Chem POST LAB 2 - Grade: A PDF

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post lab 2...

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Results (modify table as needed): Delete this and the parenthetical text Plate #

1

2

3

Components

Distance

Distance

traveled by

traveled by

solute (cm)

solvent (cm)

Aspirin

4

5

0.8

Unknown 1

2.5 and 1.1

5 and 5

0.5 and 0.22

Acetaminophen

3

5

0.6

Aspirin

4

5

0.8

Unknown 2

2.9

5

0.58

Acetaminophen

2.0

5

0.58

Unknown 1

2.4 and 1.1

5 and 5

0.48 and 0.22

Caffeine

1.1

4.8

0.23

Unknown 2

2.9

5

0.58

Solvent

Distance traveled

Distance traveled

by solute (cm)

by solvent (cm)

Anthracene

4.4

5

0.88

Benzil

4.3

5

0.86

Triphenylmethanol 4.2

4.9

0.86

95% hexane 5% t-

Anthracene

4.3

5

0.86

butyl methyl ether

Benzil

4.3

5

0.86

Triphenylmethanol 4.1

5

0.82

Ethyl acetate

Components

Rf

Rf

Discussion: During this lab, each of the known substances, aspirin, caffeine, and acetaminophen, and 2 unknown substances were placed on three TLC plates and compared. On the first plate aspirin, unknown 1, and acetaminophen were spotted. The unknown produced two distinct spots, one close to the solvent line and another close to the origin. Aspirin produced one spot that was close to the unknown spot that appeared to be streaky. Acetaminophen produced a spot that was close

to the unknown 1 origin spot. This means that unknown 1 contains acetaminophen. On the second plate aspirin, unknown 2, and acetaminophen were spotted. Aspirin produced the same spot as it did on the previous plate. Unknown 2 produced a similar spot to aspirin, as well as right next to it. Acetaminophen produced a spot that was closer to the solvent line. This means that unknown 2 contains some aspirin. Lastly, the third plate was spotted with unknown 1, caffeine, and unknown 2. The spots for unknown 1 and unknown 2 were the same for the third plate as they were for plate 1 and 2. Caffeine spotted close to the solvent line, meaning it is polar and moved slowly on the TLC plate. This also means that unknown 1 also contains caffeine. After analyzing the TLC plates, the next step was to figure out the Rf value for each of the compounds used on the three plates. Aspirin was found to have an Rf value of 0.8, acetaminophen was 0.6, and caffeine was 0.23 being the most polar compound used in this particular experiment. The Rf value’s of unknown 1 were found to be 0.22 and 0.50 since it produced two spots, while unknown 2 produced one spot with an Rf value of 0.58. The last step of this lab was to create two plates spotted with anthracene, benzil, and triphenylmethanol, except both plates were to be developed in different solvents; one being 95% hexane and 5% t-butyl methyl ether, and the other being ethyl acetate. After analyzing the plates the Rf values were found. Anthracene had a Rf value of 0.88, benzil was 0.86, and triphenylmethanol was 0.84. If the solvent is changed to a more polar mixture, then all compounds on the TLC plate will move higher up on the plate. Postlab Questions: 1.) Arrange the following compounds in order of increasing Rf in a TLC analysis: benzoic acid, benzaldehyde, 3-heptanone, nonane, and cyclohexanol. Benzoic acid, cyclohexanol, benzaldehyde, 3-heptanone, nonane. (Benzoic acid being most polar, and nonane being least polar)

2.) Why must the spot be applied to the TLC plate above the level of development solvent? It must be applied above the level of development solvent, because if it is below the compounds might end up dissolving in that solvent.

3.) What will be the result of adding too much sample to the TLC plate? The result of adding too much sample to the TLC plate is that there may be many spots, and large spots could be possible. Due to this, we would not be able to identify the Rf values.

4.) In a TLC analysis of analgesics, what would be the result if a solvent of too low polarity is used to develop the plate? If a solvent of too low polarity is used to develop the plate then the spots for the corresponding compounds would not move over thin layer chromatography.

5.) The Rf of ibuprofen was found to be 0.32 when neat t-butyl methyl ether was used as the development solvent. What effect would there be on the Rf of ibuprofen if acetone had been used to develop the TLC plate? If acetone had been used to develop the TLC plate, then the Rf value would be more since acetone is more polar that t-butyl methyl ether. The acetone would result in more distance for the ibuprofen than t-butyl methyl ether. Since the distance traveled is more, the Rf would increase....