post lab for aspirin synthesis and lab notebook set up

University of Washington – TacomaOrganic Chemistry I (THEM 251)
Autumn 2022
Applied Organic Chemistry Lab
Integrated Aspirin Synthesis, Purification, Characterization, and Application
Student Version
INTRODUCTION
Chemists do many things in the lab. They synthesize or create potentially helpful compounds
for use as drugs, containers, building materials, fabric, dyes, food preservatives, and millions
of other uses. They isolate compounds from naturally occurring sources, such as caffeine
from tea leaves. They purify the compounds they have synthesized or isolated using
techniques like recrystallization, extraction, and filtration. They track the course of these
reactions using techniques such as chromatography and spectroscopy. They characterize or
identify compounds that are found in natural products, as contaminates in food or water, or in
forensic situations. The synthesized or isolated products, once purified and characterized,
can then be tested for biological activity. Thus the work that chemists learn to do in the lab
has many important purposes. A significant number of students go on to work in a laboratory
setting that draws on many of these skills, so these are crucial things for students to learn.
Laboratory work is also the perfect place to develop problem-solving and time-management
skills. Chemistry lab is clearly a crucial part of science education! It is also fun!
In this first lab, we are going to learn and utilize several of these crucial skills. We
will first attempt to synthesize aspirin, a common pain reliever. We will purify our product,
then determine whether the product we made is indeed aspirin. The lab will conclude by
using some of the techniques we have learned to identify the presence of aspirin and other
analgesics (pain relivers) in some unknown tablets.
Aspirin can be synthesized by treating salicylic acid, a compound found in several
plants, with acetic anhydride. The structures of these three compounds are shown below.
Figure 1: Left to right, chemical structures of salicylic acid, acetic anhydirde, acetylsalicylic acid
Although we have not yet studied reactions, can you pick out what has changed between the
structure of the salicylic acid starting material and the product, acetylsalicylic acid (aspirin)?
What portion of the acetic anhydride molecule might have supplied the atoms needed to cause
this change to the salicylic acid? Acetic acid is a by-product, a compound that was not trying
to be made. Where might it have come from?
When the reaction is complete, several byproducts such as unreacted starting material
and acetic acid will be present with the desired product. The purification technique of
recrystallization will be used to try to purify the product. The purified product will be
characterized using melting point determination, a chemical test, thin-layer chromatography,
and IR spectroscopy.
Melting point determination involves measuring the temperature at which a compound
melts or transitions between the solid and liquid states. This depends on the intermolecular
forces between molecules. The melting point is a constant for any pure solid, but it is not
necessarily unique.
The product in this reaction will also be tested by a chemical test. A Chemical test is
one in which the desired product or a likely by-product reacts in a distinguishable way with a
test reagent. In this case, the final product will be tested for the presence of unreacted
salicylic acid by running a test for phenols, a hydroxyl group on a benzene ring. Phenols (see
structure in Figure 2) form an intensely purple colored complex with the Fe+3 ion in ferric
chloride. Look at the structures above and think about why salicylic acid gives a positive test
(color formation) with FeCl3 but aspirin does not.
Figure 2: General structure of a Phenol
Another way of following a reaction and examining products is to use Thin Layer
Chromatography (TLC). TLC involves placing tiny amounts of a compound onto a glass or
plastic plate coated with silica gel, then allowing a solvent or solvent mixture to wick up the
plate. The distance each compound present in the product travels depends on its size and
polarity and is described by a retention factor, or Rf.
Finally, the techniques you learned to determine whether or not you successfully
synthesized aspirin will be applied to a problem involving a medical emergency. A toddler
has ingested some unknown white pills. Were they aspirin or another analgesic?
PREPARATION FOR Week 1
1. Please read the ASPIRIN Essay from “Introduction to Organic Laboratory Techniques, 4th
ed.” by Pavia, et. al. p.61-62. This essay is posted in the lab module in CANVAS.
2. Skim the Whole Lab, then carefully read the Week 1 instructions.
3. Descriptions of the techniques you will need for each week are best found in the Organic Lab
Manual by Lisa Nichols.
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Tec
hniques_(Nichols)
Techniques you should be familiar with for week 1include:
Suction or Vacuum filtration:
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Technique
s_(Nichols)/01%3A_General_Techniques/1.05%3A_Filtering_Methods/1.5D%3A_Suction_Filtr
ation
3. Prepare your lab notebook as described below.
LAB NOTEBOOK Set-Up
• Title – Use the one given for this lab.
• Clerical Information – Your name, the name of your assigned lab partner for that lab,
station number, atomic number, and the date on which the in-lab work was started. Be
sure to also enter the lab in your Table of Contents.
• Objective – After reading the entire lab, identify and write down the objective of the lab.
The objective is the question or questions your data will hopefully allow you to answer.
• Hypothesis – For Week 1 of this lab, please write a hypothesis about what the results of
your ferric chloride test will look like.
• Physical & Chemical Properties Table – Use the format below. Include the starting
material, reagent, expected product, and catalyst. Also include test reagents. Leave some
room at the bottom of the table to add the solvents you will use for recrystallization and
TLC.
Chemical
Name
Use/Purpose
in THIS lab
Acetic
Reagent
Anhydride
Relevant Physical Properties
Hazards
Response
to hazards
Mp = -73.1oC,
MM = xx
o
but b.p. = 118 C 60.052
so liquid at
g/mole
room temp
Corrosive. Burns skin.
Vapors are a
respiratory irritant.
Reacts violently with
water
Gloves,
keep in
hood, use
dry
glassware
•
Pre-lab questions:
1. a) Redraw the structure of salicylic acid and identify and name 3 functional
groups found in it.
b) Redraw the structure of acetylsalicylic acid and identify and name 3 functional
groups found in it.
2. The introduction explains that aspirin is formed by a chemical reaction. What
changes occur when salicylic acid is converted into acetylsalicylic acid? Where
did any new atoms come from, or where did any removed atoms go?
3. Where did the acetic acid come from?
4. The phosphoric acid is a catalyst for this reaction. You learned about catalysts in
Gen Chem. What are they, and how are they different from a reagent?
5. In the introduction, you are told that you will test the product with FeCl3 to see if
any unreacted salicylic acid remains. What will you see if no reaction occurred
and your product is mostly unreacted salicylic acid? What will you see if your
product contains NO unreacted salicylic acid? What will you see if your product
is mostly aspirin but contains a little bit of unreacted salicylic acid?
6. If you used 250 mg of salicylic acid and excess acetic anhydride in the synthesis
of aspirin, what would be the theoretical yield of acetylsalicylic acid in
milligrams?
7. Most aspirin tablets contain 5 grains of acetylsalicylic acid. How many
milligrams is this? (Hint: you will need to look up what a “grain” is for
pharmacists.)
8. Challenge question (Extra Credit): Acetylsalicylic acid decomposes over time
when exposed to water vapor. This is why aspirin bottles tell you to not store
bottles of aspirin in your bathroom. Try to write an equation for this
decomposition reaction.
•
Experimental Plan – Use the Experimental directions below to write a plan for the work
you need to do in lab. A schematic is preferable to lots of words. You need to turn in the
carbon copies with the prep work up to this point prior to lab. You may not use the lab
guide during the lab period, although I will have a copy at the front of the room for
reference.
Data – Optional: Create spaces in your notebook to record all the data you will collect.
After preparing your lab notebook, please take the on-line pre-lab quiz to ensure
that you have a solid background for the investigation you will carry out in this lab.
You must have completed the pre-lab quiz with at least 70% mastery. If your score
is lower than this, you are welcome to come in and go over the lab with me; either a
score of >70% or a conversation with me is required to gain admittance to lab.
•
•
Experimental Directions for Week 1
Synthesis and Crystallization
A hot water bath (50 oC) was set up. Salicylic acid (ca. 0.210 +0.005 g) was placed in a
dry 5 mL conical vial to which acetic anhydride (0.480 mL) and phosphoric acid (exactly 1 drop
from a Pasteur pipet) were added. After inserting the magnetic spin vane, an air condenser was
attached to the top of the vial. The vial was clamped such that half of it was submerged in the 50
o
C water bath. The mixture was stirred until the salicylic acid dissolved, then stirring and
heating was continued for another 8-10 minutes. The vial was then removed from the water bath
and allowed to cool to the point it could be handled. After removing the air condenser and
magnetic spin vane, the vial was allowed to cool to room temperature, at which point crystal
formation was observed. It was cooled further in an ice bath. In runs where spontaneous
crystallization failed to occur, the solution was scratched to induce crystal formation.
After crystal formation appeared to be complete, water (3.0 mL) was added and the
mixture was stirred thoroughly. Next the mixture was vacuum filtered using a Hirsch funnel and
the vial was washed with 1.0 mL of cold distilled water. The crystals on the funnel were rinsed
with one 0.5 mL portion of cold distilled water. The crystals were allowed to dry on the funnel
with vacuum still on for another ~5minutes. A pin-head-sized amount of damp product was used
to run the Ferric Chloride test below. The remaining crystals were transferred to a labelled and
tared vial to dry completely sitting in a desiccator overnight or longer.
Ferric Chloride Test
The ferric chloride test was run by placing aliquots of water (0.5 mL) into each of three
small test tubes. A pin-head sized amount of salicylic acid was placed in the first test tube. A
similar amount of the damp product was placed in the second test tube. No solids were placed in
the third test tube. Ferric chloride solution (1%, 1 drop) was added to each of the three test tubes
and all were shaken. The color of each tube was noted.
POST LAB ANALYSIS – Week 1
Transfer the data you collected during Week 1 into the appropriate places in the post-lab
assignment. You will not turn this in until after Week 4, but by entering it now you have time to
re-do anything that did not go well, and will have less to do later. Please discuss any repeat work
with me prior to re-doing it.
PREPARATION FOR Week 2
Techniques you should be familiar with for week 2 include:
(Re)Crystallization:
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Techniques_(Nicho
ls)/03%3A_Crystallization
Melting Point Determination:
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Technique
s_(Nichols)/06%3A_Miscellaneous_Techniques/6.01%3A_Melting_Point
LAB NOTEBOOK Additions for Week 2
• Hypothesis – For Week 2 of this lab, please write a hypothesis about how the melting
points of the crude product and the recrystallized product will compare.
• Add the solvent you will use for recrystallization to your Physical/chemical Properties table.
Pre-lab questions For Week 2:
1) The solubility of acetylsalicylic acid was measured by Mala and Giulietti
(https://pubs.acs.org/doi/pdf/10.1021/je7005693) as shown in the graph below. In this graph, x
is solubility in g/mL. Use this graph to answer the following questions:
a. What is the solubility of acetylsalicylic acid at room temperature (20 oC, 293K)?
b. What is the solubility of acetylsalicylic acid in hot (not quite boiling) ethanol?
c. Use your theoretical mass of product to calculate how much hot ethanol should theoretically
be needed to dissolve your product. Note that this should be the maximum amount required, the
actual amount may be slightly less.
Experimental Directions for Week 2
Recrystallization of Crude Product
A melting point tube of the crude product was prepared, then the mass of the dry product
was measured. The theoretical amount of ethanol needed to dissolve the actual mass of product
being recrystallized was calculated. The vial containing the crude product was clamped in a ~70
o
C water bath. A small beaker containing distilled water was heated on the edge of the hotplate
for later use. A small Erlenmeyer flask containing approximately double the ethanol calculated
was warmed in the same water bath. Warm ethanol was then added dropwise to the product until
it dissolved. Then warm distilled water (~1 ml or an amount equal to the amount of ethanol
used) was added to the dissolved product. The vial was removed from the hot water bath and
allowed to cool undisturbed until it reached room temperature. At that point, it was placed in an
ice bath. The resulting crystals were filtered and transferred to a tared vial. The tared vial was
placed in a beaker and the beaker placed in a 100o C oven for 15-30 minutes to dry.
Characterization of Dry Product
The mass of the dry, recrystallized product was measured, then the melting points of both
the recrystallized and crude products were determined using the capillary method and a Vernier
Mel-Temp apparatus. The FeCl3 test was repeated for the recrystallized product.
POST LAB ANALYSIS – Week 2
Transfer the data you collected during Week 2 into the appropriate places in the post-lab
assignment. You will not turn this in until after Week 4, but by entering it now you have time to
re-do anything that did not go well, and will have less to do later. Please discuss any repeat work
with me prior to re-doing it.
PREPARATION FOR Week 3
Techniques you should be familiar with for week 3 include:
Thin Layer Chromatography – Read about it in Nichols:
https://chem.libretexts.org/Bookshelves/Organic_Chemistry/Organic_Chemistry_Lab_Tec
hniques_(Nichols)/02%3A_Chromatography/2.03%3A_Thin_Layer_Chromatography_(T
LC)
LAB NOTEBOOK Additions for Week 3
•
•
Hypothesis – For Week 3 of this lab, please write a hypothesis about which compound,
salicylic acid or acetylsalicylic acid, will have the largest Rf value.
Add the solvent(s) you will use for TLC work to your Physical and Chemical Properties
Table.
Pre-lab questions For Week 3:
1) Use the Figure of the TLC plate given to answer question 1. It is a silica gel plate which was
run in ethyl acetate (less polar than silica gel).
a. Which compound, A, B, or C, is the least polar? How do you know?
b. Which compound, A, B, or C, is most polar? How do you know?
c. Which compound, A, B, or C, is least pure? How do you know?
d. Which two compounds contain a common component?
2) Calculate the Rf values for the components of samples A, B, and C in Question 1.
Experimental Directions for Week 3
Background:
Thin layer chromatography separates compounds based on their size and polarity. The
compounds adsorb more or less strongly to a stationary phase or a mobile phase, and this
determines their rate of travel. In this lab, silica serves as the stationary phase (mounted on
plastic) and an organic solvent is the mobile phase. Any different compounds present in your
product move up the TLC plate at different rates based the competing intermolecular interactions
of the polar silica plate and the less polar solvent. More polar compounds adsorb more strongly
to the polar silica and do not move as far up the TLC plate. Less polar components will favor the
less polar solvent and move higher. The TLC of the aspirin you synthesized in lab is compared to
the TLCs of commercially aspirin and the salicylic acid starting material.
Directions:
1. Prepare a developing chamber as follows:
Add the solvent (ethyl acetate) to the TLC developing chamber (a 600 mL beaker) until the
liquid surface is about 1 cm deep. The solvent MUST be below the pencil line where the
compouds will be spotted once the plate is placed in the container. A piece of filter paper should
be stood against one wall inside of the flask. The purpose of the filter paper is to ensure that the
atmosphere inside the chamber is saturated. The chamber must also be sealed to maintain a
saturated atmosphere. Do this by placing a small piece of parafilm over the lip of the beaker and
adding a watch glass.
2. Prepare a TLC plate by drawing a pencil line 1.5 cm from the bottom of the plate.
3. Take a small amount of the salicylic acid (SA) starting material and dissolve as much as you
can in 3 drops of ethyl acetate. Add another 10 drops of ethyl acetate. Share this solution with the
other team in your hood (one group makes solution 3 and the other makes solution 4). Spot the
SA solution on the bottom left of the line on your plate. Make the spot as small but as
concentrated as possible (place a drop of solution, let it dry, then repeat 1 time). Use a UV lamp
to see if the spot is the right size (~1 mm diameter) and clearly visible before moving on. If it is
not fairly dark under the UV light, spot it as above 1-3 additional times, until it is concentrated
and clearly visible.
4. Take a small amount of the known Aspirin (ASA, provided) and dissolve as much as you can
in 3 drops of ethyl acetate. Add another 10 drops of ethyl acetate. Share this solution with the
other team in your hood (one group makes solution 3 and the other makes solution 4). Spot the
ASA solution in the middle of the line on your plate. Make the spot as small but as concentrated
as possible (place a drop of solution, let it dry, then repeat 1 time). Use a UV lamp to see if the
spot is the right size (~1 mm diameter) and clearly visible before moving on. If it is not fairly
dark under the UV light, spot it as above 1-3 additional times, until it is concentrated and clearly
visible.
5. Take a small amount of your product (P) and dissolve as much as you can in 3 drops of ethyl
acetate. Add another 10 drops of ethyl acetate. Spot the ASA solution on the right side of the line
on your plate. Each group needs to test their own product. Make the spot as small but as
concentrated as possible (place a drop of solution, let it dry, then repeat 1 time). Use a UV lamp
to see if the spot is the right size (~1 mm diameter) and clearly visible before moving on. If it is
not fairly dark under the UV light, spot it as above 1-3 additional times, until it is concentrated
and clearly visible.
6. Develop the plate by placing it in the prepared developing chamber. Make sure no sides of the
TLC plate touch the filter paper. (If the filter paper touches any side of the TLC plate, the spots
will be drawn sideways.) Be sure to recover the chamber as soon as you insert the plate. NEVER
MOVE OR DISTURB A PLATE WHILE IT IS DEVELOPING. Solvent will begin to move
up the plate. Once the ‘solvent front’ is within 1-5 cm of the top of the plate, remove the plate
from the chamber and immediately mark the solvent front line with a pencil. Do not let your
solvent front travel to the top of the TLC plate.
7. Circle any visible spots on the TLC plate with a pencil, then use a UV lamp to see spots not
otherwise visible. Measure the distance from the origin to the solvent front and from the origin to
each spot. Record a to scale drawing of your developed plate in your lab notebook. You may
also wish to take a digital picture of the plate to include with your report.
Note: Dispose of TLC spotters in the Broken Glass Containers. Do not
throw them away in the trashcans. This is a health hazard for the janitorial
staff. Liquids should be discarded in the containers in the hood labeled
“Organic Leftovers”. Used TLC plates should be discarded in the containers
in the hood labeled “Solid Leftovers”.
8. Record data neatly in a table (see post lab) and use the following equation to determine the Rf
values of the various spots on the TLC plate. Note that if a channel contains more than one spot,
a Rf is calculated for each spot.
𝒅𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝒕𝒓𝒂𝒗𝒆𝒍𝒍𝒆𝒅 𝒃𝒚 𝒔𝒑𝒐𝒕 (𝒕𝒐 𝒕𝒐𝒑)
𝑹𝒇 =
𝒅𝒊𝒔𝒕𝒂𝒏𝒄𝒆 𝒕𝒓𝒂𝒗𝒆𝒍𝒍𝒆𝒅 𝒃𝒚 𝒔𝒐𝒍𝒗𝒆𝒏𝒕 𝒇𝒓𝒐𝒏𝒕
If your TLC plate is not separating the various components, try one of these developing
solutions instead.
1. 9:1 mixture of ethyl acetate and methylene chloride
2. 1:1 mixture of ethanol and dichloromethane
3. 65:30:5 mixture of hexane, ethyl acetate and acetic acid or 45:50:5 mixture of hexane, ethyl
acetate and acetic acid.
PREPARATION FOR Week 4 – Analysis of Unknown Tablets Digested by a Toddler
LAB NOTEBOOK Additions for Week 4
•
•
Hypothesis – For Week 4 of this lab, please write a hypothesis about how you will use
your knowledge about aspirin, m.p., chemical tests, and TLC to determine what drug the
toddler in your ER may have ingested.
Add any new chemicals you may use to your Physical and Chemical Properties Table.
Pre-lab questions For Week 4:
1) Look up the chemical structures of acetaminophen, caffeine, ibuprofen, and naproxen. Draw
them, along with acetylsalicylic acid, here.
2) Rank the compounds in question 1) from most to least polar.
3) What compound out of the list above (acetaminophen, caffeine, ibuprofen, acetylsalicylic acid
and naproxen) do you think will have the largest Rf? The smallest Rf? Explain your choices.
Experimental Directions for Week 4
Background:
In this scenario, you are helping determine the appropriate treatment for a toddler who
has been brought to an ER by frantic parents. The parents found the toddler happily eating white
pills, thinking they were candy. Unfortunately, the tablets had been transferred to an unmarked
pill container. Effective medical treatment requires quick and accurate identification of the drug
which the toddler ingested. The parents believe that the pills were either aspirin, ibuprofen,
naproxen, or acetaminophen.
What technique have you learned in this lab that will be helpful in this situation? You
have available known samples of the possible drugs ingested (Advil, Aleve, Anacin, Bufferin,
Excedrin, and Tylenol). You also have pure standards of the drugs found in each (aspirin,
ibuprofen, naproxen, or acetaminophen, and caffeine.) You also have available a developing
solution composed of a 1:1 mixture of dichloromethane and ethanol, which is know to separate
these compounds well.
Write a proposed procedure for identifying the compound the toddler has ingested. You
will be asked to submit this as part of your Week 4 Pre-Lab Quiz. Once it is approved, transfer
to your lab notebook.
University of Washington – Tacoma
Organic Chemistry I (TESC 251)
Integrated Aspirin Post Lab Write-Up 100 pts
PLEASE TYPE OR WRITE IN (NEATLY) WHAT IS REQUESTED BELOW AND
SUBMIT AT THE BEGINNING OF CLASS. USE THE ORDER AND NUMBERING
WHICH THE DIRECTIONS SPECIFY. (SINCE THIS IS A WORD FILE, YOU MAY
UPLOAD IT AND TYPE INTO IT.) THE CARBON COPIES OF YOUR LAB
NOTEBOOK DATA PAGES. SHOULD HAVE BEEN TURNED IN AT THE END OF
LAB, ALONG WITH YOUR LABELLED PRODUCT.
WEEK 1 data summary (8 points total)
Yield
Mass of salicylic acid used ___________________(1 pt)
Volume of acetic anhydride used ____________(1 pt)
Mass of dry product obtained _____________________(1 pt)
Which reagent is limiting? _____________________ Show how you calculated this. (2 pt)
Theoretical yield of acetylsalicylic acid (show calculations below) _______________(2 pts)
Theoretical yield calculations:
Percent Yield of acetylsalicylic acid (show calculations below) _______________(1 pt)
Space for showing calculations:
Characterization of Product
Ferric Chloride Test (3 pt)
Test tube #
Contents
Observations with FeCl3
1
2
3
Week 1 After-Lab Questions (9 pts)
1.(3 pts) Did you follow your proposed lab steps exactly or did you make some changes? If
you made any changes, please explain why you did so.
2. (3 pts) Did the results of your Ferric chloride test uphold or disprove your hypothesis?
Explain. Do they suggest a new hypothesis?
3. (3 pts) For the aspirin synthesis, a % yield of 60-90 is typical for this synthesis. Answer one
of the following questions.
-If your yield was in this range, do you think the synthesis went smoothly? Cite
evidence that the good yield resulted from product, not by-products or contaminants.
-If your yield was not in this range, what issues might have interfered with obtaining a
good yield? Cite evidence to back up your proposed problems.
WEEK 2 Data Summary (6 pts)
Mass of crude product _____________________________ (1 pt)
Approximate volume of ethanol used ____________________ (1 pt)
Mass of recrystallized product: _______________________ (1 pt)
%Yield of Recrystallized Product: _______________ (1 pt)
Show calculations:
Melting point range of crude product
_____________________________ (1 pt)
Melting point range of recrystallized product _____________________________ (1 pt)
Week 2 After-Lab Questions (6 pts)
4. (4 pts) Was your hypothesis comparing the melting points of the crude product and the
recrystallized product upheld, disproved, or unable to be determined? Please explain.
5. (2 pts) Did the results of your ferric chloride test change? Explain what this result suggests.
WEEK 3 Data Summary
TLC Plate Summary Table (6 pts)
Channel
Distance
Solvent Front
Travelled
Distance
Spot 1
travelled
Rf of
Spot
1
Distance
Spot 2
travelled
Rf of
Spot 2
Add
columns if
> 2 spots
A
B
C
Week 3 After-Lab Questions (8 pts)
6. (4 pts) Based on your TLC results, what compounds were present in your product? Based
on the TLC results, does it appear that you synthesized aspirin? Explain how the TLC results
support your answer.
7. (4 pts) Based on your TLC results, how PURE was your product? Explain how the TLC
results support this answer.
WEEK 4 Data Summary (10 pts)
•
(5 pts) Succinctly describe your experimental plan.
•
(5 pts) Report the Data – Please include
a. A scale drawing of each TLC plate, with each initial spot labelled and the developed
spots marked and described. A photo is a great addition, but you must also make “to scale’
sketches of your plates with the distances used to calculate the R f values marked.
b. A table compiling the Rf values for each compound in each of the samples run. Give
one example showing how you calculated the Rf values.
Week 4 After-Lab Questions (8 pts)
8. (6 pts) Were you able to conclusively identify the medication the toddler ingested? If yes,
what was it? Explain what data led to this conclusion. Was your hypothesis upheld or
disproved?
9. (2 pts) Do you feel you used a good method? Would a different one possibly be better?
Explain.
OVERALL POST-LAB QUESTION
(10 pts)
10. (10 pts) Based on all the characterization methods, do you believe your aspirin synthesis
was successful at producing aspirin? How pure do you believe your aspirin was? If it was
impure, what was the likely contaminant?
As you answer the above questions, use data to support your answers.
OTHER GRADE COMPONENTS (26 pts)
• Pre-lab quiz Week 1 (5 pt)
• Pre-lab quiz Week 2 (4 pt)
• Pre-lab quiz Week 3 (4 pt)
• Pre-lab quiz Week 4 (4 pt)
• Carbons of Lab Notebook pages turned in each week, complete, legible (4 pt)
• In-lab Engagement (paid attention to safety lecture, worked safely, cleaned up, wore
protective gear, etc.) (5 pt)
University of Washington – Tacoma
Organic Chemistry I (T CHEM 251)
Acid-Base Extraction Lab
Student Version
INTRODUCTION
Organic reactions often generate multiple products that need to be separated from each
other. The separatory funnel (aka “sep funnel”) is a standard piece of glassware in the
organic laboratory that allows chemists to separate compounds based on differing chemical
solubility. This process is known as extraction and involves dissolving one substance from a
mixture of compounds into a solvent and then physically separating that solution from the rest
of the mixture. Extraction can be carried out using a variety of phases. For instance, a solid–
liquid extraction can be performed on a mixture of solids by dissolving one of them in a
solvent, then separating the solution from the solids. An example of solid–liquid extraction is
making a cup of coffee; caffeine and flavonoids are extracted from ground coffee bean solids
using hot water as the solvent.
In a liquid–liquid extraction, which is what you will perform in this lab, several
compounds are dissolved in a solvent in which both are soluble. A second solvent, which
must be both immiscible with the first solvent and a better solvent for one of the compounds
in the mixture, is then added to this solution inside of a separatory funnel, a special funnel
with a stopcock at the bottom and an opening at the top that can be sealed with a stopper. The
compound which is more soluble in the second solvent moves from the first solvent to the
second one. Because the solvents are immiscible, they separate into two layers, with the
denser solvent settling at the bottom. Opening the stopcock at the bottom of the funnel allows
the bottom layer to drain out into a collection flask. Closing the stopcock as soon as the
bottom layer has been collected allows for isolation of the top layer, which can be collected
by pouring it out the top of the funnel. This extraction process is typically repeated several
times to maximize product separation and recovery.
Because successful separation depends on differing solvent densities, it is important to
know the densities of the solvents involved before carrying out an extraction. Table 1 shows
the densities of some common organic laboratory solvents at room temperature. In the real
lab, it is sometimes difficult to visually determine which layer in the extraction is which.
Knowing the densities of the solvents helps organic chemists correctly identify the layers, a
key step toward isolating a desired product.
Solvent
Density (g/mL) at 23 °C
Pentane
0.626
Hexanes
0.653
Diethyl ether
0.713
Ethyl acetate
0.902
Water
0.998
Dichloromethane (CH2Cl2)
1.33
Chloroform (CHCl3)
1.49
(Source: Nichols, Organic Chemistry Laboratory Techniques, p. 188)
Table 1. Densities of selected solvents at room temperature.
When a reaction forms an acidic product such as a carboxylic acid, an acid–base
extraction can be used to separate the acidic compound from other organics by altering the
solubility of the compound. Deprotonation of a carboxylic acid forms a salt, which is much
more polar, and therefore more water-soluble, than its neutral organic counterpart. For
example, stearic acid, which has an 18-carbon chain that terminates with a carboxyl group, is
not water-soluble. Converting stearic acid to its sodium salt, sodium stearate, renders the
compound water-soluble (Figure 1). In this lab, you will be simulating an acid–base
extraction and exploring how differences in polarity affect water-solubility.
Figure 1. Conversion of stearic acid into sodium stearate and impact on solubility.
In this two-part lab, you will first use acid-base extraction to separate a mixture of two organic
compounds. Then, you will use TLC and melting point, along with physical characteristics, to
identify your unknown compounds.
PREPARATION FOR WEEK 1
1. Read the Whole Lab, especially the post-lab write-up instructions.
2. Learn or Review the following concepts via reading and watching:
Must read – Lab Text (Nichols): IV.A–IV.E.4.E (pp. 183–208) plus IV.F.3.A–IV.F.3.C (pp.
218–222) plus IV.G (pp.223–227) This is the section that specifically covers acid–base
extraction.
Must watch (sep funnel): https://www.youtube.com/watch?v=5mugRn5erNM
Optional reading “How to use a separatory funnel”
http://www.chem.ucla.edu/~bacher/General/30BL/tips/Sepfunnel.html
http://www.chem.ucla.edu/~bacher/Specialtopics/extraction.html
3. Prepare your lab notebook as described below.
LAB NOTEBOOK Set-Up
•
Title – Use the one given for this lab.
•
Clerical Information – Your name, the name of your assigned lab partner for that lab,
and the date on which the in-lab work was started. Be sure to also enter the lab in your
Table of Contents.
•
Objective – After reading the entire lab, identify and write down the objective of the lab.
The objective is the question or questions your data will hopefully allow you to answer.
•
Hypothesis – For this lab, please write a hypothesis about how your acidic or basic
component can be made more water soluble.
•
Physical & Chemical Properties Table – Use the format below. Be sure to include
your solvents and reagents.
Chemical
Name
Use/Purpose Relevant Physical Properties
in THIS lab
Solubility
in water
•
Reactivity
with A/B
Molar
Mass
Hazards
Density
(g/mL)
Safety – List any particular safety issues associated with this lab.
Response
to
hazards
•
Pre-lab questions:
1. What is the primary hazard associated with the use of diethyl ether?
2. Why are carboxylic acids, even large ones, soluble in aqueous base?
3. Why do we “vent” separatory funnels?
4. A student tried to extract a compound from water using ethanol. It didn’t work. Why
not?
5. If you have an aqueous and an organic layer in a separatory funnel, how could you
easily determine which is which? (Assume that you don’t know the densities.)
6. Partition coefficients describe how a solute is distributed between two immiscible
solvents. They are used in drug design as a measure of a solute’s hydrophobicity and a
proxy for its membrane permeability. If morphine has a partition coeffiecent, K, of 2 in
petroleum ether and water, and a water solubility of 1.0 g/17.6 mL, what is the solubility
of morphine in petroleum ether?
7. Solute A has a partition coefficient of 1.0 between water and diethyl ether. If a
solution which is 0.20 g of A per 4.0 mL of a water solution is extracted with one 2.0 mL
portion of ether, how much A would remain in the water?
If the same starting solution is extracted with 1.0 mL of ether TWO times, how much
A would remain in the water after the second extraction?
•
Experimental Plan – Use the Experimental directions below to create a flow chart
showing the steps you will need to carry out to separate your compounds. Your chart
should indicate what reaction occurs at each step and which compound goes with which
solvent whenever a separation occurs. Those of you who took general chemistry here at
UWT did something similar in the lab where you separated benzoic acid from salt and
sand.
•
Data – Create spaces in your notebook to record all the data and observations you will
collect. Start this on a different page from everything before this. You will use this part
of your notebook during lab time to record your data & observations.
•
Have lab notebook checked and initialed – Turn in the carbon copies of your pre-lab
(everything before the Data section) in class on Monday before lab day.
•
After preparing your lab notebook, please take the online pre-lab quiz to ensure
that you have a solid background for the investigation you will carry out in this lab.
EXPERIMENTAL DIRECTIONS
In this experiment, you will be given a mixture that contains two organic compounds.
One will be a neutral organic compound and the other will be either an organic acid or an organic
base. You will separate the two components using acid–base extractions. You will need to use
your critical thinking skills to design and successfully carry out a procedure to do the listed tasks.
Obtain an unknown sample which contains an acidic and/or a basic and/or a neutral
compound (each unknown will contain exactly two compounds). Separate this mixture, via
extraction, using a separatory funnel, and identify its components. The possible components are
listed below:
Acidic
Basic
Neutral
benzoic acid
(m.p. = 122 °C)
p-chloroaniline
(m.p. = 72 °C)
benzil
(m.p. = 95 °C)
trans-cinnamic acid
(m.p. = 133 °C)
4-nitroaniline
(m.p. = 147–149 °C)
fluorene
(m.p. = 114 °C)
p-Toluic Acid
(m.p. = 180–181 °C)
……………
(m.p. = °C)
trans-stilbene
(m.p. = 122–125 °C)
The solvents you will have available are diethyl ether, a weak HCl solution, a weak NaOH
solution, a sodium bicarbonate solution, and water. You will also have a drying agent for
removing traces of water from an organic solvent, concentrated HCl and NaOH and pH paper.
All the equipment in your drawers, including a separatory funnel, can be used.
At the end of the lab, please save your solid samples in the dessicator for
characterization.
PREPARATION FOR WEEK 2
Techniques you should be familiar with for week 2 include:
Thin Layer Chromatography – Review it in Nichols: 2.3: Thin Layer Chromatography (TLC) Chemistry LibreTexts
Melting Point Determination – Review it in Nichols: 6.1: Melting Point – Chemistry LibreTexts
LAB NOTEBOOK Additions for Week 2
•
•
Hypothesis – Based on your observations in Week 1, do you think that you successfully
separated your compounds? For Week 2 of this lab, please write two hypotheses:
o Hypothesis about what you think your TLC will look like
o Hypothesis about what you think you’ll observe upon melting point measurement
Physical & Chemical Properties Table – Use the format below for your TLC solvents.
Chemical
Name
•
Use/Purpose Relevant Physical Properties
in THIS lab
Hazards
Response
to
hazards
Safety – List any particular safety issues associated with this lab.
Pre-lab questions:
1. What hazards are associated with hexanes? Dichloromethane?
2. Based on your results last week, do you think you have an organic acid or an organic base? What
functional group do you think you have? Why?
3. What standards do you plan to run on your TLC?
4. A student runs a TLC of their neutral compound and sees two spots in that lane. What
does this indicate?
5. Your lab neighbor in lab completed their acid-base extraction. They recovered
compounds from the neutral layer and the NaOH layer. On their TLC plate for the
compound extracted from the NaOH layer, they spotted p-chloroaniline and pnitroaniline. Neither Rf matched their extracted compound! Please explain to your
neighbor why. Use a reaction scheme.
•
Data – Create spaces in your notebook to record all the data and observations you will
collect. Start this on a different page from everything before this. You will use this part
of your notebook during lab time to record your data & observations.
•
Have lab notebook checked and initialed – Turn in the carbon copies of your pre-lab
(everything before the Data section) in class on Monday before lab day.
•
After preparing your lab notebook, please take the online pre-lab quiz to ensure
that you have a solid background for the investigation you will carry out in this lab.
EXPERIMENTAL DIRECTIONS
After you believe you have separated the two components, you must confirm that they have been
separated and identify what components were in your mixture. How will you identify the
substances? Think back to the techniques you have used. Did you learn any quick and simple
ways of identifying a compound?
To ascertain that the two components of the mixture were separated, we will be using melting
point (m.p.) and Thin Layer Chromatography (TLC). Ethyl acetate, dichloromethane, and
hexanes will be available for your developing solution. My suggestion is that you spot your plate
with: i) the initial mixture, ii) component A, and iii) component B. Small amounts of the pure
components will also be available should you have a need to run a second plate to further
confirm the identity of your isolated compounds.
University of Washington – Tacoma
Organic Chemistry I (T CHEM 251)
Acid-Base Extraction Post Lab Write-Up
Post lab write-ups should be typed, double spaced, and submitted as a hardcopy
with lab notebook carbons attached. Please use my numbering/lettering system
to organize and delineate your answers.
WEEK 1
OBSERVATIONS SUMMARY
(3 pts) Create a table to summarize observations made in this lab. Be sure to include
an appropriate title. (Think about what observations are important to include. If you’re not
sure, look at the observations you recorded in your notebook during lab to see what was
useful, and look at the post-lab questions to see what will be discussed).
POST-LAB QUESTIONS
1. (3 pts) Did you follow your proposed procedure, or make any changes? If you made
changes, why?
2. (5 pts) Were your components acidic, basic, or neutral? What evidence led you to
this conclusion?
WEEK 2
DATA SUMMARY
(5 pts) Create a table to summarize the data you collected during this lab. Be sure to
include an appropriate title. (Think about what data is important to include. If you’re not
sure, look at the data you recorded in your notebook during lab to see what was useful, and
look at the post-lab questions to see what will be discussed).
POST-LAB QUESTIONS
3. (3 pts) What mass do you recover of each extract?
Mass of solid mixture (g) :___________________
Extract 1 mass (g): ____________________
Extract 2 mass (g): ____________________
Total recovered mass (g): ________________
Percent (%) mass recovered: _________________
4. (4 pts) Sketch (or include legible, annotated photos of) your TLC plate(s). For each
plate, identify what the original spot was and give distance travelled and the Rf of each
component.
5. (5 pts) What were the identities of your components? Explain what evidence supports
these identities.
6. (5 pts) How well did your separation scheme work? How pure were the extracts?
7. (5 pts) What would you do differently if you repeated the experiment:
a. To increase recovery?
b. To improve purity?
University of Washington – Tacoma
Organic Chemistry I (T CHEM 251)
Acid-Base Extraction Lab Grading Rubric
PRE-LAB QUIZ SCORES
Week 1
5 PTS
Week 2
4 PTS
LAB NOTEBOOK PREP (EACH WEEK)
5 PTS
IN-LAB NOTEBOOK (EACH WEEK)
3 PTS
POST LAB WRITE-UP
38 PTS
WEEK 1
OBSERVATIOMS SUMMARY
3 pts
POST LAB QUESTIONS
8 pts
WEEK 2
DATA SUMMARY
5 pts
POST LAB QUESTIONS
22 pts
LAB CONDUCT
4 PTS
-Safety glasses & lab coats were worn throughout the lab period.
1 pt
-Student participated with partner and demonstrated good teamwork.
½ pt
-Lab station was left clean: glassware put away correctly or returned
to cart.
1 pt
-Any spill or broken glassware was reported.
-Student followed safety protocols such as labelling containers before
dispensing chemicals into them, only dispensing the required amount
of chemicals, not returning used chemicals to the stock bottles, and
disposing of chemicals in the proper waste container.
1 pt
– Student paid attention during lab lecture & followed safety instructions ½ pt
TOTAL POINTS POSSIBLE
35 PTS