The inactivation of a pathogenic bacterium by HOCl followsChick’s law, i.e. the rate of death is a 1st orderreaction, where the death rate is proportional to the number ofbacteria at any time. 90 % of the pathogen are killed after 5 minfor a constant free chlorine concentration of 2 mg/L (assume lowpH, where all free chlorine is present as HOCl).
a)Â Â Â Â Â Â (9%) Whatis the percent kill after 10 min at the same HOClconcentration?
b)Â Â Â Â Â (8%) Whatpercentage of the free chlorine would be present as HOCl (notOCl-) at pH8 if the pKa for hypochlorous acidis 7.5?
c)Â Â Â Â Â Â (3%) Whyand how would the disinfection time have to change to still achieve90 % kill of the pathogen at pH 8 at the same free chlorineconcentration? (no need to calculate, discuss in terms of order ofmagnitude)
