Question

What happens when:
(I) $KI$ is added to $AgN{{O}_{3}}$
(II) $AgN{{O}_{3}}$ is added to $KI$

Answer 1

Hint: Try to understand the type of mixture formed by the combination of the above two compounds. It is mentioned in the chapter, Surface chemistry. Now determine the difference in the two sets of mixture taking concentration as the distinguishing factor. Based on that you can explain the subsequent consequences.

Complete step by step answer:
In chemistry, a colloid is a phase separated mixture in which one substance of dispersed particles either soluble or insoluble is suspended throughout another substance.
Unlike a solution, in which solute and solvent are present in one phase only, a colloid has two phases namely, dispersed phase and dispersion medium.
When $KI$ is added to $AgN{{O}_{3}}$ we observe that the negative ion of potassium iodide is adsorbed by $AgN{{O}_{3}}$ leading to the formation of a negatively charged sol.
However, when $AgN{{O}_{3}}$ is added to $KI$, we observe that the positive ion of silver nitrate is adsorbed leading to the formation of a positively charged sol.

Additional information:
Lyophobic sols are the colloidal sols which show no affinity towards the dispersion medium. Lyophobic sols are generally considered more stable due to the following reasons:
- Preferential adsorption of ions on their surface from the solution
- The potential difference between the fixed layer and the diffused layer of opposite charges around the colloidal particles

Note: Lyophobic sols unlike lyophilic sols cannot be prepared by directly mixing dispersed phase and dispersion medium. Additional stabilizers are added to form lyophobic sols. The particles of this sol can be detected only through an ultramicroscope.