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What's the blue/black crap in the water? (electrolysis)

  1. Mar 20, 2005 #1


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    Today I got the brilliant idea to make my own sodium hydroxide. I put some water in a glass jar, threw in some salt, connected each electrode to a terminal on a 12V DC motorcycle battery, and away the reaction went.
    My assumption was that the metal breaking apart at the positive electrode would go to the negative electrode, and my solution will stay fairly clean. My assumption couldn't have been more wrong. Right now the solution is opaque, sort of blue/black in color, and has little chunks of stuff floating around that sort of look like curdled milk. The anode is a crappy bottle opener from the 1970s, and the cathode is just a wire with about 2 inches of plastic removed from the end.

    What is this garbage? How can I make sodium hydroxide solution that is transparent?
  2. jcsd
  3. Mar 20, 2005 #2


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    I am not sure, but if the salt has some iodide in it, it might have been oxidized to elemental iodine. You don't seem to do anything wrong.

    You can filter the solution after you finish the oxidation, and evaporate the solution to dryness.
  4. Mar 20, 2005 #3


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    I just realized why my system is flawed. Hydroxides are not soluble; that completely screws up the way the ions will move.

    Now to figure out where to buy pure carbon rods.
  5. Mar 20, 2005 #4


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    You dissolved your electrodes - but that's a thing you already know :)
    Last edited by a moderator: Aug 13, 2013
  6. Mar 20, 2005 #5
    Sodium hydroxide is indeed soluble, as are all Group I and most of Group II hydroxides. The precipitate formed will probably actually work to your advantage, as it will allow you to filter out impurities by decanting/filtering/suction.

    Are the anodes or cathodes degrading/being plated? There are probably multiple reductions not only with the impurites in the water, but with the electrodes themselves.
  7. Jun 15, 2005 #6
    What kind of salt did you use? I assume table salt, Sodium Chloride.

    Assuming NaCl, and the setup that you described will not make NaOH. Because the Chloride ion oxidizes too, and then it combines with the NaOH , and makes first bleach NaOCl, and then NaOCl3 (Sodium chlorate), then eventually, NoOCl4 (Sodium perchlorate).

    Making NaOH at home is going to be very difficult, because you have to seperate the electrodes so that the NaOH, and elemental chlorine do not recombine. Just go to a hardware store, and get some red devil lye. It is fairly pure for most purposes.

    A good place for cheap graphite is www.graphitesupply.com I actually bought mine from them through ebay, and they have good prices too.
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