Chapter 5 Surface Chemistry Solutions
Question - 31 : - Give four uses of emulsions.
Answer - 31 : -
Four uses of emulsions:
(i) Cleansingaction of soaps is based on the formation of emulsions.
(ii) Digestionof fats in intestines takes place by the process of emulsification.
(iii) Antisepticsand disinfectants when added to water form emulsions.
(iv) Theprocess of emulsification is used to make medicines.
Question - 32 : - What are micelles? Give anexample of a micellers system.
Answer - 32 : -
Micelle formation is done bysubstances such as soaps and detergents when dissolved in water. The moleculesof such substances contain a hydrophobic and a hydrophilic part. When presentin water, these substances arrange themselves in spherical structures in such amanner that their hydrophobic parts are present towards the centre, while thehydrophilic parts are pointing towards the outside (as shown in the givenfigure). This is known as micelle formation.
Question - 33 : - Explain the terms with suitableexamples: (i) Alcosol (ii) Aerosol (iii) Hydrosol
Answer - 33 : -
(i) Alcosol:
A colloidal solution havingalcohol as the dispersion medium and a solid substance as the dispersed phaseis called an alcosol.
For example: colloidal sol ofcellulose nitrate in ethyl alcohol is an alcosol.
(ii) Aerosol:
A colloidal solution having a gasas the dispersion medium and a solid as the dispersed phase is called anaerosol.
For example: fog
(iii) Hydrosol
A colloidal solution having wateras the dispersion medium and a solid as the dispersed phase is called ahydrosol.
For example: starch sol or goldsol
Question - 34 : - Comment on the statement that“colloid is not a substance but a state of substance”.
Answer - 34 : -
Common salt (a typicalcrystalloid in an aqueous medium) behaves as a colloid in a benzene medium.Hence, we can say that a colloidal substance does not represent a separateclass of substances. When the size of the solute particle lies between 1 nm and1000 nm, it behaves as a colloid.
Hence, we can say that colloid isnot a substance but a state of the substance which is dependent on the size ofthe particle. A colloidal state is intermediate between a true solution and asuspension.