Monday, November 25, 2013

Purification Of Colloids: ( Sol )

( a ) Dialysis.
( b ) Electro-dialysis.
( c ) Ultra-filtration.
Dialysis:
     Dialysis is the removal of soluble impurities from sols by the use of semipermeable membrane. The ordinary process of dialysis is slow. The apparatus used for this purpose is called Dialyser.
      Cellophane bag is filled with impure colloidal solution and placed in fresh water ( distilled water ). The cellophane bag is not allow the colloidal particles to pass through, but particles of true solution can pass through it. The molecules and ions diffuse through the membrane into the outer water and pure colloidal solution is left behind. The water is renewed frequently to avoid accumulation of the crystalloid as otherwise they may start diffusing back into the bag.


Electro-dialysis:
       Electro dialysis is the removal of soluble impurities from sols by the use of semipermeable membrane in the presence of electric field.
       Cellophane bag is filled with impure colloidal solution and placed in fresh water ( distilled water ). The cellophane bag is not allow the colloidal particles to pass through, but particles of true solution can pass through it. Now the electric field is applied. The soluble particles passed through the membrane and migrate towards the oppositely charged electrodes. Leaving behind the pure colloidal solution. The most important application of dialysis process in purification of the artificial kidney mechaine, used for the purification of blood.


Ultra filtration:
       In this method, colloidal solutions are purified by carrying out filtration through special type of filters called ultra-filters. Sols pass through ordinary filter paper, So that use special filter paper. The filters are permeable to all substances except the colloidal particles. This process is very slow. Pressure are suction is applied to speed it up.



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