Mechanical or Disintegration Methods:-
- Mechanical disintegration:-this integration is carried out in a colloid mill or ball mill or ultrasonic disintegrator. A suspension of substance in water is introduced into the mill. The size of the suspension particle is reduced to that of the colloidal size.
- Electro disintegration [Bredig’s method]:- This method is applied for obtaining colloidal solution of metals like, gold, silver and platinum. Anelectric are is struck between two metallic electrodes suspended through water. The intence heat of are convert the metals into particles of colloidal size.
Peptization:-this is a process of converting a fresh precipitate into collidol particles by shaking it with the dispersion medium in the presence of small amount of some suitable electrolyte. The electrolyte added is called the peptizing agent.
Example:- (i) Areddish brown coloured solution is obtained by adding small quantity of Ferric chloride solution to freshely precipitated hydroxides.
Purification of colloidal solution:-
Purification:- the process of reducing the impurities of the electrolytes to the minimum required level is known as purification of colloidal solution.
Dialysis:-The process of separting the particles of codloids from there those of crystalloids by diffusion of the mixture though a parchment or an animal membrane is called dialysis.
Process:- The apparatus used is called a dialyser. A cellophane sheet or parchment paper is turned into a bug with a funnel tired in the mounth of the bay, for theaddition of impure sol. The impure sol is filled into the bug which is then suspended into vessel containing distilled water.
Electro dialysis:- In this method electric field is applied using the metal electrodes, and the diffusion of the given mixture through using parchment or an animal membrane is known as Electro dialysis.
Ultrafiltration:- First of all filter paper is treated with colodion or gelatin solution followed by hardening by dipping into formaldehyde. The colloid in solution used is 4% solution of nitrocellulose in a mixture of alcohol and ether. Due to this pore size of filter paper is reduced. This filter paper so obtained is called a ultra filter paper.
→ and purification by this called ultrafiltration.
Properties of colloidal solutions:–
- Stability:- Colloidal sols are quite stable. Only a few colloidal particles of comparatively lower size may settle but very slowly.
- Filterability:- Colloids may only be filtered using parchment membrane or ultra filter paper.
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