NCERT Books for Class 12 Chemistry Chapter5 - Surface Chemistry

Surface Chemistry  is the 5th Chapter Of NCERT. Surface Chemistry  explains the reactions that occur between solids, liquid, and gaseous substances. The surfaces which react with each other are represented by a hyphen or a slash. For example, the interface between a solid and gas would be written as solid-gas or solid/gas. Corrosion, electrode processes, heterogeneous catalysis, dissolution, and crystallization are all applications of surface Chemistry . In this Chapter5 Surface Chemistry , we study: 

i) Adsorption - which is the accumulation of molecules on the surface of a solid or liquid. In this section, we study the distinction between adsorption and absorption, mechanism of adsorption, its types, isotherms, adsorption from solution phase, and applications of adsorption. 

ii) Catalysis - which is when certain substances are added to a chemical reaction in order to speed up its process. In this section, we will study homogeneous and heterogeneous catalysis, adsorption theory of heterogeneous catalysis, shape-selective catalysis by zeolites, enzyme catalysis, and catalysts in industry.

iii) Colloids- which is a heterogeneous system of very fine particles in another substance. We will also study about colloids around us and about their classification based on:

• Physical State of Dispersed Phase and Dispersion Medium.

• Nature of Interaction between Dispersed Phase and Dispersion Medium,

• Type of Particles of the Dispersed Phase, Multimolecular, Macromolecular and Associated Colloids.

• Nature of Interaction between Dispersed Phase and Dispersion Medium,

• Properties of Colloidal Solutions.

iv) Emulsions - which is a colloidal system made with liquids.

What are Emulsions?

It is a colloidal system made with liquids, i.e the dispersion of fine droplets in another liquid. A coarse dispersion of one liquid in another is obtained If this mixture of two immiscible/partially miscible liquids is shaken. The two types of emulsions are:

• Oil dispersed in water (O/W type): where water acts as a dispersion medium. Eg: milk and vanishing cream. In milk, liquid fat is scattered or dispersed in water. 

• Water dispersed in oil (W/O type): In this system, oil acts as the dispersion medium. Eg: butter and cream.

An emulsifying agent is the third component that is usually added for the stabilization of an emulsion. Emulsions of oil in water are unstable in nature and separate into two layers on standing. The emulsifying agent forms an interfacial film between suspended particles and the medium, which lowers interfacial tension and results in the miscibility of the two liquids.

• Emulsifying agents for O/W emulsions: proteins, gums, natural and synthetic soaps.

• Emulsifying agents for W/O emulsions: heavy metal salts of fatty acids, long-chain alcohols, lampblack.

Any amount of the dispersion medium can be added to dilute the Emulsion, but the dispersed liquid forms a separate layer when mixed. Electrolytes can be used to precipitate the droplets in emulsions since they are often negatively charged. Emulsions can also be broken into separate liquids by heating, freezing, and centrifuging. They also show the Brownian movement and the Tyndall effect.