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 Multiple Choice QuestionsLong Answer Type

111.

Explain what is observed
(i) when a beam of light is passed through a colloidal sol.
(ii) an electrolyte, NaCl is added to hydrated ferric oxide sol.
(iii) electric current is passed through a colloidal sol?

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 Multiple Choice QuestionsShort Answer Type

112. What are emulsions ? What are their different types? Give example of each type. 
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113. What is de-emulsification ? Name two demulsifiers.
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 Multiple Choice QuestionsLong Answer Type

114. Action of soap is due to emulsification and micelle formation. Comment.
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115. Give four examples of heterogeneous catalysis. 
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116. What do you mean by activity and selectivity of catalysts?


Answer:
Activity of a catalyst. The ability of a catalyst to increase the rate of a  particular reaction is called, catalytic activity. Chemisorption is the main factor in deciding the activity of a catalyst. The catalyst tungsten increases the rate of decomposition of ammonia to the extent of 10
32 times which is otherwise slow process. The activity of a catalyst become more significant in the formation of water. Hydrogen and oxygen can be stored for years but not even a single drop of water will be produced in the absence of a catalyst. However, in the presence of platinum catalyst hydrogen and oxygen combine with explosion and form water.

H2+12O2    No reactionH2+12O2+Pt    H2O + (Pt)........explosion

Selectivity of a catalyst: The ability of a catalyst to affect only the desired reaction and to prevent any other side reaction is referred to as the selectivity of a catalyst. For example, both the dehydrogenation and dehydration of ethanol are possible. But in the presence of a suitable catalyst only one reaction occurs. Thus

(i) when nickel is ‘used as a catalyst, only dehydrogenation of ethanol occurs.
CH3CH2OH Ni CH3CHO + H2, dehydrogentatoinEthanol                      Ethanal
(
ii) When alumina (Al
2O3) is used as catalyst only dehydration of ethanol occurs.
CH3CH2OH  Al2O3 CH2 = CH2+H2O,                                    Ethene

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 Multiple Choice QuestionsShort Answer Type

117. Describe some features of catalysis by zeolites.
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118. What is shape selective catalysis?
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 Multiple Choice QuestionsLong Answer Type

119. Explain the following terms: (i) Electrophoresis (ii) Coagulation (iv) Dialysis (iv) Tyndall effect. 
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120. Give four uses of emulsions. 
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