Question

Colloids may be more than a thousand times as big as an atom but more than a thousand times smaller than an ant. These colloids can be removed from solution by:
(A) Thin piece of cloth
(B) Centrifuge
(C) Filter paper
(D) Parchment paper

Answer 1

Hint: Think about what colloids are. Recollect the particle size of colloids. The question says we need to separate the colloidal particles from a solution. In the options, four types of apparatus are given and we need to choose that apparatus which can effectively filter colloidal particles. Think about the pore size of the cloth or filter paper and parchment paper.

Complete answer:
- Colloid is a heterogenous mixture and a two phase system where dispersion medium is one phase and solute particles is another phase called dispersed phase.
- There is a definite space of separation between dispersed phase and dispersion medium.
- The particle size of the dispersed phase ranges between 1nm to 1000nm. The particles are extremely small and cannot be seen using an ordinary microscope.
- Colloidal particles are capable of easily passing through filter papers and parchment paper and can be detected by scattering of light.
- Pore size of cloth like muslin which is generally used for filtration is even greater than the pore of filter paper and parchment papers. Therefore, colloidal particles can easily permeate through the thin piece of cloth.
- Therefore, we can conclude that colloidal particles can only be separated by the process of centrifugation.
- In Centrifugation process, a centrifuge is used to rotate the colloidal suspension at a very high speed because of which solute particles settle at the bottom of the centrifuge tube and thus, colloidal particles can be separated out by just decanting the supernatant solution.

Therefore, the correct answer is option (B) Centrifuge.

Note:
Remember colloidal particles have dimensions in nanometers and they are too small to be visible to naked eye. These particles are not even visible in ordinary light microscopes. They are detected by light scattering. Since colloidal particles are present in dispersed state in the dispersion medium, they scatter the incident radiations and this phenomena of scattering of light by colloidal particles is known as Tyndall effect.