Question

When the pH of the chlorinated water is type 5.5, the predominant constituent in the free available chlorine is:

• A. HOCl
• B. OCl$^-$
• C. both HOCl and OCl$^-$ but predominantly OCl$^-$
• D. both HOCl and OCl$^-$ in almost equal proportions

Hint:

For effective chlorination, the pH of the water should be carefully controlled. At lower pH, HOCl predominates, which is more effective in killing bacteria.

Answer 1

The Correct Option is A

At a pH of 5.5, hypochlorous acid (HOCl) is the predominant constituent of free available chlorine. As the pH increases, the proportion of hypochlorite ion (OCl$^-$) increases. At this specific pH, HOCl is more effective in disinfecting water.