TBR phase change problem

[chrisharimlee]

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TBR phases and phase changes

can some one help me out?

passage X
problem 65

menthol and camphor do not dissociate once in solution. If an impurity were chosen that can dissociate into two particles in solution, how would the freezing point be affected?

A. The freezing point would decrease by twice as much as expected, if the impurity did not dissociate.

B. The freezing point would decrease by as much as expected, if the impurity did not dissociate.

C. The freezing point would decrease by half as much as expected, if the impurity did not dissociate.

D. The freezing point would remain constant.

 

[chrisharimlee]

answer: A

 

[cloak25]

ΔT = i Kf m
The problem says that the impurity dissociates into two particles in solution so i=2. This means that ΔT also changes by a factor of 2. More particles decreases freezing point and increases boiling point.

 

[chrisharimlee]

Thanks for your answer. I get that part, but in the answer choices they say that the impurity didn't dissociate. So how can it still decrease by a factor of 2?

 

[Silo004]

http://forums.studentdoctor.net/showthread.php?t=844930

Apparently the answer should be C, that's what I selected.