An engineer is designing a chlorine contact chamber to disinfect poultry-processing wastes. (Note these wastes are often contaminated with the pathogenic bacteria Salmonella). She can design the system to use chlorine gas (equivalent to using HOCl) or liquid bleach (equivalent to using sodium hypochlorite, NaOCl) as the chlorine source. The total chlorine concentration to be added is 7.1 mg/L as Cl2 (=10^-4 M chlorine). The species HOCl is a much stronger disinfectant than the species OCl-. The pKa for HOCl is 7.54.
A. If chlorine chemistry controls the pH, which system provides more disinfection? (Hint: this problem requires you to calculate equilibrium concentrations of HOCl and OCl- in 10^-4 M HOClo and 10^-4 NaOCl systems.)
B. In a complex waste stream such as this, is the assumption that chlorine chemistry controls the pH reasonable? Why or why not?