Experiment 5- TLC

pdf

School

Champlain Regional College, Saint Lambert *

*We aren’t endorsed by this school

Course

202

Subject

Chemistry

Date

Jan 9, 2024

Type

pdf

Pages

Uploaded by MajorGorillaPerson645

Thin Layer Chromatography 00004 By Kian Houman and Malake Ettabaâ Date of experiment: 1 November 2022 Date of submission: 8 November 2022

TLC 2 Procedure: Klein, David. Organic Chemistry, 4th Edition, John Wiley and Sons, Inc, 2021. 5mL of tomato paste and 5mL of ethanol in 30mL beaker covered by watch glass Filter solution by suction Boil and swirl solution on steam bath for 5 minutes Add 10mL of dichloromethane to solid residue in a 25 mL round bottom flask Filter solution by suction Heat solution in warm water for 7 minutes Evaporate solution in rotary evaporator Prepare TLC plates Place first TLC tray in developing chamber containing 3mL of petroleum ether Use capillary pipette to make dots on TLC tray Place second TLC tray in developing chamber containing 3mL of 25% dichloromethane and 75% petroleum ether mixture Mark final position of both TLC trays Circle colored spots and indicate lycopene and β -carotene spots Calculate R f values Search for additional spots on TLC trays Place one tray at a time under UV lamp

TLC 3 Data and Results:

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

TLC 4 Data Table Compound Plate 1 (eluant : petroleum ether) Plate 2 (Eluant: 25% CH2Cl2/75% petroleum ether) Rf values Rf values Diluted spot Concentrated spot average Diluted spot Concentrated spot average Lycopene 0.0615 0.0923 0.0769 0.526 0.526 0.526 β -carotene 0.138 0.169 0.154 0.702 0.702 0.702 Impurity (if applicable) X X X 0.158 0.158 0.158 Sample calculations :

TLC 5

TLC 6 POST-LAB QUESTIONS: 1. Would a more polar compound give a smaller or larger Rf value than a less polar compound? Explain your answer by referring to TLC theory (stationary phase, moving phase, polarity…). A more polar compound would give a smaller Rf value than a less polar compound. The stationary phase is highly polar, and the moving phase is also polar, and its polarity is influenced by the compounds in it and the eluent used. The higher the polarity of the compounds in the moving phase, the more it will be attracted to the solid plate through adsorption, therefore it will migrate upwards slower. At the end, the least polar substances will have reached a higher point than the more polar substance, which means that the Rf value of the more polar compound is smaller than the Rf value of the less polar compound. 2. According to your results, which is more polar, lycopene or β -carotene? Briefly explain your choice using your data. Lycopene is more polar than β -carotene. As explained above, the more polar a compound is, the more it will stick to the stationary plate, therefore migrating slower on the TLC plate. In this case, by looking at the TLC experiment done with the ether- CH 2 Cl 2 mixture, it is seen that the β - carotene climbed up to 4.00 cm of the plate, while lycopene only climbed 3.00 centimetres. The calculated Rf value of lycopene is also smaller than that of β -carotene proving once again that lyco pene is more polar than β -carotene.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version

Access to all documents
Unlimited textbook solutions
24/7 expert homework help

TLC 7 3. Would a more polar solvent increase or decrease the Rf values. Explain your answer by referring to TLC theory (stationary phase, moving phase, polarity…). A less polar solvent will decrease the values of Rf. Both the molecules of the compounds and the solvents compete for the adsorption sites. If the solvent is less polar, less of its molecules will stay attached to the surface of the solid plate, so the compound molecules will be able to stick in the adsorption sites for a longer time making them rise more slowly. In the end, the compounds would not have migrated very high up because they would have been too much attracted to the stationary plate, and because of this the Rf value would be smaller. 4. According to your results, which developing solvent system gave the better separation of lycopene and β -carotene? Briefly explain your choice using your data. 75% petroleum ether and 25% CH 2 Cl 2 is a better solvent for this experiment. The eluent was neither too polar or not polar enough, so it created a perfect balance which permitted a clear and distinguishable separation between Lycopene and β -carotene. The better solvent system is the one that separates the best lycopene and β -carotene. In 100% petroleum, the distance between the two points is 0.50 cm which is smaller than that in 75% petroleum ether and 25% CH 2 Cl 2 which had a distance of 1.00 cm showing that the ether-CH 2 Cl 2 mixture did a better job at separating the two compounds during elution.

TLC 8 5. Why must we add 1 mL of dichloromethane to our mixture of lycopene and carotene after we removed the dichloromethane on the rotary evaporator? The mixture of lycopene and β -carotene was dry and powdery after the evaporation of dichloromethane, so adding 1 mL of dichloromethane allowed us to collect some of that substance in order to spot our TLC plates. Also, it made it easier two create two spots, one diluted and one more concentrated, by simply adding more drops of the lycopene-carotene compound solution. 6. Suppose you got distracted during the development of your TLC plate and you allowed the eluent to reach the top of the plate. Would you need to start the development over again? How would this affect the Rf values you calculate? Explain. The experiment would need to be restarted. If the eluent reached the top of the plate, it wouldn’t be able to migrate higher therefore the finish line would stay the same. On the other hand, the compounds that are below the eluent would slowly keep on migrating upwards until it reaches the top of the TLC plate . If the finish Line doesn’t increase and the compound points increase, the Rf values will also increase and would no longer be correct, hence why the experiment would need to be done again.

TLC 9 Bibliography 1. Department of Chemistry, Thin Layer Chromatography. In Chemistry BLC Laboratory Manual; Champlain Regional College: St-Lambert, QC, Fall 2022; pp 1-4.

Your preview ends here

Eager to read complete document? Join bartleby learn and gain access to the full version