At what pH does the highest concentration of hypochlorous acid occur?

The highest concentration of hypochlorous acid occurs at a pH of around 4 to 5. This is because hypochlorous acid (HOCl) is the active form of chlorine used in disinfection processes in water treatment. It can exist in equilibrium with hypochlorite ion (OCl-) depending on the pH of the water.

At lower pH levels, specifically around pH 4 to 5, the concentration of hypochlorous acid is maximized due to its lower tendency to dissociate into the hypochlorite ion. As pH increases above 7, the balance shifts in favor of the hypochlorite ion, which is less effective as a disinfectant compared to hypochlorous acid. Therefore, being aware of pH levels is crucial in water treatment operations to ensure effective disinfection.

In summary, control of pH is essential to optimize the presence of hypochlorous acid, which is a key factor in ensuring effective chlorination in water treatment practices.