Question

Define the following terms giving an example of each:
(A) Associated colloids.
(B) Lyophilic sol.
(C) Adsorption.

Answer 1

Hint: We know that in colloidal state of matter, size of the particles ranges from $ 1 $ nm to $ 100 $ nm ( $ {{10}^{-9}} $ to $ {{10}^{-7}} $ m). Colloidal particles can pass through filter paper but not through plasma or animal membrane. In a colloidal system, the substance which is distributed in a medium in the form of colloidal particles is called the dispersed phase and the medium in which it is dispersed is called the dispersion medium.

Complete step by step solution:
Associated colloids: Substances when dissolved in a medium at low concentrations behave as normal electrolytes but at higher concentration aggregate to form particles which have sizes in the colloidal range are called associated colloids. The narrow concentration range over which the physicochemical properties of particles change due to the formation of oriented colloidal aggregates is called critical micelle concentration (CMC) and the aggregates formed are called micelles. For example: surface active agents like soaps and detergents. The formation of micelle takes place at a particular temperature called Kraft temperature $ {{T}_{k}}. $
Lyophilic colloid: Various substances when dissolved in suitable dispersion medium form colloids. The colloids formed are classified into lyophilic and lyophobic colloids. Lyophilic means liquid loving. Substances which when mixed with a suitable liquid as dispersion medium directly result in the formation of the colloidal sol (sols have solid dispersed phase and liquid dispersion medium) are called lyophilic colloids. For example, organic substances like gum, starch, rubber, gelatin, etc. The colloidal sol formed is called lyophilic sol. They are also called intrinsic colloids as they form colloidal sol directly. Lyophilic sols are reversible in nature, i.e. if the dispersed phase and dispersion medium are separated, the sol can be formed by remixing the dispersed phase with the dispersion medium. These colloid sols are stable and cannot be coagulated or precipitated easily.
Adsorption: Adsorption is the surface phenomenon whereas absorption is the bulk phenomenon. In adsorption, the adsorbate molecules remain on the surface of the adsorbent. On the other hand, in absorption, the adsorbate molecules penetrate the bulk of the adsorbent. Water on silica gel is an example of adsorption. Water molecules remain on the surface of silica gel. Water molecules do not enter the bulk of silica gel. During absorption, the adsorbate molecules penetrate the bulk of the adsorbent. Water on calcium chloride is an example of absorption. This is because water is added to the calcium carbonate; water goes in the bulk of the calcium carbonate.

Note:
Remember that absorption is an endothermic process. Heat energy is absorbed during absorption. Adsorption is an exothermic process. Heat energy is given out during adsorption. During absorption, the concentration is uniform throughout, whereas during adsorption, the concentration at the surface is much higher than the concentration in the bulk.