Question

Alums used for purifying water are chemically:

• A. double chlorides
• B. double sulphates
• C. sulphates of aluminium
• D. hydrated nitrates

Answer 1

Answer: (B)

double sulphates

Aluminium Sulfate, Shortly known as 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.

An alum is a type of chemical compound, usually a hydrated double sulfate salt of aluminium.

Hence option B is correct answer.