Chapter 1.
Overview
Experiment 15
Freezing Point Depression
The learning objectives of this experiment are as follows:
- Use laboratory techniques to explore the freezing point depression of a solution.
- Determine the molecular weight of an unknown compound by measuring the freezing point depression.
The Department of Chemistry and Biochemistry
The Ohio State University
Intro
Freezing point depression is an interesting property of solutions. We routinely exploit this phenomenon in clever ways. If you have made your own ice cream before then you have experimented with freezing point depression. Water will freeze to ice at 32 °F. In order to freeze the components that make up ice cream, the temperature must be lower than this. We can add salt to our water/ice mixture and this lowers the freezing point, low enough to freeze ice cream. Living in Ohio we see city trucks laying salt and brine solutions on the roads; the purpose is again to lower the freezing point of water, so that ice formation on the roads is reduced. In this lab you will determine the freezing point of a pure liquid, and then again for a solution. Using the freezing point depression you will be able to calculate the molecular weight of the unknown solute.
Procedure
Treatment of Data
The freezing point depression, ΔTf, is the difference between the freezing point (f.p.) of the pure solvent and the freezing point of the solution.
ΔTf = f.p.pure solvent − f.p.solution
Disposal of Chemicals
Credits