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Surface Chemistry

Short Answer Type

131. How does an increase in temperature affect both physical as well as chemical adsorption?

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132. A colloidal solution of Agl is prepared by two different methods shown below:

(i) What is the charge of AgI colloidal particles in the two test tube (A) and (B).
(ii) Give reason for the origin of change.

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133. Explain why hydrophillic sols are relatively more stable than hydrophobic sols?

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134.

(a) What is gel? Give an example.
(b) How is gold sol prepared by reduction method ?

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Long Answer Type

135. Explain the process of peptization Name only one hydrosol.

Answer:

Peptization may be defined as the process of
converting a precipitate into colloidal sol by shaking it with dispersion medium in the presenceof a small amount of electrolyte. The electrolyte used for this purpose is called peptizing agent.

For example, on treating a precipitate of iron (III) oxide with a small amount of FeCl₃ solution gives a reddish brown coloured colloidal solution. During peptisation, the suitable ions from the added electrolyte are absorbed by the particles of the precipitate. The charged particles repel one another and form colloidal solution. In this case, Fe³⁺ ions from ferric chloride are absorbed by Fe(OH)₃ precipitate:

Fe (OH)_{3} + {Fe}^{3 +} \to Fe (OH)_{3} + {Fe}^{3 +} Precipitate Electrolyte Colloidal sol .

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Short Answer Type

136. The adsorption of gases on solids can be described by Frundlich’s reaction:

(\frac{x}{m}) = {kp}^{1 / 4}

(i) How are the values of k and n determined experimentally?
(ii) Explain why the value of n should be equal to or greater than one?

139 Views

Long Answer Type

137.

Explain the following observations:
(a) Ferric hydroxide sol gets coagulated on addition of sodium chloride solution.
(b) Cottrell’s smoke precipitator is fitted at the mouth of the chimney used in factories.
(c) Physical adsorption is multi layered, while chemisorption non layered.

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Short Answer Type

138. Differentiate between homogeneous catalysis and heterogeneous catalysis.

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139. How will you prepare silver sol by Bredig’s Arc method?

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140. Why is smoke passed through charged plates before allowing it to come out of chimneys in factories?

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