Question

Alums purify muddy water by:
A. Dialysis
B. Absorption
C. Coagulation
D. Forming true solution

Answer 1

Hint: Alum is a type of chemical compound which generally have a hydrated double sulfate salt of aluminum and represented by the molecular formula \[XAl{{(S{{O}_{4}})}_{2}}.12{{H}_{2}}O\] where X denotes the monovalent cation which generally is potassium or aluminium. Alum is generally known to be a potassium alum or potash alum.

Complete Answer: The name alum is also used generally for salts having the same formula and structure the only change is aluminum is replaced by another trivalent metal ion such as by chromium ion and sulfur is replaced by another chalcogen called selenium and commonly known by the name chrome alum representing by the formula \[KCr{{(S{{O}_{4}})}_{2}}.12{{H}_{2}}O\] .
Alum is generally used to purify muddy water. This type of process is done by the process called coagulation in which stability of the lyophobic sols is due to presence of charge on colloidal particles. Lyophobic sols are those sols in which the dispersed phase particles have no affinity or we can say that there is no bond for the dispersion medium and these are generally irreversible in nature. If charge is removed then particles come together and settle down. Spontaneous destabilization of solution is ageing and destabilization of solution by artificial means is called coagulation. Thus we can say that alums purify muddy water by coagulation.

Option C is the correct answer.

Note: Colloids can be defined as a mixture where one of the substances is split into very tiny particles which are dispersed throughout a second substance. These tiny particles are known as colloidal particles. In another way we can also say that colloids are basically solutions in which solute particle size ranges from 1nm – 1000 nm and these are generally heterogeneous in nature.