| |
|
|
| |
 |
| Adsorption |
|
| Adsorption is a surface phenomenon. In this process, accumulation or concentration of a substance takes place at the surface or interface as compared to the bulk phases. This happens because the molecules of the bulk phase at the surface are attracted only from below and from the sides as compared to the molecule inside the bulk of the phase. In the interior, molecules experience forces of attraction from all sides. |
| |
 |
| |
| fig 7.1 - Molecules at the surface of a liquid experience a net attraction downward |
| |
| Hence, the molecules at the surface experience a net attraction downward and tend to move towards the interior to increase attractions. On account of the unbalanced forces, the surface of a liquid or solid is in a state of strain. This implies that the surface molecules have higher energy than those present in the interior. So, when the surface of liquid or solid attracts, other molecules, this energy is reduced. In other words, adsorption results in decrease of surface energy. |
| |
| The substance, which accumulates on the surface is called adsorbate and the adsorbing phase is called adsorbent. The process of removal of an adsorbed substance from the surface on which it is adsorbed is called desorption. |
| |
| The phenomenon of adsorption in solid adsorbents is enhanced when finely divided solid particles are used. This is because the surface area increases tremendously with the use of finely divided particles. Very good adsorbents such as charcoal, silica gel, alumina gel and clay have large surface areas due to their porous structures. Similarly, colloids posses enormous surface area per unit mass and are very good adsorbents. |
| |
|
|
| |
|
|
| |
|
|
|
|
|
