Question

Question: if you added ethylene glycol to your car's radiator to lower the freezing point to -31.0 degree C, what would the corresponding boiling point of the coolant in your radiator. The freezing point and boiling point constants for water are 1.86 and .510 degree C/m

The correct answer for this problem is 108.5 degree C, but i don't get how they got that. Did they use the Delta Tf=Kf. How did they plug in the numbers to get that answer. Any help on doing the problem would be great?

Answer 1

It's done this way.
delta T = Kf*m
delta T you know is 31. You know Kf. Calculate m (molality or the concentration of the ethylene glycol).
Now go to the boiling point.
delta T = Kb*m
You want to calculate delta T, you know Kb and m is what you just calculated from the first part of the problem. The answer is, indeed, 108.5 although tha's too many significant figures to use. You have 3 s.f. in your numbers; therefore, the answer should be rounded to 108 (but follows your teacher's instructions).