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

1 Answer
Aug 13, 2017

Answer:

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?