Column Chromatography Report (1) (1)

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2040

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Chemistry

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Dec 6, 2023

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pdf

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OCHEM Lab Report Saad Haq 14 November 2022 Column Chromatography Lab Report Data and Results: Compound Name Initial Weight Final Weight % Recovery Distance Moved cm (TLC Plate) Rf Values (TLC Plate) Solvent Plate 1: 3.2 Plate 2: 3.1 Given Sample 0, 0.9, 1.8, 2.6 0, 0.28, 0.56, 0.81 1- Hexane 0.02 g 0.001 g (0.001/0.02) x 100 = 5% 2.9 0.94 2- Intermediate 0.02 g 0.003 g (0.003/0.02) x 100 = 15% 2.1, 2.9 0.68, 0.94 3- 1/1 Hexane/ methylene chloride 0.02 g 0.021 g (0.021/0.02) x 100 = 105 % 2.1 0.68 4- Intermediate 0.02 g 0.012 g (0.012/0.02) x 100 = 60% 1.3, 2.1 0.42, 0.68 5- 9/1 methylene chloride/ methanol 0.02 g 0.001 (0.001/0.02) x 100 = 5% 1.4 0.45
Discussion: The main purpose of this experiment was to elute certain compounds from a column and then spot them on a TLC plate. When running each solution down the column, hexane took the longest as it is the least polar and alumina happens to be very polar. Hexane ended up giving a yellow liquid. For 1/1 hexane/methylene chloride, it traveled down the column a bit faster as it more polar and ended up mixing with hexane which resulted in a clearer substance giving our first intermediate. Once the intermediate was gone, the 1/1 hexane/methylene chloride ended up giving a orange liquid. The last solution added was 9/1 methylene chloride/ methanol. Given the fact that this was the most polar out of all the solutions, it ended up traveling down the column the fastest. It ended up mixing with the 1/1 methylene chloride still present in the column which gave our second intermediate which was dark red in color. Once the intermediate was gone, the 9/1 methylene chloride/ methanol ended up giving a lighter liquid in color compared to the intermediate. From the results above we can determine that on both TLC plates, hexane traveled the farthest due to it being the least polar which also gives it the highest Rf value. Hexane is then followed up by 1/1 hexane/methylene chloride which makes sense as it is more polar than hexane giving it the second highest Rf value. Lastly, 9/1 methylene chloride/ methanol traveled the least up the TLC plate which makes sense as it is the most polar giving it the lowest Rf value. An error that was made during this experiment was that when it came to TLC spotting, the tip of a pipette was used which caused the marks on the TLC plate to be too big. This could affect the Rf values collected and even change the TLC results. In the future, instead of using a pipette a spotter must be used to ensure the best results for the TLC. Given this error, I was still able to collect decent results and understand what each solutions polarity meant. Questions: 1. Due to the fact that both compounds have different polarities, when the two compounds mix heat will be created which may crack or injure the column. In addition, if the more
polar solvent is added first, in this case the hexane/dichloromethane, then the column will elute too quickly which will result in a less separated product. In order to fix this problem, the less polar solvent should be run through the column first, so hexane, then the hexane/dichloromethane then the dichloromethane. This will help to distinguish each separated product. 2. Two advantages that exist with using microscale column chromatography is that the process is much better for purification of a product and it is able to give off higher percent recoveries than recrystallization. 3. It is important not to let the stationary phase dry out because if it dries out then cracks and fissures can form which will prevent the solid from binding to the stationary phase. Basically, it would just run through the column without separating. 4. If some hexane remained at the top of the column and you added hexane-methylene chloride mixture that would be fine. Since hexane-methylene chloride is more polar, all you’re doing is just making the band elute faster. However, you must make sure the yellow band from the hexane solvent is completely gone before adding the hexane- methylene chloride mixture.
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