1. Oct 15, 2008

### jumbogala

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
N/A

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?

Thanks!

Last edited: Oct 15, 2008
2. Oct 16, 2008

### 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.