Q1 Chlorine disinfection Chlorine is one of the most commonly used disinfectants for water disinfection. Chlorine can be applied for the inactivation of most microorganisms and it is relatively cheap. Gaseous dichlorine (Cl) is commercially available and mostly used in disinfecting drinking water. (a) elilorine (i) To which family of the periodic table does Chlorine belong? [1] (ji) Chlorine has seven electrons on its valence shell. How many covalent bonds can it form? What does this mean it in terms of its chemieal reactivity? [3] [3] (b) When Cl2 is added to water, it hydrolyses to form the molecule HOCL. HOCl is the acid in the acid-base couple HOCVOCI. (i) What is the expression of log[HOC]loaT as a function of pH and pK ? [5] (ii) Reproduce Figure 1 and indicate which of the two curves is HOCl and which is OCl : Briefly explain your answer. [2] (iii) Estimate the value of pKA for the acid-base couple HOCUOCT tasing Figure 1 and briefly explain your answer. [2] Finure 1 Speclation of Chiorinn rpecies in fanctisn of ;ar (c) The disinfection power of the acid HOCl is 88 times better than that of its conjugated base OCl : (i) What is the value of [HOCl][OCC] for pH=6 ? And for pH=9.5 ? [3] (ii) Is disinfection more efficient at pH=6 or pH=9.5 ? Explain. [2] (d) Ammonia is a common contaminant in wastewaters. It reacts with HOCl to form monochloramine (NH2Cl) according to the equation: NH+HOClNH2Cl+H2O(Reaction1) The rate law for this reaction is: dtd[NH3]=k[HOCl][NH3] (i) What is the total order of the reaction? What is the order in respect to [NH] ]? [2] (ii) If [HOCl] is held constant and equals to 3104M, and k=5.1106L (mole.s), calculate the time required to reduce the concentration of NH3 by 4 . [5] Continued overleaf