Is it preferable to balance redox equations with $\ce{H+}$ or $\ce{H3O+}$? I think the latter, because first, the bare hydrogen proton doesn't exist in water solution. So why write down something we know not to exist?

I ask because in this problem, if we balance using both species, $\ce{H^+}$ and $\ce{H3O+}$, we achieve two different equations. Mass is conserved in both equations as well as charge; all the differs is one coefficient.

So are the two equations equivalent in that they are still describing the same reaction? I think so, because sometimes I see textbook authors write these two equations for $K_\mathrm{w}$:

$$\ce{H2O <=> H+ + OH-}$$

$$\ce{2H2O <=> H3O+ + OH-}$$

However, if we were actually going to run an experiment and needed exact quantities, we would probably prefer the second reaction both above and below because the coefficients in these reactions better represent the chemistry of the system right?

For example, which of the following is "better"?

$\ce{ClO_{3}^- + 6I^- + 6H^+ \leftrightharpoons 3I_2 + Cl^- + 3H_2O}$

$\ce{ClO_{3}^- + 6I^- + 6H_3^+O \leftrightharpoons 3I_2 + Cl^- + 9H_2O}$

  • 1
    $\begingroup$ traditionally it is balanced with $H^+$ $\endgroup$
    – permeakra
    May 30 '14 at 17:06

This is a question of "style" so there is no correct answer. In fact, just as $\ce{H^+}$ doesn't really exist in solution, neither does $\ce{H3O+}$ exist in solution. In reality higher hydrates of $\ce{H^+}$ are what exist in solution. See the first paragraph in this Wikipedia article. Again, both $\ce{H^+}$ and $\ce{H3O+}$ are just shorthand notations for reality, choose the style that you like best.

  • $\begingroup$ I agree; but H3O+ is probably a closer representation of reality than H+ (H+ is Coulombically unlikely - even more so than H3O+). $\endgroup$
    – Dissenter
    May 30 '14 at 17:10
  • $\begingroup$ Yes, $\ce{H3O^+}$ is a closer representation of reality and so if "that" is important to you, then you would use $\ce{H3O^+}$. However, I could imagine someone else arguing that neither $\ce{H^+}$ or $\ce{H3O^+}$ is correct, so using fewer keystrokes and having a "cleaner, simpler" equation is what's important to me. $\endgroup$
    – ron
    May 30 '14 at 17:16
  • $\begingroup$ I guess writing the latter with a discussion of Coulomb's law and higher hydrates also serves pedagogical purposes. $\endgroup$
    – Dissenter
    May 30 '14 at 17:28
  • $\begingroup$ What is wrong with $H_3O^{+}$? The first paragraph of that Wikipedia article you listed, does say anything about that. $\endgroup$
    – Jori
    May 30 '14 at 17:31
  • $\begingroup$ Nothing is "wrong" with $\ce{H3O+}$, but one needs to keep in mind that is a shorthand notation often used to describe reality, but it is not real itself, As the Wkipedia link says, "The reality is far more complicated, as a proton is bound to several molecules of water, such that other descriptions such as H5O2+, H7O3+ and H9O4+ are increasingly accurate descriptions of the environment of a proton in water." $\endgroup$
    – ron
    May 30 '14 at 18:35

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