Question

Municipality officials use chlorine in water purification. Why?
A.Chlorine cleans water
B.Chlorine helps water to cool easily
C.Chlorine coagulates mud particles
D.Chlorine kills harmful bacteria

Answer 1

Here, we are asked to find out the reason for which chlorine is used in purification of municipal water. Purified water is an important requirement for drinking and household purposes. Bleaching powder is an inorganic commercial product used for the disinfection of water.

Complete answer:
Chlorine effectively kills a wide range of harmful microorganisms capable of causing water-borne diseases such as typhoid fever, cholera, dysentery etc. Chlorine and chlorine-based compounds have proven to be beneficial in killing water-borne pathogens at the water treatment plant and maintaining a safe supply of disinfected water to flow to residential areas through public taps and consumers’ taps in houses.
Chlorine is a well-known powerful oxidiser used in house-hold bleaches. Since chlorine is a pungent smelling, toxic and corrosive gas, it cannot be stored in that form and used. So, bleaching agents are prepared as a formulation containing chloramine or hypochlorite which releases chlorine gas upon decomposition. The commercially used ‘Bleaching powder’ is a formulation containing calcium hypochlorite.
Calcium hypochlorite or calcium oxychloride is prepared by the action of chlorine gas on calcium hydroxide, commonly known as slaked lime.
${{Ca}}{\left( {{{OH}}} \right)_2} + {{ C}}{{{l}}_2}{{ }} \to {{CaOC}}{{{l}}_{2{{ }}}}{{ + }}{{{H}}_2}{{O}}$
On decomposition, it liberates oxygen. It is therefore a very good oxidising agent and is used in various industries as an oxidising agent. The decomposition of bleaching powder can be depicted as:
$2{{CaOC}}{{{l}}_2} \to {{ }}2{{CaC}}{{{l}}_2}{{ }} + {{ }}{{{O}}_2}$

Hence, option (D) chlorine kills harmful bacteria is the correct answer.

Additional information:
-Uses of bleaching powder
-To disinfect municipal and drinking water supply.
-To bleach wood pulp in paper industries.
-To manufacture chloroform.
-To bleach cotton and linen in textile industries.

Note:
Chlorination of water to purify the water we get in our homes has been an age-old practice due to some very distinct properties of chlorine. It is done by using bleaching powder which is manufactured by the reaction of slaked lime with chlorine gas.