Chem 231 TLC Theory and Technique Assignment Fall 2020
Instructions: Please provide your answers to the following questions in the spaces provided. Once all of your answers are provided you can save the file and upload it to the “TLC Assignment” in Canvas (Available in the “Week 9 Module” or in the “Assignments” section). This assignment should be done on your own. Students turning in similar reports may receive a reduced score for the assignment.
1. Thin-layer chromatography (TLC) can be best described as a purification technique or an analytical technique. (Choose one)
2. Arrange the following compounds in order of increasing Rf value on a TLC plate in the spaces below (e.g. write 1 under the compound that will have the smallest Rf value, etc.).
_____ _____ _____ _____
3. Suppose you are carrying out a TLC analysis of two compounds (Compounds A and B) and you determine that Compound A has an Rf value of 0.65 and Compound B has an Rf value of 0.90 using 50/50 ethyl acetate/hexanes as the developing solvent.
a) What does this tell you about the properties of these compounds in relation to each other?
b) How would you change the solvent system if you wanted to lower the Rf values for both of these compounds. Propose a different ratio of ethyl acetate/hexanes (instead of 50/50) that you could try to achieve this goal (Note: There is more than one correct answer here. Just make an educated guess).
4. Why is it important to spot a small concentrated sample on the TLC plate? What would happen if you spotted your plate with a regular sized pipette instead of a micropipette (or microcapillary tube)?
5. What is the purpose of adding a piece of filter paper in your TLC developing chamber?
6. Describe how the following errors would affect the results of your TLC analysis:
a) The solvent level in your TLC developing chamber was higher than the origin line on your TLC plate when you placed the plate in the chamber.
b) You left your TLC plate in the developing chamber too long and you can’t find the solvent front. What should you do if this happens?
7. List two methods for visualizing spots on a TLC plate (Be specific).