Follow Melting Point and TLC Guided Viewing and Post-Lab Guidelines to complete the lab report.Watch this two video and answer the obervation questionsMP Demonstration: https://www.youtube.com/watch?v=1Uz9AT9k8UQ&feature=youtu.beTLC Demonstration: https://www.youtube.com/watch?v=ZO0oNgJr7sg&feature=youtu.beCHM3140L
Dr. Osberger Fall 2020
Melting Point and TLC Guided Viewing and
Post-Lab Guidelines
Reagents used this week (look up for your pre-lab)
Phenacetin, Acetanilide, Acetaminophen, Hexanes, Ethyl Acetate, silica gel (just look up safety
information for silica gel)
Guided Viewing Questions and Observations
Try to answer these and make observations as we go through the video. (Pause and rewind are helpful
here!)
Melting Point Demonstration Video
1. Melting points are often reported as a range of temperatures. Describe what the “lower bound”
temperature and the “upper bound” temperature of a melting point are.
2. Observe the appearance of the sample as melting begins. What are the first signs?
3. Observe as the sample continues to melt and fully liquefies. What changes do you see?
4. How would the melting range of a pure sample compare to an impure sample?
5. How could you use a mixed melting point to compare an unknown sample to a known
compound?
Thin Layer Chromatography (TLC) Technique Demonstration Video
6. How much sample do you need to run a TLC?
7. Why is it important to always dissolve your TLC sample in some solvent, even if your sample is
already a liquid?
8. What important property should your solvent have if you want to use it to dissolve your
sample?
9. When marking your TLC plate, why is it important to use a pencil, and not a pen or marker?
10. How do you clean your capillary (TLC spotter) before re-use?
11. When developing the TLC plate in the chamber, explain why it is important to cap the chamber
with a cap or watch glass.
12. Observe the solvent move up the plate. What is responsible for this movement?
13. When should you remove the TLC plate from the developing chamber?
14. The “solvent front” is how far the solvent goes up the plate. Why is it important to mark this
quickly on the plate after you remove it from the chamber?
15. What are two ways to visualize the TLC plate after development?
16. Observe the TLC plate when in the UV light box. What color is the silica gel? What color is the
spot?
Data Set for Post-Lab Report
Refer to the accompanying Data Set document for the Unknown you and your partner were assigned.
CHM3140L
Dr. Osberger Fall 2020
Post-Lab Report Required Sections
1. Guided Viewing and Observations. Include your notes from the guided viewing and any
observations that you made while viewing the demonstration videos.
2. Results and Discussion: Using the data set provided for your Unknown, type the calculations and
results of all data, such as final mass, percent recovery, and Rf values. Show your calculations.
Answer the questions below using the data set provided. This typed section should be where
you explain what your collected data means. You must discuss any results you obtained. You
need to convince the reader (i.e. me) that you fully understand the experiment and what your
results mean.
a. Calculate the percent recovery for the recrystallization of your Unknown. Show your
work.
b. Discuss your melting range results. Compare the results for the impure and pure
Unknown.
c. Calculate the Rf values for your Unknown and the three knowns in TLC Experiment 1.
Show your work.
d. What does TLC experiment 2 tell you?
e. Propose an additional experiment utilizing one of the techniques we learned this week
to provide further evidence for the identity of your Unknown compound.
3. Conclusions. What do you conclude is the identity of your Unknown? Briefly describe how the
various data you have support your conclusion.
4. References. Include citations of any references you used in completing this report. This
includes any images taken from websites or information from the textbook, and the websites
used to look up information for the reagent table or literature values (e.g. for melting ranges)
that you bring up in your post-lab.
CHM3140L Fall 2020
Dr. Osberger
Melting Point & TLC Data Sets
Unknown A Data Set
Recrystallization: A sample of impure unknown A (2.047 g) was dissolved in a minimum amount of
boiling water, subjected to hot filtration to remove any insoluble impurities, and then cooled to RT
before further cooling in an ice bath. Crystallization occured after scratching the cold solution with a
glass stir rod for a few minutes. The crystals were collected via suction filtration and dried for 1 week
on a watch glass in the locker.
Note: A small amount of impure Unknown A was set aside for use in melting point and TLC
experiments.
Weight of watch glass: 22.6673 g
Weight of watch glass and recrystallized Unknown A: 24.2112 g
Melting range: The melting ranges of impure unknown A and recrystallized unknown A were obtained
on a MelTemp apparatus and data were recorded below:
Impure Unknown A Melting Range: 155-161 C
Recrystallized Unknown A Melting Range: 168-171 C
Thin Layer Chromatography: Two TLC plates were run, and are shown below.
TLC Experiment 1
50/50 EtOAc / Hexanes
UV Visualization
1 2 34
Lane
Lane
Lane
Lane
1: Phenacetin
2: Acetaminophen
3: Acetanilide
4: Recrystallized Unknown A
TLC Experiment 2
50/50 EtOAc / Hexanes
UV Visualization
12
Lane 1: Impure Unknown A
Lane 2: Recrystallized Unknown A
Unknown B Data Set
Recrystallization: A sample of impure Unknown B (2.541 g) was dissolved in a minimum amount of
boiling water, subjected to hot filtration to remove any insoluble impurities, and then cooled to RT
before further cooling in an ice bath. Crystallization occured after cooling in an ice bath for 20
minutes. The crystals were collected via suction filtration and dried for 1 week on a watch glass in the
locker.
Note: A small amount of impure Unknown B was set aside for use in melting point and TLC
experiments.
Weight of watch glass: 21.9341 g
Weight of watch glass and recrystallized Unknown B: 23.6674 g
Melting range: The melting ranges of impure Unknown B and recrystallized Unknown B were
obtained on a MelTemp apparatus and data were recorded below:
Impure Unknown B Melting Range: 103-108 C
Recrystallized Unknown B Melting Range: 112-115 C
Thin Layer Chromatography: Two TLC plates were run, and are shown below.
TLC Experiment 1
40/60 EtOAc / Hexanes
UV Visualization
1 2 34
Lane
Lane
Lane
Lane
1: Phenacetin
2: Acetaminophen
3: Acetanilide
4: Recrystallized Unknown B
TLC Experiment 2
40/60 EtOAc / Hexanes
UV Visualization
12
Lane 1: Impure Unknown B
Lane 2: Recrystallized Unknown B
Unknown C Data Set
Recrystallization: A sample of impure Unknown C (1.828 g) was dissolved in a minimum amount of
boiling water, subjected to hot filtration to remove any insoluble impurities, and then cooled to RT,
where crystals started to form. The flask was cooled in an ice bath for a few minutes to complete
crystallization. The crystals were collected via suction filtration and dried for 1 week on a weigh boat in
the locker.
Note: A small amount of impure Unknown C was set aside for use in melting point and TLC
experiments.
Weight of weigh boat: 8.5783 g
Weight of weigh boat and recrystallized Unknown C: 9.347 g
Melting range: The melting ranges of impure Unknown B and recrystallized Unknown B were
obtained on a MelTemp apparatus and data were recorded below:
Impure Unknown C Melting Range: 118-123 C
Recrystallized Unknown C Melting Range: 132-133 C
Thin Layer Chromatography: Two TLC plates were run, and are shown below.
TLC Experiment 1
60/40 EtOAc / Hexanes
UV Visualization
1 2 34
Lane
Lane
Lane
Lane
1: Phenacetin
2: Acetaminophen
3: Acetanilide
4: Recrystallized Unknown C
TLC Experiment 2
60/40 EtOAc / Hexanes
UV Visualization
12
Lane 1: Impure Unknown C
Lane 2: Recrystallized Unknown C

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