As the Haber–Weiss reaction depends on the presence of both Fe and Fe in solution, its kinetics is influenced by the respective solubilities of both species whose are directly function of the solution pH. As Fe is about 100 times less soluble than Fe in natural waters at near-neutral pH, the ferric ion concentration is the limiting factor for the reaction rate. The reaction can only proceed with a fast enough rate under sufficiently acidic conditions. At high pH, under alkaline conditions, the reaction considerably slows down because of the precipitation of Fe(OH) which notably lowers the concentration of the Fe species in solution.
Moreover, the pH value also directly influences the acid-base dissociation equilibrium involving the hydroperoxyl and the superoxide radicals (pK = 4.7) as mentioned above.