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Quick question about Electrochemistry anode and cathode

  1. Nov 28, 2012 #1
    1. The problem statement, all variables and given/known data
    Pb/Pb2+ and Ag/Ag+

    Ni/Ni2+ and Zn/Zn2+
    Which one is the anode and cathode?
    Toward which metal do the electrons flow?



    3. The attempt at a solution

    2Ag2+ + Pb ⇔ 2Ag + Pb2+

    Pb is anode
    and Ag is cathode

    e- go toward Ag.


    Zn + Ni2+ ⇔ Zn2+ + Ni

    Zn is anode
    and Ni is cathode

    e- go toward Ni.
    Is this correct?

    Thanks.
     
  2. jcsd
  3. Nov 28, 2012 #2
    Unfortunately, you got them backwards in both cases.

    Remember reduction (increase in number of electrons) occurs at the cathode while oxidation occurs at the anode. So check which of the elements is more electropositive. That element will form your anode. The periodic table will help you.
     
  4. Nov 28, 2012 #3
    I dont understand, i used the same method for other problems and I got right answer.
    This is what I did.
    because for Pb/Pb2+ and Ag/Ag+
    the standard reduction at 25 C

    Pb2+ + 2e-⇔Pb(s) E = -0.13
    Ag++e-⇔Ag(s) E = 0.80

    So flip top eq to get an oxidation of Pb and Ag is already in reduction form
    so ox = anode
    and red = cathode?

    so total E = 0.80 + 0.13 = 0.93

    thanks for your time.
     
  5. Nov 28, 2012 #4

    Borek

    User Avatar

    Staff: Mentor

    Almost correct. Ag is not 2+, but I assume it is just a typo.

    Correct.

    Although you should use → in both cases.
     
  6. Nov 28, 2012 #5
    Yes it was a typo.
    And since it is correct we can see that
    Pb lost electron so it is the anode?

    same goes for the other case.
     
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