Multiple Choice
Which of the following best describes the effect of adding a nonvolatile solute to pure fluorine on its freezing point?
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14. Solutions
Freezing Point Depression
Multiple Choice
Which aqueous solution has the lowest freezing point (assume all solutes are nonelectrolytes and the solutions are ideal)?
A
m glucose
B
m sucrose
C
m ethylene glycol
D
m urea
Verified step by step guidance1
Recall that the freezing point depression of a solution is given by the formula \(\Delta T_f = i K_f m\), where \(\Delta T_f\) is the freezing point depression, \(i\) is the van't Hoff factor, \(K_f\) is the freezing point depression constant of the solvent, and \(m\) is the molality of the solution.
Since all solutes are nonelectrolytes, they do not dissociate in solution, so the van't Hoff factor \(i = 1\) for all cases.
Because the solvent and \(K_f\) are the same for all solutions, the freezing point depression depends directly on the molality \(m\) of each solution.
Compare the molalities of the given solutions: 0.50 m glucose, 0.25 m sucrose, 2.00 m ethylene glycol, and 1.00 m urea. The solution with the highest molality will have the greatest freezing point depression and thus the lowest freezing point.
Identify the solution with the highest molality (2.00 m ethylene glycol) as the one with the lowest freezing point.
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