Objectives To determine the molar mass of an unknown solid using the colligative property of freezing point depression. When a small amount of nonvolatile solute is dissolved in a volatile solvent, the vapor pressure of the solvent over the solution will be less than the vapor pressure of the pure solvent at the same temperature.
Therefore, the temperature at which the equilibrium vapor pressure reaches atmospheric pressure is higher for the solution than for the pure solvent.
Figure 1 below illustrates this behavior for water. In this experiment you will determine the molar mass of an unknown solid by dissolving a pre-weighed sample in a solvent, and measuring the resulting freezing point depression of the solvent.
The solvent that will be used in this experiment is para-dichlorobenzene, shown in Figure 2 below. At first the temperature will fall quite rapidly.
When the freezing point is reached, solid will begin to form, and the temperature will tend to hold steady until the sample is all solid. This behavior is shown in Figure 3 below. The freezing point of the pure liquid is the constant temperature observed while the liquid is freezing to a solid.
The cooling behavior of a solution is somewhat different from that of a pure liquid, also shown in Figure 3. As discussed earlier, the temperature at which a solution freezes is lower than that for the pure solvent. In addition, there is a slow gradual fall in temperature as freezing proceeds.
The best value for the freezing point of the solution is obtained by drawing two straight lines connecting the points on the temperature-time graph. The first line connects points where the solution is all liquid.
The second line connects points where solid and liquid coexist. The point where the two lines intersect is the freezing point of the solution. Note that when the solid first appears the temperature may fall below the freezing point, but then it comes back up as more of the solid forms.
This effect is called supercooling, and is a phenomenon that may occur with both the pure liquid and the solution see Figure 3. To establish the proper straight line in the solid-liquid region it is necessary to record the temperature until the trend with time is smooth and clearly established.
Figure 3 Procedure Chemicals: Para-dichlorobenzene PDBunknown sample, acetone Equipment: Safety The PPE for this lab includes safety goggles, lab coat and nitrile gloves. Para-dichlorobenzene is used in mothballs and urinal cakes, and so it may have a familiar smell, however direct inhalation of its vapors may be harmful or even toxic.Experiment 5 Freezing Point Depression OUTCOMES After completing this experiment, the student should be able to: determine the freezing point of a pure solvent and a solution.
Feb 10, · For UTA students in General Chemistry 2 () to plot and solve the freezing point in experiment (Freezing Point Depression). This document is the lab report from the freezing point depression and colligative properties experiment.
|Disclaimer||The temperature readings for naphthalene. The temperature readings for naphthalene and substance X.|
|Eighth grade Lesson Determining Freezing Points Lab||Cause and effect relationships may be used to predict phenomena in natural or designed systems.|
|One Part of Chemistry: Determining Molecule Weight by Freezing Point Depression Method||Cause and effect relationships may be used to predict phenomena in natural or designed systems.|
|Molecular Mass by Freezing Point Depression Lab by av s on Prezi||
In this experiment, pure lauric acid and a mixture of lauric /5(12). AP Lab Report 2: Freezing Point Depression Lance Schell, Colin Livasy, Erin Tatman, and Niral Rajyaguru Park.
Hill South High School Block One Advanced Placement (AP) Chemistry January 20, Abstract In this lab, the purpose was to use the freezing point depression method to determine the molecular weight of benzoic acid/5(12).
Molecular Mass by Freezing Point Depression Prelab Purpose Graphs Conclusion 1. To determine the molecular mass of an unknown substance by finding the freezing point of two solutions (BHT and para-dichlorobenzene, and BHT and the unknown.
View Lab Report - Experiment 3 - Determination of a Molar Mass by Freezing Point Depression from CHM at University of Toronto, Mississauga.
Experiment 3 Determination of a Molar Mass by Freezing%(18).