What components make up free chlorine residual?

What components make up free chlorine residual?

• A. Chloramines
• B. HOCl + OCl⁻
• C. Breakpoint chlorination
• D. CT concept

Answer: (B)

Free chlorine residual is the portion of chlorine in water that remains available to disinfect, and it exists in two chemical forms that are in equilibrium: hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻). The total free chlorine residual is the sum of HOCl and OCl⁻. The balance between these two forms depends on pH: HOCl is the stronger disinfectant and dominates at lower pH, while OCl⁻ becomes more prevalent as pH rises. Together, HOCl and OCl⁻ make up the free chlorine residual. Chloramines are a different type of residual formed when chlorine reacts with ammonia (combined chlorine), not part of free chlorine. Breakpoint chlorination and the CT concept relate to treatment strategy and disinfection calculations, not to the chemical forms of free chlorine.

Free chlorine residual is the portion of chlorine in water that remains available to disinfect, and it exists in two chemical forms that are in equilibrium: hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻). The total free chlorine residual is the sum of HOCl and OCl⁻. The balance between these two forms depends on pH: HOCl is the stronger disinfectant and dominates at lower pH, while OCl⁻ becomes more prevalent as pH rises. Together, HOCl and OCl⁻ make up the free chlorine residual. Chloramines are a different type of residual formed when chlorine reacts with ammonia (combined chlorine), not part of free chlorine. Breakpoint chlorination and the CT concept relate to treatment strategy and disinfection calculations, not to the chemical forms of free chlorine.