[H3O+] is just the same with [H+]. There are quite a few
relationships between [H+] and [OH−]
ions. And because there is a large range of number between 10 to 10-15
M, the pH is used. pH = -log[H+] and pOH = -log[OH−]. In aqueous solutions, [H+
][OH- ] = 10-14.
