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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 ?

Answer:

(a) Gel is a colloidal solution of liquid in a solid, i.e., liquid is dispersed phase and solid is the dispersion medium. A gel is a semi-solid which melts on heating. Examples of gels are: Thin jellies, gum arobic, processed cheese, silicic acid.

(b) It is prepared by reduction of gold chloride (AuCl₃) solution with stannous chloride
2AuCl₃ + 2SnCl → 3SnCl₄ + 2Au
(Violet gold sol.)

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Long Answer Type

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

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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?

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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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