What is an adsorption isotherm? In reference to Freundlich adsorption isotherm write the expression for absorption of gases on solids in the form of an equation.

An adsorption isotherm is a graph that represents the variation in the amount of adsorbate ( x ) adsorbed on the surface of the adsorbent with the change in pressure at a constant temperature. Different adsorption isotherms have been proposed by different scientists namely, Langmuir isotherm Freundlich isotherm BET theory The graph shown above shows the isotherm proposed by Freundlich. The Freundlich adsorption isotherm for adsorption of gases on solids: x m = kP 1 / n Where n can take any whole number value which depends upon the nature of adsorbate and adsorbent. The above relationship is also called Freundlich's adsorption isotherm. It can also be written as, log x m = log k + 1 n log p Where, x = mass of adsorbate m = mass of adsorbent P = Equilibrium pressure of the adsorbate The k and n are constant for a given adsorbate and adsorbent at a particular temperature. At high pressure, 1 / n = 0 , hence, the extent of adsorption becomes independent of pressure.

What are the differences between physisorption and chemisorption? Give reason why a finely divided substance is more effective as an adsorbent.

Physisorption Chemisorption In this type of adsorption, the adsorbate is attached to the surface of the adsorbent with weak van der Waal's forces of attraction. In this type of adsorption, strong chemical bonds are formed between the adsorbate and the surface of the adsorbent. No new compound is formed in the process. New compounds are formed at the surface of the adsorbent. It is generally found to be reversible in nature. It is usually Irreversible nature. Adsorption is a surface phenomenon.The extent of adsorption depends on the surface area. Therefore, adsorption is directly proportional to the surface area. lncrease in the surface area of the adsorbent, increases the total amount of gas adsorbed. A finely divided substance like nickel, platinum & porous substances like charcoal, silica gel provides large surface area. Both physisorption and chemisorption increase with an increase in the surface area. Hence, a finely divided substance behaves as a good adsorbent.

What is shape-selective catalysis? Describe some features of catalysis by zeolites.

The catalytic reaction that depends upon the pore structure of the catalyst and the size of the reactant and product molecules is called shape-selective catalysis. Zeolites are good shape-selective catalysts because of their honeycomb-like structures. They are microporous aluminosilicates with a three-dimensional network of silicates in which some silicon atoms are replaced by aluminium atoms giving an Al–O–Si framework. The reactions taking place in zeolites depend upon the size and shape of reactant and product molecules as well as upon the pores and cavities of the zeolites. They are found in nature as well as synthesised for catalytic selectivity. Zeolites are being very widely used as catalysts in petrochemical industries for the cracking of hydrocarbons and isomerisation. An important zeolite catalyst used in the petroleum industry is ZSM-5. It converts alcohols directly into gasoline (petrol) by dehydrating them to give a mixture of hydrocarbons.

What are emulsions? What are their different types? Give examples of each type.

These are liquid-liquid colloidal systems, i.e., the dispersion of finely divided droplets in another liquid. If a mixture of two immiscible or partially miscible liquids is shaken, a coarse dispersion of one liquid in the other is obtained which is called emulsion. Generally, one of the two liquids is water. There are two types of emulsions. Oil dispersed in water (O/W type). Water dispersed in oil (W/O type). In the first system, water acts as dispersion medium. Examples of this type of emulsion are milk and vanishing cream. In milk, liquid fat is dispersed in water. In the second system, oil acts as dispersion medium. Common examples of this type are butter and cream.

What is observed when a beam of light is passed through a colloidal solution?

The Tyndall effect is due to the fact that colloidal particles scatter light in all directions in space. This scattering of light illuminates the path of beam in the colloidal dispersion.

Define the following term : Kraft temperature

Kraft temperature : It is the minimum temperature above which the formation of micelles takes place.

Give the decreasing order of flocculating power of the following ions in the coagulation of a negative sol, Na + , Ba 2 + , Al 3 + .

According to Hardy Schulze's rule, the greater the valency of the active ion or flocculating ion, the greater will be its coagulating power. The coagulate negative sol of As 2 S 3 , the coagulating power: Here, the order of valence is Al + 3 > Ba + 2 > Na + and hence the order of flocculating power.

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EMBIBE CHAPTER WISE PREVIOUS YEAR PAPERS FOR CHEMISTRY>Chapter -1 - Surface Chemistry>Assam Board-2018>Q 4

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Mention two industrial applications of colloids.

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