Freezing Point Depression Lab

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Introduction: Freezing point depression is a colligative property that calculates the decrease of the freezing point when any solute is added to a solvent. When determining changes in freezing point, solute concentration is measured in molality which is moles of solute per kilogram of solvent. The concentration unit moles per kilogram is temperature independent, because mass does not vary with temperature. The decrease in freezing point of the pure solvent is proportional to the molality of the particles of solute and is represented by the following equation: ΔTf=Kf ۰ m. By finding the freezing point of an unknown solution, it provides an opportunity to determine the molar mass of the unknown substance. Also, in this experiment a heating…show more content…
To prepare for the lab, fill one 600 mL beaker ⅔ full with tap water (roughly 400 mL full) and place on a hot plate with a thermometer. This beaker’s temperature needs to stay constant at 60℃ so the hot plate settings may need to be adjusted throughout the lab. Next, fill the 1000 mL beaker ⅔ full with cool tap water (roughly 700mL full) and place a thermometer in it. Set this beaker aside and maintain a temperature of roughly 25℃. Place the test tube of benzoic acid/lauric acid in the 60℃ water on the hot plate and when the solid solution begins to melt place the thermometer that was in the water into the test tube. Continue to heat the solution until it reaches about 55℃. Using the test tube holder, transfer the liquefied solution tube to the 25℃ water and record the temperature at 30-second intervals using a clock or stopwatch using a pencil until the solution reaches 35℃ or close to the temperature due to experimental error. While cooling, gently stir the solution using the thermometer until the solution begins to solidify. Once all the data is collected, reheat the solid solution tube in the warm water until it melts and remove the thermometer and wipe it off to avoid the solution adhering to the thermometer. After the data has been recorded, clean-up the lab station and put away the lab…show more content…
It also confirmed the idea that molar mass of a solution could be determined through the freezing point depression formula as long as one knows the freezing point depression constant of the solvent used, the mass in kilograms for the solute-solvent mixture, and the change in freezing point from the addition of a solute.

Lab Questions:
What is the freezing point for lauric acid? What is the melting point for lauric acid?
The freezing point for lauric acid in this experiment was 43℃. The melting point for lauric acid in this experiment was 50℃.
Explain what is happening during each section of the graph for both cooling and heating in terms of particle motion and energy.
When heat is added to a substance the particles in the substance vibrate faster and when vibrate faster the space between the particles increases. The hotter it gets the more the object expands and takes up more space. When a substance is cooled the particles vibrate less causing them to constrict and take up less space. The colder the solution gets the more the particles compact and
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