Question

Alums purify muddy water by :

• A. dialysis
• B. absorption
• C. coagulation
• D. forming true solution

Answer 1

The correct option is C

coagulation

Explanation for the correct option

Option C: coagulation

Alum

• Alum is a chemical compound that generally has a hydrated double sulfate salt of aluminum.
• It is represented by the molecular formula $\mathrm{XAl}{\left({\mathrm{SO}}_4\right)}_2.12{\mathrm{H}}_2\mathrm{O}$ where $\mathrm{X}$ denotes a cation which is generally potassium or sodium.

Coagulation

• Coagulation is a process of aggregation or accumulation of colloidal particles to settle down as a precipitate.

Action of alum on muddy water

• Alum removes the charge from the suspended colloid particles in the solution.
• This causes the particles to clump together and settle.
• Hence, the muddy water gets purified.

Hence this option is correct.

Explanation for incorrect options:

Option A: Dialysis

• Dialysis is the process of separating molecules in solution by the difference in their rates of diffusion through a semipermeable membrane, such as dialysis tubing.
• Alum purifies muddy water by the process of coagulation.
• Hence this option is incorrect.

Option B: Absorption

• Absorption is a physical or chemical process in which atoms, molecules, or ions enter a bulk phase.
• Alum purifies muddy water by the process of coagulation.
• Hence this option is incorrect.

Option D: Forming true solution

• A true solution is a mixture of solute and solvent that is homogeneous.
• Filtration cannot separate the solute from the solution in a true solution.
• Alum purifies muddy water by the process of coagulation.
• Hence this option is incorrect.

Hence the correct option is C, coagulation.