Explain how the hydronium and the hydroxide ions are formed?

Question

Water that has a pH of 7 has an equal amount of H3O+ ions and OH- ions.

Answer 1

The hydronium ion H3O⁺ and the hydroxide ion, OH^- are formed from water (H₂O).  When H₂O auto-ionizes you get H⁺ and OH^- but if you have TWO molecules of H₂O, the H⁺ from one H₂O molecule combines with the other H₂O molecule to produce H₃O⁺ and OH^-.  Thus, you can write this as 2H₂O ==> H₃O⁺ + OH^-

 

Since the ionization constant (Kw) for water is 1x10^-14, you can also wrote Kw = 1x10^-14 = [H3O+][OH-] and [H3O+] = [OH-] = 1x10^-7. Because pH is the negative log of [H3O+], this will have a pH = 7 when [H3O+] = [OH-].