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Redox Equation Addition

  1. Oct 15, 2008 #1
    1. The problem statement, all variables and given/known data
    OCl- is reacted with I- in acidic solution to generate I2.

    The I2 generated is then titrated using a solution of Na2S2O3.

    If you look at the sum of the two reactions above, information about S2O3- can be used to determine the amount of I2 and thus the amount of ClO-.

    Give the relevant balanced equations for the titration of OCl- with S2O32-. Including all redox half reactions there are three.

    2. Relevant equations

    3. The attempt at a solution
    First I figured out the two equations. I think they are:
    OCl- + H2O + 2I- ---> Cl- + 2OH- + I2

    I2 + 2S2O32- ---> 2I- + S4062-

    Are those correct? Is it different because it's in acidic solution? The OH- make me think I did this in basic solution, but I'm not sure.

    Then I added the two equations together to find:

    OCl- + H2O + 2S2032- -----> Cl- + 2OH- + S4062-

    If the last equation is correct, I don't see how that works. There's no I2 in the equation. The question says I need to go from thiosulfate ion, to I2, then to OCl-... hmm. What am I doing wrong?

    Last edited: Oct 15, 2008
  2. jcsd
  3. Oct 16, 2008 #2


    User Avatar

    Staff: Mentor

    OK with me.

    At first approximation - nothing. Iodine is only an intermediate product, used to transfer electrons in a controlled manner, as reaction between hypochlorite and thiosulfate is a messy one, with numerous byproducts and dubious stoichiometry.
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