Free chlorine is often used as a disinfectant for drinking water and can be added to the water by dosing with sodium hypochlorite (NaOCl). HOCl is a much stronger disinfectant than OCl-. When NaOCl is added to water is fully dissociates: NaOCl = Na+ + OCl- and the following reaction is in equilibrium: HOCl = H+ + OCl- pKa = 7.5

(a) What will be the pH of the solution if 1 mmol of NaOCl is added to 1 L of water? (4 marks)

(b) What is the pH at which 50% of the total free chlorine (OCl- + HOCl) is present as HOCl? (1 mark)

(c) What is the pKb for OCl- and to what reaction does this constant apply? (1 mark)