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:
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:
A higher osmolality or concentration will result in a higher boiling point.
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 = 2. Solving for osmolality:
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
Frequently Asked Questions
What scientific concept do you need to know in order to solve this problem?
Our tutors have indicated that to solve this problem you will need to apply the The Colligative Properties concept. You can view video lessons to learn The Colligative Properties. Or if you need more The Colligative Properties practice, you can also practice The Colligative Properties practice problems.