Question

When a small quantity of $FeC{{l}_{3}}$ solution is added to the fresh precipitate of $Fe{{(OH)}_{3}}$a colloidal sol is obtained. The process through which this sol is formed is known as:
(a)- exchange of solvent
(b)- chemical double decomposition
(c)- peptization
(d)- electrophoresis

Answer 1

Hint: A colloid is a type of solution in which the dimension of solute particles is intermediate between those in true solutions and in suspensions. For Example: - Soap solution, milk, blood, etc.

Complete step by step solution:
There are various physical methods that can be employed to obtain colloidal dispersions. Some of them include: electrophoresis, exchange of solvent, etc.

(a)- Exchange of Solvent
This method of formation of a colloidal solution involves adding an alcoholic solution of an element to excess of water. This colloidal formation can take place only when the element is more soluble in alcohol as compared to water.

(b)- Double decomposition reaction
It is defined as a reaction in which the positive ions and negative ions in two compounds (reactants) switch partners to form two new compounds.

(c)- Peptization
This method is responsible for converting precipitate into colloid by shaking it with an electrolyte. Peptization is said to be the opposite of coagulation. Coagulation uses charges to disrupt the colloid and form an aggregate while peptization uses charges to form a colloid from a precipitate. In order to carry out peptization we need an electrolyte, which is termed as a peptizing agent. The precipitate particles get adsorbed onto the ions of the peptizing agent, and then electrostatic repulsion (repulsion between two compounds with like charges) causes the precipitate particles to combine with the electrolyte ions and then get mixed with the colloidal solution, thereby forming a stable colloid.

(d)- Electrophoresis
It is a technique which is commonly used to separate macromolecules from a fluid or gel, on the basis of their charge, binding affinity, and size under the action of an electric field. This method has a wide application in separating and analyzing biomolecules such as proteins, plasmids, RNA, DNA, nucleic acids.

When a small quantity of $FeC{{l}_{3}}$ solution is added to the fresh precipitate of $Fe{{(OH)}_{3}}$a colloidal sol is obtained through the process of peptization. So, the correct option is (c).

Note: Colloids are not perfectly transparent, they are somewhat translucent. The colloidal particles cannot be seen by our naked eyes. Though, when a light source is placed near the solution, we can see small particles throughout the solution. This is called the Tyndall effect.