What pH would chlorinated water have the highest concentration of hypochlorous acid?

Chlorinated water achieves its highest concentration of hypochlorous acid at a pH of around 5. This is due to the chemistry of chlorine in the presence of water. When chlorine is added to water, it partly forms hypochlorous acid (HOCl) and hypochlorite ion (OCl⁻), which are the two main species of chlorine used for disinfection.

At lower pH values, more hypochlorous acid is formed. Specifically, at a pH of 5, the equilibrium favors the formation of hypochlorous acid, making it much more effective as a disinfectant. This is because hypochlorous acid is a neutral molecule, more penetrating and reactive with pathogens, while the hypochlorite ion, which dominates at higher pH levels, is less effective as a sanitizer.

At a neutral pH of 7, there would still be some hypochlorous acid present, but the concentration would be lower compared to pH 5. As the pH increases to around 9, the proportion of hypochlorite ion increases significantly, which diminishes the disinfecting power of chlorinated water because hypochlorite is not as effective as hypochlor