Question:medium

Which of the following aqueous solutions having same molality exhibits maximum boiling point elevation? (Assume complete dissociation)

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More ions produced = Greater change in colligative properties.
Updated On: Jun 19, 2026
  • $KCl$
  • $NaCl$
  • $AlCl_{3}$
  • $BaCl_{2}$
Show Solution

The Correct Option is C

Solution and Explanation

Step 1: Understanding the Question:
Elevation in boiling point (\( \Delta \text{T}_{\text{b}} \)) is a colligative property that depends on the total number of solute particles in the solution.

Step 2: Key Formula or Approach:

\[ \Delta \text{T}_{\text{b}} = \text{i} \times \text{K}_{\text{b}} \times \text{m} \]
Since molality (\( \text{m} \)) and \( \text{K}_{\text{b}} \) are constant, \( \Delta \text{T}_{\text{b}} \propto \text{i} \), where \( \text{i} \) is the van't Hoff factor.

Step 3: Detailed Explanation:

Let's find the value of \( \text{i} \) for each salt assuming complete dissociation:
(A) \( \text{KCl} \rightarrow \text{K}^+ + \text{Cl}^- \); \( \text{i} = 2 \)
(B) \( \text{NaCl} \rightarrow \text{Na}^+ + \text{Cl}^- \); \( \text{i} = 2 \)
(C) \( \text{AlCl}_3 \rightarrow \text{Al}^{3+} + 3\text{Cl}^- \); \( \text{i} = 4 \)
(D) \( \text{BaCl}_2 \rightarrow \text{Ba}^{2+} + 2\text{Cl}^- \); \( \text{i} = 3 \)
\( \text{AlCl}_3 \) produces the highest number of ions (4) per mole of salt.

Step 4: Final Answer:

\( \text{AlCl}_3 \) exhibits the maximum boiling point elevation.
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