Lyophillic colloids:
lyophillic colloids are those colloids in which dispersed phase exhibits definite affinity for the medium or the solvent .These have little or no charge on particle .These do not show tyndall effect .In it particles are migrate to anode or cathode or not at all.These are reversible .These are quit stable are not easily coagulated by electrolysis .
example :
dispersion of starch ,gum & protien in water.
lyophobic colloids:
lyophobic colloids are those colloids in which dispersed phase does not exhibit definite affinity towards the medium or the solvent .These carry positive or negative charge on particles .These show tyndall effect In it particles migrate either to cathode or anode .These are irriversible .These are less stable & get coagulated by electrolytes by heating or coagulating .
example:
dispersion of gold ,sulphur in water
Protective colloids :
The lyophilic solution used to protect lyophobic solution from precipitation is reffered to as protective colloids .Lyophobic solution (solution of metals like gold ,silver etc ) can be easily precipited by the addition of small amount of elctrolytes .The precipitation of these lyophobic solution can be prevented by the previous addition of some stable lyophillic colloids like gelatin, albumin etc
for example :
the gelatin used in gold solution is protective colloid
the protecting power of different protective solids expressed in terms of gold number.
lyophillic colloid+lyophobic sol=protective lyophobic solution =no precipitation
Coagulation and its mechanism :
The settling down of discharged solution particles is known as coagulation or precipitation of solution
The stability of a colloidal solution is due to the adsorption of positive or negative ions by the dispersed particles .The repulsive force between the charge particles do not allow them to settle down .
If the charge carried by dispersed particles is removed ,these colloidal particles are removed ,these colloidal particlesmay unite together to form bigger particles which are then precipitated .The coagulation of the given solution can be brought about :
- by addition of suitable electrolysis
- by electrophoresis
- by repeated dialysis
- by heating
Dialysis and electrodialysis:
Dialysis:
The process of seperating ions or mlecules from a solution by diffusion through a permeable membrane is called dialysis .
example:
If an impure solution of ferric hydroxide containig some HCl is placed in dialysis bag for some time ,the outside water gives a white precipitated with silver nitrate .After long time almost the whole of HCl is removed and pure red solution is left in the dialyser bag.
Electrodialysis:
The process of seperating ions or molecules from a solution by dialysis under the influence of electric field is called electrodialysis.the application of electric field speedup the migration of ions to the opposite electrode .
electrodialysis is really very effective at the end of ordinary dialysis ,when concetration gradient and
thus rate of diffusion is small .electro dialysis is not mean for the removal of non -electrolyte impurities like sugar .
Define gel?What are the types of gel? explain .
A gel is the colloidal system in which liquid is dispersed in solid ,under certain conditions, the lyophilic solution after coagulation give a semi solid gelly like mass inclosing all the liquid present in the solution . Gels are two types :
1.Elastic gels:
Those gels whose posses the property of elasticity are known as elastic gels .They change their shape on applying force and return to orginal shape when the force is reoved .Example :gelatin ,starch ,soap etc.
2.Non elastic gels:
Those gels which are rigid and donot posses the property of elasticity are known as no- elastic gels.Example : slica etc