Question

What are lyophilic and lyophobic sols? Give examples of each type. Which of the two types of sol is easily coagulated and why?

Answer 1

Hint: Lyophobic and Lyophilic sols are types of colloids. The term Lyo means liquid and philic means loving. Hence Lyophilic sols are liquid-loving. The term Phobic means hating, hence lyophobic sols are liquid hating sols.

Complete answer:
The colloid can be defined as a mixture in which a soluble or insoluble dispersed particle is suspended in another substance. The colloid consists of two parts: the dispersed particles and the dispersing medium. There are two types of colloids:
Lyophilic colloids: The colloidal system in which the dispersed phase or particles have a very strong affinity towards dispersing medium, is called the lyophilic sol. These sols are reversible in nature and can be very easily made by heating. They are very stable and cannot be easily coagulated. Due to the formation of Hydrogen bonds the affinity of the dispersed phase with the medium is very high. The hydration ability of these sols is very high due to which their viscosity is also higher than the medium. Examples of Lyophilic sols are rubber and starch
Lyophobic colloids: The colloidal system in which the dispersed phase and the dispersing medium has a very little affinity, is known as the lyophobic sol. These sols are irreversible in nature and cannot be easily prepared. They are prepared by special techniques. They are very unstable and can be coagulated easily with the addition of a small amount of electrolyte too. The hydration ability is low and the viscosity is almost the same as that of the medium. Example: Ferric hydroxide in water.
Out of these two types of sols Lyophobic sols are easily coagulated with addition of a small amount of electrolyte. However, Lyophilic sols can also be coagulated if a very high amount of electrolyte is added.

Note:
The irreversible nature of lyophobic sols can be explained due to the adsorption of charge or ions, present in the dispersed particle, that makes it stable. The particles have the same charge and have high coagulating properties. In lyophilic sols, the charge depends on the pH of the medium.