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Salt Bridges in a Cell

  1. Apr 25, 2017 #1
    I know that salt bridges maintain charge, thus allowing the reaction to proceed. I was wondering if the distance of the electrodes from the salt bridge affects the voltage of the cell in any way. Thanks!
     
  2. jcsd
  3. Apr 26, 2017 #2

    Borek

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    I am not convinced that's the best of wording of the salt bridge purpose (they don't 'maintain', they close the circuit and allow the charge to flow).

    Open circuit voltage - no, this is independent of the cell geometry. However, the geometry of the electrodes and size of the cell do change the internal cell resistance, so they limit maximum current battery can deliver.
     
  4. Apr 27, 2017 #3
    Salt bridges mainly destroy the junction potential between the electrolytic solution & the electrodes, thus maintaining the constant flow of current.
     
  5. Apr 27, 2017 #4

    Borek

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    And how are they going to destroy the junction potential when they are in a completely different part of the circuit?
     
  6. May 1, 2017 #5
    I think the junction potential may be fine, but the battery potential will go down.
    Consider the cathode of a lemon battery where the reaction is: Zn + 2H+ -> Zn2+ + H2. The produced positive ions will give the electrolyte a positive charge. If the positive charge can't be neutralized by ions from elsewhere, the potential of the cathode wil go down, because of all the positive charge near it, but the junction potential between the negative cathode and the positive electrolyte won't change.

    (There is another effect. The changed concentration of Zn2+ and H+ ions will lower the junction potential, but this shouldn't be affected by the length or distance of the salt bridge)

    The positive charge around the cathode and negative charge around the anode produce an electric field that drives the current through the salt bridge.
    If the salt bridge becomes longer, a larger electric field will be needed to drive the same amount of current through the salt bridge, so more positive charge will remain around the cathode, and the battery potential will go down. Increasing the current will have the same effect. The salt bridge acts just like internal resistance of the battery.
     
  7. May 1, 2017 #6

    Borek

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    Which is why in my first post I have specifically referred to the open circuit voltage.
     
  8. May 3, 2017 #7
    Thanks for all the help! I think I have a solid answer, now.
     
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