Question

Alum helps in purifying water by
(a) forming silicon complex with clay particles
(b) sulphate part which combines with the dirt and removes it
(c) coagulating the mud particles
(d) making mud water soluble

Answer 1

Hint: Alum is a type of compound which has very application in daily life which we can find in the grocery store for pickling and in the baking powder. It is also used in leather tanning as an ingredient in the aftershave and in the treatment of fire-proof textiles.

Complete step by step solution:
To understand how does alum help us to purify water we have to understand what alum is and some important information about it.
Alum is referred for a group of hydrated double salts usually consisting of aluminium sulfate, water and other elements. a series of hydrated double salts result from the hydration of the sulphate of a singly charged cation and the sulfate of any one of the triply charged cations. Aluminium sulfate can thus form alum with the sulfates of the singly charged cation and the sulfate of triply charged cations.
Aluminium sulfate can thus form alum with sulfates of singly charged cations of potassium, sodium, ammonium etc. and with the sulfates of triply charged cations of iron, chromium, manganese and other metals. Alum helps in purifying water by aluminium which helps in the coagulation of mud particles. Because of the high charge on the aluminium ion it helps the small particles of suspended solids to group together.

Hence the correct answer is option (C) i.e. Alum helps in purifying water by coagulating the mud particles.

Note: Remember that the alum is a type of chemical compound usually a hydrated double sulphur salt. Alum often refers to potassium alum. Other alums are named after the monovalent ions like sodium alum and the aluminium alum.