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Author: Subject: 12.5% NAOCl from Grocery Store!
Pommie
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Does anyone know how "available chlorine" is measured?

I can get pool chlorine that has 100g/L available chlorine for about US0.40c/L. It has a density of approx 1.2

If it only contains NaOCl then I guess it would have about 200g of NaOCl to get the density. This equates to about 95g chlorine.

So, can I assume that 1L contains 74/35*100 = 210g of NaOCl. (or the equivalent in NaCl and NaClO3)

Maybe I should just boil some down and see.

Mike.
woelen

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It is easiest to think of it as follows:

Add an excess amount of dilute HCl to the compound you have. This produces Cl2, according to the reaction ClO(-) + 2H(+) + Cl(-) --> Cl2 + H2O.

For each gram of compound you get a certain amount of chlorine gas. Available chlorine is defined as

(weight of chlorine / weight of compound) * 100%

So, with your pool chlorine, which has 100 g/L of available chlorine, you can expect 100 grams of Cl2 gas for each liter of this product, when that is added to excess HCl.

This definition even allows for more than 100% available chlorine content. An example is the compound LiClO. From each gram of LiClO you can get 1.23 grams of Cl2, so this has 123% available chlorine.

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garage chemist
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All NaClO solutions (pool chlorine and bleach) contain NaClO and NaCl in equimolar amounts.
This results from the production by leading chlorine into NaOH solution:

2 NaOH + Cl2 ---> NaCl + NaClO + H2O

The NaCl cannot be separated from the mix, so it is just sold with the NaCl in solution too.
hodges
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I checked again recently and there was a very slight pressure buildup of pressure in the bottle. I tried squeezing the bottle gently with a lighter held nearby, and the gas does appear to be at least partly oxygen. The flame got brighter and smaller.
Zinc
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I can from a supermarket buy quite concentrated sodium hypochlorite solution.
On the bottle it says: sodium hypochlorite 15%-30%
Chemist514
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Rona in Montreal...

Supreme Shock Treatment
Extra Fine Granulation
500 grams (Wow... meets my standard supply ammount.. how nice)
Guarantee : Sodium Hypochlorite 65%
Available Chlorine Content 65%

This have any actual General Chemistry uses? I bought one anyways cause you people talked about it so much and it was like 4\$. All the best peeps.
neutrino
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Hypochlorites have many uses. There's the haloform reaction, thermal decomposition into chlorates, etc, etc.

hodges
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 Quote: Originally posted by Chemist514 Guarantee : Sodium Hypochlorite 65% Available Chlorine Content 65%

I think something is not right about those percentages. Is this a solution? I doubt it could be 65% by weight. But it must be a solution because NaOCl is not stable except in solution. Are you sure it wasn't <i>calcium</i> hypochlorite? 65% is a pretty standard content for this in solid form.

Another thing, if it really was 65% sodium hypochlorite wouldn't the chlorine content be 65% * 35 / (23 + 16 + 35) = 31%?

Hodges
Chemist514
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Ack! my bad, you are indeed correct sir... Calcium Hypochlorate . I had been trying to find another product all day long that came close to 4% sodium hydroxide and so made the typo. .
hodges
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I just did a test on my product, which I purchased 2 years ago now. I diluted exactly 1ml of the solution with a liter of water, then tested it with pool test strips that test for "free chlorine". The results were off the scale. I dumped out half the solution and added water to make a liter again. This time, the results appeared to show 6 parts per million. I then repeated the dilution again and I got 3 parts per million, confirming the previous test.

Based on the dilution, the original solution has 4000 * 3 parts per million = 12 parts per thousand = 1.2 parts available chlorine per hundred. So therefore the NaOCl concentration would be (23 + 16 + 35) / 35 * 1.2% = 2.5%.

Orignially it had (according to the label, I never measured it) 12.5% NaOCl. So that would mean that in 2 years, 80% of the NaOCl was lost. Is this a reasonable average rate for decomposition of NaOCl solution? The bottle was kept in the dark and the temperature was always between 70 and 80F.

It appears the grocery store no longer sells this. I'll have to try getting some regular bleach and seeing what percentages I get.

Hodges
hodges
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I did a titration using Na2S2O3 and KI. First I made a 0.02M solution of Na2S2O3 using 3.3g in 1 liter of water (I used slightly more than calculations in case any moisture was present in the Na2S2O3 (which was supposed to be anhydrous). To test the old swimming pool chlorinator, I diluted it 99:1 with water. I then added some 3M H2SO4 and excess KI. The result was a solution containing iodine. I titrated this against the Na2S2O3 solution.

The reaction are (taken from http://web.lemoyne.edu/~giunta/chm151L/bleach.html):
OCl- + 2 I- + 2 H3O+ --> I2 + Cl- + 3 H2O
I2 + 2 S2O32- --> 2 I- + S4O62-
Therefore, my 0.02M Na2S2O3 solution would titrate 1:1 with bleach that was 0.01 molar (which would be 1 molar originally, since I diluted it 99:1).

I titrated by adding Na2S2O3 carefully until all iodine color disapeared. I found that for 100 drops of the bleach solution, I only needed 13 drops of the Na2S2O3 solution. Therefore, my old swimming pool chlorinator is only 0.13M. The calculated concentration of NaOCl is then 0.13 * (23 + 16 + 35) / 1000 = 9.6g per liter = 0.96%.

This did not seem right. So I titrated some new bleach which was supposed to be 6% NaOCl. My titration showed it as 5.5% NaOCl. Probably close enough since the 6% it left the factory with would be a maximum.

So then, how could I have gotten 2.5% by testing the swimming pool chlorinator solution with the pool test for free chlorine? Apparently, "free chlorine", when testing swimming pools, means something a bit different than the chemistry definition. Apparently it really means "free sodium hypochlorite". When I calculated 12 parts per thousand using the test strips, this was not the amount of chlorine but the amount of sodium hypochlorite. That agrees pretty closely with the 0.96% I got by titration, given the difficulty in reading the exact value based on color.

Its really strange that "available chlorine" would really mean "total sodium hypochlorite". However, I see another item of evidence for this. To test for available bromine instead of available chlorine you are supposed to multiply the values by 2. If it was only testing the amount of OCl-, or OBr-, this would not be necessary.

Hodges
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 Sciencemadness Discussion Board » Fundamentals » Reagents and Apparatus Acquisition » 12.5% NAOCl from Grocery Store! Select A Forum Fundamentals   » Chemistry in General   » Organic Chemistry   » Reagents and Apparatus Acquisition   » Beginnings   » Responsible Practices   » Miscellaneous   » The Wiki Special topics   » Technochemistry   » Energetic Materials   » Biochemistry   » Radiochemistry   » Computational Models and Techniques   » Prepublication Non-chemistry   » Forum Matters   » Legal and Societal Issues