Question

The combination of two layers of opposite charges around the colloidal particle is called Helmholtz electrical double layer. The potential difference between the fixed layer and the diffused layer of opposite charge is called :

• A. Electrode potential
• B. Zeta potential
• C. Adsorption potential
• D. Diffused potential

Answer 1

The correct option is B Zeta potential

By selective ​adsorption on the surface, a colloids acquire a positive or negative charge. The layer attracts a counter ion from medium to form a second layer​.

The combination of the two layers of opposite charges around the colloidal particle ​is known as Helmholtz electrical double layer​.

Here, the first layer ions is firmly held and second layer of ions is diffused layer​ and it is mobile.

As separation​ of charge ​results in potential, the charge of opposite sign on fixed and diffused part of double layer​ results in a potential difference​ known as Electrokinetic potential or zeta potential.​​

Presence of equal and similar charges on ​colloidal particles is ​largely responsible in providing stability to the colloidal solution.​
The repulsive forces between charged particles​ prevent them from aggregation​.

Examples:
(i) When $FeC{l}_3$ is added to excess of hot water​, a positively charged sol of hydrated ferric oxide is formed.​

(ii) When $FeC{l}_3$ is added​ to $NaOH$ solution​, a negatively charged sol is obtained with adsorption of $O{H}^{-}$ ions.​