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Copper corrosion

  1. Dec 11, 2006 #1
    I put a copper pipe in a tank of water with dissolved iron in it and applied an electric current somthing like 6 volts at 1.5 amp and the pipe was hooked up to the positive terminal. After a couple of days some tourquise or pale green substance formed, i scraped this off and there was a copper colored substance but it was a little darker and washed off to expose the copper below. Iwas wondering if the green was basic copper oxide like in the atmospheric weathering of copper.
     
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  3. Dec 11, 2006 #2

    Gokul43201

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    What do you mean by dissolved iron? Metallic iron hardly dissolves in water. Are you refering to an iron salt?

    And what about the negative terminal? As you've described it, your circuit is open, and there's no current flow.
     
  4. Dec 15, 2006 #3
    The negative terminal as also submerged in the water. The dissolved iron is most likely rust coming from the rock in the ground( the water was gotten from a 350 foot deep well). We also have a lot of clay in our soil and the water went through a water softener that adds common salt to the water. It was more than likely not iron salt. Aren't metal salts made by reacting a metal with an acid? What is the diffrience between rock salt and sodium chloride? The well water turns purple on contact with willow extract (boil willow bark in distilled water) and turns to normal color on contact with vinegar if that means anything signifigant.
     
  5. Dec 16, 2006 #4

    GCT

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    The greenish substance is probably chlorine based, e.g. Chlorine gas, I've seen in many times while making silver chloride reference electrodes with some added HCl through electrolysis.
     
  6. Dec 17, 2006 #5

    ShawnD

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    The color of a metallic salt often depends on the oxidation state of the metal. Green would be +1 copper. It's possible that your system was creating copper ions, then those ions would precipitate due to something in the water. For example, if you anodize copper in a saturated iodine solution (something like potassium iodide), you will form a precipitate of copper iodide which is insoluble. Copper iodide is the wrong color, but the same concept applies. Copper sulfate would be blue, Copper (1) Chloride has a light green color to it (maybe what GCT was talking about), same deal with Copper (II) Chloride
     
    Last edited: Dec 17, 2006
  7. Dec 17, 2006 #6

    Gokul43201

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    Not a bad guess. If I had to pick a few choices I'd go with copper hydroxide, basic copper carbonate (CuCO3.Cu(OH)2), or a copper chloride.

    Are you saying the green color comes from the anion? And how can chlorine gas form a coating that can be scraped off? I've just completely lost you here.
     
  8. Dec 18, 2006 #7

    GCT

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    I should have noted that the substance was a solid, I was under the impression that the green color had formed at a point in the solution....don't ask me why, just absent minded.
     
  9. Dec 21, 2006 #8

    chemisttree

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    Rock salt and sodium chloride are the same thing. The water softener replaces cations with sodium ions as you have surmised.
    Is the water chlorinated with hypochlorite (bleach) or gaseous chlorine (hypochlorous acid)? Either way, chloride will be present at some level and a copper chloride could form. You might check the pH of the water. If it is basic, then Gokul is right about a basic copper substance like a carbonate or chloride.

    The willow bark extract probably contains salicin. I'm not sure that salicin produces blue or purple complexes with either iron or copper but it could. Salicylic acid does produce highly colored blue and red complexes of these two metals and can be produced from salicin. Salicylic acid could be present as an impurity in your extract... and red plus blue might give you a purple color. I'm not sure that acetic acid will discharge the color of these complexes.

    Why were you electrolyzing the well water? Were you trying to remove iron?
     
  10. Dec 21, 2006 #9

    Gokul43201

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    I was going to guess that the bark had something that was behaving like a pH indicator (I don't believe phenolphthalein is present in plant tissue, but something similar might be), forming a purple complex above some pH. The acetic acid would then be simply turning the solution sufficiently acidic to destabilize the complex.
     
  11. Jan 13, 2007 #10
    What if copper chloride didn't form what other chemicals would form? The purpose of electrylosys is the extraction of Hydrogen from the water. We live on a farm so we get our water from a well. The reason I chose copper is I had no other metal but copper and steel, but that was a foolish choice for an electrode in water, but a person is limited to their materials, equipment, and their imagination. Do you know of a metal that doesn't corrode so readily in water, besides carbon? Our water tested a 7 on the PH scale. The willow extract vinegar well water mix turned purple when a base was added. I haven't got the chance to test other acids if it is just acidity doing this or is limited to acetic acid. Is Salicylic acid a liquid or a solid? What is a "complex"? A good PH indicator in plants is the juice from the Elderberry (Sambucus nigra) fruit, red is acid blue is basic, and purple is neutral, on this scale HCl turned it a bright red. What causes copper to dissolve into drinking water (mix that kind of water with an egg white, put it in the microwave and cook it and it will turn green) like that. Only sodium chloride is added no bleach or other chlorine based chemicals.
     
  12. Jan 17, 2007 #11

    chemisttree

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    The only other copper compounds I can think of are either oxides or hydroxides of copper. (hydrogen and oxygen excepted)

    Gold plated electrodes don't corrode... nor does carbon.

    Salicylic acid is a solid that dissolves in water. In this example a complex is an "association" of copper or iron ions with salicylic acid in solution. They are red and blue colored.

    Copper can corrode and produce slightly soluble oxides or hydroxides. The corrosion is a reduction/oxidation (redox) reaction that can happen during electrolysis.

    If you are trying to make Brown's gas, I wouldn't spend too much time on it since most of what is said about Brown's gas is a hoax.
     
  13. Jan 24, 2007 #12
    Wouldn't Brown's Gas be extremely dangerous and explosive because it has it's own oxygen supply?
     
  14. Jan 24, 2007 #13

    chemisttree

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    Yes. It is usually generated as fast as it is used for that reason.

    I've thought of an interesting project for you to study using hydrogen. See how an atmosphere of pure hydrogen changes the lubricity of graphite and molydisulfide greases on steel. See how an atmosphere of hydrogen and nitrogen affect the growth rate or the selection of wild algae or other bugs.


    There is an effort underway to use algae to produce hydrogen (http://www.wired.com/news/business/0,54456-0.html). To do so, the researchers will undoubtedly find that oxygen must be rigorously excluded. How might those conditions affect the equipment used to mass produce hydrogen by this "biophotolysis" method?
     
  15. Jan 24, 2007 #14
    The hyperlink doesn't work.
     
  16. Jan 25, 2007 #15

    chemisttree

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    it happens...
     
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