Part II: Cyclohexane and p-xylene were separated by distillation according to the procedure below. The collected NMR dat

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Part Ii Cyclohexane And P Xylene Were Separated By Distillation According To The Procedure Below The Collected Nmr Dat 1 (62.3 KiB) Viewed 46 times

Part Ii Cyclohexane And P Xylene Were Separated By Distillation According To The Procedure Below The Collected Nmr Dat 2 (35.38 KiB) Viewed 46 times

Part Ii Cyclohexane And P Xylene Were Separated By Distillation According To The Procedure Below The Collected Nmr Dat 3 (29.63 KiB) Viewed 46 times

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Part II: Cyclohexane and p-xylene were separated by distillation according to the procedure below. The collected NMR data follow. After reading the procedure and analyzing the results, answer the questions related to these results. Procedure a. Transfer 10 mL of the 50:50 mixture of cyclohexane and p-xylene to a 25 mL round bottom flask; add a few boiling chips. b. Assemble the apparatus shown in Figure 1 (note the setup demonstrated by your instructor). To ensure accurate temperature readings, make sure that the thermometer bulb is placed even with the joint in the adapter. Use a 10 mL graduated cylinder as the initial receiving flask. c. Place an aluminum, heating block on a hot plate. Lower the clamped, round bottom flask into the appropriate heating block. Set hot plate at a medium temperature setting. Adjust the heat until the distillate is collected at a rate of about one drop every 2-3 seconds. d. Record the temperature after each 1 ml collected. Collect the 1 mL. in a separate, 10 ml. graduated cylinder and save this fraction for 'H-NMR analysis. e. Continue recording the temperature until a total of 10 mL have been collected. f. After 10 mL have been collected, save the fraction that remains in the round bottom flask. Add this fraction, along with the first fraction to separate NMR tubes using a long stemmed Pasteur pipette. Collect NMR spectra as demonstrated by your instructor. g. Use a graphing program such as Excel to plot a graph of temperature vs. ml. collected. Use this graph to determine the boiling points of the two liquids.
Data Distillation Temperature vs mL 140 130- 120- 110- 100- 90 5 3 6 9 10 Fraction (ml) Figure 2. The temperature of the mixture as a function of the fraction collected from the distillation column. Fractions were collected in 1 ml. aliquots, so after each mL. the temperature of the mixture was recorded. Temperature
mL Cyclohexane 1 ml 2 ml 3 ml 4 ml 5 ml 6 ml 7 ml 8 ml 9 ml p-xylene 10 ml Table 1. Data used to create Figure 1. Temperature 95 C 103 C 105 C 109 C 110 C 112 C 115 C 122 C 130 C 138 C
IML 2PPM USER: DATE 1908 14.0 PTSIA BISZ 1 Figure 3. The NMR spectrum of the first fraction, first mL collected during distillation. This spectrum is poorly calibrated, so it won't perfectly match the predicted NMR. The large peak near 0.8 ppm represents absorbance by the hydrogen nuclei on cyclohexane. The 2, different hydrogen nuclei of o-xylene are represented by the small peaks near 1.5 ppm and 6.5 ppm.
10 mL EXEL 3468 UNER GATE CIRSTI PESIA AIN2 Figure 4. The NMR spectrum of the last fraction, tenth mL collected during distillation. This spectrum is poorly calibrated, so it won't perfectly match the predicted NMR. The large peak near 0.8 ppm represents absorbance by the hydrogen nuclei on cyclohexane. The 2, different hydrogen nuclei of o-xylene are represented by the small peaks near 1.5 ppm and 6.5 ppm.
Questions related to results (expand answer field where necessary) 1. List one unexpected feature that you observe in the Distillation temperature vs mL graph (Figure 2). 2. What is the most likely explanation for this unexpected feature of figure 2? 3. List one unexpected feature that you observe in figures 3 and 4. (List just one feature, it can be from either graph). 4. What is the most likely explanation for this unexpected feature in the NMR? 5. What is one additional piece of data that you would like to collect to better explain this system or to develop an alternative hypothesis?
Using NMR to monitor distillation efficiency The most popular method for separating miscible compounds with different boiling points is by simple distillation. The liquid mixture is placed in a round-bottom flask that has been fitted with a distillation head, which is in turn attached to a condenser. The end of the condenser is placed over a collection vessel in which the distillate is collected. As the flask is heated, each liquid will vaporize once its boiling point is reached. The vapor rises through the distillation head and passes into the condenser. The vapor then passes through a water-cooled condenser, which causes it to condense into a liquid and drip into the collection flask. Distillations can be monitored by observing the temperature at the entrance to the condenser; as the apparatus heats up, the vapor from the first component (with the lowest boiling point) will reach the thermometer and enter the condenser while the higher boiling point components condense lower in the apparatus. The temperature will remain constant until all of the first liquid has been removed at which point the temperature will increase and plateau again until the second liquid is distilled away; this pattern will repeat until all liquids have been distilled.
adapter Simple Distillation. thermometer H₂O out cold H₂O in boiling flask receiving vessel heating mantle Figure 1. A distillation apparatus for separating liquids in a mixture. condenser boiling chip