Thin Layer Chomatography Lab Report PDF

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Thin Layer Chromatography Ryan Huckaby CHEM 2123-540 3-5-2020

1 Ryan Huckaby Dr. Srinivasan 2423-530 3-5-2020 Thin Layer Chromatography ABSTRACT The process of thin layer chromatography allows compounds to rise a TLC plate through capillary action as the chromatogram develops. Depending on polarity of the solvent and the how tightly bonded the compounds are to the stationary phase determine how far the compound will rise the TLC plate. In this experiment fluorene, fluorenone, fluorenol, and an unknown were tested on the TLC plate. In this experiment, the unknown was confirmed to be fluorene and fluorenone by the distances traveled by the compounds and it’s Rf values. INTRODUCTION Thin Layer Chromatography is an analytical technique that is simple and inexpensive. TLC helps one determine the number of compounds in a mixture. The TLC allows one to determine whether compounds are identical. In TLC plates are coated with a thin layer of absorbent that serves as the stationary phase, while the solvent is the mobile phase that pushes compounds up the TLC plate. The solvent rises the plate through capillary action allowing the chromatogram to develop. The distance and speed travelled by solvents up the chromatogram depends on how tightly bonded the compound is to the stationary phase. Polarity of the solvent also determines how far a solvent will travel up the TLC plate. Once the solvent front is about a centimeter from the top of the plate it must be marked for the Rf value to be calculated. MATERIALS & METHODS 

Developing Chamber



TLC plate



Filter paper



Beakers



TLC capillary spotting tubes

The thin layer chromatography apparatus consists of a beaker, TLC plate, filter paper, and suitable solvent. The beaker serves as the developing chamber as the solvent pushes compounds up the TLC plate. The filter paper in the developing chamber serves as more surface area for evaporation. After the solvent has pushed the compounds 1 cm-1,5 cm from the top of the TLC plate it is marked so that Rf values can be calculated.

2 Ryan Huckaby Dr. Srinivasan 2423-530 3-5-2020 Dichloromethane MW: 84.93g/mol Density: 1.33g/cm3 Fluorene MW:166.22 g/mol Density:1.20 g/cm3 Fluorenone MW:180.19 g/mol Density:1.13 g/cm3

Hexane MW: 86.18g/mol Density: 0.661g/cm3 Fluorenol MW:182.22 g/mol Density1.51 g/cm3

PROCEDURE 1. A precoated TLC plate was obtained that was the proper size of the developing chamber 2. The edges of the TLC paper were lightly marked of the origin of line with a pencil. The plate was then spotted with 1-2% of the solutions containing the compounds to be separated. 3. A filter paper wick is added to the developing chamber. Then the suitable solvent was added to the developing chamber along with solvent vapors. 4. The TLC was placed in the developing chamber 5. The chromatogram was allowed to develop until the solvent front reached about 11.5 cm from the top of the plate. 6. The solvent front was marked immediately after removing the plate from the developing chamber. 7.

The chromatogram was visualized underneath a blue light and the separated spots were outlined.

8. The Rf value was then calculated for each compound.

3 Ryan Huckaby Dr. Srinivasan 2423-530 3-5-2020 DIAGRAMS

RESULTS & DISCUSSION Following the experiment, and observation of the chromatogram it was determined that the unknown compound was a combination of fluorene and fluorenone. The spots on the chromatogram were located in the same area proving that fluorene and fluorenone were the components of the unknown. The Rf values were also very close compared to one another in each different solving confirming that the components were fluorene and fluorenone.

Volume of Hexane

Vol. of CH2Cl2

10 mL

0 mL

Distance travelled by the solvent 57.7mm

Distance travelled Fluorene

Fluorenol

Fluorenone

Unknown

11.2mm

0.0mm

2.6mm

0.0, 13.4 mm

4 Ryan Huckaby Dr. Srinivasan 2423-530 3-5-2020 8 mL

2 mL

56.7mm

24.3mm

1.0mm

11.2mm

0 mL

10 mL

56.1mm

44.2mm

13.5mm

27.5mm

Volume of Hexane 10 mL 8 mL 0 mL

Vol. of CH2Cl2 0 mL 2 mL 10 mL

Rf of Fluorene 0.194 0.429 0.788

Rf of Fluorenol 0 0.0176 0.241

Rf of Fluorenone 0.0451 0.198 0.490

2.7, 26.5 mm 14.6, 44.0 mm

Rf of Unknown 0, 0.232 0.0476, 0.467 0.260, 0.784

CALCULATIONS Rf Values Rf =

distance travelled by compound distance travelled by solvent front

11.2 mm =0.194 Rf value of Fluorene ∈10 mL of Hexane 57.7 mm

SAFETY AND DISPOSAL All the chemicals were disposed in the sink as advised by the lab instructor. The glassware was washed with DI water and dried with paper towels. The TLC capillary tubes were disposed of in the glass disposal box.

5 Ryan Huckaby Dr. Srinivasan 2423-530 3-5-2020

CONCLUSION In conclusion, the chromatogram and Rf values have proven that the unknow compound was a mixture of fluorene and fluorenone. The chromatogram spots of the unknown travelled the same distance up the chromatogram as fluorene and fluorenone. The distance from the initial position on the TLC plate to the terminal end gave similar Rf values of fluorene and fluorenone.

REFERENCE Mohrig, J.R., Albert, D.G., Hofmeister, G.E., et al; Laboratory Techniques in Organic Chemistry, 4th ed., W.H. Freeman and Company, New York: 2014. Pp, 253-269, Chromatography

6 Ryan Huckaby Dr. Srinivasan 2423-530 3-5-2020

POST-LAB QUESTIONS 1. When 2-propanol was used as the developing solvent, two substances moved with the solvent front (Rf = 1) during TLC analysis on a silica gel plate. Can you conclude that they are identical? If not, what additional experiment(s) would you perform? In this case one can use a solvent that is less polar and observe whether the substances travel the same distance. Once the polarity of the solvent is decreased and the solutions travel the same distance again on can conclude that the substances ore identical. 2. The Rf value of compound A is 0.34 when a TLC plate is developed in diethyl ether. Compound B has a Rf value of 0.42 in pentane and 0.60 in diethyl ether. Which solvent would be better for separating a mixture of A and B by TLC? Explain. Diethyl ether should be used as the solvent because it displays a bigger difference in distance between the two substances....