Question

Which mixture of the solution will lead to the formation of negatively charged colloidal $[AgI]{{I}^{-}}$ sol?
(a)- 50 mL of 1 M $AgN{{O}_{3}}$ + 50 mL of 1.5 M $KI$
(b)- 50 mL of 1 M $AgN{{O}_{3}}$ + 50 mL of 2 M $KI$
(c)- 50 mL of 2 M $AgN{{O}_{3}}$ + 50 mL of 1.5 M $KI$
(d)- 50 mL of 0.1 M $AgN{{O}_{3}}$ + 50 mL of 0.1 M $KI$

Answer 1

$AgN{{O}_{3}}$, when dissolved in water, dissociates into silver cation and nitrate anion, and $KI$, when dissolved in water, dissociates into potassium ion and iodide ion, and when they are mixed $AgI$ will be formed. If silver iodide has to be surrounded by iodide ion then the concentration of $KI$ must be more.

Complete step by step solution:
The stability of the colloidal sol is defined by some properties. The electrical charge on the colloidal particle is one of them. The electrical charge on the colloidal particle is explained by the process of preferential adsorption of ions from the solution. During the preparation of colloidal sol, an ionic colloidal adsorb ions common to its lattice.
It can be explained by the colloidal sol $AgI$ is prepared by adding $KI$ solution to the $AgN{{O}_{3}}$ solution till $KI$ is in slight excess, iodide ion (${{I}^{-}}$) will be absorbed in the surface of $AgI$ particles thereby giving them a negative charge:
$AgI+{{I}^{-}}\to AgI:{{I}^{-}}$
The reaction that takes place when $AgN{{O}_{3}}$ and $KI$ react together is:
$AgN{{O}_{3}}+KI\to AgI+KN{{O}_{3}}$
So for surrounding the silver iodide with iodide ion, the concentration of $KI$ must be slightly more.
So, from the above options given, the options that has concentration of $KI$slightly more than $AgN{{O}_{3}}$ is option (a)- 50 mL of 1 M $AgN{{O}_{3}}$ + 50 mL of 1.5 M $KI$

Therefore, the correct answer is an option (a)- 50 mL of 1 M $AgN{{O}_{3}}$ + 50 mL of 1.5 M $KI$.

Note: You may get confused that in option (b) also the concentration of potassium iodide is higher than the concentration of silver nitrate, but the concentration of potassium iodide is double the concentration of silver nitrate due to which the coagulation of $AgN{{O}_{3}}$ will start, so this option is incorrect.