Question

The charge on colloidal particles is due to:

• A. Presence of electrolyte
• B. Very small size of particles
• C. Adsorption of ions from the solution
• D. Can't be determined

Hint:

Colloidal charge is crucial in ensuring the stability of dispersions and preventing aggregation.

Answer 1

The Correct Option is C

Step 1: Understanding Colloidal Systems 
Colloidal particles are heterogeneous mixtures with dispersed-phase particles ranging from 1 nm to 1000 nm. 
They exhibit electrical charge, which helps maintain stability by preventing coagulation.
Step 2: Mechanism of Charge Development 
The charge on colloidal particles arises primarily due to the adsorption of ions from the solution.
When a colloidal particle is in contact with a solution, selective adsorption of a particular ion occurs.
Step 3: Examples of Charge Formation 
- If AgI sol is prepared in an excess of KI, the colloidal particles adsorb \( I^- \) ions and acquire a negative charge: \[ AgI + I^- \rightarrow {Negatively charged AgI colloid} \] - If AgI sol is prepared in an excess of AgNO$_3$, the colloidal particles adsorb \( Ag^+ \) ions and acquire a positive charge: \[ AgI + Ag^+ \rightarrow {Positively charged AgI colloid} \] Step 4: Importance of Charge in Colloidal Stability 
- The mutual repulsion between similarly charged colloidal particles prevents coagulation and keeps them dispersed. - Oppositely charged colloids can undergo coagulation (precipitation) when mixed. 
Final Answer: The charge on colloidal particles is due to the adsorption of ions from the solution.