First of all - it goes in low pH, so not OH-
produced, but H+
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 I3-
. Note, that you final reaction (while incorrect in terms of H+
) can be rewritten as
O + IO3-
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 I3-
, 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?