Chromatography - Worksheet PDF

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Answer the following to the best of your ability. The point values indicated next to each question should give you insight to the depth of your answer (long/short, fact/opinion, math, etc.). For all questions involving calculations, work must be showed for credit, an answer with no work will receive zero points. Please try and convert this document to a word document and write your responses immediately following the question, and back to a PDF for submission. (Use the guidelines as previously discussed in emails.) Part 1 True or False: 5 points 1. 2. 3. 4. 5.

Ethyl acetate is non-polar organic solvent [1] FALSE Iodine smells so sweet we can waft some into our face [1] FALSE The stationary phase is polar [1] TRUE Remove the iodine from the hood and stain your plate [1] FALSE Petroleum ether is very polar [1] FALSE

Method and Procedure: 30 points 6. What is important to remember about where the solvent line is formed on the TLC experiment? [2] The solvent level should be below the spotting level on the TLC plate. It is important that we immediately mark the solvent front line to figure out the Rf values. We should make sure that the TLC plate does not touch the filter paper because the filter paper is saturated in the solvent. The solvent may go down the TLC plate instead of up. 7. What is different about ferrocene and acetoferrocene visual? [2] Ferrocene is a orageish yellow compound and acetoferrocene is a red compound. 8. Why should you cover your chamber? [2] We need to cover the chamber, because we are using volatile solvents. They evaporate when the mobile phase came up into the TLC plate. It keeps evaporating so we need to cover the chamber. 9. What is the stationary phase in column chromatography? [2] Aluminium is the polar stationary phase in column chromatography. 10. What is the purpose of the sand in the column chromatography experiment? [2] While packing the column, there is a removable tip at the bottom which contains fret in it which is very porous. It acts as a support so solvents can go through and solids sit on it. We use fine alumina as our polar stationary phase. The alumina shouldn’t get in the pores of the fret. So we and a little sand. Sand acts as a base support and keeps a surface so it doesn’t disturb the ferrocene and acetoferrocene surface.

11. Explain why isomers ortho- and para- hydroxyacetophenone have different Rf’s. [4] The ortho isomer runs much further up because it has a higher RF value compared to the hydroxyacetophenone. It has a relative polarity lower than that of the para isomer. They may have different Rf values because it changes with varying content of moisture in the adsorbent. 12. For part A of the experiment, which isomer is retained on the stationary phase more and why? [4] More polar compounds are retained by the stationary phase compared to the less polar compounds. Acetylpherrocene is significantly more polar because of its functional group.The ortho traveled further than the para hydroxyacetophenone. This is because it has weak interactions with the adsorbent. Acetylpherrocene has stronger interactions with the stationary phase will move along more slowly.Different compounds have different degrees of interaction with the adsorbent and hence they have different mobilities as well. This leads to seperation. 13. Explain how to load your column in column chromatography. (Hint: What solvents are used? what key ideas are to be remembered here? Etc.) [4] We use aluminum instead of silica. Aluminum is also a polar stationary phase. We take a sample that has equal amounts of ferrocene and acetylferrocene. We weigh out about 100 mg of that mixture and 100 mg of alumina. We start of with a low polarity solvent which is ferrocene and then acetylferrocene and dilute that. We add few drops of MtBE which will dissolve ferrocene and acetyl ferrocene as they are both soluble in MtBE. We stir it and let it dry to make it a powder and evaporate the solvent. We load this onto the alumina. Sand is very important here as it keeps the surface from getting disturbed. 14. In TLC part B, what happens if you see acetaminophen and aspirin but no caffeine, what should be done in this case? [4] We have a very small amount of caffeine, so it may be difficult to see. Nothing has just the aspirin and the acetaminophen except for goodies and Excedrin, but they both have caffeine. So we should go back to the experiment. We should try and investigate closely for the caffeine. This may require us to use a TLC plate where we spot our unknown heavily to make sure we are spotting a significant amount of caffeine to see the caffeine in our unknown. 15. Unknown number 4 had three components, what were they and how was the unknown confirmed? [4] Unknown components: aspririn, acetaminophen and caffeine. Which means it can be either goodies or excedrin. Excedrin has identical amounts of aspirin and acetaminophen. Goodies has almost twice as much aspirin as acetaminophen. In the unknown spots in the TLC plates, the aspirin spot is much more significant than acetaminophen. So we can come to a conclusion that our unknown is goodies. Method: We set up 2 TLC plates. We draw the baseline, crush the tablet and dissolve it in the ethyl acetate and then we spot from that. We spot the unknown in the middle of each TLC plate. We have the four possible unknowns that are aspirin, acetaminophen, caffeine, and ibuprofen. On one plate, we spot Acetominophen and Ibuprofen with the unknown and on the other plate we

spot Caffeine and aspirin on the other with the unknown. To identify the unknown, we co spot and so we will be able to see a separation. 16. What tool is used to spot in the TLC experiment? [3] We use Micro capillaries to do spotting. We use a different micro capillary for each spot to prevent cross contamination. 17. What is the physical principle implored in this tool? [3] When dip the micro capillary in the solution, it will draw the liquid in. If we hold the capillary down on the TLC plate it will run out which is not the right thing to do. This is because it gives us a big spot. So we quickly touch the TLC paper to make a small spot. This may not be enough compound so once its dry, we can concentrate it on the same spot and let it dry. We can keep doing it to increase the compound but so much that the mobile phase cannot dissolve it. So we need enough of the compound so we can see it but not a lot for it to streak out. 18. What happens to solid iodine at STP, how do we use this to our advantage? [3] We put the plate face down, so the iodine vapors can hit the plate. Organic compounds react with iodine to from dark brown spots. 19. How do we check the purity of our fractions in column chromatography? [3] We use melting point to confirm the identity and the purity. 20. What does adding more petroleum ether do to the column in that part of the experiment? [3] We cant allow our column to be try once we start putting the solvent onto the column. So we need to have petroleum ether and MtBe so there is constantly a solvent running down the column. We add more petroleum layer so to make sure that we don’t let the column run dry. If we let it run dry, the solvent comes down below the level of sand, we get air which will affect the chromatography....