Preparation of Colloidal Sols

Formula / Core Reaction:

$$\text{FeCl}_3(aq) + 3\text{H}_2\text{O}(l) \xrightarrow{\text{Boiling } \text{H}_2\text{O}} \text{Fe(OH)}_3 (\text{sol}) + 3\text{HCl}(aq)$$

Concept: Lyophilic sols (egg albumin, starch) form spontaneously upon direct mixing/heating with water due to high solvation affinity. Lyophobic sols (e.g., ferric hydroxide sol) require chemical methods such as hydrolysis of $$\text{FeCl}_3$$ in boiling water, followed by adsorption of $$\text{Fe}^{3+}$$ ions to stabilize the charged colloid.

Notation / Key Observation:

• Lyophilic Sol: Stable, reversible, heavily hydrated particles;
• Lyophobic Sol ($$\text{Fe(OH)}_3$$): Irreversible, positively charged sol ($$[\text{Fe(OH)}_3]\text{Fe}^{3+}$$) requiring stabilizing electrolytes.