Justify the use of gelatin as a protective colloid.

Answer:

Gelatin is made from soft bone and cartilages of an animal which have ability to form thermo- reversible gelsand amphoteric character make it as protactive colloid.
The process by which the lyophobic sols are protected from coagulation by electrolytes, because of the previous addition of lyophilic colloid is called protection; and the lyophilic colloid employed for imparting this protection, is called protective colloid, Thus when a little gelatin is added to As₂S₃ sol, the latter becomes very stable towards electrolytes and the resulting sol is not coagulated, until a large excess of electrolyte is added. Here, gelatin acts as a protective colloid.