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The Volta Pille - how COULD it work

  1. Feb 23, 2013 #1
    I am placing my question here as it is electrochemistry

    Volta, in his pile, generated voltage and at least a few mA of current

    He had 100 copper disks separated from zinc disks by wet blotting-paper

    So each gave 1.2 volts and he had lots of volts.

    But THINK about this!
    ALL surfaces are coated by a monolayer of water!
    Especially in UK where I live!

    So his battery was cu water zn water cu water zn .......
    Total 1.2 -1.2+1.2-1.2 +1.2............... = 0 volts.

    So how THICK does an electrolyte have to be to be an electrolyte?

    And WHY is copper/zinc 1.2 to 1.4 volts and lead/lead peroxide 2 to 2.7 volts
    How is it related to the electron fermi levels
    Why are the best anodes (like PbO2) semiconductors?

    Why is Zn/C 1.4 volts in NH4Cl with MnO2 "depolariser" and
    Zn/C in the dichromate cell and Grove cell 2.0 volts.

    Why don't they include non-metals in the "Electrochemical Series"?
     
  2. jcsd
  3. Feb 23, 2013 #2

    SteamKing

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    All of these are good questions. Sound like you have some research to do.
     
  4. Feb 23, 2013 #3
    Funny! I have researched this for seventy years!
     
  5. Feb 23, 2013 #4
  6. Feb 24, 2013 #5
    I tried all them
    They do not explain how the Fermi levels affect the volts, and only SAY what the volts are - not why. Nor how thick a film has to be to behave as an electrolyte.
     
  7. Feb 24, 2013 #6

    Simon Bridge

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    ... you can be forgiven for not going right to wikipedia as it did not exist 70 years ago :)
    However - those articles make a very good start. It is a big subject so you would not expect to find everything you are after in just one source. Clearly you need to look up the electrochemistry of the films in question as well.

    Aside: in 70 years diligent searching you most likely came across Faraday's work on electrochemistry ... he had a reasonably accessible description from studying Volta's work. geometry of the piles was one of the things he studied - and you'll find treatments in engineering texts to this day.

    Keep going - sounds like you have spent 70 years looking in the wrong places.
     
    Last edited: Feb 24, 2013
  8. Feb 24, 2013 #7
    Volta, not Voltaire!
     
  9. Feb 24, 2013 #8

    Simon Bridge

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    OK - typo corrected - but comments still stand.
     
  10. Feb 24, 2013 #9
    How much water is on the surface of those disks depends on several factors like air humidity, temperature, surface structure etc.
    But it doesn't matter. If a copper and zinc disk are touching there may be some moisture in between that causes an electrochemical reaction. But since the disks touch it's shorted out. A small current will flow but the voltage between the disks is 0. I don't think there is a minimum thickness an electrolyte needs to have. It's just that cells that are shorted can't contribute to the total voltage of the battery.
    In a zinc carbon cell the two electrodes are not Zn/C but Zn/MnO2. The carbon is just a conductor, it doesn't participate in the reaction. Also "depolariser" is strictly speaking not correct terminology. MnO2 is an oxidiser.
    The reaction between Zn and MnO2 produces 1.4V because the energy liberated in that reaction is approximately 2.8eV per Zn atom. Probably a little higher but I don't know the exact number. There are 2 electrons released per Zn atom so about 1.4 eV per electron => 1.4V.
    And there are lots of non-metals included in the electrochemical series
    http://en.wikipedia.org/wiki/Electrochemical_series
     
  11. Feb 24, 2013 #10

    SteamKing

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    Volta used salt water, so there should not be any resistance to current flow.
     
  12. Feb 27, 2013 #11
    There is not a film of water on everything, I do not believe that adsorption is that strong. As we would have problems isolating anything. But even such a monolayer existed, you cannot disregard the geometry. There is a diffusion of ions between the metal plates which produces the voltage. If this diffusion is much more efficient by orders of magnitude between adjacent plates than along some short cut path the voltage can still add up.
     
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