Question

When excess of an electrolyte is added, the colloidal particles are precipitated.

1. Give the reason for precipitation.

2. Arrange the following ions in the increasing order of the flocculating power in coagulation of negative sol.

K⁺, Ca²⁺, Fe³⁺

Answer 1

1. A colloid can be precipitated by an ion having opposite charge to that of the colloid. Greater the valency of coagulating ion added greater its power to precipitate.

eg: Al³⁺ > Mg²⁺ > SO₄^2- > Na⁺ > PO³⁺ > Cl^-

2. K⁺ < Ca²⁺< Fe³⁺

3. These are arranged based on Hardy-Shulze rule.