Question

When iron hydroxide colloidal sol which is positively charged, and colloidal gold which is negatively charged are mixed, which of the following observations is correct?
A.There is no effect of mixing the sols
B.Coagulation in both sols can be brought about
C.Ferric hydroxide is coagulated
D.Gold sol is coagulated

Answer 1

We know that the colloidal state of matter is the state of matter in which the particle sizes vary from 1nm to 1000nm. In a colloidal system, dispersed phase refers to the substance which is distributed in the dispersion medium in form of colloidal particles. The term dispersion medium refers to the medium in which the substance is dispersed in the form of colloidal particles.

Complete step by step answer: Methane:
When we mix two sols that are opposite in charges to each other in appropriate proportions, the colloidal particles of one sol could neutralize the charge present on the particles of the other sol and both of the solutions coagulate.
When we add excess of an electrolyte, the precipitation of colloidal particles takes place. The reason for this is that interaction of colloids with ions carrying opposite charge to that present on themselves takes place. This leads to neutralization and neutralization leads to their coagulation. Coagulating ion is the ion that is responsible for neutralization of charge on the particles. The precipitation of positively charged sol is caused by the negative ion and the precipitation of negatively charged sol is caused by the positive ion.
Therefore, when we mix a positively charged iron hydroxide colloidal sol with negatively charged colloidal gold sol, coagulation takes place on both of the sols.
Hence option B is correct.

Note:
We can also achieve coagulation of the colloidal solution by electrophoresis and persistent dialysis.
Electrophoresis: In the process of electrophoresis, the migration of charged colloidal particles to oppositely charged electrodes takes place and they get discharged. This leads to the coagulation of the solution.
Persistent dialysis: When sol undergoes persistent dialysis, the traces of electrolyte passes through the membrane. In the absence of the electrolyte, sol becomes unstable and it gets coagulated.