During the municipal treatment of water for public consumption, alum, Al_2(SO_4)_3, is add… — JAMB UTME

During the municipal treatment of water for public consumption, alum, $Al_2(SO_4)_3$ , is added to untreated river water. What is the primary chemical function of adding alum in this process?

To cause coagulation and sedimentation of fine suspended impuritiesAnswer
B
To kill disease-causing pathogenic microorganisms in the water
C
To eliminate permanent hardness caused by dissolved calcium salts
D
To neutralize alkaline industrial effluents and adjust pH

Answer

The primary function of adding alum in municipal water treatment is to cause coagulation and sedimentation of fine suspended impurities.

Alum (

Al_2(SO_4)_3

) serves as a coagulating agent during water treatment. It destabilizes colloidal particles suspended in water, allowing them to join together into heavy flocs that settle out easily during sedimentation.

Step-by-Step Solution

Identify the role of alum (

Al_2(SO_4)_3

) in water purification

Alum provides trivalent aluminum ions (

Al^{3+}

) which neutralize the negative surface charges on microscopic suspended particles.

Neutralizing these surface charges causes the tiny particles to clump together into larger, visible aggregates called flocs.

Distinguish coagulation from other treatment stages

The heavy flocs created by coagulation settle to the bottom of sedimentation tanks by gravity.

Disinfection (destroying pathogens) is performed later using chlorine gas or sodium hypochlorite, while softening removes dissolved calcium and magnesium ions.

Key Concept

Coagulation and Flocculation in Municipal Water Treatment

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