wht is preferential adsorption of colloidal sol?explain
The colloidal particles have a tendency to preferentially adsorb a particular type of ions from the solution. A colloidal particle usually adsorbs those ions which are in excess and are common to its own lattice. This preferential adsorption of a particular type of ions imparts a particular type of charge to colloidal particles.
For example, when colloidal sol of AgI is prepared by adding a small quantity of silver nitrate (AgNO3) solution to a large quantity of potassium iodide (KI) solution, the colloidal particles of silver iodide adsorb I– from the solution to become negatively charged, (at this stage KI is in excess, and I- is common to lattice of AgI).
AgI + I– → (AgI) : I–
(Colloidal (in excess (Colloidal particle
particle) in the medium) becomes negatively charged)
But, when colloidal sol of AgI is prepared by adding a small quantity of potassium iodide (KI) solution to a large quantity of silver nitrate solution (AgNO3); the colloidal silver iodide particles adsorb Ag+ from the solution to become positively charged, (at this stage AgNO3 is in excess and Ag+ is common to lattice of AgI).
AgI + Ag+ → (AgI) : Ag+
(Colloidal (in excess (Colloidal particle
particle) in the medium) becomes positively charged)