How does pH affect chlorine activity in water treatment?

The impact of pH on chlorine activity is significant, particularly in the context of water treatment disinfection. At a lower pH, the equilibrium shifts toward the formation of hypochlorous acid (HOCl), which is a more effective disinfectant than its counterpart, hypochlorite ion (OCl-). This shift occurs because the dissociation of hypochlorous acid is pH-dependent.

When the pH of water decreases, the concentration of hypochlorous acid increases, enhancing the overall efficacy of chlorine as a disinfectant. This is crucial for effective removal of pathogens and ensuring safe drinking water. Maintaining an optimal pH balance is, therefore, essential for maximizing disinfection performance.

Other options do not accurately describe the relationship between pH and chlorine activity. Higher pH does not result in an increase in hypochlorous acid and would actually decrease its effectiveness. The statement that pH has no effect on chlorine activity is incorrect, as it plays a critical role in determining the form of chlorine present in water. Lastly, while temperature can impact chlorine's disinfection efficiency, suggesting that pH only affects temperature fails to recognize its key role in disinfectant performance.