Question

The freezing point of equimolal aqueous solutions will be highest for

• A. C$_6$H$_5$NH$_3$Cl
• B. AgNO$_3$
• C. Ca(NO$_3$)$_2$
• D. La(NO$_3$)$_3$
• E. D-fructose

Hint:

Higher dissociation → lower freezing point. Non-electrolytes always give highest freezing point.

Answer 1

Answer: (E)

Concept:
Freezing point depression: \[ \Delta T_f = i K_f m \] Where $i$ = van’t Hoff factor.
• Larger $i$ → more depression → lower freezing point
• Smaller $i$ → less depression → higher freezing point

Step 1: Evaluate nature of solutes.

• C$_6$H$_5$NH$_3$Cl → electrolyte (dissociates)
• AgNO$_3$ → strong electrolyte (2 ions)
• Ca(NO$_3$)$_2$ → 3 ions
• La(NO$_3$)$_3$ → 4 ions
• D-fructose → non-electrolyte ($i=1$)

Step 2: Compare $i$.
Electrolytes have $i>1$, while D-fructose has $i=1$ (minimum).

Step 3: Conclusion.
Least depression → highest freezing point: \[ \text{D-fructose} \]