Question

Explain the following terms:
(i) Electrophoresis
(ii) Coagulation
(iii) Tyndall effect

Answer 1

Hint: Colloidal particles have large surface area when compared with the surface area of an equal volume of larger particles. More extended particle means greater its specific surface and greater the force of attraction between particles of dispersion medium and dispersed phase. Colloidal particles show different types of optical, electrical and mechanical properties.

Complete step by step answer:
Colloids are substances which are microscopically dispersed in another substance. For example, milk is a colloid in which fat globules are dispersed in water dispersion medium. Similarly fog, synthetic polymer, blood, jam, smoke are some examples of colloids.
(i) Electrophoresis is the electrical property of colloids. It is the movement of colloidal particles towards a particulate electrode under the influence of an electric field. Colloidal particles with positive charge move towards cathode when subjected to an electric field. The term electrophoresis refers to the movement of the charged particles under the influence of electric field.
(ii) Coagulation is the destabilization of colloids by addition of chemicals that neutralize the negative charges. The chemicals are called coagulants, usually higher valence cationic salts. Coagulation is essentially a chemical process. With destabilization, colloids aggregate in size and start to settle.
(iii) Tyndall effect is the major optical property shown by colloids. When an intense converging beam of light is passed through a colloidal solution kept in dark, the path of the beam gets illuminated by bluish light. This is referred to as Tyndall effect and the illuminati path is called Tyndall cone. This is due to the scattering of light by colloidal particles.

Figure showing tyndall effect from canopy of trees.

Additional information:
Colloids can pass through a filter paper, but not through a semipermeable membrane. They can be settled through centrifugation. Their particles are not as small as solution and as large as suspension.


Note:
Tyndall effect can be used to differentiate between true solutions and colloidal solutions. In electrophoresis, particles can move but not the medium. In electro osmosis, the medium can move but not the particles.