The Determination of the Freezing Point of Lauric Acid Purpose The intention of this experiment was to quantitatively calculate the freezing point/melting point of lauric acid through melting and cooling the lauric acid and finding the freezing point on the graph of its temperature change over time. Then the determined freezing point was used to determine the effect of varying concentrations of benzoic acid on the freezing point of lauric acid. This experiment was to further understand on the nature of pure substances and their physical properties, in this case freezing point, both as pure and with impure molecules. Introduction With the freezing of substances, normally the molecules have a tighter molecular arrangement and thereby making them into a more dense solid that would require significant amounts of energy to break these strong intermolecular forces. However, impurities can disrupt these naturally strong intermolecular forces and thereby making the substance to be easier to melt but harder to freeze as greater amounts of energy would need to be put into the system. The greater amount of energy needed to solidify the substance would correspond to a lower freezing point as more energy would be taken out resulting in the driving down of temperature. A common example is the sprinkling of ionic salts, most commonly calcium chloride, to lower the melting point of water so that ice can melt at lower amounts of energy as the calcium chloride disrupts the hydrogen bond lattice created present in ice, and less energy is required to break these hydrogen bonds. As a note, it is significant to know that freezing point and melting point are the same value and to the use of the terms depend on the direction of phase change; if it is from liquid to solid, the correct term is freezing point, and if solid to liquid, the correct term is melting point. In this experiment, the two terms will be used interchangeably. Procedure The process for first determining the freezing point of the lauric acid is done in three parts. First, the pure lauric acid was melted in a beaker of boiling water. Once all of
Using Freezing-Point Depression to Find Molecular Weight Formal Lab Report Purpose: The purpose of this lab is to be able to use the freezing point of a substance to find the molecular weight of it. To do this, we will use the Logger Pro program to obtain the freezing point of lauric acid and a solution of benzoic acid and lauric acid. Then, we’ll go calculate the freezing point depression of the solution and the molecular weight of benzoic acid. Procedure Summary: Obtain lab goggles and a lab apron before you begin.
Connect a temperature probe to channel 1 of the vernier computer interface. Connect the other cable to the computer. Engage Logger Pro and open the file titled “04 Freezing Point” in the “Advanced Chemistry with Vernier” folder. Part 1: Determine the Freezing Point of Pure Lauric Acid Fill a 400 mL beaker with 300 mL of 20 – 24 oC tap water and insert it in the ring stand. Use the utility clamp while obtaining a hot test tube containing hot, melted lauric acid from your instructor. Fasten the clamp at the top of the tube.
Put the temperature probe into the hot lauric acid and begin to collect data. Attach the utility clamp to the ring stand so that it’s above water. Lower the test tube in the water to where the water line is above the lauric acid that is inside the test tube. In an up-and-down motion, stir the lauric acid continously with the temperature probe for ten minutes. When you finish collecting data, use the hot water to melt the lauric acid enough to remove the temperature probe from the test tube. Wipe off the excess lauric acid on the probe with a paper towel. Find the freezing temperature.
Part 2: Determine the Freezing Point of a Benzoic Acid and Lauric Acid Solution Get a test tube filled with 1 g of benzoic acid dissolved 8 g of lauric acid. Record the precise masses. Repeat steps 1 to 7. Find the freezing temperature. Record findings in data table. Print graph. Data and Calculations: When putting the lauric acid in into the water, our group noticed that the lauric acid froze almost instantly while the benzoic-lauric acid solution, it took a while to freeze. |Mass of lauric acid (g) |8. 10 g | |Mass of benzoic acid (g) |0. 8 g | |Freezing temperature of pure lauric acid (oC)|42. 97 oC | |Freezing point of the benzoic acid (oC) |40. 43 oC | Conclusions and Questions: At the end of our experiment, we found the freezing point of the benzoic-lauric acid to be , and the molecular weight of the benzoic acid to be . 42. 97 – 3. 9 = 39. 07 = ? T m = 10. 02 mol/kg (m) 8. 10 g lauic acid / 1000 g = 0. 081 mol benzoic acid (12. 011 X 7) + (1. 008 X 6) + (15. 9 X 2) = 122. 123 g/mol C6H5COOH
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