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Surface Chemistry

Long Answer Type

101. What is an adsorption isotherm ? Describe Freundlich adsorption isotherm.

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Short Answer Type

102. What do you understand by activation of adsorbent? How is it achieved?

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103. What role does adsorption play in heterogeneous catalysis?

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104. Why is adsorption always exothermic?

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Long Answer Type

105. How are the colloidal solutions classified on the basis of physical states of the dispersed phase and dispersion medium?

Answer:
A dispersed phase or dispersion medium in colloidal solution may be a solid, liquid or gas. Based on physical states, 8 types of colloidal systems are possible (gas in gas is not possible as gases are always miscible in all proportions forming homogeneous mixure). All other takes of combinations of gases, liquids and solids may exist as colloidal solutions. Examples are given in the following table:

Internal phase of Dispersed phase	External phase or Dispersion medium	Colloidal name	Example
Solid	Solid	Solid sols	Alloys, Ruby glass, Gems or precious stones, marbles, optical and vision glasses.
	Liquid	sols	Muddy water, gold sol, protein, starch, agar, gelatin in water, paints, pigments in water.
	Gas	Aerosols (or solids	Smoke, particulate clouds.
Liquid	Solids	Gels	Cheese, jems, jellies, plants, fruits, vegetables
	Liquid	Emulsions	Butter, milk, cosmetic products, e.g., shampoo, creams, emulsified oils, polish and medicines.
	Gas	Aerosols (or liquids)	Fog, clouds, mist.
Gas	Solid	Solid foams	Pumicestone, styrene foam, foamed rubber, porous pot. thermocole rubber pillows and mattresses.
	Liquid	Foams and froths	Lather, soap seeds, air bubble.
	Gas	Homogeneous system	Do not exist as colloids.

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106. Discuss the effect of pressure and temperature on the adsorption of gases on solids.

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107. What are lyophilic and lyophobic sols? Give one example of each type. Why are hydrophobic sols easily coagulated?

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108. What is the difference between multimolecular and macromolecular colloids? Give one example of each. How are these two types of colloids different from these two types of colloids?

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109. What are enzymes? Write in brief the mechanism of enzyme catalysis.

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110. How are colloids classified on the basis of
(i) physical states of components
(ii) nature of dispersed phase and
(iii) interaction between dispersed phase and dispersion medium?

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