JAMB 2012 Chemistry · Question 20

Chlorination of water for town supply is carried out to

Options

A.make the water colourless
B.remove germs from the water
C.make the water tastedful
D.remove odour from the water

Answer: B. remove germs from the water

Explanation written with AI and checked against the answer key

Analyze the question: It asks why chlorine is added to water meant for town (public) supply.

Explain the concept: Water treatment has several stages:

Sedimentation and coagulation (using alum) remove suspended particles.
Filtration removes the remaining solids.
Chlorination is the final stage. Chlorine is a strong oxidising and disinfecting agent. It reacts with water to form hypochlorous acid:

Cl₂ + H₂O → HCl + HOCl

HOCl kills disease-causing microorganisms such as bacteria, viruses and other germs. This helps prevent waterborne diseases like cholera, typhoid and dysentery.

Evaluate the options:

A. Make the water colourless: Colour is mainly removed by coagulation and filtration, not chlorination. Wrong.
B. Remove germs from the water: This is the main purpose of chlorination, which is disinfection. Correct.
C. Make the water tasteful: Chlorine does not improve taste, and it can even leave a slight taste. Wrong.
D. Remove odour from the water: Odour is removed by aeration or activated charcoal. Chlorine is not used mainly for this. Wrong.

Answer: The correct option is B.

Exam tip: Link each treatment step to its job:

Alum → coagulation (removes suspended particles)
Filtration → removes solids
Charcoal or aeration → removes odour and taste
Chlorine → kills germs

If you see "chlorine" and "water supply" together, think "germs".

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