How come the oxygens transferred in redox reactions are always the $\ce{O^{2-}}$anion?

For example, I have this set of rules, and the rules are implicitly referring to the $\ce{O^{2-}}$ anion, a potent base (otherwise the rules wouldn't make sense; for example, it makes sense that a base in acidic solution is protonated to water, and that a strong base in basic solution is leveled to hydroxide ion).

In other words, how come, when electrons are transferred, such as in this unbalanced reaction:

$\ce{ClO_{3}^- + 6I^- \leftrightharpoons 3I_2 + Cl^-}$

The $\ce{O^{2-}}$ anion is formed (if only to be consumed again)? I remember my prof would say that specifically 3 $\ce{O^{2-}}$ anions "disappear".

Why not the $\ce{O^{-}}$ anion or simply $\ce{O}$? Does this have to do with stability?

enter image description here


I think you are misunderstanding the meaning of superoxide and the rules.

Superoxide is $\ce{O_2^-}$

Superoxide is NOT $\ce{O^{2-}}$ as you have written.

The rules are referring to hydroxide which is $\ce{OH^-}$, not superoxide.

The reason hydroxide is used to balance equations in basic aqueous solution is:

$\ce{H_2O \leftrightharpoons H^+ + OH^-}$

There is hydroxide present in aqueous solution, but not superoxide, peroxide, hydroxyl radial, etc.

  • $\begingroup$ What's the origin of this hydroxide ion? $\endgroup$ – Dissenter May 30 '14 at 18:40
  • $\begingroup$ water is in equillibrium with hydroxide and hydronium, according to the equillibrium constant $K_w$. The rules are for aqueous solutions. In high pH aqueous solution there is necessarily a high concentration of OH- $\endgroup$ – DavePhD May 30 '14 at 18:42
  • $\begingroup$ But in the case of the chlorate anion, the disappearing oxygen goes where? And the oxygen comes from water? $\endgroup$ – Dissenter May 30 '14 at 18:43
  • $\begingroup$ Well, in acidic conditions this can happen: ClO3− + I− + 2H+ → HOI + HClO2 en.wikipedia.org/wiki/Iodine_clock_reaction, but if you are following the rules, oxygen would go to water or hydroxide depending upon pH $\endgroup$ – DavePhD May 30 '14 at 18:47
  • $\begingroup$ water or hydroxide will form from protons or water and the oxygen of the reactant(s) $\endgroup$ – DavePhD May 30 '14 at 18:52

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.