Question

Why do we add alum to purify water?
NCERT Class XII
Chemistry - Exemplar Problems
Chapter 5. Surface Chemistry

Answer 1

Alum, when added to raw water reacts with the bicarbonate alkalinities present in water and forms a gelatinous precipitate. This floc attracts other fine particles and suspended material in raw water, and settles down at the bottom of the container.

Answer 2

Aluminium sulfate, shortly known as alum,when added to raw water reacts with the bicarbonate alkalinities presents in water and forms a gelatinous precipitate.this floc attracts other fine particles and suspended material in raw water,and Settles down at the bottom of the container. It also destroy the germs present in water. It removes dust particle from water.
In water treatment plant, it is very useful for purification of water for treatment of water.

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