# electrolysis of aqueous zinc nitrate

Can anyone explain why in the electrolysis of aqueous solutions such as zinc nitrate, the oxidation half equation shows hydroxide ions forming oxygen and water - can this half equation be balanced producing oxygen and hydrogen ions - if not why not?

• Indeed it can. It might even be more appropriate that way. Also, welcome to Chem.SE. – Ivan Neretin Mar 7 '16 at 6:27

You mean, why we write $\ce{4OH- -> O2 + 2H2O + 4e-}$ and not $\ce{4H2O -> O2 + 4H+ + 4e-}$?
Indeed, you may find both these reactions in the table of standard electrode potentials (at $E^0=+0.401$ and $+1.229$, correspondingly; also, note the reversed direction). In some sense, the second equation may even be considered more appropriate, since $\ce{H+}$ is a more abundant species in the solution than $\ce{OH-}$ (zinc salts would produce slightly acidic solutions due to hydrolysis).
But the first reaction was chosen not without reason. See, when we electrolyze something, it is anions that rush to the anode to get oxidized. Water molecules are neutral; electric field would not drag them in either direction. So this might be the reason why the equation is written this way, even if the amount of $\ce{OH-}$ is minuscule and the overall reaction looks more like the second one.
• That's out of question. There is no such thing as H, to begin with. If you mean $\ce{H2}$, then it is still impossible. You just can't have both oxidation and reduction in one half-reaction. – Ivan Neretin Mar 8 '16 at 20:32