Balanced Redox Equations for OCl- Titration with S2O32-

[jumbogala]

Homework Statement

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 S₂O₃^2-. Including all redox half reactions there are three.

Homework Equations

N/A

The Attempt at a Solution

First I figured out the two equations. I think they are:
OCl- + H₂O + 2I- ---> Cl- + 2OH- + I₂

I₂ + 2S₂O₃^2- ---> 2I- + S₄0₆^2-

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 + 2S₂0₃^2- -----> Cl- + 2OH- + S₄0₆^2-

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?

Thanks!

 

[Borek]

First I figured out the two equations. I think they are:
OCl- + H₂O + 2I- ---> Cl- + 2OH- + I₂

I₂ + 2S₂O₃^2- ---> 2I- + S₄0₆^2-

OK with me.

OCl- + H₂O + 2S₂0₃^2- -----> Cl- + 2OH- + S₄0₆^2-

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?

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.