Question

A reddish positive charged sol is obtained by adding small quantity of `FeCl_(3)` solution to freshly prepared and well washed `Fe(OH)_(3)` precipitate. How does it take place?

Answer 1

It is due to adsorptions of `Fe^(3+)` ions on the surface of `Fe(OH)_(3)` which gives colloidal sol.
`Fe(OH)_(3) ("ppt.")+Fe^(3+)("ions adsorbed") rarr [Fe(OH)_(3)]Fe^(3+)` ("colloidal sol.)