Lab Report Freezing Point Depression Constant of Lauric Acid PDF

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This is the lab report for Lab of Freezing Point. Abstract Intro and results included...

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  LAB 10 : Freezing Point Depression Constant of Lauric Acid Abstract The purpose of this lab experiment is to determine the freezing point depression constant (Kf) for lauric acid by using LabPro. We use this method because lauric acid is a nonelectrolyte. This lab teaches us about the process of melting and freezing. 

Introduction For the process of freezing , impurities in a substance may interfere with normal molecular interactions. In order for a system to solidify, more energy must be taken out of the system. In other words, the temperature must be lowered. The amount that the freezing point is lowered is told by the equation: ΔT=Kfm “Delta T” represents the lowering of the freezing point in degrees celsius for the solution. The variable “m” represents the molality (contrast from molarity) which is defined as the number of moles of solute divided by the mass of the solvent. Specifically of this experiment we use benzoic acid as the solute and lauric acid as the solvent. The basis of this experiment can somewhat be useful and applicable to the real world situations such as cold winter and snow in helping us understand the true effects of freezing/melting point.  Procedure SUPPLIES ● 400 mL beaker ● Hot plate ● Temperature probe ● Test tube  

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Ice chips 1.5 g Lauric acid 0.75 g benzoic acid

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Obtain the supplies needed for the experiment. Get a tube of 1.5 g Lauric acid and 0.75 g benzoic acid. Place test tubes in a beaker of water on the hot plate and melt the mixtures. When fully melted, take it out of hot water bath. Add the temperature probe and click ‘collect’ on the computer using the LabPro system. Obtain the freezing curve for the solution. While the data has started collecting, place the tube into a room temperature water bath and stir. 8. Determine the freezing point. 9. Calculate the ΔT and molality of this solution.

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Data & Results

   The graph readings of Lauric acid and benzoic acid had the appropriate pattern that we expected. Initially there is a spike then a drop in temperature as time progresses. Within a matter of minutes the temperature curve has reached its flat portion that indicates the freezing point. Although unlikely, error could have happened throughout this experiment when using the Lab Pro system and software. If the equipment was not working properly, the freezing points found would be inaccurate, affecting the resulting calculations.     Kf Lauric Acid Data & Calculation Sheet Mp of pure Lauric Acid Avg: 42.32 °C The freezing point (43.32°C) was found by highlighting the flat part of the curve on Lab Pro & clicking line of best fit. It is the y-intercept.

Benzoic Acid: MW 122.12 g/mol Freezing Point Depression Data: 1.5 g Lauric Acid m: .936 ΔT: (43.22°C-37.68°C) → 5.54°C 0.75 g Benzoic Acid m: .767 ΔT: (43.22°C-41.81 °C) → 1.41 °C AVERAGE Kf: 3.88

Kf: 5.92 Kf: 1.84

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Conclusion In conclusion, we were able to determine the freezing point depression constant for lauric acid using the temperature probe and the graph on the Lab Pro software. Also, calculations using the formulas- ΔT=Kfm and molality mol/kg - were useful for understanding and analyzing the data we obtained. Overall, the lab carried out its purpose We were able to successfully use the procedure to determine the freezing point depression constant using a simple method....