At a pH of less than 2.0, the Fenton reaction occurs to a very small extent due to the production of complex molecules such as [Fe(H2O)6] 2+ and [H3O2] + [3]. At a pH greater than 4.0, there is significant production of ferric hydroxide precipitate. In acidic solution, Ferric Hydroxide becomes more soluble due to the presence of acid. In neutral and basic solution, however, iron(III) ions react with water to form ferric hydroxide and other iron hydroxides.