What is included in the definition of free chlorine?

The definition of free chlorine encompasses a combination of dissolved chlorine gas, hypochlorous acid, and hypochlorite ion. Free chlorine is a term used to describe the forms of chlorine that are available in the water to disinfect and kill pathogens effectively. Hypochlorous acid is a weak acid that forms when chlorine gas is dissolved in water, and hypochlorite ions are produced when sodium hypochlorite is added. Both of these forms contribute to the overall effectiveness of chlorine as a disinfectant.

The significance of understanding free chlorine lies in how it plays a crucial role in water treatment processes. Monitoring and maintaining an appropriate level of free chlorine is essential for ensuring the water is adequately disinfected and safe for public use. This is particularly important in wastewater treatment, where pathogens need to be eliminated before the effluent can be safely released or reused.

The option that states free chlorine does not exist in water is incorrect, as it implies a misunderstanding of chlorine chemistry in aqueous solutions. Additionally, the choice that refers only to hypochlorite ions is incomplete since it does not account for all the forms of free chlorine present. Finally, the option discussing chlorine combined with organic matter refers to combined chlorine, which is different from free chlorine, as