Question

Define Lyophilic and Lyophobic colloids with examples. Why is Lyophobic colloids easily coagulated?

Hint:

Lyophilic = solvent-loving (stable); Lyophobic = solvent-hating (easily coagulated by electrolytes).

Answer 1

Step 1: Definition.
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Lyophilic colloids: Colloids in which the dispersed phase has high affinity for the dispersion medium. They are stable and reversible.
Example: Starch sol, Gum, Gelatin.
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Lyophobic colloids: Colloids in which the dispersed phase has little or no affinity for the dispersion medium. They are unstable and irreversible.
Example: Gold sol, Sulphur sol, As$_2$S$_3$ sol.
Step 2: Reason for easy coagulation of lyophobic colloids.
Lyophobic sols are not strongly solvated and lack strong interactions with the solvent. They are stabilized mainly by charges on their particles. When an electrolyte is added, these charges are neutralized, leading to easy coagulation (precipitation).
Conclusion:
Lyophilic sols are stable due to strong solvation, while lyophobic sols are easily coagulated because they rely only on electrostatic stabilization.