Hydroxide
The solubility in water of the other hydroxides in this group increases with increasing atomic number. Magnesium hydroxide Mg(OH) is a strong base (up to the limit of its solubility, which is very low in pure water), as are the hydroxides of the heavier alkaline earths: calcium hydroxide, strontium hydroxide, and barium hydroxide. A solution or suspension of calcium hydroxide is known as limewater and can be used to test for the weak acid carbon dioxide. The reaction Ca(OH) + CO Ca + + OH illustrates the basicity of calcium hydroxide. Soda lime, which is a mixture of the strong bases NaOH and KOH with Ca(OH), is used as a CO absorbent.
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).