Thin layer Chromatography Worksheet PDF

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OCHEM I LAB Thine layer chromatography Worksheet...

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Texas A & M University - Corpus Christi Department of Physical and Environmental Sciences Organic Chemistry I Laboratory

Student Name:_______________________________________________ Lab Section:____________ Date:___________ Thin Layer Chromatography Worksheet IMPORTANT: Have you completed the Lab Safety Seminar Quiz on Blackboard located under the course SMTE0093? (Please complete the quiz with a 100% score, you may be dropped from CHEM 3411 by the Registrar’s Office, if left uncompleted) Purchasing the recommended textbook listed on the class syllabus is highly beneficial to the student. It will not only help the student understand basic Organic Chemistry I Laboratory topics but will also help the student apply this knowledge for each lab exercise assignment throughout the semester. Recommended Textbook: ISBN: 1308551576, “Microscale & Miniscale Organic Chemistry - Laboratory Experiments”, Schoffstall, A. M., 2nd Ed, McGraw-Hill Recommended Reading from textbook: Chapter 3: Melting Points and Boiling Points (pages 38 – 45) Reviews intermolecular bonding Chapter 8: Thin Layer Chromatography (pages 172 – 182) Reviews TLC principles and practical technique methods Lab Demonstration: https://www.youtube.com/watch?v=MHCR06rxYYg&list=PLfTBHopaZH38pmnCt0WkO2z8vdyCTEvGK&index=1 Additional Resources (available online): https://chemistryhall.com/thin-layer-chromatography/#And_How_Does_a_TLC_Work https://www.khanacademy.org/science/class-11-chemistry-india/xfbb6cb8fc2bd00c8:in-in-organic-chemistry-somebasic-principles-and-techniques/xfbb6cb8fc2bd00c8:in-in-methods-of-purification-of-organic-compounds/v/thin-layerchromatography https://www.chemistry.mcmaster.ca/adronov/resources/Stains_for_Developing_TLC_Plates.pdf

INTERACTIONS BETWEEN THE COMPOUND AND THE ADSORBENT 1. Highly polar molecules interact strongly with the polar SiOH groups at the surface of these adsorbents and will tend to stick or adsorb onto the fine particles of the adsorbent. The more polar the compound spotted, the less it traveled up the polar TLC plate the smaller the Rf value. More polar molecules may interact more strongly by a variety of mechanisms including dipole-dipole interactions, coordination, and hydrogen bonding. (True or False) 6pts 2. The polarity of the mobile phase (eluent, developing solvent) also determines the speed at which substances being analyzed will elute- they will affect how easily the compound is pulled back into solution away from the surface of the silica. Generally, any solute will elute more rapidly in a more polar eluent. (True or False) 6pts 3. A solvent that does not cause any compounds to move from the original spot is not polar enough (thus small Rf values), whereas a solvent that causes all the spotted material to move with the solvent front is too polar (thus too large of Rf values). (True or False) 6pts

Texas A & M University - Corpus Christi Department of Physical and Environmental Sciences Organic Chemistry I Laboratory APPLIED TLC PRACTICE PROBLEMS 2. List the common types of Adsorbents (stationary phase) used in chromatography, in decreasing power of adsorption: 6pts • Alumina • Activated Charcoal • Magnesium Silicate • Silica • Starch

3. List the following solvents from most polar to least polar: hexanes, methanol, dichloromethane, acetic acid, ethyl acetate. 6pts Answer: acetic acid, methanol, ethyl acetate, dichloromethane, hexanes

5. What does retention factor mean? How do you calculate retention factor on TLC? 6pts The retention factor is the distance that a compound travels through the silica plate respect to the total distance the eluent front has moved. Rf = (distance compound moved from the baseline)/ (distance of eluent front from the baseline).

8. Development and visualization of a TLC plate showed a single spot at the origin. The lab worker concluded that the sample consisted of a single pure compound. Was this conclusion justified? Why or why not? 6pts The conclusion was not justified. You do not know how many components may be present because nothing has moved. The only conclusion that can be made is that a more polar developing solvent should be tried.

TROUBLESHOOTING TLC 1. What could happen if you used ink to prep the TLC plate? 6pts Answer: The ink might travel with the eluting solvent and separate into its component pigments, giving you a lot of extraneous spots.

3. What would happen if the solvent level is above or even with the initial TLC spots? 6pts Answer: The spots would dissolve into the reservoir of eluting solvent....