Question

On adding a few drops of dil HCl to freshly precipitated ferric hydroxide, a red coloured colloidal solution is obtained. The phenomenon is known as:
A.Protective action
B.Flocculation
C.Coagulation
D.Peptization

Answer 1

Hint: When we add a few drops of dilute hydrochloric acid to ferric hydroxide, we get ferric chloride and water as the product. In this reaction, we can see that the precipitated is turned into colloidal sol and the process is called deflocculation.

Complete step by step answer:
When small quantities of lyophilic colloids keep lyophobic colloids from precipitation under the coagulation action of electrolytes is called as protective action.
Therefore, the option (A) is incorrect.
We can say the precipitation of colloidal solution, with the support of addition of excess of an electrolyte is called flocculation or coagulation. The electrolyte is called a flocculating agent. The power of an electrolyte to precipitate a colloidal solution is called flocculating power.
Therefore, the option (B) and (C) are incorrect.
We can define peptization as the technique of converting precipitate into colloidal sol. It is shaken with a dispersion medium in the presence of a small amount of electrolyte and the electrolyte used for this purpose is called a peptizing agent.
The addition of dilute hydrochloric acid to freshly ferric hydroxide to get red coloured colloidal solution is peptization. The precipitate is broken with the help of electrolyte and is dispersed into colloidal medium to form stable colloids.

So, the correct answer is Option D.

Note: We must remember that the deflocculation is the opposite of flocculation, also called peptization. An example is sodium silicate. The additive termed as deflocculant prevents the formation of flocs by colloids. We can use flocculation for the purification of water, and is also used in the extraction of corrosive elements from water.