Gas chromatography is performed to check correct distillation of mixture by observing the peaks on the graph. The first peak observed in the graph is a result of less polar compound, which has short retention time, measured in seconds and second peak results in more polar compound, which has larger retention time. Moreover, area under peak is also calculated and is proportional to the moles of compound eluted. Overall, chromatography test determines many characteristics of mixture.
Experimental Procedure
The simple distillation apparatus was constructed accordingly to the diagram seen in the textbook, page 56. The 100 mL round bottom flask was equipped with a stillhead, west condenser (thick column), bend vacuum adapter, thermometer, and thermometer adapter. The equipments were tightly clipped to prevent vapor from escaping apparatus. A thermometer was placed into stillhead with the support of thermometer adapter. The thermometer was suppose to be kept below the entrance of condenser to endure that the mercury bulb of thermometer is immersed thoroughly in vapors. Then, two water tubing were obtained and were hooked with west condenser. One of the water tubing allowed the water into condenser and the other was there to drain it. Also, a cylinder was placed by the open end of bent vacuum to collect three fractions. See figure 2. 30 mL of the 1:1 mixture of EtOAc/ BuOAc was obtained and added to the round bottom flask. The thermowell was initially set to 60 in order to heat the apparatus, and then lowered to 40 in order to maintain a 1 drop per second rate. The temperature was recorded for every ml of liquid distilled. The first fraction was collected until the temperature began spiking (temperature close to 77° C). The second fraction was collected until the temperature again reached a plateau. The last fraction was collected until the initial volume was completely distilled (temperature around 126° C). Each fraction was covered with a watch glass to minimize evaporation.
Figure 2 - Simple Distillation Apparatus
Each fraction was then analyzed by the Gas Chromatography machine. The syringe used for injection was cleaned drawing in some of the fraction and expelling it. Then, for each fraction 10 mL was drawn, and injected into port A, which used a carbowax stationary phase. The resulting data was then printed and analyzed.
***Note: for the second part of the lab, we were to work with partner due to lack of time, therefore, the data for fractions may result differently from the one collected in first part of the lab.
Data acquisition/ presentation
Part one: Simple Distillation
Before performing simple distillation, boiling points of both compounds were considered as it helped in collecting three fractions. First, fraction was collected at 94° C, second fraction was collected at 121° C and third fraction was collected at 120°C. The table below illustrates the data observed for three fractions.
Fraction one: Ethyl Acetate
Mole fraction = 0.89
Molecular Weight = 88 g/mol
Boiling Point = 77° C
Fraction two: Ethyl Acetate and Butyl Acetate
Fraction three: Butyl Acetate
Mole Fraction = 0.74
Molecular Weight = 116 g/mol
Boiling Point = 126° C
Graph 1: Volume vs. Temperature for the simple distillation results
Calculation
The gas chromatography was performed and the graph with two peaks was observed for each fraction. Once the resulting data was printed, peaks for each fraction were analyzed and the mole percentages were calculated. The graphs of three fractions are attached.
Mol % (of compound A) = Area of compound A x Mf (A) _ x 100
[(Area of compound A x Mf) + (Area of compound B x Mf)]
Fraction one
Peak one Peak two
Area – 1625 mV*s Area – 19.25 mV*s
Retention time – 18.5s Retention time – 50s
Identity – Ethyl Acetate Identity – Butyl Acetate
Mol % - 99% Mol % - 0.98%
Fraction two
Peak one Peak two
Area – 1763 mV*s Area – 1843 mV*s
Retention time – 18.5s Retention time – 50s
Identity – Ethyl Acetate Identity – Butyl Acetate
Mol % - 53.5% Mol % - 46.5%
Fraction three
Peak one Peak two
Area – 0 mV*s Area – 4146 mV*s
Retention time – 0s Retention time – 51 s
Identity – Ethyl Acetate Identity – Butyl Acetate
Mol % - 0% Mol % - 100%
Calculation for Mole percent corrected
Fraction one:
Peak one: Mol % = (1625 mV*s x 0.89)/ [(1625 mV*s x 0.89) + (19.25 mV*s x 0.74)]
x 100 = 99 %
Peak two: Mol % = (19.25 mV*s x 0.74)/ [(1625 mV*s x 0.89) + (19.25 mV*s x 0.74)]
x 100 = 0.98 %
Fraction two:
Peak one: Mol % = (1763 mV*s x 0.89)/ [(1763 mV*s x 0.89) + (1843 mV*s x 0.74)]
x 100 = 53.5 %
Peak two: Mol % = (1843 mV*s x 0.74)/ [(1763 mV*s x 0.89) + (1843 mV*s x 0.74)] x 100 = 46.5%
Fraction three:
Peak one: Mol % = (0 mV*s x 0.89)/ [(0 mV*s x 0.89) + (4146 mV*s x 0.74)] x 100
= 0 %
Peak two: Mol % = (4146 mV*s x 0.74)/ [(0 mV*s x 0.89) + (4146 mV*s x 0.74)]
x 100 = 100 %
Conclusion
Distillation is one of many techniques used in separating a mixture of compounds. The objective of this lab was to separate a 1:1 mixture of ethyl acetate and butyl acetate, and then collect three fractions considering the boiling point of both components. Those fractions were then analyzed by gas chromatography to confirm correct separation if compounds by observing peaks in the graph. In performing distillation part of the experiment, there were some difficulties faced. First, it was difficult to record temperature for every milliliter of condensed liquids as it was happening rapidly. Second, the heat setting was being changed in every few minutes to have control over the drops. Finally, due to lack of time, the second part of the experiment was done with a partner instead of individually. Therefore, the analyzed results from the gas chromatography were based on one individual data rather than all the data collected. However, in the end, the experiment was done successfully.
First fraction of condensed liquid was collected at 94° C, which is close to the boiling point of ethyl acetate, for 13 mL. The first fraction was ethyl acetate as it boils at the lower temperature due to its Van der Waals. Second fraction collected was for 13 mL and third fraction was collected at 120° C, which is close to the boiling point of butyl acetate, for 4 mL.
Furthermore, to confirm correct separation of mixture, gas chromatography was performed. The peaks in the graph confirmed that the first peak is assumed to be ethyl acetate due to its lower boiling point, meaning short retention time. Second peak is assumed to be butyl acetate as it requires a higher boiling point, meaning large retention time. Thus for fraction one, peak one has a large area of 1625 mV*s due to the presence of ethyl acetate in the fraction and peak two has an area of 19.25 mV*s for butyl acetate. For fraction two, the area for peak one was analyzed to be 1763 mV*s (ethyl acetate) and for peak two to be 1843 mV*s (butyl acetate). There were some error as both ethyl acetate and butyl acetate was to be equalized, due to fraction two being a mixture. For fraction three, peak one took the area of 0 mV*s to show the presence of no ethyl acetate and peak two with the area of 4146 mV*s to show the presence of only butyl acetate. Furthermore, every first peak had short retention time as they require lower boiling point.
By performing simple distillation and gas chromatography, we were able to separate a 1:1 mixture of ethyl acetate and butyl acetate along with analyzing the separation. Through distillation, we separated the mixture and chromatography helped us in confirming whether the separation was done correctly. The hypothesis that the first compute to elute from the column would be ethyl acetate and last compound to elute would be butyl acetate was correct. This hypothesis was based the theory London Dispersion Forces and compounds affinity to two immiscible phases: stationary and mobile phases.
Reference
Gilbert, John C. and Martin, Stephan F. Experimental Organic Chemistry: A Miniscale and
Microscale Approach, fourth edition. United States: Thomson Brooks/Cole, 2006
by
nighatali (student)
