SC CHEM 333 - Fractional Distillation of Organic Molecules Post-Lab (4 pages)

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Fractional Distillation of Organic Molecules Post-Lab



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Organic Chemistry 333L Section 03M Laboratory Post Lab Fractional Distillation of Organic Molecules By Cameron Kahn 14 January 2019 TA James Collie 03M 1 Results The objective of the experiment was to use fractional distillation to distill an unknown mixture and record the temperature in 0 5 mL increments The experiment starts with a 1 1 mixture of cyclohexene and nbutyl acetate The mixture consisted of 8mL of each liquid The goal was to collect a sample of each distillate and then determine the identity of each using IR spectroscopy The barometric pressure during the experiment was noted at 30inHg The actual boiling point of cyclohexene is 83 C and n butyl acetate is 126 1 C An observation from the data collected shows that the measured boiling point for cyclohexene was around 47 C and the measured boiling point of n butyl acetate was around 65 4 C The graph of volume versus temperature shows the peak temperatures of each liquid The peaks represent the boiling point of each liquid in the mixture The first fraction was cyclohexene The theory behind distillation agrees with the result that cyclohexene separated first from the mixture because cyclohexene has a lower boiling point due to the compounds weak intermolecular attractions The second fraction was n butyl acetate The theory behind distillation agrees with the result that n butyl acetate has a higher boiling point because the compound has stronger intermolecular attractions than cyclohexene However the actual boiling points of each compound in the mixture did not match up to the measured boiling points The differences in boiling points show that there were human or mechanical errors that hindered the fractional distillation of the compounds to reach their intended boiling points The experiment took an observed time of 75 minutes to complete Volume vs Temperature 70 0 C 60 0 C f x 1 42x 25 99 R 0 52 Second Fraction 50 0 C First Fraction 40 0 C 30 0 C Linear 20 0 C 10 0 C 0 0 C L m 5 0 5 1 5 2 5 3 5 4 5 5 5 6 2 5 7 5 8 5 9 10 5 11 5 IR Spectroscopy Sample 1 Aromatic C H stretch CH3 C H bend C O Carbonyl group stretch C H aromatic stretching C H Alkyl group stretch Sample 3 Alcohol OH stretch Alkyl C H stretching C O C stretching Tert butyl C CH3 3 C O Carbonyl group stretch Sample 1 and sample 3 are shown The first sample is 5mL of the first distillate and the third and last sample is 4mL of the other distillate The x axis is the wavenumber cm 1 and the y axis represents transmittance From the IR spectra there are several impurities including in sample 3 which should have been more pure due to being the last compound left to distill The third sample shows an alcohol group which should not be present This could have been due to dirty test tubes or the fractionating apparatus In general the fractional distillation was a success 3 because one can properly identify the compounds in the mixture based on the analysis of the IRspectroscopy Conclusions Fractional distillation is used to separate chemicals that have boiling points close together a difference less than 20 C The learning outcomes from the experiment were to set up the fractionating distillation apparatus distill an unknown mixture and use IR spectroscopy to identify the mixture The experiment did not work as planned The boiling points measured in the experiment did not come close to the actual boiling points for both of the compounds in the mixture This is due to a number of errors including but not limited to dirty test tubes heating element not operating at correct temperature indicated on the variac settings estimating temperature on thermometer Another important thing to note is that the lab had low levels of 10mL graduated cylinders to measure out the two liquids used in the mixtures The use of 25mL graduated cylinders was used in absence of the 10mL graduated cylinder This causes inaccurate volumes of each liquid in the mixture and altered our desired results 4


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