Chemistry Class 12 NCERT Solutions: Chapter 5 Surface-Chemistry Part 6

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Q: 25. What are micelles? Give an example of a micelles system.

Answer

Micelle formation is done by substances such as soaps and detergents when dissolved in water. The molecules of such substances contain a hydrophobic and a hydrophilic part. When present in water, these substances arrange themselves in spherical structures in such a manner that their hydrophobic parts are present towards the centre, while the hydrophilic parts are pointing towards the outside (as shown in the given figure). This is known as micelle formation.

Q 25 Iamge of Micelle Formation

Q 25 Iamge of Micelle Formation

Q 25 Iamge of Micelle Formation

Q: 26. Explain the terms with suitable examples:

(i) Alcosol

(ii) Aerosol

(iii) Hydrosol

Answer:

(i) Alcosol

A colloidal solution having alcohol as the dispersion medium and a solid substance as the dispersed phase is called an Alcosol.

For example: colloidal sol of cellulose nitrate in ethyl alcohol is an alcosol

(ii) Aerosol:

A colloidal solution having a gas as the dispersion medium and a solid as the dispersed phase is called an aerosol.

For example: fog

(iii) Hydrosol

A colloidal solution having water as the dispersion medium and a solid as the dispersed phase is called a hydrosol.

For example: starch sol or gold sol

Q: 27. Comment on the statement that “colloid is not a substance but a state of substance”.

Answer:

Common salt (a typical crystalloid in an aqueous medium) behaves as a colloid in a benzene medium. Hence, we can say that a colloidal substance does not represent a separate class of substances. When the size of the solute particle lies between and , it behaves as a colloid.

Hence, we can say that colloid is not a substance but a state of the substance which is dependent on the size of the particle. A colloidal state is intermediate between a true solution and a suspension.