Question

1mol NaCl in 1000g ${{H}_{2}}O$will change the boiling water to
A. 100.51
B. 101.04
C. 101.53
D. 101.86
E. 103.62

Answer 1

Hint: The boiling point of a liquid is the temperature at which the vapor pressure of the liquid becomes equal to the atmospheric pressure. At this temperature the liquid is converted into a vapor. Boiling point of water is ${{100}^{{}^\circ }}C$.

Complete answer:
Boiling point elevation defines the increase in the boiling point of a solvent by the addition of a solute. When a non-volatile solute is added to a solvent the resulting solution has a higher boiling point than that of the pure solvent. In this case salt is added to water which increases its boiling point.
Elevation in boiling point represented by $\Delta {{T}_{b}}$where it can be calculated by the formula
$\Delta {{T}_{b}}=i{{K}_{b}}m$, where i and ${{K}_{b}}$are van’t hoff factor of NaCl and constant of water respectively.
Van’t hoff factor of NaCl = 2
Molality of NaCl = $\dfrac{1}{1000}\times 1000=1m$
\[{{K}_{b}}={{0.512}^{{}^\circ }}C/molal\]
\[\Delta {{T}_{b}}={{T}_{final}}-{{T}_{initial}}=i{{K}_{b}}m\]
\[{{T}_{final}}=100+2\times 0.512\times 1\]
\[{{T}_{final}}=100+1.024={{101.024}^{{}^\circ }}C\]

Thus we can say that option B is the correct answer.

Note:
Van’t Hoff factor can be defined as the ratio of the concentration of particles formed when a substance is dissolved to the concentration of the substance by mass. The extent to which a substance associates or dissociates in a solution is described by the Van’t Hoff factor.