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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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Short 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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Long Answer Type

114. Action of soap is due to emulsification and micelle formation. Comment.

Yes, action of soap is due to emulsification and micelle formation. Soaps are sodium salts of higher fatty acids such as sodium stearate, C₁₇H₃₅COO^–Na⁺, which ionises as

The anionic head of stearate ion (—COO^–) is hydrophobic in nature and has great affinity for water, while the hydrocarbon part (C₁₇H₃₅) is hydrophobic in nature and great affinity for oil grease etc.(see Fig.(a))
Yes, action of soap is due to emulsification and micelle formation. S

Yes, action of soap is due to emulsification and micelle formation. S

Fig. 5.19. (b) Hydrocarbon chains of soap anions dissolve in grease (or oil).
Fig. 5.19. (c) Grease-micelles formed are carried away by rinsing water. When soap is used in water, the anions (C₁₇H₃₅COO^–) form micelle and due emulsification encapasulate oil or grease inside. (See fig. (b))These micelles are removed by rinsing with water; while free dirt (from oil or greese) either settle down or are washed away by water. Thus the main function of a soap is to entrap oil or grease with the micelles through emulsification, thereby freeing dirt from greese and oil.

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