Simple Distillation and Gas Chromatography Discussion Questions

Alyssa Winborne

10/19/14

Ochem 237 Section 511

Simple Distillation and Gas Chromatography Discussion Questions

1. In this experiment we learned how to purify volatile compounds by simple distillation and we learned how to use gas chromatography to quantitatively determine the relative proportions of volatile compounds in the samples we were given. Volatile compounds are compounds that can be converted to a gas phase and won’t decompose at an average temperature. In the distillation process, we heated our liquid sample to boiling and then collected the condensed vapors in a different container. Simple distillation was a necessary technique because our two given compounds, heptane and hexane, had very similar boiling points. We had to take three fractions of the distilled liquid and form there we performed gas chromatography to see what compounds existed at what temperature.

1. There were a lot of room for errors in this experiment as it consisted of many steps and we were working in pairs. When you work with pairs, you take away some of the consistency present when doing an experiment alone. In this particular experiment, I collected the fractions of distillate while my partner completed the gas chromatography of each distillate I brought to him. In this time frame, errors could have resulted. There was no way for us to make sure the other person was correctly following the procedure and since different people were doing different steps, there was no consistency without our experiment. Some error might have occurred when collected the fractions of distillate. Our chromatography graphs from our first and second fraction look exactly the same with only one compound, hexane, having a peak. This could have resulted from various mistakes. When collecting the fractions, I may have not waited long enough before collected the second one. On the other hand, I may have collected it too soon and it was composed of exactly the same compounds as the first. Also, error could have occurred on my partner’s part when he did the gas chromatography. Although there was a TA to help us through that part of the lab, it was our first time to ever work with the equipment and machinery so it could have been used incorrectly.

1. Results: We collected three different fractions of distillate and tested the remaining distillate for a total of four different chromatography graphs. Our first distillate was captured at 57.4’C and finished at 59.4’C. It’s graph only had one peak at 450 mV and showed to only contain Heptane. Our second fraction was collected at 61.9’C and finished at 62.6’C. it has a graph identical to the first fraction. It had one Heptane peak at around 450 mV. Our third fraction was collected at 63.9’C and finished at 65.1’C. This graph had two peaks, Heptane with a sharp peak at 600 mV and Hexane with a peak at around 300 mV. The final fraction was taken from the remaining distillate in the beaker. Its graph had a very small heptane peak at barely 100 mV and a very large hexane peak at 600 mV.

1. Conclusion: In the end our experiment was successful as we were able to purify volatile compounds and quantitatively determine the proportions of volatile compounds in a sample. Although our first two graphs may have been the result of some errors because they were exactly the same, we can still determine which compound had the higher boiling point. Hexane has a much lower boiling point than Heptane. This is reflected in our graphical data. At higher temperatures, Hexane is detected in greater amounts as distillate, meaning it boiled off first and more easily.