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Homework Help: Balancing redox reactions

  1. Sep 20, 2009 #1
    1. The problem statement, all variables and given/known data

    HIO3 + FeI2 + HCl ==> FeCl3 + ICl + HOH

    2. Relevant equations
    Directions say it's in an aqueous solution, and HCl is a reactant, so you can add H2O and H+ to balance, right?

    3. The attempt at a solution
    I first found all the oxidation states:
    H = +1
    I = +5
    O = -2

    Fe = +2
    I = -1

    H = +1
    Cl = -1

    Fe = +3 (oxidation)
    Cl = -1

    I = +1 (reduction)
    Cl = -1

    H = +1
    O = -2

    Then tried writing/balancing the half reactions.

    FeI2 ==> FeCl3 + e-

    But I'm kind of stuck here, can I use HCl to balance? How else do I balance that Cl? And what about the I?
  2. jcsd
  3. Sep 20, 2009 #2
    Do you have to balance the equation given or something else (net ionic equation, half-reaction)?

    To balance the equation you gave, first balance iodine and chlorine, then oxygen and then hydrogen, then keep going. That should help get you started.
  4. Sep 20, 2009 #3
    I have to balance the equation given, but obviously using half reactions and such since it's a redox equation.

    I'm not sure exactly what you mean by "first balance iodine and chlorine".
    If I have "FeI2 ==> FeCl3 + e-" as part of one half-reaction, how exactly do I balance the iodine and chlorine? Since ICl is a product, can I use that to help balance?
    ie, FeI2 ==> FeCl3 + e- + 2ICl
    ? And then from there how would I balance the Cl?
  5. Sep 20, 2009 #4
    I meant in the original chemical equation.
  6. Sep 20, 2009 #5
    So I have to balance the original equation before trying to balance it the redox way? That seems like it would take forever, I thought that was the point of the half-reactions and such :p
  7. Sep 20, 2009 #6
    I think it can be done in 10-15 minutes that way, if you don't make a mistake.

    Half-reactions or some other way might be easier or faster, but I've never worked with them.
  8. Sep 20, 2009 #7


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    Staff: Mentor

    This one is tricky, there are two things being oxidized and two being reduced at the same time. I would go for algebraic approach (of balancing chemical equations). If you were told to balance, but method was not enforced, you should select the one that gets job done. Doesn't matter which one it is.

  9. Sep 20, 2009 #8
    Well, we weren't specifically told how, but it's practicing balancing redox equations and that's the way we were taught, so I assume that's the way the teacher wants it done. I'll check out your link though, thanks.
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