Question

Which of the following has the highest boiling point?
A. 0.01 M $N{{a}_{2}}S{{O}_{4}}$
B. 0.015 M Sucrose
C. 0.015 M Glucose
D. 0.01 M $NaN{{O}_{3}}$

Answer 1

Boiling point elevation describes the phenomenon that the boiling point of a liquid will be higher when another compound is added which clearly tells that solution has a higher boiling point than a pure solvent.

Complete Step by step solution: Boiling point elevation is a colligative property which describes that it is dependent on the presence of dissolved particles and their number but not on their identity. It is an effect of the dilution of the solvent in the presence of a solute. In the above solution we can tell the highest boiling point with the help of van’t hoff factor. Higher the value of van’t hoff factor higher is the boiling point. Formula used for the calculation of elevation in boiling point:
$\Delta {{T}_{b}}=i\times {{k}_{b}}\times m$
where,
$\Delta {{T}_{b}}$= change in boiling point
${{k}_{b}}$ = boiling point constant
m = molality
i = Van't Hoff factor
Now we have to calculate the Van't Hoff factor for the given solutions.
A. $N{{a}_{2}}S{{O}_{4}}$
Dissociation can be shown as; $N{{a}_{2}}S{{O}_{4}}\to 2N{{a}^{+}}+S{{O}_{4}}^{2-}$
Van't Hoff factor = Number of solute particles i.e. 2 + 1 = 3
B. Sucrose: is a nonelectrolyte solute which maintain their molecularity and will not undergo any type of association or dissociation reaction so their Van't Hoff factor = 1
C. Glucose: It is also a non-electrolyte solute having Van't Hoff factor = 1
D. $NaN{{O}_{3}}$
The dissociation of $NaN{{O}_{3}}$ can be shown as,
$NaN{{O}_{3}}\to N{{a}^{2+}}+N{{O}_{3}}^{2-}$
Van't Hoff factor = 1 + 1 = 2

From the above discussion we conclude that higher the van’t hoff factor higher is the boiling point so the option A is correct.

Note: The van 't Hoff factor is defined as the ratio between the actual concentration of particles produced when the substance is dissolved and the concentration of a substance as calculated from its mass. The van 't Hoff factor is essentially 1 for non-electrolytes which dissolved in water and equal to the number of discrete ions in a formula unit of the substance for ionic compounds dissolved in water.