't directly effect the chemical, other than evaporating it, which if it is in a contained system will only recondense back into solution again. In the washing machine, hot water will evaporate the chemical out of solution quicker, but not at a rate sufficient to diminish the effectiveness of the application.

Sunlight can ionize the chemical, much the same as it does water, into it's elemental compounds (sodium, chlorine, hydrogen, and oxygen). Unless the sunlight is concentrated, this process is relatively slow.

Posted by: JohnN

Re: Bleach Potency - 01/26/06 04:09 PM

Hi Benjammin,

Quote:
Wow, that thread was chock full of nonsense.


Most threads are, here included! Welcome to the Internet! :-)

If you read the thread through, they do correct most of the mistatements people made and cover most of the points you bring up.

-john
Posted by: Susan

Re: Bleach Potency - 01/26/06 07:16 PM

Thank you for the information. It confirmed what I suspected but didn't know for sure.

I am in the habit of keeping a never-opened bottle of plain bleach with my jugs of stored water. Now I don't have to worry about it breaking down in time. If it's sealed so it doesn't evaporate, isn't exposed to direct sunlight or excessive heat, it's still good.

That's what I wanted to know. <img src="/images/graemlins/smile.gif" alt="" />

Sue
Posted by: Arney

Re: Bleach Potency - 01/26/06 08:02 PM

Sorry, Sue, maybe we're not done with this topic yet. A bit technical here...

I'm not a chemist so perhaps someone with a chemistry background out there can give me a thumbs up or down on this idea, but I thought that a slow reaction of HCl with Na+ ions gradually degrades the disinfecting power of bleach by reducing the concentration of hypochlorous acid (the source of the HCl), irrespective of whether any chlorine gas is allowed to escape from the bleach container. In this way, even an unopened, sealed bottle of bleach can gradually degrade over time. Comments?

By the way, here's a webpage from Cornell University with a response from Clorox about stability. It doesn't say whether we're talking about opened or unopened, but it does state that the concentration will diminish.
Posted by: frenchy

Re: Bleach Potency - 01/28/06 11:18 AM

FWIW : found in chemistry books :

bleach ("eau de javel") will have lost half of its active component ("hypochlorite") after three years.
Posted by: Susan

Re: Bleach Potency - 01/29/06 05:36 AM

So if it loses it, where does it go???

Sue
Posted by: frenchy

Re: Bleach Potency - 01/29/06 08:33 AM

Bleach is not stable.

excerpt from this web site :

Propri?t?s chimiques !
les eaux et extraits de Javel se d?composent lentement ? temp?rature ambiante avec formation de chlorate et de chlorure de sodium et lib?ration d'oxyg?ne.
3 NaClO --> NaClO3 + 2 NaCl
2 NaClO --> 2 NaCl + O2
La d?composition est acc?l?r?e par la lumi?re, la chaleur et la pr?sence de nombreux m?taux.... Les eaux de javel dilu?es sont beaucoup plus stables que les extraits.


(loosely translated ... or is it loosy translation ??? <img src="/images/graemlins/grin.gif" alt="" />)

Chemical properties :
bleach will slowly degrade at room temperature giving off chlorate, sodium chloride and oxygen (re formulae : NaClO = NaOCl)
Decomposition (or is it "Breaking down" ?) will be faster if light, heat or some metals are present.
Diluted bleach is more stable than extracts.
__________________________________

another web page, in english
Physical properties

3.3.3 Description
.........
Boiling Point: Decomposes above 40?C (104 deg F)
...............
Odour chlorine (bleach) odour
Odour Threshold: Not applicable. Odour is due to
breakdown products such as chlorine.
________________________________________________________
another one...
sodium hypochlorite
n.
An unstable salt, NaOCl, usually stored in solution and used as a fungicide and an oxidizing bleach.
________________________________________________________
web page
Stability:
Slowly decomposes on contact with air. Rate increases with the concentration and temperature. Exposure to sunlight accelerates decomposition. Sodium hypochlorite becomes less toxic with age.
Hazardous Decomposition Products:
Emits toxic fumes of chlorine when heated to decomposition. Sodium oxide at high temperatures.
Hazardous Polymerization:
Will not occur.
Incompatibilities:
Ammonia (chloramine gas may evolve),amines, ammonium salts, aziridine, methanol, phenyl acetonitrile, cellulose, ethyleneimine, oxidizable metals, acids, soaps, and bisulfates.
Conditions to Avoid:
Light, heat, incompatibles.
_____________________________________
Posted by: countrymouse

Re: Bleach Potency - 01/29/06 08:54 AM

That's French Bleach - American Bleach never breaks down!

Seriously, thanks for the info. <img src="/images/graemlins/smile.gif" alt="" />
Posted by: Arney

Re: Bleach Potency - 01/29/06 06:49 PM

I've been doing more research into the topic (finding the right Google terms make all the difference!) and what I found confirms my previous claim--even an unopened bottle of bleach does have a limited shelf life.

First of all, to my surprise, Google turned up this hit on the ETS website itself. It says, "Bleach has a limited shelf life and for best results you should use fresh bleach no more that a few months old." Sounds a lot like that Clorox statement on the Cornell link I referenced in an earlier post. Speaking of Clorox, here's a Clorox webpage that has the "3-6 months for optimum performance" statement that I previously referenced on that Cornell University webpage. We should ask Doug where he got his information from.

Here's another link, and here's another one about the limited shelf life of bleach. They don't specify whether the bottle needs to be opened or not, but it doesn't seem to matter.

As for the reason why bleach degrades (or "where does it go?"), this webpage from the CDC describes the particular chemical reaction that is the source of the degradation. When bleach is just sitting in its bottle, there's a chemical reaction that I mentioned previously where underchloric acid (HOCl) breaks down into hydrochloric acid(HCl). There is sodium ion floating around in bleach and the hydrochloric acid reacts with the sodium to form sodium chloride, aka "table salt". Over time, you lose the disinfecting HOCl as dissolved salt. Salt is very stable so the process is basically irreversible under storage conditions.

The manufacturer makes "straight" bleach strongly alkaline (pH 11) by adding sodium hydroxide (NaOH), to minimizes the amount of HOCl around, so this degradation is relatively slow in the original container. However, once you dilute the bleach with water, the pH drops to around neutral, which highly favors HOCl. That is a good thing because you want lot's of HOCl around to zap the bad stuff, but it's also bad because with so much HOCl around, this degradation reaction occurs much more quickly. That's one (the main?) reason why once you mix up some disinfecting solution, you can't keep it long regardless of how carefully you store it. There is some offgassing of chlorine gas, but I have yet to read anything that attributes offgassing as a major reason for bleach's limited shelf life. Logically, you would think so (seems logical to me, too), but I guess it doesn't. Anyway, regarding how long your disinfecting solution can last, most hospital/lab disinfection protocols I read instruct you to make up a fresh batch every 24 hours. Others say you can keep the solution for up to a month before throwing it out.

Anyway, based on what I read (much more than what I reference here), for optimal drinking water disinfection, it seems that you should rotate the bleach stock out at six month intervals if you want to be reasonably certain of using bleach that is strong enough to conform to the typical water treatment guidelines (e.g. X drops for clear water, Y drops for cloudy). As the bleach ages and weakens, you could adjust the dilution to get the proper disinfecting concentration, but it's hard to know how much to adjust it unless you actually tested the chlorine concentration.

We are always instructed to utilize the "smell test" after treating water with bleach, and I guess that is supposed to be a crude way of seeing if there was enough HOCl around to properly treat the water. If the bleach is old and much of the chlorine is bound up as salt, not enough will be left to turn into enough chlorine gas to smell once added to the proper volume of water. That would also mean that there might not be enough to kill all the microorganisms properly. So, add more bleach and try it again.

The loss of concentration figures I have uncovered range from 20-50% per year. Alain's figure of weakening to 50% after three years is consistent with a 20% weakening/year. But at 50%/year, it would only be a fourth as strong after three years, which is a significant difference.

So, whether you're storing French eau de javel or American Chlorox, bleach does not have an indefinite shelf life.

I must sound like the Alton Brown of bleach (for those of you familiar with the science-oriented Food Network cooking show). <img src="/images/graemlins/grin.gif" alt="" />
Posted by: Susan

Thanks Everyone - 01/30/06 06:54 AM

Okay, all that sort of seems to make sense... chemistry wasn't my forte in school. I'll date it, then use the old stuff to wash the moss off the deck.

Sue (39th continuous day of rain here in WA--- blech!)
Posted by: JohnN

Re: Thanks Everyone - 01/30/06 08:20 PM


Quote:
Sue (39th continuous day of rain here in WA--- blech!)


Yah, quite a drag, eh? My yard turned into a swamp last night...

-john