In order to obtain a free residual of chlorine of 0.5 mg/L, a dose of 10 mg/L is added to a 36400 m3 /day water treatment plant. NB It is common practice to apply Cl2:NH3 dosage ratios of 3:1 (i) Calculate the amount of Cl2 and NH3 required to achieve this. (8) (ii) Explain why it is sometimes necessary to add ammonia during the disinfection process and what is the reasoning behind using a 3:1 Cl2:NH3 dosage ratio (6) d. Chlorine usage in a 20 000 m3 /day treatment plant is 8 kg. The residual after 10 min contact time is 0.15 mg/L. What is the chlorine demand of the water? (4) e. The graph below shows the log-concentration diagram of a system containing 5 x 10-4 M NH3 and an unknown amount of Sodium hypochlorite. Determine. i. The unknown species A to F (6) ii. The sodium concentration (2) iii. The pH (2) iv. In a similar system, the NH3 is substituted with 2.5 x10-4 M NH4Cl and 2.5 x10-4 M NH3 Will the log-concentration diagram shift? If so, how