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Thread: Scientific chemistry question

  1. Back To Top    #1

    Join Date
    Sep 2011
    Location
    Atlanta Ga
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    309

    Scientific chemistry question

    Chlorine breaks down over time due to sunlight and other factors and has to be replaced in the pool.

    I don't understand this.

    Chlorine is a basic element, CL, number 17 on the periodic table of elements. Molecules composed of basic elements break down into the individual elements, but the individual elements, such as CL, only break down during nuclear fission, if I remember correctly from science classes years ago.

    What is really happening to the CL in the pool water?
    36 x 18 oval pool, inground, plaster pool.
    27000 gallons
    1 hp pump. Sand filter
    Pool built in 1971.

  2. Back To Top    #2

    Re: Scientific chemistry question

    Sodium hypochlorite breaks down and has to be replaced. Chlorine itself is a gas.
    18K Gals, Intelliflo VSD, Pentair Catridge, SWG, Solar & Gas Heat, Pebble Tec, Jandy AquaLinks, Pool Pal for Android.

  3. Back To Top    #3

    Join Date
    Mar 2007
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    San Rafael, CA USA
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    12,082

    Re: Scientific chemistry question

    When we say "break down" we don't mean it changes to a different element. We mean that the chlorine chemical changes from one type to another and in this case it changes its oxidation state from +1 in hypochlorous acid (HOCl) or hypochlorite ion (OCl-) to -1 in chloride ion (Cl-). Some technical details of how chlorine gets used/consumed are in this post.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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  4. Back To Top    #4

    Re: Scientific chemistry question

    Quote Originally Posted by TomAtlanta
    Chlorine breaks down over time due to sunlight and other factors and has to be replaced in the pool.

    I don't understand this.

    Chlorine is a basic element, CL, number 17 on the periodic table of elements. Molecules composed of basic elements break down into the individual elements, but the individual elements, such as CL, only break down during nuclear fission, if I remember correctly from science classes years ago.

    What is really happening to the CL in the pool water?
    Wikipedia is your friend

    http://en.wikipedia.org/wiki/Sodium_hypochlorite

    This is probably the normal reaction, probably somewhat catalyzed by UV
    4 NaClO + 2 H2O ? 4 Na+ + OH- + 2 Cl2 + O2
    17,800 gallon, IG pool, 595 sq feet (17x35x4.5 avg rectangle), Hayward 525 cartridge filter, diamondbrite, 2 hp 2 speed hayward tristar filter, Stenner 45mhp10 automatically chlorinating

  5. Back To Top    #5

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

    Re: Scientific chemistry question

    Quote Originally Posted by march2012
    4 NaClO + 2 H2O ? 4 Na+ + OH- + 2 Cl2 + O2
    As is sometimes the case, Wikipedia is wrong about this. Look at the above reaction. It isn't even balanced for charge or for hydrogen or oxygen. Even if you add a "4" before the hydroxyl, it still isn't what happens unless you continue to simply the formula by dissolving the chlorine gas into water. However, the above is just plain wrong in terms of explaining what goes on. I already gave a link to the post that shows the correct reactions and it has a link to another post that goes into the more detailed free radical reactions that show that a UV photon of light breaks apart the bond between the oxygen and the chlorine in hypochlorous acid and in hypochlorite ion. From there it's just a matter of eventually getting to a chloride ion and oxygen gas.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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