Question

Chlorine is often added as the last step in municipal water treatment. The reason for use of chlorine is

• A. in water, chlorine forms $HCl$, a strong acid; and $HOCl$, an oxidising agent, both of which kill pathogens
• B. as a toxic gas used in World War I, chlorine’s presence deters theft
• C. chlorine is a reducing agent and helps precipitate undesirable heavy metals out of drinking water
• D. chlorine promotes the growth of fungi that produce antibiotics and help sanitize the water

Answer 1

Answer: (A)

Chlorination is the process of adding the element chlorine to water as a method of water purification to make it fit for human consumption as drinking water. Water which has been treated with chlorine is effective in preventing the spread of disease. The use of chlorine has greatly reduced the prevalence of water borne disease as it is effective against almost all bacteria and viruses. Chlorination is also used to sterilise the water in swimming pools and as a disinfection stage in sewage treatment. When chlorine is added to water, hypochlorous and hydrochloric acids form, an oxidising agent and a strong acid, respectively: $Cl_2 +H_2O \rightarrow HClO +HCl$