Question

The origin of charge on colloidal solutions is due to:

• A. Frictional rubbing
• B. Electron capture during Bredig’s arc method
• C. Selective adsorption of ion on their surface
• D. Addition of protective colloids

Answer 1

Answer: (A), (B), (C)

Selective adsorption of ion on their surface

The correct options are (a), (b)and (c).
a) It is believed that some charges appear on colloidal particles due to rubbing of the dispersed phase particles with the dispersion medium.
b) The Bredig's arc method helps in the preparation of colloidal solution of metals like gold, silver or platinum. Due to the heat of the arc, the metals get vaporized and condense under cold water. The colloidal particle prepared, are stabilized by adding small amount of KOH. Colloidal solutions prepared by this method acquire charge by capturing electrons.
c) The dispersed phase of a colloid adsorb those ions preferentially which are common with their own lattice ions. The colloidal solution is said to be positively or negatively charged depending on the charge on the particles of the dispersed phase.
d) A protective colloid is a colloid that resists the coagulation of another colloid in presence of an electrolyte. So, it has no affect on the charge of a colloidal solution.