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Net ionic equation and Redox equation confused

  1. Nov 1, 2009 #1
    1. The problem statement, all variables and given/known data
    Write the net ionic equation for H2SO4(aq) to the KMnO4(aq)


    2. Relevant equations



    3. The attempt at a solution
    I am confused on which one should i write.
    The first method is to list all the species, then use the data book to find which one is the strong OA and SRA. Multiply one or both half equation by the number that will bring the number of electrons to the lowest common multiple. Add them together and cancel the identical ion.
    The second is net ionic equation, H+ +SO4- + K+ MnO4- --> ...
    I got two different answer. I have to no idea when to use redox or net ionic...
    If anyone can tell me the difference...
    thanks
     
  2. jcsd
  3. Nov 1, 2009 #2

    Borek

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    Staff: Mentor

    There is no reducing agent in the question; something is wrong.

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  4. Nov 1, 2009 #3
    Isn't water act as RA?
     
  5. Nov 1, 2009 #4

    Borek

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    Staff: Mentor

    And what is it oxidized to?

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  6. Nov 1, 2009 #5
    I don't know, but this is i work...
    H+ SO42- K+ MnO4- H2O
    SOA: MnO4- + 8H+ +5e---> Mn2+ + 4H2O
    since H2O is the only RA, so water will be the SRA
    SRA: 2H2O ---> O2 + 4H+ +4e
    the balanced redox equation:
    4MnO4- + 12H+ ---> 4Mn2+ + 6H2O + 5O2
     
    Last edited: Nov 1, 2009
  7. Nov 1, 2009 #6

    Borek

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    Staff: Mentor

    In permanganate decomposition it is not water that is getting oxidized, but oxygen from permanganate.

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  8. Nov 1, 2009 #7
    I don't understand...:\
    How can i solve it?
    Btw, The followed question is why it would not be a good idea for us to add the H2SO4 directly to the KMnO4 solution during this lab?
    this is one of my lab question. In the lab, we were trying to find the concentration of KMnO4 using the primary standard, and then use the calculated concentration to find another concentration of the H2O2 solution.
    H2SO4 was added into the primary standard and H2O2 solution..
     
    Last edited: Nov 1, 2009
  9. Nov 2, 2009 #8

    Borek

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    Staff: Mentor

    I told you much earlier - there is no reducing agent in the system. To some extent there is no solution - unless you will treat decomposition of the permanganate as redox reaction, but then both reduction and oxidation occur in the same molecule. Which technically can be classified as redox.

    Read about solutions used in permanganate titration.

    http://www.titrations.info/permanganate-titration

    Sulfuric acid is necessary to have high enough oxidation potential of the permanganate solution.

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    methods
     
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