Question

How do you separate colloids?

Answer 1

Colloids can be precipitated through induced aggregation by adding some suitable electrolyte and the name of this method is called coagulation or flocculation.

Complete answer:
The coagulation of a colloidal solution by an electrolyte does not take place until the time that the electrolyte gains a certain minimum concentration in the solution. The minimum concentration of the electrolyte in millimoles to which 1 litre of sol gets added so that complete coagulation is brought out is called the coagulation value or flocculation value of the electrolyte for the sol.
Different electrolytes have different coagulation values. As the coagulation value of the electrolyte is smaller, the more large its precipitating or coagulating power becomes. This can be expressed as follows:
$precipitating\,pwr=\dfrac{coagulation\,val\,of\,electrolyte\,1}{coagulation\,val\,of\,electrolyte\,2}$
The behaviour of coagulation of various electrolytes was studied in detail by Hardy and Schulze. They observed that:
(i) The ions which carry opposite charge to that of sol particles play an active role in causing the coagulation of the sol. We call these ions as flocculating ions or active ions.
(ii) Coagulating power of an electrolyte has a relationship of direct proportionality to the fourth power of the valency of the active ions. This shows us that as the valency of the flocculating ion is more, more is its power to cause precipitation.
Water is sprinkled before sweeping the room as it helps to coagulate the dust particles. Light particles after coagulation become heavier and settle down due to which it becomes easier to remove them easily.
Colloids generally don't separate on standing. they're not separated by filtration. The homogeneous mixtures which have particles possessing diameters ranging greater than 1000 nm, 0.000001 meter, are called suspensions. the scale of the particles is great enough in order that they are visible to the optic.

Note:
The lyophilic sols are relatively more stable than lyophobic sols. The stability of lyophilic sols are due to:
(i) Charge present on the colloidal particles.
(ii) Greater attractive forces between dispersed phase and dispersion medium helps in more solvation.