<h2>Answer:</h2>
Colloidal suspension cannot be separated by normal filtration.
<h2>Explanation:</h2><h3>Colloids</h3>
Colloids are mixtures with particle sizes that consist of clumps of molecules. The particles have dimensions between 2 to 1000 nanometers.
The colloid looks homogeneous to the naked eye. Fog and milk are examples of colloids.
<h3>
Suspensions</h3>
Suspensions are homogeneous mixtures with particles that have diameters greater than 1000 nm, 0.000001 meter. The size of the particles is great enough so they are visible to the naked eye. Blood and aerosol sprays are examples of suspensions. Suspensions are "murky" or "opaque". They do not transmit light. Suspensions separate on standing. The mixture of particles can be separated by filtration.
<h3>Purification of Colloidal Suspension</h3>
Colloidal suspension cannot be separated by normal filtration. Because the pore size of colloidal suspension is smaller than pores of normal filter paper so they pass through it. Various techniques for purification of colloidal solution are as follows:
1. By Dialysis:
It is done by dialysis. Dialysis is the process which is used for the separation of crystalloids from a colloid by filtration or diffusion through parchment paper or animal membrane. The apparatus employed for this purpose is called dialyser. This process is based on the fact that membranes contain very small pores through which only dissolved molecules and ions of the true solution can pass readily.
2. Ultra filtration:
Here colloids are separated from crystalloids with the help of ultra filter papers. Which are obtained by treating simple filter paper with gelatin or collodion so, that the pores become less or narrow in size through which only crystalloid particles can pass.
3. Centrifugation:
Here impurities are removed from colloids with the help of a machine of high speed called centrifugal machine. Here colloids settle down while impurities remain in centrifuge.
