Thermal decomposition of stored bleach

Hi
I stored my newly acquired Walmart Ultra bleach jugs near my shed. I thought that inside the shed it would be warmer, and since the containers are opaque, the active chlorine wouldn’t decompose by sunlight.

Nevertheless, the direct exposure to the sun was harmful. The sealed jugs inflated, indicating a buildup of gas pressure in them. The process was irreversible – putting them in a cooler place and shaking didn’t cause deflation. When a jug was opened the bleach solution had a fainter than normal green color. This led to the conclusion that the bleach decomposed, emitting oxygen, similar to UV decomposition. I now store the bleach in a shaded area.

We’re expecting a few hot days with temps up to 90. So far when, the decomposition happened, temp didn’t reach 80.

Does anyone have an idea if bleach is stable in the shade when air temp is 90 or higher?

The table at the bottom of this link will give you an idea of the stability of chlorine at various concentrations and temperatures. Roughly speaking, chlorine degrades twice as fast as the square of the concentration and with every 10F increase in temperature. For 6% bleach, the half-life at 90F ambient temperature is around 330 days, but that's for well-made bleach without contaminants.

I suspect that direct exposure to sunlight had the liquid in the container go to 110F if not more and that would have been a half-life of 80 days or so, but a drop to 5% would occur in about 20 days. Even with an opaque container, it still probably got quite warm in direct sunlight, especially if it wasn't all pure white.

I keep my 12.5% chlorinating liquid in a shed, but the temperature usually only varies from 60F - 80F and doesn't get above 90F very often. I've only noticed a small degradation from 12.5% to around 11.5% after about a month during the hottest months.

Richard

how do you test the strength of the bleach

Dilution of bleach or chlorinating liquid by 1 in 10,000 will result in a measured ppm that is the Trade % of the original liquid. So two dilutions of 1 in 100 are the easiest to do. That is about 1-1/4 fluid ounces (about 7-3/4 teaspoons) in one gallon, done twice (i.e. dilute once, then take 1-1/4 fluid ounces and add to another gallon, mix and measure). Or you can do 2 teaspoons in one quart, done twice.

Be sure and test the FC of the tap water you are using and subtract that (once) from your measured result.

I've also tested it in actual use, seeing the FC rise in the pool compared to what I expected (I measure within a half hour of addition -- it's pretty thoroughly mixed after 20 minutes).

Richard

Here's an even easier way (and it works!)

Get a measured eye-dropper at a drug store--one that measures from .2 ml up to 1.0 ml--they sell them, I have one. Get a glass one just to be safe.

Fill up an empty 2liter soda bottle with tap water to the same level they fill it with soda.

Use the eyedropper to add .2 ml of the LC or bleach you are testing to the soda bottle. Cap and shake.

Now measure the chlorine level of the soda bottle just like it was a pool. That number will be the concentration of your liquid chlorine. I tested my "12%" from a car-boy and it tested at 14%.

Don't forget to test your tap water first as Chem_Geek said and subtract that number from your total.

0.2 ml is about 4 drops. Although by your routine you dilute 1 by 10,000 as chem geek suggested, you compromise on the accuracy significantly by dropping in only 4 drops.
I wouldn't measure anything less than 1 ml - that's about 20 drops. You can do two dilutions of 1 ml into 34 fl oz and you get your 1 in 10,000 dilution.

Quote:

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Originally Posted by Water_man

0.2 ml is about 4 drops. Although by your routine you dilute 1 by 10,000 as chem geek suggested, you compromise on the accuracy significantly by dropping in only 4 drops.
I wouldn't measure anything less than 1 ml - that's about 20 drops. You can do two dilutions of 1 ml into 34 fl oz and you get your 1 in 10,000 dilution.

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I'm not using drops--the eyedropper is marked off in .1 ml units, but starts at .2 ml. It's a marked line. Besides, if my LC tests at 15% or 12% I don't care--schocking your pool isn't an exact science nor does it need to be. But, like horseshoes and hand-grenades, close is good enough.

But if the LC has degraded and tests at 5%, it will certainly be captured.

Besides, for greater precision, using my method, all you need to do is pour five of those 2 liter soda bottles worth of tap water into a five gallon bucket and use the eyedropper at the 1.0 ml level. Takes a little longer.

Our water district uses CC instead of FC so you might want to check that as it will throw off the measurement. According to my brother in-law who works at the regional water district, quite a few plants do this. So you might want to use distilled water instead of tap water or pre-shock the tap water and let the chlorine drop a bit before the test.

Quote:

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Originally Posted by mas985

Our water district uses CC instead of FC so you might want to check that as it will throw off the measurement. According to my brother in-law who works at the regional water district, quite a few plants do this. So you might want to use distilled water instead of tap water or pre-shock the tap water and let the chlorine drop a bit before the test.

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I'm not sure I understand this--if you are testing your LC/bleach for its strength, you want to test FC. I'd be shocked if CC > 0 shows up.

CC is a perfectly reasonable test of tap water to see if there's some contamination of that resulted in a CC > 0.

My point was to make sure that there is no CC in the tap water or the results may not be very accurate.

Chemgeek had mentioned that one should measure the FC of the tap water before adding the LC which is a good idea but many water districts use CC instead of FC in tap water, it lasts longer. This could cause a significant error in the LC measurements if not taken into account. Adding FC to tap water with CC will convert some of the CC into FC but from what I understand about the process, there is a net loss of FC.

So if you use tap water with CC and then add LC, it is likely to underestimate the strength of the LC. I am sure that Chemgeek has a way to take the CC conversion into account but it may just be easier to avoid it all together buy using distilled water or water without any CC.