Question

One desires to prepare a positively charged silver iodide sol. This can be achieved by

• A. Adding a little AgNO₃ solution to KI solution in slight excess
• B. Adding a little KI solution to AgNO₃ solution in slight excess
• C. Mixing equal volumes of equimolar solutions of AgNO₃ and KI
• D. None of these

Answer 1

Answer: (B)

In the preparation of positive sol of $AgI$ , the excess of $AgN{O}_3$ is added to potassium iodide solution.
If potassium iodide is taken slight excess, negative sol of silver iodide is formed.
$KI+AgN{O}_3\to AgI+KN{O}_{3}AgN{O}_3\to A{g}^{+}+N{O}_3^{-}AgI+A{g}^{+}\to AgI/A{g}^{+}$