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ETK 64 - Quiz 1 - Spring 96Name: CHM114 –Summer 2021 Assignment 3 (Ch 15 & 16 Tro) Sheet 1 of 1 Name_____________ No collaboration! Due Monday, 7/19/2021. You must show your calculations. 1.) Chapter 15, Kinetics: The tabulated data were collected for this reaction at a certain temperature: X2Y 2X + Y Time (hr) [ X2Y] (M) 0.0 0.1000 1.0 0.0856 2.0 0.0748 3.0 0.0664 4.0 0.0598 5.0 0.0543 a) (20 pts) Determine the order of the reaction and the value of the rate constant at this temperature. For determining the order of the reaction, you are advised to take the spreadsheet “Integrated Rate Law Spreadsheet” in the Session 6 folder and replace the data with the data given above to determine the reaction order. b) (10 pts) What is the half life for this reaction (at the initial concentration)? c) (10 pts) What is the concentration of X after 10.0 hours. 2.) Chapter 16, Exothermic reaction equilibrium: This reaction is exothermic: C6H12O6(s) + 6O2(g) 6CO2(g) + 6H2O(g) a) (30 pts) Predict the effect (shift right, shift left, no effect) of increasing and decreasing the reaction temperature Increasing temperature: ______________ Decreasing temperature: ______________ b) (30 pts) How does the equilibrium constant depend on temperature? Experiment 5 Experiment 6: Molar Mass of a Molecular Solid from Freezing Point-Depression Measurement (original prepared by Kelemu Woldegiorgis) With added videos and virtual data Objective:- To determine the molar mass of benzoic acid from freezing-point depression measurement BACKGROUND Colligative properties of solutions are properties that depend upon the concentration of solute molecules or ions, but not upon the identity of the solute. Colligative properties include freezing point depression, boiling point elevation, vapor pressure lowering, and osmotic pressure. At the freezing point, a pure liquid and its solid are in equilibrium, and have the same vapor pressure. When a solute is dissolved in a pure liquid, the freezing temperature is lowered in proportion to the number of moles of solute added. This lowering of temperature is called freezing point depression. Since the vapor pressure is lower in the solution than in the pure liquid, it requires a lower temperature to achieve equilibrium between solid and solution. The expression for the freezing point depression Tf is: Tf = Kf . m (1) where Kf is the freezing point depression constant for the solvent and m is the molality of the solute. Molality is defined as the number of moles of solute in 1.0 kg of solvent. When working with colligative properties it is convenient to express the solute concentration in terms of its molality: (2) In this experiment, you will first find the freezing temperature of the pure solvent, lauric acid, CH3(CH2)10 COOH. You will then add a known mass of benzoic acid solute, C6H5COOH, to a known mass of lauric aicd, and determine the lowering of the freezing temperature of the solution. By measuring the freezing-point depression, Tf, you can calculate the molality of the solution; Kf = 3.9 oC kg/mol for lauric acid. The number of moles of the solute, benzoic acid, is then calculated from the calculated molality of the solution. Finally, the molar mass of benzoic acid is calculated using equation 3. (3) MATERIALS: Computer, Vernier computer interface, Logger Pro, Extra long temperature Probe, 400-mL beakers, ring stand, utility clamp, two 18 x 150 mm test tubes, lauric acid, benzoic acid, thermometer, weighing boats (large and small). PROCEDURE PART I. Freezing Temperature of Pure Lauric Acid 1. Add about 300 mL of tap water to a 400-mL beaker and to start to heat it to about 60 oC using a hot-plate (preferably in a fume hood). 2. Prepare the computer for data collection. Connect the temperature probe to the LabPro. Connect the LabPro to the USP port of the computer using the Vernier computer interface. Make sure that the LapPro has its own power supply. 3. Double-click on the loggerPro3.3 software on the desktop. From the “file” menu, click on “open”, then select “chemistry with computers”. From the list of chemistry experiments that show up, double click on “Freezing point depression” experiment. 4. Calibrate the Temperature Probe against an alcohol or mercury thermometer. Pour about 300 mL tap water in a beaker. Place the probe and the alcohol thermometer in the water. From the “Experiment” menu, select “calibrate”. Select “Extra long temperature probe” from the drop-down box. 5. Click on “calibrate now” and type in the temperature reading of the thermometer and then click on “keep”. 6. Replace the tap water with the same amount of hot water. Wait until the thermometer gives a stable reading. Then, type in the temperature and click on “keep”. To finish the two-point calibration, click on “Done”. At this point, you should see the response of the probe on the left-bottom side of the monitor. 7. Weigh out about 8.0 grams of lauric acid on a large weighing boat and transfer the solid to an 18 x 150 mm test tube. Attach the test tube to a ring stand using a utility clamp and lower (place) it into the hot water bath to melt the solid completely. 8. When the solid is all melted, remove the test tube, while still clamped to the ring stand, from the hot water bath. Insert the Temperature Probe (should be clean and dry) into the melted lauric acid (55 – 60 oC). About 30 seconds are required for the probe to warm up to the temperature of its surroundings and give correct temperature readings. 9. From the “Experiment” menu, select “data collection”. The default length of time you could collect data is 10 minutes. Accept the default set up by clicking “Ok”. Then, click on “collect” to begin data collection. With a very slight up and down motion of the Temperature Probe, continuously stir the lauric acid during the cooling. 10. Continue with the cooling process until data collection has stopped after 10 minutes. 11. When finished collecting data, select “store latest run” under the “Experiment” menu. Hide the curve of your first run by double-clicking on the vertical axis of the graph and then un-checking “temperature” under the “Run 1” box. Click “ok”. 12. Re-melt the solid and collect a new data by clicking on “collect”. When data collection is finished, click on “store latest run” under the “Experiment” menu. At this point, you have done two runs (Run 1 and Run 2). 13. To remove the Temperature probe from the solid, heat the test tube in the hot water bath to melt the solid completely. Rinse the probe with hot water and carefully dry the probe with a paper towel or tissue. Return the test tube containing lauric acid to the place directed by your instructor. 14. To determine the freezing temperature of pure lauric acid, you need to determine the mean (or average) temperature in the portion of graph with nearly constant temperature. Move the mouse pointer to the beginning of the graph’s flat part. Press the mouse button and hold it down as you drag across the flat part of the curve, selecting only the points in the plateau. Then, click on the Statistics button”1/2 STAT”. The mean temperature value for the selected region of the data is listed in the statistics box on the graph. Record this value as the freezing point of lauric acid. Click on the upper-right corner of the statistics box to remove it from the graph. After you have read the procedure for Part 1: 1. View a video of: Lauric Acid Cooling Curve, uploaded by Dana Daugharthy, Oct 26, 2016: https://www.youtube.com/watch?v=5E3z9jUXfbw 2. To obtain virtual data for the freezing point of Lauric Acid, view a short video of: Lauric Acid Freezing, uploaded by Joshua Hartzog, Jul 28, 2016: https://www.youtube.com/watch?v=M2Ev1XDa0ZA PART II. Freezing Temperature of a Solution of Benzoic Acid and Lauric Acid 15. Weigh out ~ 8 g of lauric acid (use a large weighing boat) and ~ 1 g of benzoic acid (use a small weighing boat) separately. Transfer the solids to a clean 8 x 150 mm test tube and start heating in a water bath to completely melt the solids. 16. When the mixture of the two solids is all melted, collect data (cooling) in the same way you did for pure lauric acid in Part I. Save your data by clicking on “store latest run” under the “Experiment” menu before you start a new run. 17. When you have completed the data collection, click on the Examine button “ x = ?”. The freezing point of the benzoic acid - lauric acid solution is the temperature at which the mixture initially started to freeze. Unlike pure lauric acid, cooling a mixture of benzoic acid and lauric acid results in a gradual linear decrease in temperature during the time period when freezing takes place. As you move the mouse cursor across the graph, temperature (y) and time (x) data points are displayed in the examine box on the graph. Locate the initial freezing temperature of the solution and record it in your data table. 18. To print a graph of temperature vs. time showing both runs: a) click the temperature vertical axis label of the graph. To display sample runs from Part I and Part II, check the Run 1 and Latest boxes. Click “ok”. b) Label both curves by choosing Make Annotation form the Analyze menu, and typing “Lauric acid” (or “Lauric acid-benzoic acid solution”) in the edit box. Then drag each box to a position on or near