Chapter 15, Problem 15.141QP

Calcium hypochlorite [Ca(OCl)₂] is used as a disinfectant for swimming pools. When dissolved in water it produces hypochlorous acid:

$\begin{array}{l}{\text{Ca(OCl)}}_{\text{2}}(s)+2{\text{H}}_2\text{O}(l)\stackrel{}{\rightleftharpoons }\\ \text{2HClO}(aq)+\text{Ca(OH}{)}_2(s)\end{array}$

which ionizes as follows:

$\begin{array}{l}\text{HClO}(aq)\stackrel{}{\rightleftharpoons }{H}^{+}(aq)+{\text{ClO}}^{-}(aq)\\ K_{\text{a}}=3.0\times {10}^{-8}\end{array}$

As strong oxidizing agents, both HClO and ClO⁻ can kill bacteria by destroying their cellular components. However, too high a HClO concentration is irritating to the eyes of swimmers and too high a concentration of ClO⁻ will cause the ions to decompose in sunlight. The recommended pH for pool water is 7.8. Calculate the percent of these species present at this pH.