JEE Main 2021 · 27 August · evening · Single correct · +4 / −1
Lyophilic sols are more stable than lyophobic sols because :
- (a) there is a strong electrostatic repulsion between the negatively charged colloidal particles.
- (b) the colloidal particles have positive charge.
- (c) the colloidal particles have no charge.
- (d) the colloidal particles are solvated.
Answer and solution
Answer (d) the colloidal particles are solvated.
Solution
Chemistry ma’am · 4 steps
Lyophilic means solvent-loving: each particle wraps itself in a coat of solvent, and that coat keeps it safe.
- Two sources of stability. A colloidal particle can be kept from clumping by its charge, which makes particles repel each other, and by solvation, a layer of solvent molecules held tightly around it.
- Lyophobic sols. Particles such as gold or As₂S₃ do not attract the solvent, so charge is their only protection. Add a little electrolyte, the charge is neutralised, and the sol coagulates. Once settled, it cannot be turned back into a sol by adding solvent.
- Lyophilic sols. Particles such as starch, gum or gelatin attract the solvent strongly. Even if their charge is removed, the solvent layer keeps them apart, so a large amount of electrolyte is needed to coagulate them. They are also reversible.
- So. The extra stability comes from the solvent layer, not from the sign or size of the charge. The answer is (d): the colloidal particles are solvated.
The idea to keep. Lyophobic sols depend on charge alone. Lyophilic sols have charge and solvation, so removing the charge is not enough to make them coagulate.
Answer from the NTA final answer key. Solution by PrepWiser.