Solution (a): Differences between Lyophilic and Lyophobic Sols
Step 1 (Definition and Basis of Classification): [1 Mark]
The classification is based on the affinity between the dispersed phase and the dispersion medium. Lyophilic sols are "liquid-loving," while Lyophobic sols are "liquid-hating."
Step 2 (Comparative Analysis): [1 Mark]
- Lyophilic Sols: These are reversible sols. They are self-stabilized due to strong forces of interaction between the dispersed phase and the dispersion medium.
- Lyophobic Sols: These are irreversible sols. They are unstable and require stabilizing agents (electrolytes) to prevent coagulation.
Step 3 (Final Tabular Distinction): [1 Mark]
| Property | Lyophilic Sol | Lyophobic Sol |
|---|---|---|
| Preparation | Directly formed by mixing with the medium. | Prepared by special methods only. |
| Stability | Quite stable. | Less stable; easily coagulated. |
| Viscosity | Much higher than that of the medium. | Same as that of the medium. |
Solution (b): Conceptual Questions
(i) Dispersed Phase and Dispersion Medium of Milk: [1 Mark]
Step 1 (Identification): Milk is an emulsion of liquid in liquid.
Step 2 (Classification): Dispersed Phase = Fat; Dispersion Medium = Water.
(ii) Cause of Brownian Movement: [1 Mark]
Step 1 (Governing Principle): Brownian movement is the continuous zig-zag motion of colloidal particles.
Step 2 (Mechanism): It is caused by the unbalanced, continuous bombardment of the colloidal particles by the molecules of the dispersion medium, which are in constant thermal motion.
(iii) Temperature Effect on Physisorption: [1 Mark]
Step 1 (Governing Law): Physisorption is an exothermic process governed by the equilibrium: $$\text{Gas} + \text{Solid} \rightleftharpoons \text{Gas-Solid Adsorbate} + \text{Heat}$$
Step 2 (Le Chatelier's Principle): According to Le Chatelier's principle, increasing the temperature shifts the equilibrium in the backward direction (endothermic direction) to absorb the excess heat, thereby decreasing the amount of gas adsorbed.
💡 EL10 Concept Insight:
Think of physisorption like a weak magnet sticking to a fridge; if you heat it up, the molecules start vibrating so wildly that they "shake off" the surface, which is why adsorption drops as things get hotter!