CHEMISTRY 122
Laboratory Manual
Winter 2009
Last printed 2/6/2016 3:48:00 AM
0
Table of Contents
Exp. #
Title of Experiment
Page
Lab Safety
2
Record Keeping (Laboratory Notebook)
3
Lab # 1: Organic Structure, Isomers, and Geometrical Shape
5
Lab # 2:
Separation of Plant Pigments
7
Lab # 3:
Simple Distillation
11
Lab # 4:
Fractional Distillation
14
Lab # 5:
Identification of Hydrocarbons
18
Lab # 6:
Alcohols
24
Lab # 7:
Synthesis of Aspirin
29
Lab # 8:
Analysis of Aspirin and Vitamin C Tablets
26
Lab # 9
Properties of Carboxylic Acids and Esters
38
Lab #10
TLC Analysis of Analgesic Drugs
42
Lab #11
Isolation of Caffeine from Tea
45
Last printed 2/6/2016 3:48:00 AM
1
Laboratory Safety
General Safety Rules
Safety goggles must be worn in the laboratory at all times. The first thing you should do when entering
the laboratory is to put on your safety goggles, and the last thing you do is to remove your safety goggles.
Eating, or drinking in the laboratory is strictly prohibited. Laboratory chemicals that may have toxic
properties dissolve in foods, or beverages in the laboratory.
Know the location and operation of the laboratory safety equipment. This includes the eye wash, fire
extinguishers, deluge shower, and fire blanket. In case of fire, or other emergency, do not panic calmly
seek help from the nearest possible source.
Do not use Bunsen burners or other ignition sources in the Organic laboratory. Occasionally the
instructor will allow the use of open flames in the laboratory, but only in the absence of volatile organic
vapors.
Avoid skin contact with chemicals. If you spill a chemical on your skin, immediately wash it off with
soap and water. Do not touch your face or rub your eyes after handling chemicals; wash your hands after
handling chemicals; always wash your hands after leaving the laboratory.
General Guidelines for Working with Chemicals
Follow experimental procedures and directions explicitly. Be sure to check the labels of laboratory
reagents, and double check to be sure that you are using the correct chemical for the experiment.
Clean up spills immediately. Neutralize acid spills with sodium bicarbonate, and check with the
instructor if you are unsure of how to clean up a spill.
Never return used reagents to their original containers. Adding a chemical to its original container can
contaminate the entire container. If you have more than you need, then dispose of the rest in the correct
waste container.
Material Safety Data Sheets (MSDS) Chemical manufactures are required by law to provide a MSDS
sheet for each chemical sold. They contain information about the physical and chemical properties of the
chemical and a list of hazards of that chemical.
The MSDS sheets also specify safe handling procedures.
Hazard Diamond Labels Chemical are rated for hazard relative to health, fire, reactivity, and skin contact
on a scale of 1-4, with 4 representing high hazard as in the example below.
Last printed 2/6/2016 3:48:00 AM
2
GUIDELINES FOR RECORD KEEPING:
Since all of you have had exposure to at least one chemistry lab (Chem. 101),
it is now time to start a more realistic, accurate, and detailed record-keeping
procedure. Whether you work in a health-related profession or in a lab setting, it is
of the utmost importance to learn how to keep accurate records of any procedure
performed. In Chemistry 102 we shall start to introduce you to this by requiring
that you keep a lab notebook and that you submit written reports after each lab is
completed.
In all laboratories, data taken in the lab is written down (in pen) in a lab
notebook with numbered pages. All entries must be kept current and entered as the
work is performed. Strict guidelines have been developed for those working in all
types of lab settings: Biotechnology, chemical, analytical chemistry, environmental
labs, etc. The purpose of this strict record keeping is to insure that anyone can
duplicate your work, if necessary. If patents have to be applied for, the date and
time of your original work can be documented and proven in court and you can take
your work and produce professional reports for submission to your boss or other
authorities. The lab notebook will be collected and graded at the end of the quarter.
Here are the guidelines for record keeping in Chem. 122 lab:
1. Each experiment should contain the Title of the experiment and date recorded on
the top of the right hand page
2. Following the title should be any physical constants, or other information needed
to be used during lab time, such as melting points, boiling point, density,
molecular weight.
3. Balanced chemical equations, if there are any.
4. Data should come next. Data is all of the measurements taken, plus observations
5. Next Results and calculations. In this section the Results will clearly be stated,
with any supporting calculations.
6. Finally a conclusion, where problems with the lab and possible improvements, if
you or someone else is going to do this lab again.
1. Purchase from the bookstore a hardbound notebook (composition book). Pages
should be numbered (by hand is acceptable).
2. On the outside, write your name and course number clearly so you can identify your
book easily.
3. On the inside cover, draw a diagram of the lab highlighting the safety equipment.
This drawing must be shown to the instructor on the second lab day.
4. Use the second right-side page to construct a Table of Contents and keep this current
with titles of experiments and page numbers. Be sure to reserve the second page for a
Table of Contents, as well. As you come to lab each week, your instructor will initial
your new entry after checking that you’re pre-lab is complete.
Last printed 2/6/2016 3:48:00 AM
3
5. PreLab questions are to be completed before lab and handed in at the beginning of the
lab period. In addition to answering PreLab questions, you should have an updated table
of contents, experiment title, date, lab reference, purpose, balanced equations, and
physical properties written in you lab book before coming to class.
Note: Use the right-hand pages for records and data; leave the left-hand pages
empty or use them for scratch paper, preliminary observations, notes and
calculations. All notebook entries are to be done in pen only.
6. As you perform the experiment, record all data in ink in the notebook. Include
descriptions and observations. The notebook should be a diary of your work with
sufficient information such that an outsider can repeat the experiment and reproduce the
results following your procedure.
8. When at home results, calculations required for results should be completed at home.
Following this should be the conclusion, which is a restatement of the purpose, showing
that the purpose was accomplished, along with information pertaining to the quality of
your results, such as % yield, or percent relative error.
WEEKLY LAB REPORT
This report is to be on notebook paper in ink containing the following sections.
Computer generate reports are always welcome. Your lab report is a neat presentation of
the information contained with in your lab notebook
I. Titl, date
II. Purpose, a short one or two sentence description of why the lab is being done.
III. Data
a. Observations( Colors, textures, physical states of reactants and products)
b. Measurements( include units and the number of significant figures)
IV. Results and calculations; show all calculations, including work.
V. Conclusion; a restatement of the purpose showing that the purpose for the experiment
was achieved. In addition, what went wrong, how the lab can be improved, a brief
description of the quality of the experimental results, such as % yield, % relative error.
VI. Questions; answer all questions from the lab manual
Last printed 2/6/2016 3:48:00 AM
4
Experiment
1
Organic Structures, Isomers, and Geometrical Shape
Purpose:
Using a model kit from the supplies counter, construct models of different organic compounds,
using these to determine geometrical shape, bond angles, polarity, and to investigate structural or
geometric isomers. Answer all questions in your laboratory notebook; a photocopy of these
pages constitutes the lab report for this experiment. No pre-lab is required for this lab only.
Procedure:
1. Construct a molecule of methane (CH4). Use a black ball for the carbon atom and white
balls for the hydrogen atoms.
a. Sketch a picture of your model of methane.
b. What geometrical shape is methane?
c. What are the bond angles?
d. Does methane display any carbon-carbon rotation about the single bonds?
e. Is methane a polar molecule?
f. Remove one of the hydrogen atoms. The remaining group of atoms is a methyl
group CH3-; sketch its picture.
g. What are the bond angles?
2. Replace one of the hydrogen atoms with a chlorine atom (green ball). This is a model of
chloromethane.
a. Sketch a picture of your model of chloromethane.
b. What geometrical shape is chloromethane?
c. Are the bond angles the same as for methane?
d. Does chloromethane display any carbon-carbon single bond rotation?
e. Is chloromethane a polar molecule?
3. Replace a second hydrogen atom with another chlorine atom. This molecule is
dichloromethane.
a. Sketch a picture of your model of dichloromethane.
b. What geometrical shape is dichloromethane?
c. What are the bond angles?
d. Is dichloromethane a polar molecule?
4. Assemble a model of pentane (C5H12, linear).
Last printed 2/6/2016 3:48:00 AM
5
a. Sketch a picture of your model of pentane.
b. What geometrical shape is pentane?
c. What are the bond angles?
d. Is pentane a polar molecule?
5. Using five carbon atoms and twelve hydrogen atoms construct as many different
molecules as you can.
a. Sketch a picture of each different model of C5H12.
b. Give the geometrical shapes of each of your different structures.
c. In each case give the bond angles.
d. Describe the polarity of each molecule.
e. Give each of your models an IUPAC name.
6. Construct a model of ethene (C2H4, with a double bond between the two carbon atoms).
a. Sketch a picture of your model of ethene.
b. What geometrical shape is ethene?
c. What are the bond angles?
d. Is ethene a polar molecule?
e. Does ethene display any carbon-carbon rotation about the double bond between
the two carbon atoms?
7. Construct a model of ethyne (C2H2, with a triple bond between the two carbon atoms).
a. Sketch a picture of your model of ethyne.
b. What geometrical shape is ethyne?
c. What are the bond angles?
d. Is ethyne a polar molecule?
e. Does ethyne display any carbon-carbon rotation about the bond between the two
carbon atoms?
8. Create as many molecules as you can with the formula C2H2Cl2.
a. Sketch pictures of each different molecule (remembering geometric isomers).
b. Give each molecule an IUPAC name.
c. Describe the geometry of each molecule.
d. Determine the bond angles.
e. Describe the polarity of each molecule.
f. Do any of these molecules display carbon-carbon bond rotation about the double
bond between the two carbon atoms?
9. Construct a model of cis and trans 1,2-dichlorocyclobutane.
a. Sketch pictures of both molecules.
b. Describe the geometry of each molecule.
c. Determine the bond angles.
d. Describe the polarity of each molecule.
e. Is there any bond rotation about any of the bonds between two carbon atoms?
10. Construct mirror images of the two molecules from question 9. A mirror image is how
the molecule would look if held up to a mirror. Assume the space between the two
models is a mirror and the second molecule is its reflection.
a. Sketch pictures of each of the pairs of molecules.
b. Give an IUPAC name for each molecule.
c. Which of the molecules are identical and which are different? Try stacking one
on top of another (called superimposing) to see if they are identical.
Last printed 2/6/2016 3:48:00 AM
6
Experiment
2
Separation of Plant Pigments
Purpose:
Mixtures of organic compounds can usually be separated by chromatography. In this
experiment two colored organic substances (β- carotene and lycopene) found in tomato paste
will be separated, using a technique called thin layer chromatography(TLC).
Background:
There are various different types of chromatography techniques available to the organic
chemist, some examples of which include: column chromatography, gas chromatography, and
high pressure liquid chromatography. These techniques are routinely used for compound
separation, but they can also be qualitatively and quantitatively. All chromatography
techniques require two phases: the mobile and the stationary phase. The compounds to be
separated are first adsorbed onto the stationary phase, and then dissolved into the mobile
phase as it moves up the stationary phase. This process of adsorbing and dissolution occurs
many times as the solvent passes up the stationary phase. The separation of compounds is
due to the fact that different compounds have different adsorption- dissolution times, thus
causing some compounds to travel up the paper faster than others. In this experiment the
stationary phase will be a commercial TLC slide, and the mobile phase will be the solvent
that travels up the slide carrying the components of the tomato paste pigments with it. One
way to quantify a chromatography experiment is to calculate the Rf value, is defined by the
following mathematical formula: Rf = Distance traveled by the compound/Distance traveled
by the solvent.
Procedure:
1. Obtain a TLC slide from the supplies counter. Draw a light pencil line 1 cm from the
bottom (along the long edge of the paper). Now pencil in 5 light x’s equally spaced along
this line from the center of the paper outward about 2cm apart. That would make two x’s
from either side of the center x, with spacing of 3cm.
Last printed 2/6/2016 3:48:00 AM
7
2. Pigments of tomato paste will be extracted in two steps.
a. Weigh about 10 g of tomato paste in a 50 mL beaker. Add 15 mL of 95%
ethanol. Stir the mixture vigorously with a spatula until the paste will not stick to
the stirrer. Place a small amount of glass wool (about the size of a pea) in a small
funnel blocking the funnel exit. Position the funnel over a 50 ml Erlenmeyer
flask and pour the tomato paste-ethanol mixture into the funnel. When the
filtration is completed, squeeze the glass wool lightly with your spatula. The
collected alcohol solution will contain water from the paste since both the alcohol
and the water are polar compounds. The less polar pigments will remain in the
solid material on top of the glass wool. This residue should be squeezed to
remove any water that might be present. Discard the water alcohol solution, and
carry the solid material on to the next step.
b. Place the residue from the glass wool in a 50 ml beaker. Add 10 mL petroleum
ether and stir the mixture for about two minutes to extract the pigments. Filter
the extract as before through a clean funnel with glass wool blocking the exit into
a clean 50 mL beaker. The pigments will be in the petroleum ether solution; any
solid material remaining on top of the glass wool may be discarded. Place the
beaker on a hot plate (in the hood) and evaporate the solvent down to a final
volume of about 1 mL. Use low heat and take care not to evaporate all the
solvent. After evaporation, cover the beaker with aluminum foil.
3. Place your TLC slide on a clean flat surface in order not to contaminate it. Obtain two
micro capillary tubes—one for your tomato paste extract and the other for the β- carotene
solution. Take care not to get these mixed up, in order to avoid contamination. First
apply your capillary to the extracted pigment by dipping it into the solution, and allowing
the capillary action to partially fill the tube with your extract. Now quickly touch the
capillary to the crossed lines of the second x on your paper, just long enough to make a
small spot (no larger that 2 mm). Repeat this spotting process with short contact time
giving 4 touches for the second x, 8 touches for the third x, and 10 touches for the fourth
x, still keeping a small spot. Reapplying like this causes the concentration of the pigment
to build up in a small area. Following the same procedure (with your second micro
capillary tube), place spots of the provided β-carotene solution on the first and fifth x
mark. The spotting process should be repeated 2-3 times for the β-carotene solution, a
much lighter pigment. Allow the spotted paper to dry for several minutes.
4. Pour 20 mL of the developing solvent into a 400 mL beaker, making sure that the depth
of the solvent will not touch the spots that you placed on the TLC slide.
5. Roll a piece of filter paper (4 by 8in) placing it around the walls of the beaker, but
touching the solvent on the bottom a 400 mL beaker. Then place your TLC slide into the
beaker, preferably not touching the paper lining the side of the beaker.
6. Cover the beaker with aluminum foil, and allow the solvent to creep up the TLC slide.
Remove the TLC slide when the solvent is approximately 1.0 cm from the top of the
slide. Immediately upon removal mark the line the solvent makes with a pencil (before it
disappears).
7. Mark the spots of the pigments by circling them with a pencil. Note the colors of the
spots in your note book and draw a picture of your chromatogram in your notebook.
Measure the distance from the top of each spot to the starting x. Measure the distance the
Last printed 2/6/2016 3:48:00 AM
8
solvent traveled from the starting line. Now calculate and record the Rf values for each
spot by dividing the distance that the spot traveled by the distance that the solvent
traveled. Show these calculations neatly and clearly in your notebook, and circle the
result.
8. Your spots will lighten on standing. Since these separated compounds contain
conjugated double bonds, they can be seen with ultraviolet light. Also, iodine will react
with them if the chromatogram is placed in a sealed jar containing some iodine crystals.
Check your chromatogram with ultraviolet light. Record any new spots that might be
present in your laboratory note book. Then place your chromatogram in an iodine jar, put
the lid on the jar, and wait about a minute. Remove your chromatogram, and describe
any changes to any of the spots in your laboratory note book.
Required Chemicals and Equipment
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
Micro capillary tubes
Glass wool
Whatman no.1 filter paper cut to 4X8 in size.
Hot plate
Tomato paste
Low boiling petroleum ether
Ethanol, 95%
Developing solution (88% petroleum ether : 10% hexane : 2% toluene)
0.55% β- carotene in pet ether
Iodine crystals in a large jar with lid
UV lamps
Ruler
Last printed 2/6/2016 3:48:00 AM
9
PRE-LAB QUESTIONS
(to be answered in your lab notebook and shown to your instructor at the beginning of the
lab period, along with the material discussed in the “Record Keeping” section of this Lab
Manual, pages 3-4)
1. Look up the structures of β- carotene and lycopene (textbook, library, or internet) and
draw their structures below, labeling each structure with the compound’s color.
a. What is the basic difference between the structures of these two pigments?
b. To what class of hydrocarbons do these pigments belong?
c. Do the names of these pigments indicate their chemical classification?
2. What is the stationary phase in this experiment?
3. What is the mobile phase?
LAB QUESTIONS
(to be answered in your lab notebook; a photocopy of all notebook pages pertaining to this
experiment constitutes the lab report for this experiment)
1. Did your tomato paste contain lycopene? What support is there for your answer?
2. Which spot gave the best results for the pigment? (2,3, or 4)
3. Suppose you used carrot juice instead of tomato paste and you find a spot with the
same Rf as β- carotene. What could you conclude?
4. What would you predict if a solution of Br2 is added to a chromatogram containing a spot
corresponding to β- carotene?
Last printed 2/6/2016 3:48:00 AM
10
Experiment
3
Simple Distillation of a Hydrocarbon Mixture
Purpose:
To separate the liquid components of a hydrocarbon mixture using boiling point.
Background Information:
Distillation is a widely used technique for the separation and purification of mixtures
relative to their boiling points. When a liquid phase mixture is boiling, the vapor above
the boiling liquid will not have the same composition as the liquid, but will be richer in
the more volatile or lower boiling component. If the vapor above the liquid is collected
and cooled, the liquid that condenses will have the same composition as the vapor and
thus richer in the more volatile component. The boiling mixture then should have a lower
concentration of the less volatile component of the mixture. In this experiment the
temperature of the distillate vs. the volume will be recorded. The separation improves as
the boiling points of the components are further apart. The graph of temperature vs.
volume should have plateaus representing the boiling points of the individual components
of the mixture.
CAUTION!! Volatile, flammable liquids, such as hydrocarbon liquids; avoid flames, do
not evaporate to dryness.
Equipment:
Clamps
Suspend the apparatus securely and see that both the flask and condenser are
clamped. The adapter need not be clamped. The height of the assembled
equipment should be arranged so that the receiver can rest on the laboratory
bench.
Last printed 2/6/2016 3:48:00 AM
11
Thermometer
Thermometers are manufactured with varying lengths of extensions below the
standard taper joint, or rubber connector, as in this experiment. Choose a
thermometer of such length, or if using a rubber connector, be sure that the entire
mercury bulb extends below the delivery tube.
Condenser
Be certain that water is flowing through the condenser before the distillation is
started. Only a small stream of water, flowing from the bottom to top, is needed
to cool the condenser; the critical factor is the rate of heat transfer through the
glass.
Heating Mantle
Place a heating mantle on an iron ring, connected to a variac set at 4 (See photo 1)
The variac will regulate the amount of electricity flowing into the heating mantle,
thus controlling the temperature of the experiment. After connecting the plug of
the heating mantle into the variac, the plug the variac into the electrical outlet
located in the hood. Do Not Plug the Heating Mantle into the Outlet!!!
Boiling Chips
For a liquid to boil, it must be brought to a temperature slightly above its boiling
point so that bubble formation can begin. If a bubble of vapor appears within this
liquid, it may do one of two things: collapse, if it is below a minimum size,
because of surface tension of the liquid; or grow and rise to the surface of the
liquid if it is larger than the critical size. If a liquid , free of solid impurities or
dissolved gases, is heated slowly, a temperature well beyond the boiling point can
be reached without any boiling actually taking place. This superheati9ng occurs
because added energy is required to initiate bubble formation. If a bubble then
starts to form in the superheated liquid, it may suddenly grow with almost
explosive violence and jar the container vigorously enough to shatter it. This
problem, called bumping, can be overcome by adding a piece of porous material
called a boiling chip to the liquid before it is heated to the boiling point. The
pores act as built-in bubbles so that a liquid cannot superheat. The air in these
pores is replaced by vapor of the distilling material as the distillation proceeds,
but this vapor cannot condense because the temperature of liquid is slightly above
its boiling point. However, whenever a distillation is stopped and then started
again, a new boiling chip will be needed because the vapor in the pores will have
condensed and filled the pores with liquid.
Procedure:
Pour 25 mL of a toluene cyclohexane mixture into a dry 100 mL distillation flask, then
add two or three boiling chips. Arrange a simple distillation assembly as shown in the
photograph 1 below. Be sure to apply grease to each standard tapered joint to prevent
them from “freezing” the joints. Turn on the cooling water and heat the flask at such a
rate that distillate drops off the condenser at the rate of about 1 drop per second (not
easy); you will have to increase the variac setting as necessary. Record the temperature
Last printed 2/6/2016 3:48:00 AM
12
after each mL of distillate has been collected in your laboratory notebook. Graph these
results at home in your laboratory note book. Continue the distillation process until there
is about 1-2 mL of liquid left in the flask. Dispose to all organic waste in the waste hood
in the labeled containers.
Photo #1
Last printed 2/6/2016 3:48:00 AM
13
Experiment
4
Fractional Distillation of a Hydrocarbon Mixture
Purpose:
To separate the liquid components of a hydrocarbon mixture using boiling point.
Background Information:
Consider the separation of cyclohexane and toluene. When distilled in a simple distilling
apparatus a mixture of these two miscible liquids starts to distil somewhat above the
boiling point of cyclohexane and stops distilling somewhat below the boiling point of
toluene. All fractions of the distillate are mixtures and little separation of the two
components is achieved. A better separation could be obtained by redistillation of each
fraction. If redistillation is repeated often enough, the two components of the mixture
will eventually be separated. Fortunately this series of condensations and redistillations
is done automatically in a fractionating column.
The fractionating column shown above the distillation flask in the picture below contains
a stainless steel scouring sponge, which provides a porous packing for equilibration of
vapor and condensate. At the start of the distillation of a mixture of cyclohexane and
toluene the mixture boils and the vapors condense in the lowest part of the fractionating
column. The composition of this condensate is similar to that of the first fraction
collected in a simple distillation-richer in cyclohexane than in toluene, but by no means
pure cyclohexane. Then, as more cyclohexane and toluene boil, the temperature of these
vapors is higher than that of the first portion of the mixture, because this portion contains
less cyclohexane and more toluene. These hot vapors contact the liquid already in the
fractionating column from the first part of the distillation and the heat transfer takes
place, which causes the less volatile component (cyclohexane) to boil from that liquid. A
succession of these condensations and redistillations occur throughout the column. The
efficiency of a column is rated by the number of simple distillations that take place within
the column. After cyclohexane-toluene vapor has warmed the entire length of the
column, the less volatile part condenses and trickles down over the surface of the
packing, while fresh vapor from the flask forces its way through the descending
condensate with attendant heat interchange. A number of equilibrations between
Last printed 2/6/2016 3:48:00 AM
14
ascending vapor and descending condensate take place throughout the column. The
vapor that eventually passes into the receiver is highly enriched in the more volatile
cyclohexane, whereas the condensate that continually drops back into the flask is
depleted of the volatile component and enriched with the less volatile toluene. The
packing is used in the column to increase the vapor-liquid contact area. Since
equilibration is fairly slow, slow distillation effects better separation.
CAUTION!! Volatile, flammable liquids, such as hydrocarbon liquids; avoid flames, do
not evaporate to dryness.
Equipment:
Clamps
Suspend the apparatus securely and see that both the flask and condenser are
clamped. The adapter need not be clamped. The height of the assembled
equipment should be arranged so that the receiver can rest on the laboratory
bench.
Thermometer
Thermometers are manufactured with varying lengths of extensions below the
standard taper joint, or rubber connector, as in this experiment. Choose a
thermometer of such length, or if using a rubber connector, be sure that the entire
mercury bulb extends below the delivery tube.
Condenser
Be certain that water is flowing through the condenser before the distillation is
started. Only a small stream of water, flowing from the bottom to top, is needed
to cool the condenser; the critical factor is the rate of heat transfer through the
glass.
Heating Mantle
Place a heating mantle on an iron ring, connected to a variac. The variac will
regulate the amount of electricity flowing into the heating mantle, thus controlling
the temperature of the experiment. After connecting the plug of the heating
mantle into the variac, the plug the variac into the electrical outlet located in the
hood. Do Not Plug the Heating Mantle into the Outlet!!!
Boiling Chips
For a liquid to boil, it must be brought to a temperature slightly above its boiling
point so that bubble formation can begin. If a bubble of vapor appears within this
liquid, it may do one of two things: collapse, if it is below a minimum size,
because of surface tension of the liquid; or grow and rise to the surface of the
liquid if it is larger than the critical size. If a liquid , free of solid impurities or
dissolved gases, is heated slowly, a temperature well beyond the boiling point can
be reached without any boiling actually taking place. This superheati9ng occurs
because added energy is required to initiate bubble formation. If a bubble then
Last printed 2/6/2016 3:48:00 AM
15
starts to form in the superheated liquid, it may suddenly grow with almost
explosive violence and jar the container vigorously enough to shatter it. This
problem, called bumping, can be overcome by adding a piece of porous material
called a boiling chip to the liquid before it is heated to the boiling point. The
pores act as built-in bubbles so that a liquid cannot superheat. The air in these
pores is replaced by vapor of the distilling material as the distillation proceeds,
but this vapor cannot condense because the temperature of liquid is slightly above
its boiling point. However, whenever a distillation is stopped and then started
again, a new boiling chip will be needed because the vapor in the pores will have
condensed and filled the pores with liquid.
Procedure:
Construct the setup as described in the picture below. The setup is essentially the same
as last week, except a fractionating column is placed above the round bottom boiling
flask. The boiling flask should be charged with 50 mL of the toluene (bp110.8°) and
cyclohexane ( bp 81.4°) plus a couple of boiling stones. Quickly bring the mixture to a
boil by placing the variac to the second highest setting. As soon as boiling starts, turn
down the variac down to 4. A ring of condensate will rise slowly through the column; if
you cannot at first see the ring locate it by touching the column with the fingers. The rise
should be gradual, in order that the column can acquire a uniform temperature gradient.
Do not apply more heat until you are sure that the ring of condensate has stopped rising
then increase the heat gradually. In a properly conducted operation, the vapor-condensate
mixture reaches the top of the column only after several minutes. Once the distillation
has commenced, it should continue steadily without any drop in temperature at a rate not
greater than 1 ml in one to two minutes. Observe the flow and keep it steady by slight
increases in heat as required. Protect the column from drafts by pulling down the hood
window. Record the temperature as each ml of distillate collects and making more
frequent temperature recordings as the temperature starts to rise rapidly, by recording
temperatures at each half mL (approx. 10 drops). Collect a series of fractions in a series
of labeled 25-mL Erlenmeyer flasks. Fraction 1 should contain the distillate collected up
until a temperature of 85°. Fraction 2 should contain the distillate collected from 86° to
92°. Fraction 3 should contain the distillate collected from 93° until there is 5 mL left in
the distillation pot. Plot a distillation curve and record what you observed inside the
column in the course of the fractionation. Fractions collected while the temperature is
increasing rapidly, are probably not pure and should contain similar portions of the two
liquids.
Last printed 2/6/2016 3:48:00 AM
16
Photo #1
Questions:
1. What is meant by flooding in the fractionating column? What effect does
this have on the separation?
2. What is the purpose of using boiling stones in the experiment?
3. Why is it dangerous to attempt to carry out a distillation in a completely
closed apparatus, one with no vent to the atmosphere?
4. Why would a longer fractionating column provide better separation of the
hydrocarbon mixture?
Last printed 2/6/2016 3:48:00 AM
17
Experiment
5
Identification of Hydrocarbons
Purpose:
To explore simple laboratory tests that can distinguish between the different classes of
hydrocarbons. In this experiment the exploration of hydrocarbons is limited to saturated and
unsaturated hydrocarbons. Alkanes have the highest ratio of hydrogen to carbon allowed in
organic compounds, while unsaturated compounds have a lower ratio of hydrogen to carbon.
Formulas for these ratios are found in the lecture textbook. Compounds with a lower ratio of
hydrogen to carbon have structural differences—multiple bonds between carbon atoms, or cyclic
structures. These structural differences are the keys to differentiating between the different types
of hydrocarbons. The simple tests outlined below are designed specifically for the type of
unsaturation caused by carbon-carbon multiple bonds. If the test fails, then one can conclude that
the hydrocarbon is probably saturated.
Background Information:
The number of known organic compounds total into the millions. Of these compounds
the simplest types are those that contain only hydrogen and carbon atoms. These are
known as hydrocarbons. Because of the number and variety of hydrocarbons that exist,
some means of classification is necessary.
One means of classification depends on the way in which carbon atoms are connected.
Aliphatic hydrocarbons are compounds consisting of carbons bonded either in a single
chain or in a branched chain. Cyclic hydrocarbons are compounds having the carbon
atoms bonded in a closed polygon. For example, n-hexane and 2-methylpentane are
aliphatic molecules, while cyclopentane is a cyclic system:
CH3CH2CH2CH2CH2CH3
n-hexane
Last printed 2/6/2016 3:48:00 AM
CH3CHCH 2CH2CH3
CH3
2-methylpentane
18
cyclopentane
Another means of classification depends on the type of bonding that exists between
carbons. Hydrocarbons which contain only carbon-to-carbon single bonds are called
alkanes. They are also referred to as saturated molecules. Hydrocarbons containing at
least one carbon-to-carbon double bond are called alkenes, and those compounds with at
least one carbon-to-carbon triple bond are alkynes. Alkenes and alkynes are also referred
to as unsaturated hydrocarbons. Finally a special class of cyclic hydrocarbons, which
have a high degree of unsaturation and a unique set of reactions, are called aromatic.
The following are examples of each of the above categories:
CH 3
CH 3CH 2CH2CH 3
n-butane (alkane)
CH3CH2CH2CH=CH2
CH 3CH 2CH2CCH
1-pentane (alkene)
1-pentyne(alkyne)
toluene (aromatic)
In looking at the types of bonds which each of these compounds contains, one realizes
that all of these molecules are nonpolar. Recall that the electronegativity difference
between carbon and hydrogen is only 0.4 and that qualifies this bond as a nonpolar bond.
In general, hydrocarbons do not mix with polar solvents such as water or ethyl alcohol.
On the other hand, hydrocarbons mix with relatively nonpolar solvents such as ligroin (a
mixture of alkanes), carbon tetrachloride or dichloromethane. Since the density of most
carbon-hydrogen containing compounds is less than that of water, they will float. Crude
oil and crude oil products (home heating, oil and gasoline) are mixtures of hydrocarbons;
these substances, when spilled on water, spread quickly along the surface because they do
not mix with water and float.
The type of bond in the compound determines the chemical reactivity of hydrocarbons.
While saturated hydrocarbons, alkanes, will burn (undergo combustion), they are
generally unreactive to most reagents. Unsaturated hydrocarbons, alkenes and alkynes,
not only burn, but also react by addition of reagents to the double or triple bonds. The
addition products become saturated, with fragments of the reagent becoming attached to
the carbons of the multiple bonds. Aromatic compounds, with a higher carbon to
hydrogen ratio than nonaromatic compounds, burn with a sootier flame as a result of
unburned carbon particles being present. Aromatic compounds are resistant to addition
reactions.
Combustion: The major component in “natural gas” is the hydrocarbon methane. Other
hydrocarbons used for heating or cooling purposes are propane and butane. The products
from 100% combustion are carbon dioxide and water:
2 CH3CH2CH2CH3 + 13 O2
Last printed 2/6/2016 3:48:00 AM
19

8CO2 + 10 H2O
Reaction with Bromine. Unsaturated hydrocarbons react rapidly with bromine in a
solution of carbon tetrachloride. The reaction is the addition of the elements of bromine
to the carbons of the multiple bonds:
Br
+
Br2
Br
red
colorless
The bromine solution is orange; the product that has the bromine atoms attached to
carbon is colorless. Thus a reaction has taken place when there is a loss of color from the
bromine solution and a colorless solution remains. Since alkanes have only C-C bonds
present, no reaction with bromine is observed—the orange color of the reagent would
persist when added. Aromatic compounds resist addition reactions because of their
unique characteristics; the orange color of the bromine reagent will persist when added to
an aromatic compound as well.
Reaction with Potassium permanganate. Unsaturated hydrocarbons will also react
with a potassium permanganate solution. The reaction is the addition of hydroxyl groups
to the carbons of the multiple bonds:
OH
+
OH
KMnO4
purple
brown
The KMnO4 solution is purple; the product that has the hydroxyl groups attached to
carbon is brown. Thus a reaction has taken place when there is a color change from
purple to brown. Neither alkanes nor aromatic compounds react with KMnO4; the
original purple color will persist when a potassium permanganate solution is added to
these compounds.
Procedure:
CAUTION!! Assume the organic compounds are highly flammable. Use only small
quantities. Keep away from open flames except as directed. Assume they are also toxic
and can be absorbed through the skin. Avoid contact. Wash if any chemical spills on
your skin. Potassium permanganate and bromine are also toxic and may cause burns to
the skin. All organic wastes are to be disposed of by pouring them into the appropriate
waste containers under the hood. Be sure that your individual student hoods are on and
that the solutions are placed under these when working with them.
Last printed 2/6/2016 3:48:00 AM
20
Chemicals and Equipment: Most of the chemicals are reagents will be found in
dropper bottles in the hood. Bromine will also be found in the hood. Obtain unknowns
from the instructor. Each student will have two unknowns that must be classified as
alkanes, alkenes or aromatic compounds. The hydrocarbons hexane, cyclohexene and
toluene will be available to perform the tests on and record observations from which the
chemical classification of the unknowns may be deduced.
Physical Properties of Hydrocarbons:
Mix approximately 1.0 mL (20 drops) of hydrocarbon with 1.0 mL of the solvent. Use
your small test tubes for these tests. When mixing the compounds, grip the test tube
between thumb and forefinger. It should be held firmly enough to keep from slipping but
loosely enough so that when the third and fourth fingers tap it, the contents will be
agitated enough to mix. Watch for formation of layers, appearance of cloudiness, or oily
droplets that do not disappear. All the above indicate that the two substances are not
miscible.
1. Water solubility of hydrocarbons. Label your small test tubes with the name of the
substance to be tested: Hexane, cyclohexene, toluene, unknown A, and unknown B.
Place 20 drops of the appropriate hydrocarbon in each test tube, then add 20 drops of
water. Mix the contents as described above and observe the result. Is there separation of
layers? Which component is on the bottom and which is on the top? What can you
conclude about the solubility of the hydrocarbons and unknowns in water? To further
verify the results, record the densities of each of the known hydrocarbons by looking
them up in The Merck Index. Record these values, along with the proper reference, in
the data section of your lab notebook.
2. Solubility of hydrocarbons in CH2Cl2. Repeat the test as described above, except
use 20 drops of dichloromethane as the solvent. Mix the contents and observe the results.
Compare these test tubes to those from part 1 and clearly describe your observations.
Comment on the solubility of the compounds in this solvent. Is this what you would have
expected? Why or why not?
Chemical Properties of Hydrocarbons:
1. Combustion. Perform this test in the hood designated for combustion. Do not
ignite your samples anywhere else in the lab. Place about ten drops of each
compound to be tested on a small watch glass or crucible. Carefully ignite each sample
with a match. Observe the flame, color of the smoke, and amount of residue for each of
the compounds. Record your observations. Perform this test on hexane, cyclohexene,
toluene, unknown A, and unknown B.
Last printed 2/6/2016 3:48:00 AM
21
2. Reaction with bromine. Label five clean, dry test tubes with the name of the
substance to be tested. Place five drops of hexane, cyclohexene, toluene, unknown A,
and unknown B in the appropriately labeled test tube. Under the hood carefully add
the 1% bromine in cyclohexane solution, dropwise with shaking. Keep track in your
notebook the number of drops added and any color changes, or other observations; but
do not add any more than ten drops of the bromine solution.
3.Reaction with potassium permanganate. Label five clean, dry test tubes with the
name of the substance to be tested. Place five drops of hexane, cyclohexene, toluene,
unknown A, and unknown B in the appropriately labeled test tube. Carefully add 1%
the aqueous KMnO4 solution., dropwise with shaking. Keep track in your notebook the
number of drops added and any color changes, or other observations; but do not add
anymore than ten drops of KMnO4 solution.
Identification of Unknowns:
By comparing the observations you made for your unknowns with those of the known
hydrocarbons, you can identify classify unknowns A and B as alkanes, alkenes or
aromatic compounds. Record their classifications and offer an explanation for your
choice.
TREATMENT OF DATA AND REPORT FORMAT:
Before coming to lab, prepare a Data Table in your notebook similar to the model shown
below. Allow enough room to take down observations. Your instructor will sign this
table at the conclusion of the lab. Use pen only and make neat, clear tables.
DATA SHEET FOR LAB 3: Hydrocarbons
I. Physical Properties of Hydrocarbons
Hydrocarbon
Solubility*
H20
Density (g/mL)**
CH2Cl2
Hexane
Cyclohexene
Toluene
Unknown #
Unknown #
* Describe, observations
reference
Last printed 2/6/2016 3:48:00 AM
22
**Include
II. Chemical Properties of Hydrocarbons.
Hydrocarbon
Hexane
Cyclohexene
Toluene
Unknown #
Unknown #
Combustion
Bromine Test
KMnO4 Test
Note: Leave much more space for each result, as complete observations are to be
recorded. E.g. In describing the Bromine test for cyclohexene an appropriate comment
might be: “The reddish color of the bromine reagent disappeared when added to the
colorless hydrocarbon. The color of the bromine persisted only after 10 drops had been
added; the solution then became pale orange in color.”
Report Format
(Please note that this is the basic lab report format that will be used for the
remaining experiments as well as this one.)
1. Title of the Experiment.
2. Brief purpose and goals statement.
3. Data sheet (a copy of the one in your notebook).
4. Conclusions and Discussion. Begin by writing chemical reactions for all of
the tests performed. If the compound failed to react, indicate this by writing “N.R.” Use
the chemical formula for the knowns, and for the unknowns just the unknown number
and a description of what happened. Follow this by a statement indicating the possible
classification of each of your unknowns. Justify your “educated guess” by citing clearly
the results obtained which led you to your conclusions. A Reporting Table should be
included here to highlight your findings. Sample is shown below:
REPORT TABLE
Unknown #
34
25
Classification
Alkane
Aromatic
End your report with a paragraph of discussion. Using complete sentences,
describe what properties of hydrocarbons you have investigated and how these allow you
to distinguish between the various categories. Any comments on the procedure, unusual
happenings and results can be included.
Last printed 2/6/2016 3:48:00 AM
23
Experiment
6
Alcohols
Purpose:
The purpose of this lab is to study the properties of alcohols, contrast these to the
behavior of phenols, and to classify an unknown compound by comparing the results of
chemical tests.
Background:
Specific groups of atoms in an organic molecule can determine its physical and chemical
properties. These groups are referred to as functional groups. Those hydrocarbons that
contain the functional group –OH, the hydroxyl group, are called alcohols.
Alcohols are important commercially and are used as solvents, drugs and disinfectants.
The most widely used alcohols are methanol or methyl alcohol, CH3OH; ethanol or ethyl
alcohol, CH3CH2OH; and 2-propanol or isopropyl alcohol, (CH3)2CH2OH. Methyl
alcohol is found in automotive products such as antifreeze and “dry gas”. Ethyl alcohol
is used as a solvent for drugs and chemicals, but is more popularly known for its effects
in alcoholic beverages. Isopropyl alcohol, also known as “rubbing alcohol” is an
antiseptic.
Alcohols may be classified as primary, secondary or tertiary, depending on what
kind of carbon the –OH group is attached to. If the hydroxyl group is attached to a
primary carbon, then it is considered to be a primary alcohol. If the hydroxyl group is
attached to a secondary carbon, then it is considered to be a secondary alcohol, and so
forth. Classification of carbons depends on how many other carbon atoms it is attached
to. If a carbon is not attached to another carbon, it is referred to as methyl. If it is
attached to one other carbon then it is a primary carbon. If a carbon is attached to two
other carbons then it is called a secondary carbon. If a carbon is attached to three other
carbons then it is a tertiary carbon. Attachment to four carbons affords a quaternary
carbon. For example, consider the following alcohols:
Last printed 2/6/2016 3:48:00 AM
24
CH3
CH3CH2OH
CH3CCH3
CH3CHCH3
OH
OH
Ethanol
Primary alcohol
2-Propanol
Secondary alcohol
tert-butyl alcohol
Tertiary alcohol
Phenols bear a close resemblance to alcohols structurally since the hydroxyl
group is present. However, since the –OH group is bonded directly to a carbon that is
part of an aromatic ring, the chemistry is quite different from that of alcohols. Phenols
tend to be more acidic than alcohols. They do not give the characteristic reactions with
chromic acid or Lucas reagents. Concentrated solutions of the compound phenol are
quite toxic and can cause severe burns. Phenol derivatives are found in medicine: for
example, thymol is used to kill fungi and hookworms.
CH3
OH
OH
Phenol
Thymol
(2-isopropyl-5-methylphenol)
Physical Properties:
Since the hydroxyl group is present in alcohols and phenols, these compounds
may be polar. The polarity of the hydroxyl group, coupled with its ability to form
hydrogen bonds, enables small alcohols and phenols to mix with water. Since these
compounds also are carbon containing, they show additional solubility in many organic
solvents, such as dichloromethane and diethyl ether.
Hydrogen bonding between an alcohol and water
Last printed 2/6/2016 3:48:00 AM
25
Chemical Properties:
The chemical behavior of the different classes of alcohols and of phenols can be
used as a means of identification. Quick, simple tests that can be carried out in test tubes
will be performed. Please note that although the mechanisms of these reactions may be
unknown to you, each of them is accompanied by definite visual changes (cloudiness,
color change, etc.) which can be used in the “Real World” as well to identify substances.
E.g.: The common “breathalyzer” used in determining whether a person is driving after
ingesting too much alcohol contains an oxidizing agent which will change colors after
oxidizing the ethanol to acetaldehyde and then to acetic acid exactly like the Chromic
acid test explored in this lab.
1. Manifestation of acidity. Ordinary alcohols do not exhibit much acidity. They are
generally neutral in aqueous solutions and, if insoluble in water, will not dissolve in
sodium hydroxide. Phenols, on the other hand, are much more acidic and will react with
bases such as sodium hydroxide to form soluble salts. This difference is a good way to
distinguish between the two types of compounds. Can you think of a reason why phenols
would be much more acidic than other alcohols? Some research in Organic Chemistry
texts might help to answer the puzzle and maybe earn some extra points.
OH
+
ONa
NaOH
+
H2O
soluble salt
ROH + NaOH 
N.R.
2. Lucas Test. This test is used to distinguish between primary, secondary and tertiary
alcohols. The reagent is a solution of zinc chloride in concentrated hydrochloric acid,
HCl. Tertiary alcohols react rapidly and give an insoluble white layer containing the
corresponding alkyl chloride. A secondary alcohol reacts more slowly (within 15
minutes; slight heating may be required); and a primary alcohol does not react
appreciably under these conditions. The formation of an emulsion, cloudiness or milky
solution is a positive test. Phenols will not react at all with the Lucas reagent.
ZnCl2
RCH2OH
+
HCl
R2CHOH
+
HCl
R3COH
+
HCl

no reaction
ZnCl2

R2CHCl + H2O
(insoluble)
ZnCl2
Last printed 2/6/2016 3:48:00 AM
26

R3CCl
+ H2O
(insoluble)
3. Chromic acid test. This test is used to distinguish primary and secondary alcohols
from tertiary alcohols. Using acidified dichromate solution, primary alcohols are first
oxidized to aldehydes, and then further oxidized to carboxylic acids. Secondary alcohols
are oxidized to ketones, which are resistant to further oxidation. Tertiary alcohols are not
oxidized. In the oxidation, the orange-red of the chromic acid changes to a blue-green
solution. Phenols are slowly oxidized to nondescript brown masses.
O
||
RCH2OH + H2CrO4 + H2SO4

RCOH
+ Cr2(SO4)3
green
O
||
R2CHOH + H2CrO4 + H2SO4

RCR
+ Cr2(SO4)3
green

R3COH + H2CrO4 + H2SO4
no reaction
4. Ferric chloride test. Addition of aqueous ferric chloride to a phenol gives a colored
solution. Depending on the structure of the phenol, the color can very from green to
purple. Alcohols will not react with aqueous ferric chloride.
OFeCl 2
OH
+
+
FeCl3
HCl
violet
light yellow
PROCEDURE:
CAUTION!! Chromic acid is very corrosive. Any spill should be immediately flushed
with water. Dispose of reaction mixtures and excess reagents in the waste containers.
You will test the alcohols 1-butanol (a primary alcohol); 2-butanol (a secondary
alcohol), t-butanol (a tertiary alcohol), a phenolic compound, and two unknowns obtained
from the instructor. Test the unknowns at the same time as you run the tests on the
knowns for comparison.
1. Into separate small test tubes labeled with the names/unknown numbers of the
compounds to be tested, place 20 drops of each sample. Dilute by mixing with about
3 mL of distilled water. Observe the formation of any cloudiness as you add the water.
Which alcohols were soluble in water?
2. Test the pH of each of the aqueous solutions. Do the test by first dipping a clean glass
rod into the solutions and then transferring a drop of liquid to pH paper. Use a broad
indicator paper and read the value of the pH by comparing the color to the chart on the
dispenser. Record the results.
Last printed 2/6/2016 3:48:00 AM
27
3. Lucas test. Into separate, clean, dry small test tubes labeled with the names/unknown
numbers of the appropriate compounds to be tested, place 10 drops of each sample. Add
40 drops of Lucas reagent; mix well by stopping each test tube with a cork and shaking
vigorously for a few seconds, remove the cork after shaking and allow each test tube to
stand for 5 minutes. Look carefully for any cloudiness that may develop. If there is no
cloudiness after that time period, warm the clear test tubes in a 60’ C water bath. Record
observations.
4. Chromic acid test. Place 5 drops of each compound to be tested into separate clean,
dry test tubes labeled as before. To each test tube add 10 drops of reagent grade acetone
and 2 drops of chromic acid. Mix well and note the color of each solution. Record your
observations.
5. Ferric chloride test. Into separate clean, dry test tubes labeled as before, place 20
drops of each sample to be tested. Add 5 drops of ferric chloride solution to each. Note
any color changes and record your observations.
Note: Reagents will be provided in dropper bottles in the hood.
Treatment of data and report format:
Please refer to the instructions given in Lab 3 (Hydrocarbons) for the format. As before,
you will prepare a Data Sheet before you come to lab. Reactions for all of the tests
performed are to be included, as well as a Report Table and discussion. Below is a
sample Data Sheet. You are to make one of your own and allow much more space for
complete observations and comments.
DATA SHEET FOR LAB 4: Alcohols
TEST
1-butanol 2-butanol t-butanol Phenol Unknown #1 Unknown #2
Solubility
PH
Lucas
Chromic Acid
Ferric Chloride
Note: Be sure to allow enough space to include enough observations! These samples are
only guidelines for you to improve on!
As before, finish the report with a Reporting Table and a paragraph of discussion of your
results.
Last printed 2/6/2016 3:48:00 AM
28
Experiment
7
Synthesis of Aspirin
Purpose:
Aspirin will be prepared by heating salicylic acid with acetic anhydride in the presence of
a catalytic amount of phosphoric acid according to the following equation:
COOH
COOH
+ CH3COOCOCH3
H3PO4
+ CH3COOH
OCOCH 3
OH
Salicylic acid
Acetic anhydride
Aspirin
Acetic acid
We have not discussed this reaction in class yet; the pertinent details may be found in
Chapter 11 of the text. The resultant crude product will then be tested for unreacted
salicylic acid using iron(III) chloride. Some additional tests will be performed on
commercial aspirin.
Background Information:
Aspirin is one of the most amazing medicines known. Currently, 30,000,000 pounds are
sold in the United States each year, enough for more than 200 five-grain tablets for every
person in the county. It is an effective antipyretic; it reduces fever but does not lower
normal body temperatures. It has analgesic (pain-reliever) properties and is effective
against pains accompanying headaches, colds, flu, nervous tension, rheumatism, and
arthritis. Recent evidence suggests that continues small doses over long periods of time
could decrease the chances of heart problems and increase the chances of surviving a
heart attack.
The name aspirin comes from that of a willow, Salix spirea. In the seventeenth century,
it was found that extracts of willow bark had fever reducing properties. In 1826 the
Last printed 2/6/2016 3:48:00 AM
29
active principle, salicylic acid, was isolated. By 1852 salicylic acid had been
independently synthesized, and by 1874 relatively large-scale production had made it
available as a medicine. Although salicylic acid is an effective antipyretic, it causes
severe stomach irritation in some people, and for this reason the search for a pain reliever
continued in the late 1800s. Many derivatives of salicylic acid have been investigated to
try and relieve the stomach the stomach irritation problems. Toward the end of the
nineteenth century Felix Hofmann, working for the Bayer Company, was investigating
derivatives of salicylic acid. He tested acetyl salicylic acid on his father, who suffered
from arthritis. This and other tests revealed its excellent medicinal properties and
decreased frequency of gastric irritation. Acetylsalicylic acid, aspirin, was first marketed
in 1899 by the Bayer Company.
Procedure:
Weigh 1.5 g of salicylic acid, placing it in a 125-mL Erlenmeyer flask. Then add 4 mL
of acetic anhydride and 4 drops of 85% phosphoric acid. Measure the acetic anhydride
under the hood since it is highly irritating to the nose. Stir the reaction mixture
thoroughly. Heat the Erlenmeyer flask in a boiling water bath for 5 minutes, with
frequent stirring. Remove the flask from the bath and stir 3 mL of water at once into the
hot mixture. Continue to stir for a couple of minutes in order to destroy any excess acetic
anhydride, and then continue to stir while you add 30 mL of water. At this point, aspirin
will begin to precipitate from the solution. Complete the precipitation by cooling the
flask in an ice-water bath for about 5 minutes, with stirring.
Isolate your aspirin using vacuum filtration. Using a side-armed filter flask equipped
with a Buchner funnel, and attached to the vacuum outlet (with a trap in between),
rapidly pour your reaction mixture on to a piece of wet filter paper inside the Buchner
funnel. Use your spatula to remove most of the crystals from your flask. Wash your
aspirin crystals thoroughly with 10 mL of water by pouring the water slowly over the
crystals as you gently stir them. Distribute the crystals across the bottom of the Buchner
funnel with a spatula and dry them by pulling air through the Buchner funnel for a few
minutes. Gently stir the crystals frequently with your spatula so that they will all be
exposed to the passing air. Weigh your dried aspirin and determine the yield, then the %
yield.
Last printed 2/6/2016 3:48:00 AM
30
Product analysis:
A test for unreacted salicylic acid
The ferric chloride test (from Lab 4: Alcohols) is used to determine if there is any
unreacted salicylic acid present in aspirin. Your aspirin and a commercial sample will be
used for this test. Proceed as follows. Add about 0.1 g of salicylic acid (for comparison)
to 2 mL of 1% ferric chloride solution in a test tube. Then add about 0.1 g of your aspirin
to the same amount of ferric chloride in a second test tube, and finally add about 0.1 g of
finely crushed commercial aspirin to 2 mL of ferric chloride solution in a third test tube.
Stir each solution thoroughly. Note the color, if any, in each case. Is either your aspirin
or commercial aspirin contaminated with salicylic acid?
Starch binder test
Commercial aspirin is only 70% to 90% acetylsalicylic acid; most of the remainder is a
binder, usually starch, which holds the tablet together. To confirm that starch is the
binder, dissolve some crushed commercial aspirin (the size of a pea) in a couple of mL of
water, while stirring. Now add 1 drop of dilute iodine solution, and see whether the
characteristic pale blue-black starch-iodine complex is formed.
Acidity test
Add 100 mg (an amount the size of a large pea) of your aspirin, commercial aspirin,
Bufferin, and salicylic acid to 2 mL of distilled water in four separate test tubes. Stir the
solutions. Use a narrow-range pH paper to determine the pH of the solutions. Add
100 mg of solid sodium bicarbonate to your aspirin solution. Is a gas formed? If so what
is the gas? Record your observations, making a special note in your lab book.
The ester test
Dissolve 0.2 g of crushed commercial aspirin in 1 mL of 10% sodium hydroxide in a test
tube (test the solution with litmus paper to confirm that it is basic), and heat the test tube
in a boiling water bath for several minutes. To the hot solution add concentrated
hydrochloric acid, stirring it in drop by drop, until the solution is just acidic (test the
solution with litmus paper). Smell the contents of the test tube. Do you smell acetic acid
(vinegar)? Now add several drops of ferric chloride solution. Does a colored complex
form? Record your observations.
Last printed 2/6/2016 3:48:00 AM
31
Treatment of data and report format:
Please refer to the instructions given in Lab 3 (Hydrocarbons) for the format. Your data
sheet should collect together the results of your product/commercial aspirin analysis. All
reactions conducted are to be included, as well as a Report Table (summarizing the
success of your synthesis, weight and % yield) and a discussion. Additionally, include
answers to the following questions in your lab report.
Questions:
1. Why is it important to drink water immediately after taking aspirin?
2. Sodium salicylate has been used as an analgesic. Draw the structure of this
compound and show how you could prepare it from salicylic acid.
3. The analgesic Tylenol is often taken by persons who are allergic to aspirin.
Tylenol contains acetoaminophen (structure shown) as the active ingredient.
NHCOCH 3
OH
Is the structure of acetoaminophen similar to the structure of aspirin? Would
acetaminophen give a positive phenol test? What products would be obtained if
acetaminophen were hydrolyzed in acidic aqueous solution?
4. How is unreacted acetic anhydride removed from the aspirin product?
5. What was your percent yield for the aspirin synthesis? Give some logical reasons
why you did not get 100% yield.
Last printed 2/6/2016 3:48:00 AM
32
Experiment
8
Analysis of Aspirin and Vitamin C Tablets
Purpose:
Measured amounts of aspirin and vitamin C will be titrated with sodium hydroxide to
determine the amount of organic acid present. The mass of acid in each sample will be
compared to the original weight of the tablet to find what percent of each sample is acid.
Background:
Titrimetric analysis of consumer products is routinely carried out by the FDA to
safeguard that consumers get “what they paid for”. Although it may appear trivial, the
labels are trusted by millions of us every day and in some cases, overdoses or not enough
of the active ingredient can cause very harmful side effects. The analytical technique to
be investigated here is simple and very accurate.
Aspirin is one of the most amazing medicines known to man. It is an effective pain
reliever and antipyretic (reduces fever), and is employed for a variety of ailments
including the aches, pains, and fever due to colds, flu, tension, rheumatism and arthritis.
Inexpensive, easily produced, and non habit-forming, it is the most common of all overthe-counter medications. Pain relievers containing aspirin are widely available, but
ignoring the fancy additives, the active ingredient is still the same, acetylsalicylic acid
(ASA). As the name indicates, the chemical is a carboxylic acid and that is why it causes
severe irritation to the lining of the stomach and should be taken with lots of water.
Commercial aspirin contains 5 grains of ASA per tablet. One gram is equal to 15.432
grains, or 1.00 gram = 15.432 grains. This is only an approximate guide to the weight of
a tablet, due to binders such as starch which are added to hold it together. Since many
steps are employed in the manufacture of the millions of tablets of aspirin containing
products, the final tablets may vary in their ASA content. Quality control necessitates
that samples be analyzed to insure that the variation in the amount of active ingredient is
not larger than about 5 %. In your experiment you will analyze at least three tablets from
the same bottle of aspirin, comparing your results to each other and to the label on the
bottle.
Last printed 2/6/2016 3:48:00 AM
33
Ascorbic acid (Vitamin C) is present in a variety of foods. Citrus fruits contain 50 to 75
mg per 100 g of juice. Scurvy, a disease associated with long sea voyages and abnormal
living conditions, is characterized by a marked tendency to hemorrhage and by structural
changes in cartilage, bone and teeth. It was recognized in the mid 1700’s that a diet
including fresh fruit decreased the appearance of the disease, but it wasn’t until 1917 that
vitamin C deficiency was found to be the cause of scurvy. Although the FDA
recommends a daily intake of 60 mg/day, the actual amount that we need is still a
mystery. Linus Pauling was fond of saying that he took up to 17 grams/day to ward off
colds and other diseases. Ascorbic acid is also used as an antioxidant to preserve the
flavor and color of foods and beverages. It is added to orange juice, tomato juice, cereals,
cosmetics, hair dyes, and plastics. The ascorbic acid content of tablets can be determined
easily by titration with a base, such as NaOH. Although a quick inspection of the
structure of ascorbic acid does not clearly reveal the acid group, it will be recognized that
it is a cyclic ester (lactone) and as such will react with the NaOH by undergoing
saponification.
O
COOH
O
OH
HO
OCOCH 3
OH
Acetyl Salicylic Acid
(Aspirin)
OH
Ascorbic Acid
Titration is the name given to the process used to determine the volume of a solution
needed to react with a given mass (or volume) of an unknown sample. We will use this
process to quantitatively study the reaction between an acid (ASA and ascorbic acid) and
a base (NaOH). The hydrogen ion from the R-COOH reacts with the hydroxide ion from
the NaOH to produce water and a salt. Phenolphthalein will be used as an indicator since
it gives a vivid color change (colorless to pale pink) at the endpoint of the titration. The
endpoint signals that the acid is all gone, leaving just salt and water. The volume of the
base is recorded after the end point is achieved. The data recorded in a titration
experiment, namely the volumes of the acid and base required, along with the
concentration of the base, can easily be converted into the concentration of the acid, using
the molar ratios contained within the balanced equation.
PROCEDURE:
I. Analysis of ASA found in an aspirin tablet.
a. Weigh three aspirin tablets (from the same bottle) on a balance separately and record
their masses to three decimal places. Place each tablet in a separate Erlenmeyer flask
(125 or 250 mL).
b. Add about 25 mL of 95% ethanol/water solution into each flask. The ASA is more
soluble in ethanol and this will make the titration proceed faster. Swirl the flasks to
dissolve the ASA. You may use your stirring rod to gently crush the tablet. If you are
Last printed 2/6/2016 3:48:00 AM
34
using a coated tablet, the crushing may be harder. Be aware that binders and coated
buffers may not dissolve, thus the solution may be cloudy or slightly colored. Add 25
mL of distilled water to each of the flasks.
c. Obtain a stirrer, stir bar, buret, buret clamp, ring stand, and some standard NaOH
solution. Be sure to record the exact molarity on the stock bottle in your laboratory
notebook. Take about 75 mL of sodium hydroxide in a small beaker or flask back to your
work area.
d. Rinse the buret with a small amount of sodium hydroxide, by placing about 5 mL in
the buret and swishing the solution about the buret by holding it horizontally. Allow the
rinse to coat all parts of the buret, then drain the NaOH into the sink via the stopcock.
This avoids any dilution of the base by water that might have remained in the buret. Fill
the buret with NaOH and allow some to drain through the tip to get rid of all bubbles.
e. Place the stir bar carefully into one of the flasks with the dissolved ASA, add a few
drops of phenolphthalein, then position the flask on the stirrer, with the tip of the buret
over the mouth of the flask. Start the stirrer motor slowly and adjust for a smooth stirring
action. Avoid splashing.
f. Record the initial volume reading of the buret to the nearest 0.01 mL. Note that the
volume markings on the buret likely read from the top down, not from the bottom up.
Start dispensing the base into the flask slowly until you reach the endpoint, marked by a
faint pink color persisting for at least 30 seconds. When nearing the endpoint, slow the
addition of base to a drop at a time. A good endpoint is reached when one drop of base
causes the solution to go from colorless to a very pale pink. If you miss the endpoint by
adding too much base, you will have to start all over again. Record the final volume
reading of the buret at the end of the titration. Now you are ready for the second tablet—
which should go much faster, as you have an approximate idea how much base you will
need to add.
g. You may pour the neutralized solutions down the drain, but do not allow the stir bar to
go down the drain!! Rinse the bar, place it in the second flask and perform the remainder
of the titrations as before. Be sure to record all volume readings before and after titration
to two decimal places (0.01 mL). Add more base to your buret as needed, making sure to
record the volumes. When done with the experiment, make sure no one else needs your
sodium hydroxide solution, then it pour it into the sink. Sodium hydroxide = Draino—
today is “clean out the lab sinks” day!
Last printed 2/6/2016 3:48:00 AM
35
II. Analysis of Vitamin C Tablets.
Perform the titrations as described above, with the following modifications:
a. Use three commercial Vitamin C tablets (from the same bottle), each having
approximately 500 mg of ascorbic acid. Weigh each tablet and record the masses to three
decimal places.
b. Place the tablets in flasks as before, but add 50 mL of water. Crush the tablets with
your stirring rod and heat gently on a hot plate to dissolve. The binder may not dissolve.
When most of the tablet has dissolved, cool the solution and add a few drops of
phenolphthalein. Titrate as above.
PRE-LAB EXERCISE and DATA TABLE:
1. Pre-Lab Exercise: Before coming to lab, in addition to the usual pre-lab material, do
the following exercise in your lab notebook.
a. Using your text, lecture notes or other sources, write complete structures for the
reaction of acetylsalicylic acid (ASA) with sodium hydroxide. Refer to the structures
given here. (Hint: this is an acid-base reaction.)
b. Using the data given in this lab, calculate how many mg of ASA may be found in a 5
grain tablet.
c. Calculate the molar mass of ASA.
d. Assuming that a particular ASA-containing tablet weighed 0.380 g and that it required
17.00 mL of 0.1051 M NaOH to titrate to a phenolphthalein endpoint, calculate the mg of
ASA in the tablet and the % of the tablet which is ASA. Show all calculations clearly!!
2. Data Table. Using the hints from previous labs, prepare two Data Tables for this lab
(one for aspirin, one for ascorbic acid) as part of the pre-lab exercise. Each table should
be neat and clear, with enough room allowed for the following:
Brand of Tablet used
Weights of all three tablets (include balance name and #)
Molarity of the NaOH used
Amount of phenolphtalein added
Buret readings before and after each titration run
Last printed 2/6/2016 3:48:00 AM
36
Treatment of data and report format:
Please refer to the instructions given in Lab 3 (Hydrocarbons) for the format. Include a
copy of the data tables from your lab notebook. Do a separate calculation for each of the
titrations, tabulating the following pertinent information:
Weight of tablet
Volume of NaOH used
Moles of NaOH used
Moles acid present
Grams of acid in sample
% of acid in tablet
Weight of acid claimed on label
End the report with a short discussion of your results in which you compare the tablet
contents to each other and to the manufacturer’s claim. Are you getting your money’s
worth?
Last printed 2/6/2016 3:48:00 AM
37
Experiment
9
``
Properties of Carboxylic Acids and Esters
Background:
Carboxylic acids are structurally like aldehydes and ketones in that they contain the
carbonyl group. However, and important difference is that carboxylic acids contain a
hydroxyl group attached to the carbonyl carbon. This combination gives the group its
most important characteristic; it behaves as an acid.
As a family, carboxylic acids are weak acids that ionize only slightly in water. In
aqueous solution, typical carboxylic acids ionize to the extent of one percent or less.
O
+ H
RCO
RCOH
At equilibrium, most of the acid is present as unionized molecules. Dissociation
constants, Ka, of carboxylic acids, where R is an alkyl group, are 10-5 or less. Water
solubility depends to a large extend on the size of the R-group. Only a few low
molecular weight acids (up to four carbons) are very soluble in water.
Although carboxylic acids are weak, they are capable of reacting with bases stronger than
water. Thus while benzoic acid shows limited water solubility, it reacts with sodium
hydroxide to form the soluble salt sodium benzoate, which is used to preserve soft drink
beverages. Sodium carbonate, Na2CO3, and sodium bicarbonate, NaHCO3, solutions can
neutralize carboxylic acids, as well.
Combining a carboxylic with an alcohol using an acid catalyst produces an ester. This
reaction is sometimes called a condensation reaction, since the other product is water.
Unfortunately it is an equilibrium reaction, so Le Chateliers Principle must be employed
in the laboratory to shift the equilibrium to the right, thus increasing the percent yield.
Water is a reactant in the reverse process, so this process is referred to as hydrolysis.
Last printed 2/6/2016 3:48:00 AM
38
Esters can also be decomposed by using a base, such as sodium hydroxide, giving an
alcohol and carboxylic acid salt as products. This process is called saponification¸ which
means soap making, and when employed on fatty acids (such as stearic acid) a soap is
formed.
Carboxylic acids have characteristic physical properties. Their sour taste and unpleasant
odors are quite well known, while esters on the other hand have pleasant odors, and are
often times used in perfumes and synthetic food products. The fragrances of bananas,
pineapple, wintergreen, peach, and pears, as well as many other fragrances, are due to
esters. Carboxylic acids form hydrogen bonds with themselves and water, since they
contain an oxygen hydrogen bond. Thus their vapor pressure is quite low. Esters, on the
other hand, do not hydrogen bond, and their relatively weak intermolecular forces result
in a higher vapor pressure; esters readily evaporate to produce pleasant fragrances.
Procedure:
Properties of acetic acid:
1. Place 2 mL of water and 10 drops of glacial acetic acid, in a small, clean, dry test
tube. Note its odor. Of what does it remind you?
2. Take a glass rod and dip it into the solution. Using wide range indicator paper
(pH 1-12), test the pH of the solution by touching the paper with the wet glass
rod. Determine the value of the pH by comparing the color of the paper with the
chart on the dispenser.
3. Add 2 mL of 2 M NaOH to the solution. Cork the test tube and sharply tap it with
your finger. Remove the cork and determine the pH of the solution as before;
continue to add sodium hydroxide (dropwise) as needed until the solution is basic.
Note the odor, comparing it to the odor of the solution before the addition of the
base. Would you conclude that a chemical change has taken place?
4. Add 3 M HCl (dropwise) to the test tube from part #3 until the pH paper indicates
that it has the same pH as the acetic acid that you started with. Check the odor
and compare it to the original odor of the acidic acid from part #2. What kind of
change has taken place, if any?
Properties of benzoic acid:
1. Weigh out about 0.1 g benzoic acid (±0.03 g) in a small test tube, add 2 mL of
water, and mix by tapping with your finger. Note the odor and solubility of the
benzoic acid.
2. Next add 1 mL of 2 M NaOH to this solution, cork the test tube and mix by
tapping the test tube with your finger. What happens to the solid benzoic acid? Is
there any color or odor change? Write a balanced equation for this process in
your notebook.
3. Reacidify this solution by adding 3 M HCl (dropwise) until acidic (using pH
paper to check). What do you observe now?
Last printed 2/6/2016 3:48:00 AM
39
Esterification:
1. Into five clean, dry test tubes (small), add 10 drops of liquid carboxylic acid or 0.1
g of solid carboxylic acid and 10 drops of alcohol according to the scheme below.
Note the odor of each reactant.
Test Tube No.
Carboxylic Acid
Alcohol
1
Formic
Isobutyl
2
Acetic
Benzyl
3
Acetic
Isopentyl
4
Acetic
Ethyl
5
Salicylic
Methyl
2. Add 5 drops of concentrated sulfuric acid to each test tube and mix the contents
throughly by tapping the test tube with your finger. Caution: sulfuric acid causes
burns. Wash any spill with lots of water.
3. Place the test tubes in a warm water bath at about 60ºC for 15 minutes. Remove
the test tubes from the water bath, cool, and add about 2 mL of water to each.
Note that there is a layer on top of the water in each test tube. With a Pasteur
pipet, take a few drops from this top layer and place on a watch glass. Note the
odor. Match the ester from each test tube with one of the following odors:
banana, peach, raspberry, nail polish remover, and wintergreen.
Saponification:
1. Place 10 drops of methyl salicylate and 5 mL of 6 M NaOH into a large test tube.
Heat in a boiling water bath for 30 minutes. Watch what happens to the ester
layer, and record observations in your lab notebook.
2. Cool the test tube to room temperature by placing it in an ice-water bath.
Determine the odor of the solution and record your observations. Did a chemical
change take place? If so, write and balance this chemical equation in your
notebook.
3. Carefully add 6 M HCl to the solution, 2 mL at a time, until the solution is acidic.
After each addition, mix the contents and test the solution with litmus paper.
When the solution is acidic, what do you observe? What is the name of the
compound formed? Answer these questions in your notebook.
Required Chemicals and Equipment:
1. Glacial acetic acid
2. Formic acid
3. Benzyl alcohol
4. Isobutyl alcohol
5. Methyl alcohol
6. 3 M HCl
7. 2 M NaOH
8. Concentrated H2SO4
9. Litmus paper
10. Hot plate
Last printed 2/6/2016 3:48:00 AM
11. Benzoic acid
12. Salicylic acid
13. Ethanol
14. Isoamyl alcohol
15. Methyl salicylate
16. 6 M HCl
17. 6 M NaOH
18. pH paper (1-12)
19. Pasteur pipet
40
Treatment of data and report format:
Please refer to the instructions given in Lab 3 (Hydrocarbons) for the format. Your lab
notebook should have a data sheet collecting together the observed properties of
carboxylic acids and esters; include a photocopy of this sheet with your report. Chemical
equations for all reactions conducted are to be included, as well as a discussion.
Additionally, include answers to the following questions in your lab report.
Questions:
1. Write the structural formulas for the following carboxylic acids:
a. Formic acid
b. Benzoic acid
c. Acetic acid
2. Write the products formed from the reaction of acetic acid and sodium hydroxide.
3. Ethyl formate has the flavor of rum. What alcohol and carboxylic acid would
produce the ester?
4. Write balanced equations for the esters produced in this experiment.
5. Butyric acid has a putrid odor. Suppose you got some on your hands and water
did not wash it off. What might you do to remove the acid? (Hint: how could
you make it soluble in water?)
Last printed 2/6/2016 3:48:00 AM
41
Experiment
10
TLC Analysis of Analgesic Drugs
Purpose:
To use thin-layer chromatography (TLC) to separate and identify the active
ingredients of over-the-counter analgesic drugs.
Background Information:
Thin-layer chromatography is another form of chromatography that is used by organic chemists
to monitor the course of a chemical reaction, separate components of a reaction mixture, or to aid
in the identification of unknown substances. In a previous experiment, paper chromatography
was used to separate several different natural products. The difference in this experiment is that
the stationary phase is not filter paper, but a commercially prepared thin strip of plastic coated
with silica gel (sand), with a fluorescent indicator. The compounds to be separated and identified
are referenced to a variety of known analgesic compounds, which have been used in the past by
natives to provide relief of pain, reduce swelling and to lower fever. Commercial drug companies
have isolated, identified, and in many cases synthesized (with some structural modifications)
these analgesic compounds. Depending on the brand of the analgesic, the active ingredient is
most likely acetaminophen, aspirin, or ibuprofen. In this experiment these compounds are
referred to in alphabetical order to help minimize the possibility of mixing them up. Most
commercial products containing these analgesic compounds have a binder, typically starch, to
hold them together, and sometimes caffeine is added as a stimulant. In this experiment you will
run a TLC chromatogram of pure samples of acetaminophen, aspirin, caffeine, and ibuprofen, the
known compounds of interest, to determine the Rf values of these individual compounds. Two
unknown over-the-counter samples will be also be analyzed by TLC, alongside the known
compounds, to determine the Rf of the active ingredient(s) and compare it to the Rf values of the
known analgesics. If the Rf value of an active ingredient found in the unknown compound
matches one of the Rf’s of the knowns, then you have successfully identified the active ingredient
of that unknown.
Chromophore is a word used in Organic chemistry to describe a particular type of organic
structure that will allow an organic molecule to absorb ultraviolet radiation. A chromophore
usually is a conjugated double bond, which means two double bonds separated by a single bond.
The next page contains structural formulas of the compounds to be investigated in this
experiment. Can you identify the chromophores in each compound?
Last printed 2/6/2016 3:48:00 AM
42
NH
COOH
O
HO
OCOCH 3
Acetominophen
Aspirin
O
N
N
O
N
OH
N
O
Ibuprofen
Caffeine
When a UV sensitive silica gel strip is exposed to ultraviolet light the silica gel will glow. If a
compound is present on the strip, it will show up as a dark spot that does not glow. If that
compound contains a chromophore, then it will appear as a dull purple spot. Both placement and
appearance of these spots will help you to identify the active ingredients present in your
commercial analgesic unknowns.
Required Equipment, Glassware, and Reagents:
Equipment
400-mL beaker
Test tubes
Stirring rod
Mortar and pestle
Water bath
Watchglass
TLC strips
UV lamp
Micro capillary tubes
Reagents
5% solution acetaminophen
5% solution of aspirin
5% solution of caffeine
5% solution of ibuprofen
assortment of analgesics
methylene chloride
ethanol
ethyl acetate
Procedure:
1. Obtain a TLC strip from the supplies counter, handling the strip by the edges being careful not
to bend the strip. Using a lead pencil (not a pen) lightly draw a line across the plate about 1 cm
from the bottom (across the short edge). Using a centimeter ruler, lightly mark off six equally
spaced intervals along your line. These are the points at which the samples will be spotted.
You will spot two unknown analgesic samples and each of the reference compound solutions
containing: acetaminophen, aspirin, caffeine, and ibuprofen. Be sure to keep them in
alphabetical order.
2. Obtain half a tablet of each of the two unknown analgesics to be analyzed. Crush the tablets by
using a mortar and pestle. Transfer each crushed half-tablet to a small, labeled test tube.
3. Add to each test tube about 5 mL of a 1:1 solution of methylene chloride/ethyl alcohol to each
of the test tubes and then heat each of them gently for a few minutes in a water bath. The
tablets will not completely dissolve due to the insoluble binder, or buffered coating.
Last printed 2/6/2016 3:48:00 AM
43
4. After heating the samples, allow them to settle and then spot the clear liquid extracts on the
TLC plate. To spot the plate, dip a micro capillary tube into the extract. Lightly touch the
capillary tube to the plate being careful not to dislodge the silica gel. Allow just a small spot of
liquid onto the plate. Once the initial spot is dry, repeat the spotting procedure. Do the same
for the second unknown, using a fresh micro capillary tube.
5. Next spot the four reference solutions, acetaminophen, aspirin, caffeine, and ibuprofen, onto the
plate in the same manner, using a fresh micro capillary tube for each spot. Acetominophen and
ibuprofen will likely be fine with a single spotting; the aspirin solution should be spotted twice,
and the caffeine will require three applications in all. If you are uncertain as to whether you’ve
gotten enough material onto the TLC plate, or if your spots are small enough, preview the
undeveloped plate under the UV lamp.
6. Once the plate has been spotted, it is ready to be placed in a 400 mL beaker containing the
developing solution (ethyl acetate). This beaker should be equipped with a filter paper liner to
help insure an environment saturated with solvent vapor inside the beaker. Be sure that the
developing solution is below the level of your spots and that the TLC plate does not come into
direct contact with the filter paper liner. After placing your TLC strip into the beaker, cover it
with a watchglass or aluminum foil.
7. When the solvent has risen to a level of about 1 cm from the top of the TLC plate, remove the
plate from the chamber and immediately mark the position of the solvent front using a lead
pencil. Let the plate dry. When the plate is dry, observe it under a short-wavelength UV lamp.
Lightly outline all the observed spots with a pencil. Sketch the plate in your lab notebook,
describing the appearance of each spot.
8. Calculate the Rf values of each spot.
Treatment of data and report format:
Please refer to the instructions given in Lab 3 (Hydrocarbons) for the format. Be sure to
include the unknown numbers, identities of your unknowns, a drawing of your TLC plate (or a
photocopy of the one in your lab notebook), the Rf values of each substance (showing
calculations), and a discussion. Additionally, include answers to the following questions
in your lab report.
Questions:
1. What is the purpose of the piece of filter paper inside the 400 mL beaker?
2. Did you observe any spots other than the ones expected?
3. What would happen if you used 100% ethanol, instead of the 1:1 methylene
chloride/ethanol mixture, to extract the active ingredients from the commercial
unknowns?
4. What is a chromophore?
5. How (thinking on the techniques learned in this lab) might one tell if some
unknown powder is, for example, cocaine or not?
Last printed 2/6/2016 3:48:00 AM
44
Experiment
11
Extraction of Caffeine
Purpose:
To extract, purify, and quantify caffeine from tea leaves.
Background:
In this lab we shall explore a process called extraction. Many organic compounds found
in nature are obtained through this technique. This method takes advantage of the
solubility characteristics of a particular substance with a solvent of choice. Caffeine is
readily soluble in hot water and can be separated from the rest of the compounds in tea
leaves. As much as 5% by weight of leaf material in tea consists of caffeine. This very
popular compound is also found in kola nuts, cocoa beans and of course, coffee (as those
addicted to our morning latte know so well!).
The structure of caffeine is shown below. The compound belongs to the family of
alkaloids, meaning that it is a basic compound containing nitrogen and generally found in
plants. Many alkaloids, such as morphine, reserpine, and mescaline have powerful
effects on the chemistry of the brain.
O
H3C
O
N
CH 3
N
N
N
CH 3
Caffeine
Caffeine is the most widely used of all the stimulants. Small doses of this chemical (50
to 200 mg) can increase alertness and reduce drowsiness and fatigue. The popular “NoDoz” tablet has caffeine as the main ingredient. In addition, it affects blood circulation
since the heart is stimulated and blood vessels are relaxed (vasodilation). It also can act
Last printed 2/6/2016 3:48:00 AM
45
as a diuretic. Side effects of caffeine include insomnia, restlessness, headaches, muscle
tremors and also physical dependence.
Tea leaves consist mainly of cellulose (the principal structural material of all plant cells)
which is insoluble in water, so that by using a hot water extraction, the more soluble
caffeine can be isolated. Complex substances called tannins are also water-soluble and
are extracted with the caffeine. These are colored phenolic compounds of high molecular
weight which are slightly acidic (remember our alcohol/phenol lab?). If a basic salt such
as Na2CO3 is added to the water solution, the tannins can react to form a salt. These salts
are insoluble in organic solvents such as chloroform or methylene chloride, but are
soluble in water.
Although caffeine is soluble in water, it is much more soluble in the organic solvent
methylene chloride. Since the two solvents do not mix, caffeine can be extracted from
the basic tea solution, leaving behind the tannins. Evaporation of the methylene chloride
yields the caffeine.
Procedure:
1. Before coming to lab, prepare a Data Table containing the following information:
a. The solubility of caffeine in water and the accepted melting point of the pure
substance. This information can be obtained from the Merck Index. If you cannot
locate one in the Library, ask your instructor to allow you to borrow the lab copy.
Be sure you include the proper reference.
b. A neatly constructed table to enter the information you will gather in the lab,
namely:
Balance # and name
Weight of tea in two tea bags
Weight of 50 ml beaker
Weight of beaker, and crude caffeine
Melting point of your caffeine
Brand of tea used in the experiment
Name of Melting Point Apparatus
2. On the day of the lab, pay very close attention to the instructions you will be given on
the use of the separatory funnel and melting point apparatus. Much of this lab
involves learning new techniques, so be ready to take good notes and to listen very
closely.
Last printed 2/6/2016 3:48:00 AM
46
3. Weigh two tea bags on an analytical balance and record the weight. The empty
weight of the two tea bags is 0.250 g; subtract this from your initial weight to obtain
the weight of the tea. Next you will be making a nice strong cup of tea. Pour 100 mL
of distilled water into a 250 mL beaker. Heat the water on a hot plate until the
temperature is between 97-99 ºC. When the water reaches that temperature (about 15
minutes), place the two tea bags in the beaker and gently stir with a stirring rod for
one minute.
4. At the end of one minute pull the tea bags out of the solution and place them between
two large watch glasses. Gently squeeze the excess liquid into the beaker with the tea
solution. Discard the tea bags. Cool the beaker with the tea solution on the counter
top for 5 minutes, then in an ice water bath for another 5 minutes.
5. Place a small piece of glass wool into the neck of a powder funnel. Support a 125 mL
separatory funnel in a ring clamp on a ring stand (demonstrated by your instructor),
placing the funnel with the glass wool on top of the separatory funnel. Pour the tea
solution slowly through the glass wool plug into the separatory funnel. Be sure to
rinse the beaker with a small amount of cold water (about 2-3 mL) and pour this
solution as well into the separatory funnel. Remove the powder funnel from the
separatory funnel and discard the glass wool plug in the trash.
6. Carefully add 10.0 mL of methylene chloride to the separatory funnel. Stopper the
funnel and lift it from the ring clamp by holding it with both hands as demonstrated to
you earlier. By holding the stopper in place with one hand, invert the funnel. Make
sure the stopper is held tightly and no liquid is spilled; open the stopcock, being sure
to point the opening away from you and your neighbors. Built up pressure caused by
gases accumulating inside will be released. Now close the stopcock and gently mix
the contents by inverting three or four times gently so that the layers mix thoroughly.
Release the pressure that is built up inside the funnel by periodically opening the
stopcock as demonstrated by your instructor.
7. Return the separatory funnel to the ring stand, remove the stopper and allow the layers
to separate. The methylene chloride layer will be at the bottom (why?). If an
emulsion forms (from shaking vigorously), it can be broken by gently swirling the
contents of the separatory funnel or by gently stirring the emulsion with a glass rod.
8. Carefully drain the lower layer into a 125 mL Erlenmeyer flask. Manipulate the
stopcock gently to prevent any contamination from the water layer.
9. Repeat the extraction (steps 6-8) with two additional 10.0 mL portions of methylene
chloride (3 extractions total). Collect all methylene chloride extracts (all three bottom
layers) into the same 125 mL Erlenmeyer flask. Discard the upper aqueous layer in
the waste container and rinse the funnel with distilled water.
Last printed 2/6/2016 3:48:00 AM
47
10. Pour the methylene chloride solution back into the separatory funnel and add 10.0
mL cold 6M NaOH. Follow the same extraction procedure outlined in steps 6-8.
Discard the upper aqueous NaOH layer. Pour the methylene chloride solution back
into the separatory funnel and repeat this process with a 10.0 mL portions of cold 6M
NaOH, and finally one 10.0 mL portion of cold distilled water. You may want to
keep a waste beaker in your hood to transfer unwanted layers to before transferring
the whole to the waste container at the end of the lab—that way if you accidentally
discard the wrong layer, you don’t have to start over.
11. After the last step add about 2 grams of anhydrous sodium sulfate (Na2SO4) to the
methylene chloride layer in the 125 mL Erlenmeyer flask. Swirl the flask and stopper
it with a cork while you perform the next step. The sodium sulfate is a drying agent
and will remove any moisture or water that may be present in the methylene chloride
layer.
12. Weigh a clean and dry 50 mL beaker and a boiling chip. Record the weight. Filter
the methylene chloride solution (containing the caffeine) from the used sodium
sulfate by supporting a powder funnel (equipped with a piece of filter paper) on a
ring/ring stand and pouring the solution through the powder funnel into the preweighed beaker. Rinse the residue on the filter paper with an additional 2.0 mL of
methylene chloride.
13. Evaporate the methylene chloride in your hood by placing the 50 mL beaker on a
wire screen that is kept over a 400 mL beaker of gently boiling water. Overvigorously boiling water may cause water to condense inside the beaker containing
the methylene chloride; this is to be avoided. Use a hot plate to heat the water bath.
The hood draft along with a stream of dry compressed air (your instructor will show
you the setup) will remove the methylene chloride more efficiently. Be careful not to
overheat the beaker, since some of the solvent may foam over. When all the solvent
has been evaporated, dry the side of the beaker with a paper towel and allow it to
cool. Reweigh the cooled beaker containing the crude caffeine. Obtain the weight of
the crude caffeine by difference.
14. Scrape as much of the caffeine as you can onto a clean small watch glass. Store the
crystals as instructed, and obtain the melting point (as demonstrated by your
instructor) during the next lab period.
Last printed 2/6/2016 3:48:00 AM
48
Treatment of data and report format:
Please refer to the instructions given in Lab 3 (Hydrocarbons) for the format. Include a
photocopy of the data sheet from your lab notebook with your report. Make drawings of
the specialized equipment you used in this experiment and explain the function of each
piece of equipment. Included should be: the powder funnel set-up, the separatory funnel
set-up, evaporation set-up, and a description of the melting point apparatus used. It is not
necessary to be artistic! This is standard procedure in labs when new techniques are
used. Construct a Report Table as follows:
REPORT TABLE FOR CAFFEINE EXPERIMENT
Weight of caffeine obtained
Percent yield of caffeine*
Melting point of your caffeine
Literature melting point
g
%
o
C
o
C
*Percent yield = (weight of crude caffeine/weight of tea) X 100
Additionally, after a brief discussion, include answers to the following questions in your
lab report.
Questions:
1. Name some sources of caffeine.
2. What part of the caffeine structure gives it the alkaloid properties?
3. What are some of the ways caffeine can affect an individual?
4. How can you test the purity of a sample of caffeine?
5. How do you know that methylene chloride is more dense than water?
6. Why was the caffeine eventually recovered from the methylene chloride extract
rather than directly from initial the hot water extract?
7. Does caffeine contain a chromophore (refer back to experiment 8)?
8. Do you think that caffeine would show up on a UV active TLC strip?
Last printed 2/6/2016 3:48:00 AM
49