The disinfecting action of chlorine during chlorination is mainly due to the action of: September 2011

Ans. C: Hypochlorous acid During chlorination of water, hypochlorous acid (HOC1) has main role in disinfection Chlorination of water When chlorine is added to water, it reacts to form a pH dependent equilibrium mixture of chlorine, hypochlorous acid and hydrochloric acid: C12 + H20 HOC1 + HC1 Depending on the pH, hypochlorous acid paly dissociates to hydrogen and hypochlorite ions: HOC1 H+ + C10- In acidic solution, the major species are C12 and HOC1 while in alkaline solution effectively only C10- is present. Very small concentrations of C102-, 0103-, C104- are also found Disinfection by chlorination can be problematic, in some circumstances. Chlorine can react with naturally occurring organic compounds found in the water supply to produce compounds known as disinfection byproducts (DBPs). The most common DBPs are trihalomethanes (THMs) and haloacetic acids (HAAS). Due to the potential carcinogenicity of these compounds, drinking water regulations across the developed world require regular monitoring of the concentration of these compounds in the distribution systems of municipal water systems. There are also other concerns regarding chlorine, including its volatile nature which causes it to disappear too quickly from the water system, and aesthetic concerns such as taste and odour.