First of all - it goes in low pH, so not OH
- produced, but H
+ consumed.
Honestly, I have problems following what you wrote. I don't think you have followed my advice - as you were balancing all the time using I
3-. Note, that you final reaction (while incorrect in terms of H
+/OH
-) can be rewritten as
3H
2O + IO
3- + 5I
- -> 3I
2 + 6OH
-Difference - three I
- on both sides - can be treated as a spectator, as it doesn't take part in the redox reaction itself, iodides react with the produced iodine AFTER redox took place.
What I have proposed was not meant to be the only correct approach. Reaction can be balanced using I
3-, it is just easier to ignore them doing redox.
But if I extract half reaction
I2 > I3-
Extract from what? Iodine was not betwen reactants.
It appears a reduction half reaction just as is
IO3- + I- > I3-
Have you tried to assign oxidation numbers to see if you have reduction or oxidation?