JEE Main 2023 · 13 April · morning · Single correct · +4 / −1
What happens when a lyophilic sol is added to a lyophobic sol?
- (a) Film of lyophobic sol is formed over lyophilic sol.
- (b) Lyophilic sol is dispersed in lyophobic sol.
- (c) Film of lyophilic sol is formed over lyophobic sol.
- (d) Lyophobic sol is coagulated
Answer and solution
Answer (c) Film of lyophilic sol is formed over lyophobic sol.
Solution
Chemistry ma’am · 4 steps
The lyophilic sol coats each lyophobic particle like a raincoat, so the sol is protected.
- Two kinds of sol. A lyophobic sol, like gold or Fe(OH)₃ sol, has particles with little attraction for the medium, so a small amount of electrolyte coagulates it. A lyophilic sol, like gelatin or starch, has particles strongly solvated by the medium, so it is very stable.
- Lyophilic coat forms. When the two are mixed, the lyophilic particles form a thin layer around each lyophobic particle. The lyophobic particle is now surrounded by a solvated coat.
- Why this protects. Electrolyte ions can no longer reach the lyophobic particle to neutralise its charge, so it does not coagulate. This is why lyophilic sols are called protective colloids, and their strength is measured by the gold number.
- So. A film of lyophilic sol forms over the lyophobic sol, which is option (c).
The idea to keep. A lyophilic sol is a protective colloid: it wraps the lyophobic particles and shields them from electrolytes. The smaller the gold number, the better the protection.
Answer from the NTA final answer key. Solution by PrepWiser.