Obviously, this formation of acids affects pH. Explanation of pH. Furthermore, pH is a major factor because HOCl is a weak acid whose undissociated form is 20 to 50 times more effective for killing than is its ion OCl¯ . The free available chlorine for disinfection is both the HOCl and OCl- together. Chlorine, being a very reactive element, will oxidize organic and inorganic matter alike when added to water. Therefore not all of the chlorine added to water will result in the production of free available chlorine. The chlorine demand is the quantity of chlorine that will react with inorganics and organic impurities. Before free available chlorine can be formed, the chlorine demand must be satisfied
The ionization constant for HOCl is
2.5 x 10 at
20C. Cell membranes are rapidly penetrated by HOCl because
lipid structures accept non-polar materials. Passage of OCl¯
is much slower, and this mitigates its killing. Although low pH is
best for disinfection with chlorine, the pH is often adjusted upward
to reduce the chlorine-like odor and because swimmers suffer eye
irritation when the concentration of HOCl is high.