Problem: The freezing point of t-butanol is 25.50°C and Kf is 9.1°C • kg/mol. Usually t-butanol absorbs water on exposure to air. If the freezing point of a 10.0-g sample of t-butanol is 24.59°C, how many grams of water are present in the sample?

🤓 Based on our data, we think this question is relevant for Professor Weiss' class at OREGONSTATE.

FREE Expert Solution

We’re being asked to determine the mass of water present in a 10.0 g sample of t-butanol with a freezing point of 24.59°C.


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:


ΔTf=Tf, pure solvent-Tf, solution


The change in freezing point is also related to the molality of the solution:


ΔTf=imKf


where: 

i = van’t Hoff factor

m = molality of the solution (in m or mol/kg)

Kf = freezing point depression constant (in ˚C/m)


Recall that the molality of a solution is given by:


molality=moles solutekg solvent



To solve this problem, we shall follow these steps

Step 1: Calculate for ΔTf.

Step 2: Determine the molality of the solution.

Step 3: Calculate the mass of H2O.


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Problem Details

The freezing point of t-butanol is 25.50°C and Kf is 9.1°C • kg/mol. Usually t-butanol absorbs water on exposure to air. If the freezing point of a 10.0-g sample of t-butanol is 24.59°C, how many grams of water are present in the sample?

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 Freezing Point Depression concept. If you need more Freezing Point Depression practice, you can also practice Freezing Point Depression practice problems.

What professor is this problem relevant for?

Based on our data, we think this problem is relevant for Professor Weiss' class at OREGONSTATE.

What textbook is this problem found in?

Our data indicates that this problem or a close variation was asked in Chemistry: An Atoms First Approach - Zumdahl 2nd Edition. You can also practice Chemistry: An Atoms First Approach - Zumdahl 2nd Edition practice problems.