Question

Which of the following exhibits the highest boiling point?

• A. $0.1\text{m urea}$
• B. $0.05\text{m}NaCl$
• C. $0.025\text{m}Al(OH{)}_3$
• D. $\text{All of the above will have same boiling point}$

Answer 1

The correct option is D $\text{All of the above will have same boiling point}$

Boiling point of a solution is a colligative property. So number of solute particles plays an important role here.
A) Urea does not dissociate
$\text{So effective molality}=0.1\text{m}$
B) $NaCl$ in solution dissociates as $N{a}^{+}$ and $C{l}^{-}$ ion. So van't Hoff factor for $NaCl$ is $2$
$\text{So effective molality}=0.05\times 2=0.1\text{m}$
C) $Al(OH{)}_3$ in solution dissociates as $A{l}^{3+}$ and $3O{H}^{-}$. So van't Hoff factor for $Al(OH{)}_3$ is $4$
van't Hoff factor for $Al(OH{)}_3$ is $4$
$\text{So effective molality}=0.025\times 4=0.1\text{m}$
Hence all of them has the same boiling point