Sodium hypochlorite is a chemical compound with the formula NaClO. It is usually called bleach, or liquid chlorine. The disinfection compound in the sodium hypochlorite is hypochlorous acid. Hypochlorous acid (HOCl or HClO) is an acid that is formed when chlorine gas dissolves in water. The hypochlorous acid can not be isolated from sodium hypochlorite solution, because it exists in equilibrium with its precursors. This equilibrium depends on numerous factors. One of the most important factors is pH. The disinfection efficiency of sodium hypochlorite depends on pH of solution. Hypochlorous acid reacts with organic compounds and forms THMs (trihalomethanes). It also reacts with ammonia and forms chloramines, which are used as week secondary disinfectant.