In this article we will discuss about:- 1. Definition of Adsorption 2. Characteristics of Adsorption 3. Principles Governing 4. Importance 5. Arrangement of Molecules at an Interface.
Definition of Adsorption:
The process of taking up substances from solution on surface is called adsorption.
Characteristics of Adsorption:
1. Adsorption is a surface phenomenon.
2. The attractive forces on the surface are limited to distances one molecule deep.
3. The extent to which adsorption takes place is dependent upon the nature of both adsorbing agent and the substances adsorbed.
4. The greater the surface of the adsorbing agent, the greater is the adsorption.
5. Charcoal becomes activated when it is heated at 700°-800°C in a closed container and adsorption takes place on the activated charcoal due to the attraction of oppositely charged ions. Salts, acids and alkalis restrict it.
6. It has got much importance in industry.
Principles Governing Adsorption:
1. Adsorption is a reversible process.
2. It decreases with the rise in temperature.
3. This process takes place relatively quickly. Equilibrium is reached within one hour.
4. Adsorption is proportional to the surface area and it varies with the nature of the surface of the adsorbent and of the substances to be adsorbed.
5. It proceeds best from dilute solutions.
6. Narrow pores on the surface of the adsorbing agent are more effective than globular openings.
7. Heat is given off in all adsorption.
8. The molecules adsorbed on the surface are oriented and arranged in a definite manner.
Importance of Adsorption:
1. Many chemical reactions are speeded up by the presence of adsorptive surface. Oxygen and hydrogen are adsorbed together upon platinum black and combine rapidly at ordinary temperature to form water.
2. Surface adsorption helps to combine enzymes with substrates to give reaction products.
3. Adsorption processes taking place on the cell membranes promote many vital chemical reactions and also cause changes in surface tension and cell consistency.
4. Drugs and poisons which are adsorbed on cell surfaces exert their effects from that location. Selective adsorption may be related to specific action.
5. The process of adsorption is applied in the purification of enzymes.
Arrangement of Molecules at an Interface:
Solute molecules accumulated at an interface tend to arrange themselves in a definite pattern if the molecules are unsymmetrical, (i.e. if they have -COOH, -OH, and –NH2 groups), they have water attractions; whereas the arrangement is symmetrical within the solution.
The unsymmetrical molecules align themselves so that the polar groups are directed towards water and the non-polar groups at the other end of the molecule remain away from it (orientation). At an oil-water interface the orientation would be especially favoured since the oil would attract the non-polar groups in addition to the water attracting the polar groups.
In the cell (which contains both water and lipids), it is likely that some cell constituents are oriented in this way. The cell membrane absorbs oriented molecules. Orientation is an important factor in adsorption and enzyme reactions. In this way, one part of a molecule can be presented to a reacting substance.