Question

Colloidal particles tend to be electrically charged and when they are dispersed through a liquid dispersion medium, they tend to attract oppositely-charged counter ions or dipoles to their vicinity from the dispersion medium. The parallel layers of charge surrounding the dispersed phase particles is called:

• A. Double layer
• B. Electric double layer
• C. Helmholtz Double layer
• D. Electrokinetic potential
• E. Zeta potential

Answer 1

Answer: (A), (B), (C)

Helmholtz Double layer

We know that colloidal particles tend to be electrically charged and this is because they tend to selectively adsorb either positively or negatively charged ions. Do note that adsorption is a surface phenomenon and the ions give rise to surface charges. In general, the particles of the dispersed phase all carry equal and similar charges and naturally repel each other. Therefore, the particles neither settle down nor aggregate together.
These charged colloidal particles will attract oppositely-charged counter ions or dipoles to their vicinity from the dispersion medium, forming a layer of compensating charge around each particle. The entire assembly is called a Helmholtz electric double layer. It is also called a double layer or an electric double layer. The first layer of adsorbed ions is believed to be firm while the second layer of compensating charges surrounding compensating.
Across the double layer, since we have a charge separation, there arises a potential difference called the electrokinetic potential or zeta potential