Explain the existence of hydronium ion in aqueous solution.

1.	Explain the existence of hydronium ion in aqueous solution.
Answer» Solution :Hydrogen ion `(H^+)` by itself is a bare (i) PROTON with very small size (~`10^(-15)`m radius) (ii) proton intense ELECTRIC field. So, proton binds itself with the water molecule at one of the two available LONE pairs on it by coordinate bond and giving `H_2O^+`. This hydronium ion is `H_3O^+`SPECIES and contain trigonal pyramidal geometry. This `H_3O^+` species has been detected in many compounds like `H_3O^(+)Cl^-`in solid state. Similarly the hydroxyl ion is hydrated to give several ionic species like `H_5O_2^(+), H_7O_3^(+) , H_9O_4^(+)` etc. `H_2O overset(H^+)to H_3O_((aq))^(+) overset(+H_2O)to H_5O_2^+ overset(+H_2O)to H_7O_(3(aq))^(+) overset(+H_2O)to H_9O_(4(aq))^(+)` So, proton does not exist independent in aqueous solution, but it exist as hydronium ion or oxonium ion.

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