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  15.13  Write the name and structure of one of the common initiators used in free radical addition polymerisation.

The common initiator used in free radical addition polymerisation is benzoyl peroxide. The structure is 

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

Common salt is behaving as a colloidal particle in benzene as a dispersion medium. It means the solute particles attain a size of the colloidal range of (1-1000 nm). So, we can say that the colloid is not a substance but a state of substance which depends on the particles size.

5.26    Explain the terms with suitable examples:

                  (iii)  Hydrosol 

Hydrosol-  In THis type of colloidal solution the water is dispersion medium and a solid substance is a dispersed phase. example- starch sol and gold sol.

5.26        Explain the terms with suitable examples:

                    (ii) Aerosol 

Aerosol- A colloidal solution of the dispersion medium is a gas and the dispersed phase is a soil substance. example- fog.

5.26     Explain the terms with suitable examples:

                  (i) Alcosol 


Alcosol-  A solution in which the dispersion medium is alcohol and the dispersed phase is a solid substance. examples- colloidal sol of cellulose nitrate in ethyl alcohol is an alcosol.  

5.25        What are micelles? Give an example of a micellers system.


When the long chain of fatty acids like soap and detergent is added to water the hydrophobic part of their chain is aligned towards the centre in such a manner that they form a spherical shape and their hydrophilic part is facing towards outside. This spherical like structure is known as a micelle.                                 Structure of sodium soap(Left side - hydrophobic part, Right...

5.24       Give four uses of emulsions.


Four use of emulsions- The cleansing action of soap to make medicins by emulsification process Digestion of fats in the intestine  Antiseptic and disinfectant when adding to water form emulsion.   

5.23         Explain the following terms:

                      (iv) Tyndall effect

Tyndall effect-  When a beam of light is passed through the colloidal solution the colloidal particles scatter the light and make the beam visible in colloidal solution. This effect is observed by Faraday and later on detail in studied by Tyndall and is known as the Tyndall effect.

5.23        Explain the following terms:

                     (iii)  Dialysis 

Dialysis-  The process of removing a dissolved substance from the colloidal solution by means of diffusion through a suitable membrane. The principle behind this is small molecules and ions can pass through the animal membrane.

5.23        Explain the following terms:

                      (ii)  Coagulation 

Coagulation- The settling down of the lyophobic sol due to the presence of charge on colloidal particles

5.23    Explain the following terms:

                      (i) Electrophoresis 

Electrophoresis- The movement of colloidal particles under the influence of electric current is known as electrophoresis. The negatively charged particles move towards the cathode and positive charge particles move towards the anode.  

5.22  What is shape selective catalysis?

Shape-selective catalysis, in which the reaction mainly depends on the size of the reactants and product molecules and also the pore structure of the catalyst. Ex. zeolites are good shape selective catalyst.

5.21     Describe some features of catalysis by zeolites.

Zeolites are good shape selective catalyst due to their honeycomb-like structures. They are alumino-silicates that are microporous in structures. They are the 3D network of silicates in which some atoms of silicon are replaced by aluminium giving  framework.  Size and shape of reactant and product molecules, as well as pores and cavities of zeolites, are the reaction determining factors in zeolites.

5.20    What do you mean by activity and selectivity of catalysts?  

(i)The activity of the catalyst is to increase the rate of a particular reaction. It depends on the strength of chemisorption to a large extent. Adsorption of reactants should be neither too high nor too weak. It should just be optimum so that the catalyst is staying active. (ii)The selectivity of catalyst is the ability to direct the reaction to give a particular product when under the same...

5.19    Give four examples of heterogeneous catalysis.


 Four examples of heterogeneous catalysis- 1. oxidation of sulphur dioxide into sulphur trioxide in the presence of Pt.   2. the combination between dinitrogen and dihydrogen to form ammonia 3. Hydrogenation of vegetable oils in the presence of Ni  as a catalyst   4. Ostwald Process - oxidation of ammonia into nitric acid in the presence of Pt  

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

The cleansing action of soap is because of emulsification and micelle formation. Soaps are sodium or potassium salts of long chain fatty acids, represented as  (e.g. sodium stearate ). when dissolved into the water it dissociates into  and  ions. . The long carbon chains are non-polar in nature (hydrophobic) and  are polar in nature (hydrophilic part). When the soap is added to dirt containing...

5.17      How do emulsifiers stabilise emulsion? Name two emulsifiers.

The emulsifying agents are also known as emulsifiers. For stabilisation of emulsion, they form an interfacial film between suspended particles and medium. Example- for O/W gums, natural and synthetic soaps for W/O heavy salts of fatty acids, long chain alcohols  

5.16     What are emulsions? What are their different types? Give example of each type.


The colloidal solution in which both the dispersed phase and dispersion medium are liquid in nature are called emulsions. There are two types of emulsions- (i) oil in water (O/W) -Oil is dispersed phase and water is dispersion medium (milk)              (ii) water in oil (W/O)- Water is the dispersed phase and oil is dispersion medium (cold  cream, butter etc.)

5.15          Explain what is observed 

                    (iii) electric current is passed through a colloidal sol?

Under the influence of electric current, the colloidal particles start moving towards the oppositely charged electrode.

5.15           Explain what is observed 

                   (Ii) an electrolyte, NaCl  is added to hydrated ferric oxide sol.

The sol gets precipitated because of the neutralisation reaction. The ferric oxide sol is positive in nature and we get chloride ion from NaCl.