Question

Lyophilic colloidal sols are much more stable than lyophobic colloidal sols. This is due to the extensive solvation of lyophilic colloidal sols, which form a protective layer outside it which prevents it from forming associated colloids. Lyophilic colloidal sols also protect lyophobic colloidal sols from precipitation by the action of electrolytes. This is due to the formation of a protective layer by the lyophilic sols outside lyophobic sols. Lyophilic sols are also called protective sols.
Gelatin (lyophilic) protects gold sol (lyophobic) from coagulation on the addition of a solution of sodium chloride. The protective powers of different colloidal sols are measured in terms of gold number.
Gold number is defined as the amount of protective sol in milligrams that prevents the coagulation of 10 mL of a given gold sol on adding 1 mL of a $10\%$ solution of sodium chloride. Thus, the smaller the gold number of a lyophilic sol, the greater is the protective power.

$\left[AgI\right]I^{-}$ colloidal sol can be coagulated by the addition of a suitable cation. 1 mol $\left[AgI\right]I^{-}$ requires $AgN{O}_3,Pb(N{O}_3{)}_2$ & $Fe(N{O}_3{)}_3$ as (in moles):

• A. $1,1,1$
• B. $1,2,3$
• C. $1,\frac{1}{2},\frac{1}{3}$
• D. $6,3,2$

Answer 1

The correct option is C $1,\frac{1}{2},\frac{1}{3}$

$\left[AgI\right]I^{-}$ is a negatively charged solution.

1 mole of $\left[AgI\right]I^{-}$ requires:

1 mole of $AgN{O}_3$ since 1 mole of $AgN{O}_3$ provides 1 mole of $N{O}_3^{-}$ ions.

1/2 mole of $Pb(N{O}_3{)}_2$ since 1 mole of $Pb(N{O}_3{)}_2$ provides 2 moles of $N{O}_3^{-}$ ions.

1/3 mole of $Fe(N{O}_3{)}_3$ since 1 mole of $Fe(N{O}_3{)}_3$ provides 3 moles of $N{O}_3^{-}$ ions.