UNIT 5 SURFACE CHEMISTRY
- Adsorption is the phenomenon of attracting and retaining the molecules of a substance on the surface of a solid resulting into a higher concentration on the surface than in the bulk.
- The substance that is adsorbed is called the adsorbate and the substance on which adsorption takes place is called the adsorbent.
- Almost all solids adsorb gases. The extent of adsorption of a gas on a solid depends upon:
- the nature of gas
- the nature of the solid
- surface area of the solid
- pressure of gas
- temperature of gas
- The relationship between the extent of adsorption and the pressure of the gas at constant temperature is known as adsorption isotherm.
- A catalyst is a substance which enhances the rate of a chemical reaction without itself getting used up in the reaction. The phenomenon using catalysis is known as catalysis.
- Homogeneous catalysis: The catalyst is in the same phase as the reactants.
- Heterogeneous catalysis: The catalyst is in a different phase from that of the reactants
- Colloidal solutions are intermediate between true solutions and suspensions. The size of colloidal particles range from 1 to 1000 nm.
- A colloidal system consists of two phases: the dispersed phase and the dispersion medium.
- Colloidal system can be classified in three ways depending upon the:
- Physical states of the dispersed phase and the dispersion medium
- Nature of interaction between the dispersed phase and the dispersion medium
- Nature of particles of dispersed phase
- The process of changing the colloidal particles in a sol into the insoluble precipitate by addition of some suitable electrolytes is known as coagulation.
- Emulsions are colloidal systems in which both the dispersed phase and dispersion medium are liquids. The process of making emulsions is called emulsification.