What is produced when chlorine is added to water, primarily?

When chlorine is added to water, the primary compound produced is hypochlorous acid (HOCl). This reaction occurs as chlorine gas (Cl2) dissolves in water, where it can react with water molecules. The dissociation of chlorine in water predominantly leads to the formation of HOCl, which is a powerful disinfectant used in water treatment processes.

HOCl is effective at killing bacteria, viruses, and other pathogens, making it essential for maintaining safe drinking water and sanitation in various settings. The pH of the water can influence the equilibrium between HOCl and its dissociated form, hypochlorite ion (OCl-). At lower pH levels, HOCl predominates, while at higher pH levels, more OCl- is present.

While chlorine gas and hydrochloric acid (HCl) can be associated with the chlorination process, chlorine gas is not a product of this reaction under typical conditions, and HCl is a byproduct that is usually present only in small amounts. Ozone is another powerful disinfectant but is not produced directly from the chlorination of water. Thus, the formation of HOCl is the primary and most important outcome of adding chlorine to water in disinfection processes.