Chlorine and the Effect of pH
The most important reaction in the chlorination of
an aqueous solution is the formation of
hypochlorous acid, a form of chlorine very
effective for killing germs. Hypochlorous acid is a
‘weak’ acid, meaning that it tends to undergo
partial dissociation to form a hydrogen ion (H+)
and a hypochlorite ion (OCl-) in a water
environment HOCl tends to dissociate into these
ions.
(5) HOCl H+ + OClIn water between 5 pH and 8.5 pH, the reaction is
incomplete and both species are present to some
degree. Since H+ is one of the ions formed and its
concentration is expressed as pH, changing pH
levels will influence the balance of this reaction
and with it, the availability of hypochlorous acid
for reaction. Therefore, in an aqueous
environment, the water pH will affect the
chemistry of chlorine through its pH sensitivity;
this is important as the pH value increases.