Which of the following is included in free residual chlorine?

Free residual chlorine consists of the chlorine in water that is available for disinfection and includes both molecular chlorine and hypochlorous acid. Molecular chlorine (Cl2) is the gaseous form of chlorine that can dissolve in water to form a mixture of hypochlorous acid (HOCl) and hypochlorite ions (OCl-). Hypochlorous acid is a weak acid that is a potent disinfectant, making it a significant component of free residual chlorine.

Understanding the composition of free residual chlorine is crucial because it impacts water quality and disinfection efficacy. The presence of molecular chlorine and hypochlorous acid indicates that there is effective chlorine available to inactivate pathogens and bacteria in drinking water systems. This is essential for maintaining safe drinking water and preventing waterborne diseases.

In contrast, dissolved organic substances, combined residual chloramines, and suspended mineral substances do not constitute free residual chlorine. Dissolved organic substances can react with chlorine, potentially leading to the formation of disinfection by-products rather than serving as a direct disinfectant themselves. Combined residual chloramines refer to chloramines that result from the reaction between chlorine and ammonia, which are part of the combined chlorine, not the free chlorine. Suspended mineral substances do not contain chlorine