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Voltaic cell question

  1. Apr 21, 2015 #1
    Extract From Wikipedia explaining zinc voltaic cell :
    metallic zinc at the surface of the zinc electrode is dissolving into the solution
    Can you explain what makes zinc atoms dissolve into the solution? Why are solid zinc atoms losing electrons?The solution is just a mix of Zn2+ and SO42-. Do Zn atoms react with Zn2+ or S042- ? Or it is because copper electrode is pulling the electrons

    Thank you
     
  2. jcsd
  3. Apr 22, 2015 #2
    Well, in case of a voltaic cell, when you look at each half cell, since ions are in the solution and atoms in the electrodes, there exists a potential difference here, this shall be its standard reduction potential. When two half cells are combined, the reaction at each electrode actually depends on the relative Std reduction potentials. In case of the voltaic cell we are referring to here, The value for Zn(ion)= -0.76V and for Cu(ion)= -0.34V. As seen here Zn has a greater negative value,meaning, it has a greater tendency to undergo oxidation and lose electrons as compared to Cu. Thus it loses electrons and I would name its relative std reduction potential as the reason for this.
     
  4. May 9, 2015 #3
    Without going into complicated surface electrochemistry, some atoms on the surface of a zinc object will dissolve when a lump of zinc is placed in water.

    Atoms on any surface are less tightly held than atoms inside a body and those sitting on small surface asperities are held even more loosely.

    In the case of a zinc electrode, crudely put, zinc will dissolve until the negative charge on the electrode surface is sufficiently strong to pull the dissolved zinc ions back to it.

    The actual science is far more detailed than that. You get anodic and cathodic areas on the surface of the electrode, so zinc is dissolved in some areas and redeposited in others. I'm not well-read on zinc specifically, but I would imagine that there would also be some reactions with water, involving some hydrated species.

    If I have understood the reason for your question, fundamentally why a nominally insoluble metal should dissolve, I hope the basic answer given above meets your need.
     
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