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If water is exposed to high voltage, it will ionize.

  1. Jan 13, 2007 #1
    if water is exposed to high voltage, it will ionize. What is the minimum voltage needed for that to happen? Thanks!
     
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  3. Jan 14, 2007 #2

    Andrew Mason

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    What is the energy required to remove an electron from a hydrogen or oxygen molecule?

    AM
     
  4. Jan 14, 2007 #3

    Gokul43201

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    This will only give you an estimate of the ionization potential for H2O(gas). In the liquid state, the number is much lower, due to several effects that are not easy to calculate (you can think of these as described by a local dielectric constant). I believe the number for water is about 1 volt.

    EDIT: Yup, the standard reduction potential tables tell me it's 0.83V
     
    Last edited: Jan 14, 2007
  5. Jan 15, 2007 #4
    so, say a circuit is submerged in the water. The circuit requires only a 0.83V to ionize the surrounding waters?!? Wow! I though it wouold be much higher than that!
     
  6. Jan 15, 2007 #5

    disregardthat

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    Wasn't that for 1 molecule?
    So if you had millions of molecules it'd take millions of volts right?
     
  7. Jan 15, 2007 #6

    Andrew Mason

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    Multiply that by the number of coulombs of charge to get the energy. So the energy to remove an electon from a water molecule in the liquid state is .83eV or .83 x 1.6e-19 C = 1.3e-19 Joules.

    AM
     
  8. Jan 16, 2007 #7
    so is this true? Thanks!
     
  9. Jan 16, 2007 #8

    Gokul43201

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    No, it's not. It does not take 2 million volts to produce hydrogen from the electrolysis of water (it takes about 2 volts). The Daniell (Cu|CuSO4||ZnSO4|Zn Galvanic) cell produces an EMF of about 1.1V (not millions, billions or an Avogadro number of volts).

    The real number will be about 1 or 2V. There will be a deviation from the ideal ionization potential, in a real electrolytic cell, that depends on the electrodes used. An ideal, inert electrode will get you closest to the ideal number. Any other electrode will require an overvoltage to produce the same current as the ideal cell.

    Heard of anyone that killed their cell phone by dropping it in water? Typical phone batteries run at somwhere between 3V and 4V - easily enough to ionize a path through water (if the phone case isn't watertight) and make a short.
     
    Last edited: Jan 16, 2007
  10. Jan 16, 2007 #9
    I'm sorry..I think I didn't explain my situation well enough. I am asking, in terms of say....

    suppose we have a heating element submerged in water. (e.g. a coffee maker, or amny other possible everyday things). When the current is passed through the nichrome heating element, will the current ionize the surrounding waters? is it powerful enough?

    Sorry if I didnt explain myself well before, and thanks for all your help!
     
  11. Jan 16, 2007 #10

    Gokul43201

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    To the best of my knowledge, all immersion heaters have an electrically insulating (but thermally conductive) coating over the nichrome element. I'd expect the outer case to be grounded.
     
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