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Chem Concept

  1. Jul 23, 2006 #1
    My chem teacher is having trouble explaining the a particular happening in a fuel cell to the class. In a galvanic cell +ve ions move towards the +ve electrode and -ve to the -ve. In electrolytic cells the +ve ions move towards the -ve electrode and -ve to the +ve. He says that the reason why it is opposite in electrolytic cells is because it is being forced by the battery to do the opposite, but he is at a loss as to how to explain why +ve ions move towards +ve electrodes in the "natural" situations (ie. not being forced).

    Any help with how to describe why this happens will be much appreciated.
  2. jcsd
  3. Jul 23, 2006 #2


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    You are looking at a problem with "conventions." Obviously, your teacher ain't familiar at all with 'em. If you're interested in the chemistry, you look at the electrode-solution contact, and the electrode furnishing electrons to the solution is the cathode; to do this, it must accept electrons from outside the cell --- where it would be called an anode. Which is it? Cathode or anode? There is no absolute answer. You have to state, or know in which context you're naming it. Your teacher is laboring under an impression that a cathode is always a cathode, rather than understanding that it's a cathode at one end, and an anode at the other --- it carries a current.
  4. Jul 24, 2006 #3
    Not sure what you mean by "a cathode is always a cathode". If you are refering to the fact that a Cathode can be both +ve and -ve (as well as an anode) then yes he has explained that fact. That rather then anode and cathode being specified by charge that it is specified due to which is oxidized and which is reduced. If not then could you elaborate?
  5. Jul 24, 2006 #4
    the convention: the reduction takes place at the kathode and the oxidation occurs at the anode.

    In a galvanic cell the reductor donates electron to the negative elektrode and becomes negatively charged due to a surplus of electrons compared to the other electrode --> this is an oxidation and thus this is the anode.

    Reaction taking plase: [itex]M \longrightarrow M^{n+} + ne^{-}[/itex]

    At the other electrode electrons are lost by the oxidator taking them from the elektrode. This electrode becomes positively charged when compared to the other electrode --> this is the kathode.

    Reaction taking place: [itex]M^{n+} + ne^{-} \longrightarrow M[/itex]
    Last edited: Jul 24, 2006
  6. Jul 24, 2006 #5
    Yes, thats what I meant. And my teacher understands and explains this but he is at a loss as to explain why in a galvanic cell the positive ions move towards a positive electrode.
  7. Jul 24, 2006 #6


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    It does not appear that your teacher really understands very much of either. You're being taught this whole concept backwards.

    I would suggest instead that you study out of a half-decent physical/general chemistry text. Whatever textbook you're using would do a better job, I'd imagine.
  8. Jul 25, 2006 #7
    see my above explanation ;) but that doesn't have to be the case all the time though.
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