Pre-Lab:Lab Report #1 CHEM2123
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Hannah Klug Pre-Lab Lab 1: TLC Based on the number and polarity of the functional groups in aspirin, acetaminophen, ibuprofen, and caffeine, whose structures are shown on page 184, predict which of these four compounds has the highest R
f
value and which has the lowest. Based on the number and polarity of the functional groups in aspirin, acetaminophen, ibuprofen, and caffeine, I predict that ibuprofen will have the highest R
f value and caffeine will have the lowest. 1- Why might it be very difficult to visualize the separation of cis- and traiis-2-butene by TLC? The butenes are quite volatile and will evaporate before they can be detected. 2. What error is introduced into the determination of an Revalue if the top is left off the developing chamber? The chamber’s environment needs to be constant and therefore it is saturated with eluted vapor. If the top were to be left off the chamber, the solvent will evaporate from the top of the TLC plate while the eluted compounds travel upward. This will cause the R
f
values to be too large. 3. What problem will ensue if the level of the developing liquid is higher than the applied spot in a TLC analysis? The prepared mixture being measured will dissolve in the developing liquid and will not travel up the TLC plate. 4. In what order (from top to bottom) would you expect to find naphthalene, butyric acid, and phenyl acetate on a silica gel TLC plate developed with dichloromethane? The least polar compound, naphthalene, will have the largest R
f
value and therefore it would be observed at the top of the plate. Butyric acid is a highly polar compound, it will have the lowest R
f
value, which can be observed at the bottom of the plate. Phenyl acetate can be observed in between the two. 5. In carrying out an analysis of a mixture, what do you expect to see when the TLC plate has been allowed to remain in the developing chamber too long, so that the solvent front has reached the top of the plate? The spots will grow larger. If the solvent does not evaporate from the top of the plate after remaining in the chamber for too long, then the R
f
values should not change.
Hannah Klug CHEM 2123-11417 Dung Nguyen 1 Thin-Layer Chromatography (TLC) Lab Report Performed August 30, 2022 Pre-Lab 1.
Based on the number and polarity of the functional groups in aspirin, acetaminophen, ibuprofen, and caffeine, I predict that ibuprofen will have the highest R
f value and caffeine will have the lowest. 2.
2.1.
The -butenes are quite volatile and will evaporate before they can be detected 2.2.
The chamber’s environment needs to be constant and therefore it is saturated with eluted vapor. If the top were to be left off the chamber, the solvent will evaporate from the top of the TLC plate while the eluted compounds travel upward. This will cause the R
f
values to be too large. 2.3.
The prepared mixture being measured will dissolve in the developing liquid and will not travel up the TLC plate. 2.4.
The least polar compound, naphthalene, will have the largest R
f
value and therefore it would be observed at the top of the plate. Butyric acid is a highly polar compound, it will have the lowest R
f
value, which can be observed at the bottom of the plate. Phenyl acetate can be observed in between the two. 2.5.
The spots will grow larger. If the solvent does not evaporate from the top of the plate after remaining in the chamber for too long, then the R
f
values should not change. Purpose
Hannah Klug CHEM 2123-11417 Dung Nguyen 1 To identify an unknown by analyzing the TLCs of known analgesics and the unknown and comparing corresponding spots and R
f
values. Table of Physical Constants Substance Molecular Weight (g/mol) Melting Point (
o
C) Boiling Point (
o
C) Density (g/ml) Hazards acetaminophen 151.17 168-172 >500 1.263 eye and skin irritation, may be harmful if swallowed aspirin 180.160 138-140 140 1.40 toxic if swallowed, eye, skin, and respiratory tract irritant caffeine 194.0956 237 178 1.23 harmful if swallowed, may cause eye, skin, and respiratory tract irritation, digestive tract irritation with nausea, vomiting, and diarrhea. May cause cardiac disturbances. May cause central nervous system effects ibuprofen 206.27 75-78 157 1.029 harmful if swallowed, causes serious eye irritation. May cause respiratory irritation (5% acetic acid + 45% hexane + 50% ethyl acetate) 174.28 flammable, irritant, health hazard, environmental hazard Experimental Procedure/Observation/Data 1.
In 8 labeled test tubes, the known analgesics were collected, and the unknown solution was prepared.
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Hannah Klug CHEM 2123-11417 Dung Nguyen 1 2.
Marked 8 TLC plates with a line 1 cm from the bottom. 3 evenly spaced tick marks were drawn on the line and their location labeled for the corresponding sample. 3.
Using capillary tubes, TLC plate 1 was spotted with aspirin on the first tick mark, acetaminophen on the second, and anacin on the third. This was repeated for TLC plates 2-
8. 4.
Prepared a developing chamber using a 150 mL beaker with (5% acetic acid + 45% hexane + 50% ethyl acetate) as the solvent/eluent, filter paper, and a watch glass for the lid. The level solvent was measured to hit below the baseline of the TLC plate. 5.
Placed each plate one at a time into the chamber to sit and were removed once the solvent rose to about 2 cm from the top of the plate. 6.
Observed the plates under ultraviolet light. The appearance and measurements of the spots were recorded in a lab notebook. Plate a = distance traveled by solvent in cm b= distance traveled by spot(s) in cm 1 4.70 aspirin acetaminophen anacin 3.70 0.80 3.60 0.450 2 5.20 ibuprofen caffeine anacin 4.90 0.70 3.90 0.30 3 4.10 aspirin acetaminophen vanquish 2.60 0.90 0.90 1.050 2.60 4 4.70 ibuprofen caffeine vanquish 3.10 0.30 1.0 0.250 2.650
Hannah Klug CHEM 2123-11417 Dung Nguyen 1 5 4.450 aspirin acetaminophen maxigesic 3.70 0.850 1.0 2.70 6 4.40 ibuprofen caffeine maxigesic 2.950 0.30 0.80 3.10 7 4.40 anacin unknown vanquish 3.50 0.350 0.80 0.30 2.20 0.30 2.20 8 4.10 unknown maxigesic 0.250 2.750 2.20 0.850 1 2 3 4 5 6 7 8 Calculations Plate a = distance traveled by solvent in cm b= distance traveled by spot(s) in cm Calculated R
f
values 1 4.70 aspirin acetaminophen anacin 3.70 0.80 3.60 0.450 0.787 0.170 0.766 0.096 2 5.20 ibuprofen caffeine anacin 4.90 0.70 3.90 0.30 0.942 0.135 0.75 0.0577
Hannah Klug CHEM 2123-11417 Dung Nguyen 1 3 4.10 aspirin acetaminophen vanquish 2.60 0.90 0.90 1.050 2.60 0.634 0.220 0.220 0.256 0.553 4 4.70 ibuprofen caffeine vanquish 3.10 0.30 1.0 0.250 2.650 0.660 0.0638 0.213 0.0532 0.564 5 4.450 aspirin acetaminophen maxigesic 3.70 0.850 1.0 2.70 0.831 0.191 0.225 0.607 6 4.40 ibuprofen caffeine maxigesic 2.950 0.30 0.80 3.10 0.670 0.0682 0.182 0.705 7 4.40 anacin unknown vanquish 3.50 0.350 0.80 0.30 2.20 0.30 2.20 0.795 0.0795 0.182 0.0682 0.500 0.0682 0.500 8 4.10 unknown maxigesic 0.250 2.750 2.20 0.850 0.610 0.671 0.537 0.207 Results and Discussion The results from the experiment show that a solution’s polarity determines the distance it will travel up the TLC plate, as well as the R
f values. For example, caffeine had lowest R
f
values and did not move far up the plate, while ibuprofen had the highest R
f
values and did move far up the plate. Caffeine is the most polar and ibuprofen is the least polar. Some R
f
values for a single substance vary too much. This could be due to errors in measuring distances, or in preparing the TLC plates. The tested amount spotted onto the plates may have been too much or too little. However, the results are clear enough to compare the R
f
values of the known analgesics
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Hannah Klug CHEM 2123-11417 Dung Nguyen 1 to those of the unknown. Due to the appearance of 2 spots on plates 7 and 8, we can see that the unknowns consist of two substances, one of which has R
f
values that are close to aspirin. Conclusion The purpose of the Thin-Layer Chromatography Lab was to identify an unknown by analyzing the TLCs of known analgesics and the unknown and comparing corresponding spots and R
f
values. If the experiment were to be conducted again, I would make sure an appropriate amount of each substance was spotted on the TLC plate. Post-Lab 6. decane, 2-octanone, acetaldehyde, acetic acid, 1-butanol. 7. The spots of different substance will overlap, and the results would be compromised. 8. To prevent the solvent from evaporating off the top of the TLC plate, causing the compounds to continue traveling upward and resulting in incorrect R
f
values. 9. A solvent of too low polarity would stay absorbed the silica gel and not move from its starting point. A solvent of too high polarity would dissolve the substances and travel with them. 10. Two spots with R
f
values of 0.50 and 0.52. 11. Ibuprofen. 12. 0.720.
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