Chemistry - Liquid Solution Question with Solution | TestHub

Explain the question : Find solution with least freezing point depression.

Concept : This question is based on $\Delta {\mathrm{T}}_{\mathrm{f}}=\mathrm{i}{\mathrm{K}}_{\mathrm{f}}\mathrm{m}$, where i is van't hoff factor; larger $\mathrm{i}\to$ more particle count ⟶ lower freezing point.

Solution :

For 0.1 m glucose (non-electrolyte), $\mathrm{i}=1$

For 0.1 m NaCl , ideally $\mathrm{i}=2\left({\mathrm{Na}}^{+}+{\mathrm{Cl}}^{-}\right)$.

For $0.1\mathrm{m}{\mathrm{AlCl}}_3$, ideally $\mathrm{i}=4\left({\mathrm{Al}}^{3+}+3{\mathrm{Cl}}^{-}\right)$.

For $0.1\mathrm{m}{\mathrm{K}}_4\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]$, dissociation: $4{\mathrm{K}}^{+}+{\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]}^{4-}$, so $\mathrm{i}=5$

Thus, the depression order : glucose $<{\mathrm{NaCl}}_3<{\mathrm{K}}_4\left[\mathrm{Fe}(\mathrm{CN}{)}_6\right]$. The highest freezing point corresponds to smallest depression, i.e. glucose solution.

Final answer : A