Hydroxide
The hydroxides of the transition metals and post-transition metals usually have the metal in the +2 (M = Mn, Fe, Co, Ni, Cu, Zn) or +3 (M = Fe, Ru, Rh, Ir) oxidation state. None are soluble in water, and many are poorly defined. One complicating feature of the hydroxides is their tendency to undergo further condensation to the oxides, a process called olation. Hydroxides of metals in the +1 oxidation state are also poorly defined or unstable. For example, silver hydroxide Ag(OH) decomposes spontaneously to the oxide (AgO). Copper(I) and gold(I) hydroxides are also unstable, although stable adducts of CuOH and AuOH are known. The polymeric compounds M(OH) and M(OH) are in general prepared by increasing the pH of an aqueous solutions of the corresponding metal cations until the hydroxide precipitates out of solution. On the converse, the hydroxides dissolve in acidic solution. Zinc hydroxide Zn(OH) is amphoteric, forming the tetrahydroxidozincate ion in strongly alkaline solution.
Electrolysed water
The electrolysis occurs in a specially designed reactor which allows the separation of the cathodic and anodic solutions. In this process, hydrogen gas and hydroxide ions can be produced at the cathode, leading to an alkaline solution that consists essentially of sodium hydroxide. At the anode, chloride ions can be oxidized to elemental chlorine, which is present in acidic solution and can be corrosive to metals. If the solution near the anode is acidic then it will contain elemental chlorine, if it is alkaline then it will comprise sodium hydroxide. The key to delivering a powerful sanitising agent is to form hypochlorous acid without elemental chlorine - this occurs at around neutral pH. Hypochlorous is a weak acid and an oxidizing agent. This "acidic electrolyzed water" can be raised in pH by mixing in the desired amount of hydroxide ion solution from the cathode compartment, yielding a solution of Hypochlorous acid (HOCl) and sodium hydroxide (NaOH). A solution whose pH is 7.3 will contain equal concentrations of hypochlorous acid and hypochlorite ion; reducing the pH will shift the balance toward the hypochlorous acid. At a pH between 5.5 and 6.0 approximately 90% of the ions are in the form of hypochlorous acid. In that pH range the disinfectant capability of the solution is more effective than regular sodium hypochlorite (household bleach).