# Problem: Which of the following aqueous solutions has the highest boiling point? Kb for water is 0.52 degrees C/m.A) 0.2 m KClB) 0.2 m Na2SO4C) 0.2 m Ca(NO3)2D) A and BE) B and C

###### FREE Expert Solution

We’re being asked to determine the solution that has the highest boiling point

Recall that the boiling point of a solution is higher than that of the pure solvent and the change in boiling point (ΔT­b) is given by:

The change in boiling point is also related to the molality of the solution:

$\overline{){{\mathbf{\Delta T}}}_{{\mathbf{b}}}{\mathbf{=}}{{\mathbf{imK}}}_{{\mathbf{b}}}}$

where:

i = van’t Hoff factor

m = molality of the solution (in m or mol/kg)

Kb = boiling point elevation constant (in ˚C/m) of the solvent

The problem states that we have aqueous solutions which means the solvent is water.  This means the value of Kb is the same for all the given solutions.

Therefore, ΔTb will just depend on the osmolality of each solution, given by:

$\overline{){\mathbf{Osmolality}}{\mathbf{=}}{\mathbf{i}}{\mathbf{×}}{\mathbf{m}}}$

higher osmolality or concentration will result in a higher boiling point.

• 0.2 m KCl

The molality of the solution is 0.20 m. KCl is an electrolyte that dissociates in the following manner:

KCl K+ + Cl

The dissociation formed a total of 2 ions which means i = 2Solving for osmolality:

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###### Problem Details

Which of the following aqueous solutions has the highest boiling point? Kb for water is 0.52 degrees C/m.
A) 0.2 m KCl
B) 0.2 m Na2SO4
C) 0.2 m Ca(NO3)2
D) A and B
E) B and C