Question

Are there actual `H^+` or `H_3O^+` ions in aqueous solution?

Answer 1

It would not be my rationalization.......

Explanation:

Water is a so-called protic solvent, and it can exchange protons with itself, and with other species in solution. We represent this reaction by the so-called autoprotolysis reaction:

`2H_2OrightleftharpoonsH_3O^(+) + HO^-`

Under standard conditions of temperature and pressure, we measure the extent of this equilibrium:

`K_w=[H_3O^+][HO^-]=10^-14`

And taking `log_10` of each side......

`log_10K_w=log_10[H_3O^+] + log_10[HO^-]`, and on rearrangement.....

`-log_10K_w=-log_10[H_3O^+] - log_10[HO^-]=-log_10(10^-14)`,

and thus.....

`14=underbrace(-log_10[H_3O^+])_(pH)-underbrace(-log_10[HO^-])_(pOH)`, i.e. `14=pH+pOH`

So back to your question (finally!), we CONCEIVE of the acidium species in water as `H^+` or `H_3O^+` and represent it like that. The actual acidium species may be a cluster of water molecules with an extra proton, i.e. `H_3O^+`, or `H_5O_2^+`, or `H_7O_3^+`, with the protium ion exchanged between clusters. We happily use `H^+` or `H_3O^+` as labels of convenience.

Are you happy with this treatment?