Question

What is peptization?

Hint:

Peptization = conversion of precipitate → colloidal sol by electrolyte. The electrolyte ions stabilize the colloid.

Answer 1

Step 1: Definition.
Peptization is the process of converting a freshly precipitated substance (precipitate) into colloidal particles by adding a small amount of suitable electrolyte.
Step 2: Mechanism.
During peptization, the ions of the added electrolyte adsorb on the surface of precipitate particles. This develops an electric charge on the particles and prevents them from coagulating, leading to formation of a stable colloidal sol.
Step 3: Example.
When freshly prepared ferric hydroxide (\(Fe(OH)_3\)) precipitate is treated with a small amount of ferric chloride (\(FeCl_3\)) solution, a reddish brown colloidal sol of ferric hydroxide is formed.
\[ Fe(OH)_3 \text{ (ppt)} + Fe^{3+} \rightarrow Fe(OH)_3 \text{ (sol)} \] Step 4: Importance.
Peptization helps in obtaining colloidal solutions from precipitates without complete dissolution.