We’re being asked to determine the solution that has the lowest freezing point
Recall that the freezing point of a solution is lower than that of the pure solvent and the change in freezing point (ΔTf) is given by:
The change in freezing 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)
Kf = freezing point elevation constant (in ˚C/m) of the solvent
The problem states that we have aqueous solutions which means the solvent is water.
Therefore, ΔTf will just depend on the osmolality of each solution, given by:
A higher osmolality or concentration will result in a lower freezing point.
The molality of the solution is 0.40 m. K2SO4 is an electrolyte that dissociates in the following manner:
K2SO4 → 2 K+ + SO42-
The dissociation formed a total of 3 ions which means i = 3. Solving for osmolality:
Which of the following aqueous solutions would be expected to have the lowest freezing point?
A) 0.400 m K2SO4
B) 0.400 m NaCl
C) 0.400 m C6H12O6 (glucose)
D) 0.040 m K2SO4
E) 0.040 m NaCl
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