Question

Explain any one method for coagulation.

Answer 1

The flocculation and setting down of the sol particles is called coagulation.

Various methods of coagulation are given below:

1. Addition of electrolytes
2. Electrophoresis
3. Mining oppositely charged sols
4. Boiling.

Addition of electrolytes:
A negative ion causes the precipitation of positively charged sol and vice versa. When the valency of an ion is high, the precipitation power is increased. For example, the precipitation power of some cations and anions varies in the following order

Al³⁺ > Ba²⁺ > Na⁺

Similarly \[\ce{[Fe(CN)6]^{-3} > SO^{-2}_4 > Cl^-}\]

The precipitation power of electrolyte is determined by finding the minimum concentration (millimoles/lit) required to cause precipitation of a sol in 2 hours. This value is called flocculation value. The smaller the flocculation value greater will be precipitation.