How does chlorine interact with pH levels during disinfection?

How does chlorine interact with pH levels during disinfection?

• A. It becomes less effective as pH increases
• B. It becomes more effective as pH increases
• C. pH does not affect chlorine efficacy
• D. It is always effective regardless of pH

Answer: (A)

Chlorine is widely used as a disinfectant in water treatment processes, and its effectiveness is closely related to pH levels. As pH rises, the effectiveness of chlorine decreases. This is primarily because chlorine exists in two forms in water: free chlorine (which includes hypochlorous acid, HOCl, and hypochlorite ion, OCl⁻). At lower pH levels, there is a higher proportion of hypochlorous acid, which is more effective at killing bacteria and other pathogens due to its better ability to penetrate cell membranes. Conversely, as pH increases, the equilibrium shifts toward the hypochlorite ion, which is less effective as a disinfectant. Higher pH levels reduce the overall available active chlorine that is capable of disinfection. Therefore, controlling pH in water treatment processes is crucial to maintaining optimal chlorine efficacy and ensuring effective disinfection. While some may think that chlorine is always effective regardless of pH, or that it becomes more effective with increasing pH, the chemistry of chlorine and its interaction with water demonstrates that pH indeed plays a significant role in its disinfecting capabilities.

Chlorine is widely used as a disinfectant in water treatment processes, and its effectiveness is closely related to pH levels. As pH rises, the effectiveness of chlorine decreases. This is primarily because chlorine exists in two forms in water: free chlorine (which includes hypochlorous acid, HOCl, and hypochlorite ion, OCl⁻). At lower pH levels, there is a higher proportion of hypochlorous acid, which is more effective at killing bacteria and other pathogens due to its better ability to penetrate cell membranes.

Conversely, as pH increases, the equilibrium shifts toward the hypochlorite ion, which is less effective as a disinfectant. Higher pH levels reduce the overall available active chlorine that is capable of disinfection. Therefore, controlling pH in water treatment processes is crucial to maintaining optimal chlorine efficacy and ensuring effective disinfection.

While some may think that chlorine is always effective regardless of pH, or that it becomes more effective with increasing pH, the chemistry of chlorine and its interaction with water demonstrates that pH indeed plays a significant role in its disinfecting capabilities.