Question

When an excess of a very dilute aqueous solution of KI is added to a very dilute aqueous solution of silver nitrate, the colloidal particles of silver iodide are associated with which of the following Helmholtz double layer?

• A. AgI ⋮ Ag⁺ ⋮ I^–
• B. AgI ⋮ K⁺ NO₃^-
• C. AgI ⋮ NO₃^- ⋮ K⁺
• D. AgI ⋮ I^– ⋮ K⁺

Answer 1

The correct option is D AgI ⋮ I^– ⋮ K⁺

As excess of KI has been added, $I^{-}$ ions are adsorbed on AgI forming a fixed layer (and giving it a negative charge). It then attracts the counter ions $K^{+}$ from the medium forming a second layer (diffused layer).