During disinfection at large water treatment plants, operators add chlorine gas to water to make hypochlorous...

During disinfection at large water treatment plants, operators add chlorine gas to water to make hypochlorous acid (HOCl is weak acid with pKa = 7.54). In backyard swimming pools, homeowners accomplish disinfection by adding sodium hypochlorite (NaOCl). Predict the qualitative change in pH (up or down) due to (a) adding HOCl to water and (b) adding NaOCl to water. Explain your reasoning based on LeChatelier’s Principle.

Expert Solution

a) adding HOCl to water gives dillution of HOCl.so that,equilibrium shift towards right,that results increase in H+ ions..then pH decreases.

HOCl + H2O <------> H3O+(aq) + OCl^-(aq)

pH of weak acid =1/2(pka-logC)

b) adding NaOCl to water , NaOCl -------------> Na+(aq) + OCl^-(aq)

OCl^-(aq) is strong base,which on hydrolysis gives oH- ions.

OCl^-(aq) + H2O -----> HOCl + OH^-(aq).

here, OH^- increases,pH increases

queen_honey_blossom answered 2 years ago

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