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.

Answer 2

Step 1: Understanding Colloidal Particles
Colloidal particles are small particles dispersed in a medium, typically ranging in size from 1 to 1000 nanometers. These particles carry an electric charge, which plays a crucial role in their stability and behavior in the dispersion.

Step 2: Source of Charge on Colloidal Particles
The charge on colloidal particles is not inherent but acquired from the surrounding medium. When colloidal particles are dispersed in a solution, ions from the solution get adsorbed onto the surface of these particles.

Step 3: Adsorption of Ions
Depending on the nature of the colloidal particle and the solution, either positive or negative ions are adsorbed onto the surface. This adsorption leads to the development of a charged layer around the particle, which prevents particles from aggregating by electrostatic repulsion, thus stabilizing the colloid.

Step 4: Final Conclusion
Therefore, the charge on colloidal particles arises primarily due to the adsorption of ions from the solution, which creates an electric double layer around the particles and helps maintain colloidal stability.