Careful experiment established the following equilibrium in aqueous solution:
H2O⇌H++HO−
Which has an alternative representation:
2H2O⇌H3O++HO−
Kw=[H3O+][HO−]=10−14 under standard conditions.......
So what is the acidium ion? As far as anyone knows it is a cluster of 3 or 4 or so water molecules with an extra H+, to give, say...........
H7O+3 or H9O+4; the extra H+ can tunnel between clusters of water molecules VERY rapdidly - think of a maul when you play rugby.
When acids are added to water solvent, we conceive that the acid protonates the solvent to give hydronium ions:
HX(aq)+H2O(l)⇌H3O++X−
The H3O+ ion, the hydronium ion is thus a conceptual species, but this conception allows us to solve quantitative problems in stoichiometry. We write H+ or H3O+ as a shorthand. The completion of the equilibrium, i.e. how far to OUR right as we read the page, is a measure of the strength of the acid. For strong acids, HClO4, H2SO4, HX (X≠F), the equilibrium lies almost entirely to the right.
