How to remember the charge of electrodes?

  1. How do I remember that anode is positive in electrolysis but negative in electrochemical cells?
    I always forget it :|
     
  2. jcsd
  3. ACID = Anode Current Into Device

    Although you have to remember this is conventional current flow
     
  4. I did not understand that. How do we remember positive or negative from it?
     
  5. alxm

    alxm 1,864
    Science Advisor

    One's where an oxidation occurs and the other is where a reduction occurs.

    I think. I have to admit I never can remember that either. I just look it up again whenever i need to know. Even got confused about it when defending my Master's Thesis a number of years ago.. :) The only ones I know who seem to get it right consistently are actual electrochemists.

    I can do tensor calculus, but plus and minus still manages to baffle me...
     
  6. DrDu

    DrDu 4,449
    Science Advisor

    alxm is right. Kathode is always where reduction occurs. Best you figure it out when you need it from some easy reaction. E.g. in electrolysis of a copper sulfate solution positive copper 2+ ions get reduced to metallic copper by taking up two electrons which have to be delivered by the negative electrode.
    In the case a copper rod acts as an electrode in a battery, the copper will get oxidized and will deliver two electrons whence the electrode is negative again but this time it is the anode (due to oxidation).
     
  7. I always remembered that the cathode is where reduction occurs because both start with consonants; oxidation corresponds to the anode and both begin with vowels. Weird little mnemonic devices like that are what got me through general chem...
     
  8. Borek

    Staff: Mentor

    Cathode is where the cations go.
     
  9. DrDu

    DrDu 4,449
    Science Advisor

    Not in a battery.
     
  10. in valves (showing my age here) the cathode was where the electrons came from and the anode is where they go to
     
  11. Haha...good to see I have got a company here :wink:
     
  12. valves :confused: ?
     
  13. How do you decide the charge of electrodes from this?
     
  14. Borek

    Staff: Mentor

    Positive charge is attracted by the negative charge. It works nicely for electrolysis.
     
  15. Tubes if you're American
     
  16. "Red cat, Anny Ox" (Reduction at the cathode, oxidation at the anode. )and "LEO says GER" (Lose electron oxidation/ gain electron reduction).

    Knowing these two phrases (?) you will know how electrons flow and can tell which is positive and negative with ease.
     
    Last edited: Dec 23, 2010
  17. No we cannot tell which one is positive/negative from that. In both electrolytic and electrochemical cells, electrons flow from anode to cathode outside the cell but still they have different signs in 2 cases.
     
  18. I found out one easy word to remember.
    In electrolytic cells, remember the word PANIC.
    Positive=Anode & Negative Is Cathode.
    So whenever you forget about the signs in electrolytic cells, don't panic :wink:

    If you remember this, the charges of electrodes in electrochemical cells is opposite to it.
     
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