CHEMISTRY 1121
INTRODUCTION TO GENERAL &
ORGANIC CHEMISTRY PART 2
ORGANIC CHEMISTRY
LABORATORY MANUAL
SPRING 2018
EDITED BY:
Ishwar Sadarangani, Ph.D.
CHE 1121 Lab Supervisor
Table of Contents
General Chemistry Post-Laboratory Questions..................................................................................1
Chemical Kinetics..........................................................................................................................................1
Chemical Equilibrium....................................................................................................................................1
pKa of a Weak Acid........................................................................................................................................2
Molar Mass from Freezing Point Lowering.........................................................................................3
Introduction..................................................................................................................................................3
Procedure.....................................................................................................................................................5
Figure 1. Hot-water bath setup.....................................................................................................................6
Post-Laboratory Questions...........................................................................................................................8
REPORT SHEET..............................................................................................................................................9
Thin Layer Chromatography (TLC) – Separation of Analgesics...........................................................11
Structures of Analgesics..............................................................................................................................11
Introduction................................................................................................................................................11
Procedure...................................................................................................................................................13
Post-Laboratory Questions.........................................................................................................................14
REPORT SHEET............................................................................................................................................15
Column Chromatography - Separation of the Pigments in Spinach Extract.......................................16
Pigment Structures.....................................................................................................................................16
Introduction................................................................................................................................................16
Procedure...................................................................................................................................................18
Post-Laboratory Questions.........................................................................................................................21
REPORT SHEET............................................................................................................................................22
Distillation: Separation of an Acetone-Water Solution.....................................................................24
Introduction................................................................................................................................................24
Procedure...................................................................................................................................................26
Figure 2. Simple Distillation Apparatus.......................................................................................................26
Post-Laboratory Questions.........................................................................................................................27
REPORT SHEET............................................................................................................................................28
Resolution of Racemic Phenylsuccinic Acid......................................................................................29
Chemical Reaction......................................................................................................................................29
Introduction................................................................................................................................................29
Procedure...................................................................................................................................................33
Figure 3. Vacuum filtration apparatus........................................................................................................34
Post-Laboratory Questions.........................................................................................................................36
REPORT SHEET............................................................................................................................................37
Synthesis of tert-Butyl Chloride (2-Chloro-2-methylpropane)..........................................................38
Chemical Reaction......................................................................................................................................38
Introduction................................................................................................................................................38
Procedure...................................................................................................................................................40
Figure 4. Extraction apparatus....................................................................................................................41
Figure 5. Unpacked-column distillation apparatus.....................................................................................42
Post-Laboratory Questions.........................................................................................................................42
REPORT SHEET............................................................................................................................................43
Synthesis of 2-Methylbut-2-ene.......................................................................................................44
Chemical Reaction......................................................................................................................................44
Introduction................................................................................................................................................44
Procedure...................................................................................................................................................46
Post–Laboratory Questions........................................................................................................................47
REPORT SHEET............................................................................................................................................48
General Chemistry Post-Laboratory Questions
Chemical Kinetics
1. What three (3) factors affect the rate of a chemical reaction? (3 points)
2. Why is the concentration of the sulfite anion (SO32-) solution a constant in all five trials? (3 points)
3. For trials #1-5, the concentration of KIO 3 is increasing. What effect does this increased
concentration have on the reaction time for each solution? (2 points)
4. How many grams of CuBr2 (MM = 223.35 g/mol) are required to prepare 25.0 mL of a 0.10 M CuBr 2
solution? (4 points)
5. Based on your answer to Question #4, describe how you would accurately prepare 25.0 mL of the
0.10 M CuBr2 solution. (3 points)
Chemical Equilibrium
1. After setting the spectrometer to Zero Absorbance, you accidentally get fingerprints on the
cuvette. What effect will this have on:
a) Further absorbance measurements? (1 point)
b) The equilibrium value for [Fe3+]? (1 point)
c) Your calculated value of KC? (1 point)
SO2 (g) + O 2 (g)
SO 3 (g)
2. Write the Kc expression for the above reaction. NOTE! Reaction is NOT balanced. (2 points)
3. If 0.20 M SO2 reacts with 1.0 M O2 to form 0.50 M SO3, calculate the Kc value for this reaction.
(1 point)
4. Based on your Kc value from Question #3, would the equilibrium reaction favor the reactants or
the product? (1 point)
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5. Le Chatelier’s principle states that if an equilibrium reaction is subjected to any type of stress
(ex. change in concentration, temperature, pressure, etc), the reaction will proceed in the
direction that offsets this stress. In this manner, the reaction will once again reach a state of
equilibrium. For the formation of the iron thiocyanate complex ion, predict which direction the
reaction will favor if the following stress is applied. (8 points – 2 points each)
Fe 3+ (aq) + SCN- (aq)
Fe(SCN)2 + (aq)
DIRECTION OF REACTION
[Reactant (R) or Product (P)]
TYPE OF STRESS
1. [Fe3+] is increased
R/P
2. [Fe(SCN)2+] is decreased
R/P
3. [SCN-] is decreased
R/P
4. Aqueous Hydrochloric acid is added
(**see reaction below)
R/P
Fe 3+ (aq) + SCN - (aq)
yellow
Fe(SCN) 2+ (aq)
colorless
+ HCl (aq)
dark red
FeCl4- (aq)
light orange
The net reaction when HCl is added is:
Fe
3+
(aq) + 4 Cl- (aq)
FeCl4- (aq)
pKa of a Weak Acid
1. Define pH. (1 point)
2. Why is it necessary to calibrate the pH meter with buffers 4.00 and 7.00 prior to each titration?
(1 point)
3. What is the chemical significance of the equivalence point? (2 points)
4. Why does the pH of the solution increase dramatically past the equivalence point? (2 points)
5. Write out the dissociation (ionization) reaction for butanoic acid, CH 3CH2CH2COOH. (3 points)
6. Write out the dissociation constant expression for butanoic acid, CH3CH2CH2COOH. (3 points)
7. An aqueous solution contains 0.50 M of butanoic acid and 0.25 M of potassium butanoate. If the
pH of this solution was measured to be 3.50, calculate the pKa of butanoic acid. (3 points)
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Molar Mass from Freezing Point Lowering
Introduction
A solution, by definition, contains a solute dissolved in a solvent. In this experiment, the colligative
properties of a solution will be investigated to obtain the molar mass of an unknown solute through
the freezing point lowering of a stearic acid-unknown solution. The freezing point lowering of a
solution can be categorized as an intensive property as it depends only on the amount of solute
present (concentration) and not on the characteristic properties (type) of the solute.
Freezing point is the temperature at which an equilibrium exists between liquid and solid molecules
for a particular substance.
liquid D solid
Sometimes this freezing point temperature is difficult to determine, but can be obtained by plotting a
cooling curve. To construct a cooling curve, the sample (solvent or solution) is heated to a
temperature above their melting point, and then allowed to gradually cool. As the sample cools, the
temperature is recorded over a period of time. When the sample starts to solidify, the change in
temperature will decrease, and at the equilibrium point, the temperature will remain constant until
the entire sample has solidified. A graph of temperature vs time is then plotted (Graph 1).
64
62
Temperature (oC)
60
58
Tf solvent
56
54
Tf solution
52
50
0
50
100
150
200
250
300
350
400
450
Time (s)
Graph 1. Cooling curves for a pure solvent and solution
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The difference in temperature between the freezing points of the pure solvent and the solution is
called the freezing point lowering (DTf).
DTf = Tf solvent – Tf solution
Eq 1
The freezing point lowering is directly proportional to the molal concentration of the solution.
DTf = Kf m
Eq 2
where m is the molality of the solution expressed as moles of solute per kg of solvent (mol/kg), and k f
is the molal freezing point constant (units: C kg/mol) for the solvent.
In this experiment, you will first determine the freezing point of pure stearic acid (solvent) followed by
the freezing point of a stearic acid-unknown solution. Cooling curves for both the solvent and solution
will be plotted to graphically obtain their freezing points. From the freezing point lowering and
Kf (4.5 C kg/ mol), the molality of the solution is then calculated.
m=
ΔT
Kf
Eq 3
Since the mass of the solvent is known, the moles of solute can be calculated using the equation,
moles of unknown (solute) = molality x kg solvent
=
Eq 4
moles of unknown
x kg of solvent
kg of solvent
Finally, the molar mass (g/mol) of the unknown sample can be determined by taking the mass of the
unknown and dividing it by the number of moles.
Molar mass =
CHE 1121 Lab Manual
g of unknown
moles of unknown
Eq 5
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SAFETY PRECAUTIONS
1. Safety goggles and lab coats must be worn at all times while an experiment is in progress.
2. The hot-water bath is being heated on a hot plate in this experiment. Always use a “HOT-HAND”
to handle extremely hot glasswares.
3. The hot plate MUST be completely cool before it can be returned to the storage cabinet.
4. No chemicals can be disposed in the sink. Always discard the chemical in its appropriate waste
container. If unsure, consult your instructor.
Materials Required
CHEMICALS
1. Stearic acid
2. Unknown sample
3. Acetone
EQUIPMENT
Glasswares
• 600 mL Beaker
• 6-inch Test tube
• Powder funnel
Heat source
• Hot plate
Other
• Digital thermometer with wire stirrer
• Timer
• Hot-hand
Procedure
A. Freezing Point of pure Stearic Acid
1. Obtain a digital thermometer with a wire stirrer, a timer and an unknown sample from your
instructor. Record the unknown # on your instructor’s sign-in sheet and in your notebook.
2. On a weighing boat, measure 4.9 – 5.1 g of stearic acid and transfer it to a clean, dry 6-inch test
tube using a clean, dry powder funnel.
3. Place 400 mL of very hot tap water in a 600 mL beaker and assemble it as a hot-water bath. Clamp
the 6-inch test tube so that it is well immersed in the bath, but ensure the bottom of the test tube
is NOT touching the bottom of the beaker. Heat the water bath on a hot plate (T = 450 °) until the
stearic acid starts to melt. Once sufficiently melted, turn on the digital thermometer and place it
along with the wire stirrer in the test tube (Figure 1).
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Thermometer
Wire stirrer
Clamp
Hot-water bath
Hot plate
Figure 1. Hot-water bath setup
4. Shut off the hot plate once the temperature of the stearic acid reaches 90C. Carefully agitate the
contents in the test tube with the wire stirrer until the stearic acid has completely melted
(~85-90C). Transfer the beaker to your bench top using the “hot-hand” and allow to cool with the
test tube immersed in the hot-water bath.
5. Once the temperature decreases to 73C, start the timer and begin recording the temperature
every 30 seconds.
TEMPERATURE MEASUREMENTS
CHE 1121 Lab Manual
•
For optimum temperature measurements, stir the solution constantly with
the wire stirrer before recording the temperature.
•
Occasional stirring will cause the temperature to fluctuate resulting in poor
data!
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6. Continue recording the temperature every 30 seconds until you have reached the freezing point of
pure stearic acid. At the freezing point, the temperature will remain constant. Stop recording the
temperature after you have obtained 6 – 8 constant temperature measurements.
7. Reheat the water bath with the stearic acid on the hot plate and perform Steps #8 – 11 for the
stearic acid-unknown mixture.
B. Freezing Point of the Stearic Acid-Unknown Mixture
8. On a weighing boat, measure 0.45 – 0.55 g of your unknown sample. Remember to record the
unknown number in your notebook!
9. Once the stearic acid has completely melted (~85-90C), shut off the heat and add all of the
unknown to the test tube using the powder funnel. Stir very quickly with the wire stirrer until the
unknown has completely dissolved and you have a clear-colorless uniform solution. If the
unknown does not dissolve, consult your instructor. Transfer the beaker from the hot plate to
your bench top using the “hot-hand.”
10. When the temperature of the solution decreases to 73C, start the timer and record the
temperature every 30 seconds until you have reached the freezing point of the stearic acidunknown solution. This is indicated by 6-8 CONSTANT temperature measurements.
REMINDER! For optimum measurements, stir the solution constantly with the wire stirrer before
recording the temperature.
CLEANING THE THERMOMETER / WIRE STIRRER
•
Reheat the water bath until the stearic acid-unknown mixture has COMPLETELY melted.
•
Shut off the heat and carefully take out the thermometer / wire stirrer.
•
Give the thermometer / wire stirrer to your instructor and he/she will clean it for you.
HAZARDOUS WASTE
•
Use the “hot-hand” to carefully remove the test tube from the hot-water bath. Allow
the test tube to cool completely to room temperature.
•
Once the contents of the test tube have solidified, discard the ENTIRE test tube in the
designated waste container.
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11. After cleaning your bench area, plot the graph for Trial #1 (Temperature vs Time) on Excel and have
your instructor inspect it.
C. Next Lab Period
12. Repeat Steps #1 – 11 for Trial #2. Upon completion of the 2 nd trial, clean your bench area, plot the
graph and have your instructor inspect it.
Post-Laboratory Questions
1. Define molality. (1 point)
2. Why is the concentration of stearic acid (solvent) being expressed in units of molality instead of
molarity? (2 points)
3. How will the following scenarios affect your results? Scenario A: Some of the unknown sticks to
the walls of the test tube; Scenario B: Some of the unknown does not completely dissolve.
Indicate whether the values will increase (I), decrease (D) or remain unchanged (U)? (8 points)
QUANTITY
A
B
a) Freezing point of solution
b) Molality
c) Moles of Unknown
d) Molar mass of Unknown
4. To 10.0 g of water, some sucrose (table sugar) was added. The freezing point of the resultant
solution was measured to be -2.5 °C. Calculate (a) the molality of this aqueous sucrose solution,
and (b) the mass of sucrose (in g) added to the 10.0 g of water. (4 points)
(Tf water = 0.0 °C, Kf water = 1.86 °C kg/mol, MM sucrose = 342.30 g/mol)
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Molar Mass from Freezing Point Lowering
REPORT SHEET
Data
Trial #1
Trial #2
Mass of Stearic acid
± 0.005 g
± 0.005 g
Mass of Unknown
± 0.005 g
± 0.005 g
Trial #1
Time
(s)
Stearic Acid
Temp (°C)
Trial #2
Stearic AcidUnknown
Temp (°C)
Time
(s)
30
CHE 1121 Lab Manual
Stearic Acid
Temp (°C)
Stearic AcidUnknown
Temp (°C)
30
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Plot your data (Temperature vs Time) on Excel and follow the instructions given to obtain the freezing
points of pure stearic acid and the stearic acid-unknown solutions. Record the freezing point values in
the appropriate spaces below.
Results
Trial #1
Trial #2
Freezing point of pure Stearic acid
C
Freezing point of the Stearic acid-Unknown solution
C
Freezing point lowering, ΔTf
± 0.1 C
Average Freezing point lowering, ΔTf
C
Molality of Unknown
mol/kg
Moles of Unknown
mol
Molar Mass of Unknown
g/mol
Average Molar Mass of Unknown
g/mol
Uncertainty Calculations
Trial #1
Trial #2
Fractional uncertainty in the Mass of Stearic acid
Fractional uncertainty in the Mass of Unknown
Fractional uncertainty in the Freezing Point Lowering
Fractional uncertainty in the Molar Mass of Unknown
Uncertainty in the Molar Mass of Unknown
Average Uncertainty in the Molar Mass of Unknown
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±
g/mol
Page 10
Thin Layer Chromatography (TLC) – Separation of Analgesics
Structures of Analgesics
O
HN
CH3
O
O
NH2
OH
O C CH3
O
OH
Acetaminophen
Aspirin
O
OH
Salicylamide
H 3C
O
CH3
N
N
N
N
CH3
Caffeine
Introduction
Chromatography is an analytical technique that is used for the separation and possible identification
of different compounds. Thin layer chromatography (TLC) is a simple, rapid and inexpensive type of
chromatography. In TLC, a glass or plastic plate that is coated with a thin layer of adsorbent (called the
stationary phase) is spotted with the compound or mixture to be analyzed. A suitable solvent (called
the mobile phase) is allowed to ascend the layer of adsorbent by capillary action. This mobile phase is
the transport medium for the compounds that are to be separated. The movement of the compounds
during TLC is the result of three factors:
1. The strength of the stationary phase (adsorbent),
2. The polarity of the mobile phase (solvent),
3. The polarity of the compound (solute) to be separated.
In TLC, the distance that the compound travels up the plate is compared to the distance that the
mobile phase travels. This ratio of compound movement to solvent movement is called the R f value
for that particular compound. Every compound, given the right conditions, has its own characteristic
Rf value; therefore, an unknown compound can be identified by comparing its R f value to the Rf values
of known compounds.
In this experiment, you will determine the Rf values of commercially prepared and purified
components of common analgesics. You will then use this information to determine the identity of
two unknown samples.
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Distance solvent
travels (in cm)
Rf =
distance compound travels
distance solvent travels
Distance compound
travels (in cm)
SAFETY PRECAUTIONS
1. Safety goggles and lab coats must be worn at all times while an experiment is in progress.
2. The solvents used in this experiment are extremely volatile and will evaporate rapidly from an
open container at room temperature. Obtain the solvent(s) only when needed.
3. All used capillary tubes MUST be discarded in the red broken-glass container. Do not dispose
them in the trash can or leave them on the bench top.
4. Turn off the UV lamp after use to minimize radiation exposure.
5. No chemicals can be disposed in the sink. Always discard the chemical in its appropriate waste
container. If unsure, consult your instructor.
Materials Required
CHEMICALS
EQUIPMENT
1. Aspirin
5. Caffeine
2. Salicylamide
6. Unknown samples
3. Reference
7. Ethyl acetate
4. Acetaminophen
8. Ethanol-DCM (50:50)
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TLC apparatus
• 3 TLC chambers
• 3 TLC plates
• 1 TLC Capillary tube
• UV lamp
Page 12
Procedure
1.
Obtain 3 clean and dry TLC chambers. Add 5 mL of ethyl acetate (mobile phase) to each chamber.
2.
Obtain 3 TLC plates (8.3 cm x 3.5 cm) and draw a line 1 cm from the top and bottom of the plate
on the silica gel side using a pencil. Do not press too hard with the pencil.
3.
On the first plate, using a capillary tube, place a small spot of the acetaminophen solution on one
of the line. On the same plate, spot the caffeine sample using a different capillary tube.
4.
On the second plate, spot the aspirin, salicylamide and reference samples using 3 different
capillary tubes. The reference sample is a mixture of the four standard compounds.
5.
Obtain two unknown samples from your instructor and record their unknown numbers in your
notebook. Take ½ spatula full of each unknown and place them into two separate clean, dry 4inch test tubes. Add ~2 mL of a 50:50 ethanol-dichloromethane (DCM) solvent mixture to each
test tube. Mix the contents for ~ 30 seconds. Allow any undissolved solid to settle.
6.
Obtain 1 capillary tube from your instructor and break it in half. Spot your two unknown samples
on the third TLC plate using these 2 capillary tubes.
7.
Place each of the 3 plates into a TLC chamber. Cap the chambers and do not disturb them while
on the bench top.
8.
When the solvent (ethyl acetate) reaches the top line, remove the plate from the chamber
immediately and air dry for ~1 minute.
9.
Observe all three (3) plates at the same time under a short-wave UV lamp. Outline all the
observed spots by lightly drawing a circle around each spot. CAUTION! Do NOT look directly at
the UV light. Also avoid directing the light rays to the skin. SHUT OFF the lamp after use!
10. Measure the distance the compound traveled (in cm) and divide it by the distance the solvent
traveled (in cm) to calculate the Rf value for each compound.
11. To identify your unknown samples, compare their R f values to the Rf values of the standard
samples. Report your results on the appropriate line on the report sheet.
HAZARDOUS WASTE
•
Discard the ethyl acetate in the ORGANIC solvent waste container.
•
Discard the UNKNOWN samples in a SEPARATE designated waste container.
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Post-Laboratory Questions
1. State 2 reasons as to why it was necessary to cover the TLC chamber while the TLC plate was being
developed? (2 points)
2. Name all the compounds that were present in the reference sample. (4 points)
3. For the reference sample, only 3 spots are observed under the UV lamp. Give an explanation for
this phenomenon. Be specific. (3 points)
4. Calculate the Rf value for an unknown compound that traveled a distance of 4.2 cm on the TLC
plate while the distance traveled by the solvent was 6.0 cm. Show ALL calculations. (2 points)
5. In a TLC separation of a mixture of compounds, the compound with the largest R f value is less
polar than the compound with the smallest R f value. Based on your results, rank the 4 analgesics
in increasing order of polarity (least polar → most polar). (4 points)
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Thin Layer Chromatography
REPORT SHEET
NAME
DATE
Standard Samples
Compound
Distance Compound
Traveled (cm)
Distance Solvent
Traveled (cm)
Rf Value
Acetaminophen
Caffeine
Aspirin
Salicylamide
Reference
Unknown Samples
Unknown #
Distance Unknown
Traveled (cm)
Distance Solvent
Traveled (cm)
Rf Value
Name of Unknown
Compound
Draw your 3 TLC plates below (does not have to be to scale) showing the relative position of each
compound spot. Label the distances (in cm) traveled by the compounds and the solvent.
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Column Chromatography - Separation of the Pigments in
Spinach Extract
Pigment Structures
beta-Carotene (yellow/orange)
OH
HO
Xanthopyll (yellow)
N
R
N Mg N
O
N
O
H 3C
O
O O
Chlorophyll a, R = CH3 (blue-green)
Chlorophyll b, R = CHO (bright green)
Figure 1. Structures of beta-carotene, xanthophyll and chlorophyll a and b.
Introduction
Chromatography is an analytical technique that is used for the separation and possible identification
of different compounds. There are several types of chromatography, such as liquid chromatography
(LC), gas chromatography (GC), high performance liquid chromatography (HPLC), and thin layer
chromatography (TLC). This experiment deals with column chromatography.
A Russian biologist by the name of Tswett was the first to use column chromatography. He used this
technique to separate plant pigments that he was working with.
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In this experiment, column chromatography will be used to separate the pigments present in spinach
(Figure 1). The factors that govern the separation of compounds in chromatography are: 1) The
polarity of the solvent (mobile phase), 2) The polarity of the compounds to be separated, and
3) The polarity of the adsorbent (stationary phase). The adsorbent used in this experiment is alumina
and it will be packed into a chromatography column (glass buret).
Given the right conditions, no two compounds travel through the adsorbent at the same rate,
therefore, a mixture of compounds can be separated. The moving compound is attracted to the polar
sites on the adsorbent, which tend to keep the compound from moving down the column. On the
other hand, the compound also interacts with the mobile phase, which moves the compound through
the column. Depending on the polarity of the compound, it will tend to associate either with the less
polar mobile phase and move more rapidly through the column, or with the more polar adsorbent and
travel more slowly through the column.
The solvents (mobile phase) used in this experiment are petroleum ether (non-polar) and acetone
(polar).
SAFETY PRECAUTIONS
1. Safety goggles and lab coats must be worn at all times while an experiment is in progress.
2. Alumina is an irritant. Avoid inhaling the particulates when transferring it into the column.
3. Both solvents, petroleum ether and acetone, are extremely volatile and will evaporate rapidly
from an open container at room temperature. Obtain the solvent(s) only when needed.
4. Handle the column (glass buret) with extreme care to prevent breakage.
5. No chemicals can be disposed in the sink. Always discard the chemical in its appropriate waste
container. If unsure, consult your instructor.
Materials Required
CHEMICALS
1. Alumina
2. Sand
3. Petroleum ether
4. Acetone
EQUIPMENT
Glasswares
• Chromatography column (buret)
• Twenty 4-inch test tubes
• Powder funnel
• Long stem funnel
• Erlenmeyer flask
Other
• Test tube rack
• Buret clamp
• Glass wool
• Transfer pipet
5. Spinach extract
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Procedure
Chromatography Column Preparation – Refer to Figure 2 for Steps #1 – 3
Sand
.. .. . . .. .
Mobile phase
Petroleum ether + acetone
Stationary phase
Alumina (Al 2 O3 )
Glass wool
.
.
.. .. ..
.
Sand
Figure 2. Column set-up.
1. Put a plug of glass wool into the bottom of a clean, dry column followed by a small amount of sand
(½ inch high) so that it sits on top of the glass wool.
2. In a 50 mL beaker, weigh out 10 g of alumina (stationary phase) and transfer it to the column using
a dry powder funnel. Then add some more sand (¼ inch) above the alumina.
3. Measure 50 mL of petroleum ether using a graduated cylinder. Using a long stem funnel, carefully
fill the column one-half (½) way with petroleum ether. Open the stopcock and let the petroleum
ether drain into a clean, dry 125 mL Erlenmeyer flask until the level of liquid is about ¼ - ½ inch
above the alumina. The petroleum ether collected will be reused later in Step #7.
SOLVENT LEVEL IN THE COLUMN
• Always keep a ¼ to ½ inch of solvent above the sand surface.
• Never allow the top of the sand to run dry.
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Pigment Separation
4. Set-up a test tube rack with twenty 4-inch test tubes (label them 1-20) to collect 4 mL aliquots of
the separated components. These aliquots are called fractions. Use a test tube containing 4 mL of
water as a reference when collecting the fractions.
5. Once your column has been prepared, your instructor will add 1 mL of the spinach extract directly
into your column. After the addition, open the stopcock and drain the extract mixture until its
level is ~¼ inch above the sand.
6. Use a clean pipet to rinse the inner walls of the column with some petroleum ether (~2-3 mL).
Drain the solvent until its level is ~¼ inch above the sand. The sand will take on the green color of
the extract.
7. Pipet some petroleum ether into the column until there is ~3-4 inches of solvent above the sand.
Then use the long stem funnel to fill the column one-half (½) way with petroleum ether ( First use
the petroleum ether collected in Step #3).
8. Open the stopcock and allow the solution to drip from the column into the first test tube. The
yellow-orange color component will start eluting first. Continue collecting 4 mL fractions in each
test tube until the liquid dripping into the test tube is colorless. Be sure to add more petroleum
ether to the top of the column so that the liquid level never goes below the sand level.
9. Prepare 50 mL of a 70:30 petroleum ether-acetone mixture (35 mL petroleum ether + 15 mL
acetone) in a clean, dry 125 mL Erlenmeyer flask. Add this solvent mixture to the column. Open
the stopcock and continue collecting the fractions.
10. The light yellow component will start eluting. Collect 10 fractions of this pigment.
OBSERVING THE XANTHOPHYLL PIGMENT
• The light-yellow xanthophyll pigment is extremely
faint when dissolved in the petroleum ether-acetone
solvent mixture, and will appear colorless.
Look from
above
• To view this pigment, look at the solution from above
and place a piece of white paper towel underneath
the test tube.
• Compare the xanthophyll fractions with the water
test tube to observe the differences in color.
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11. Measure 20 mL of acetone and pour it into the column. Open the stopcock and collect 5-6
fractions of the light green-colored component.
12. The dark green band will not be collected, however, note its presence in the alumina.
13. Once you have completed the separation of the 3 pigments, take the test tube rack with your
collected samples to your instructor and he/she will evaluate your separation.
HAZARDOUS WASTE
•
Discard all solvents in the ORGANIC solvent waste container.
CLEANING THE COLUMN
1. Drain any remaining solvent from the column into a beaker and discard it in the organic solvent
waste container.
2. Remove the buret tip on your bench top and take the column to the hazardous waste hood.
3. Use a pair of forceps to remove the glass wool and discard it in the solid waste container.
Attach one end of a clear PVC tubing to the air jet, then place the other end of the tubing to the
top of your column.
4. With the bottom of the column placed directly into the solid waste container, gently turn on the
air to push out all the solid. NO SOLIDS SHOULD GO IN THE SINK!
5. Wash the column with some water followed by rinsing it with some acetone. Rinse the buret tip
with some acetone as well. Dry the column and buret tip with air.
6. Return the cleaned column to your instructor.
CLEANING YOUR TEST TUBES
1. Rinse all test tubes with some acetone. Discard the acetone in the acetone-waste bottle or the
organic solvent waste container.
2. Then wash the test tubes with hot tap water. Remove all labels and discard them in the trash
can, NOT THE SINK!!
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Post-Laboratory Questions
1. Why is it necessary to leave a ¼ – ½ inch of solvent above the sand surface when performing the
separation? (2 points)
2. Compare the structures of beta-carotene and xanthophyll. Why is xanthophyll more polar than
beta-carotene? (2 points)
3. Compare the structures of chlorophyll a and b. Why is chlorophyll b more polar than chlorophyll
a? (2 points)
4. From the previous TLC experiment, aspirin and salicylamide had similar R f values. Would you be
able to separate a mixture of these 2 compounds using column chromatography? Why/Why not?
(3 points)
5. You are given a sample mixture containing 3 compounds, A (slightly polar), B (very polar) and
C (non-polar). For their separation, you need to use a mobile phase containing a mixture of 2
solvents, n-hexane (non-polar) and ethyl acetate (polar) prepared according to the ratios listed in
the table below. For each trial, indicate which compound will elute from the sample mixture
based on the mobile phase used. (6 points)
Trial #
Ratio of n-hexane to ethyl acetate
Which compound will elute from the mixture?
1
98:2
A, B or C
2
80:20
A, B or C
3
40:60
A, B or C
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Column Chromatography of Spinach Extract
REPORT SHEET
YOUR NAME
DATE
PARTNER'S NAME
LAB DAY
TIME
1. List the names, colors and fraction #s collected for each pigment from the spinach extract.
NAME OF PIGMENT
COLOR OF PIGMENT
TEST TUBE #s CONTAINING
PIGMENT
2. Which pigment was not separated from the extract?
3. List all the pigments present in spinach (including the one that was not separated) in increasing
order of polarity.
Least polar
CHE 1121 Lab Manual
Most polar
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4. In this experiment, you began the separation process with 100% petroleum ether. What
complication would arise in the separation process if a 50:50 petroleum ether-acetone solvent
mixture was used instead? HINT: a) First state what is the difference in polarity between 100%
petroleum ether and the 50:50 solvent mixture. b) How will the 50:50 mixture affect the
separation of the pigments from each other?
5. The separation of compounds in thin layer chromatography (TLC) is opposite to that of column
chromatography. For instance, a compound which is least polar will travel the highest distance on
a TLC plate and will elute first in column chromatography. Using this information and your
observations/conclusions from this experiment, draw a hypothetical TLC plate illustrating the
separation of all the spinach pigments (including the one not separated). Label each pigment spot
with its corresponding name.
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Distillation: Separation of an Acetone-Water Solution
Introduction
Distillation is a process used to separate and purify liquids. The purpose of this experiment is separate
a solution containing acetone and water using a simple distillation apparatus.
The reason why distillation works can be explained using Raoult’s Law, which states that the vapor
above a boiling solution will always contain more of the lower boiling component than the solution
that is boiling. In this experiment, we will start with a 50:50 solution of acetone (bp 56°C) and water
(bp 100 °C). As the solution is heated and starts to boil, the vapor above the boiling solution will
contain more acetone, the lower boiling liquid. As this acetone rich vapor moves away from the heat
source and cools, this new solution still contains more acetone and less water. Eventually, this
acetone rich solution will be vaporized again. This vapor will contain more acetone and less water.
Depending upon the amount of surface area between the boiling liquid and the water cooled
condenser, many of these vaporizations/condensations can take place. Therefore, the greater the
surface area, the greater the separation of the two liquids.
In today’s experiment, you will distill a solution of acetone and water, trying to separate, as best as
possible, the two liquids. This will be accomplished by collecting three fractions and measuring their
volumes. Fraction 1 will be collected from a temperature range of 56-62 °C, therefore this fraction will
contain only acetone. Fraction 2 will be collected between 63-90 °C. This second fraction contains a
mixture of acetone and water. Fraction 3, the last fraction, contains only water. Ideally, to achieve the
best separation, one should get all the acetone in Fraction 1, no Fraction 2, and all the water in
Fraction 3.
WHEN DISTILLING, ALWAYS:
1. Add one (1) boiling chip to the distilling flask. NEVER add a boiling chip to a hot liquid.
2. Use a thin film of grease when connecting all the glass joints. The condenser must be secured to
the two connecting tubes using Keck clips.
3. Insert a greased thermometer into the adapter, which is wrapped in a towel. Don’t force the
thermometer!! The bulb of the thermometer should be just below the junction in the 3-way
connecting tube.
4. Cooling water for the condenser enters at the lower spout and exits at the top. Turn on the water
very gently.
5. A good rate of distillation is 1 – 2 drops per second.
6. The distillation receiver is always a round bottom flask.
7. Never leave your distillation unattended.
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SAFETY PRECAUTIONS
1. Safety goggles and lab coats must be worn at all times while an experiment is in progress.
2. Acetone is a flammable solvent. Never leave it in an open container close to any heat source.
3. No chemicals can be disposed in the sink. Always discard the chemical in its appropriate waste
container. If unsure, consult your instructor.
4. Always use a “HOT-HAND” to handle extremely hot glasswares.
Materials Required
CHEMICALS
1. Acetone
CHE 1121 Lab Manual
EQUIPMENT
Distillation apparatus
• 100 mL RBF
• 50 mL RBF
• 25 mL RBF
• 3-way connecting tube
• Vacuum connecting tube
• Distillation condenser
• Thermometer
• Thermometer adapter
SPRING 2018
Heat source
• Heating mantle
• Temperature controller
Other
• Boiling chips
• Grease
Page 25
Procedure
1. Add 15 mL of acetone, 15 mL of distilled water and 1 boiling chip to a clean 100 mL round bottom
flask (RBF).
2. Set-up the apparatus for a simple distillation (Figure 2). Make sure all glass joints are tight.
Thermometer
Attach Keck clips at these two joints
Thermometer
adapter
Condenser
3-way connecting tube
Water
out
Distilling flask
Boiling chip
X
Vacuum
connecting tube
Water
in
Receiving flask
Beaker of ice/water
cooling flask if necessary
Heating mantle
Figure 2. Simple Distillation Apparatus
3. Get your apparatus checked by your instructor. Turn on the water very gently until you see a
steady stream of water coming out of the condenser.
4. Heat the solution with a heating mantle and set the temperature controller to 25 volts. Once the
temperature has stabilized between 56 – 62 °C, pure acetone will start dripping into the 50 mL
receiving flask at a rate of 1-2 drops per second.
5. Once most of the acetone has distilled over, if the temperature of the boiling solution has
decreased by more than 5 °C (bp < 51 °C) and the distillation rate has slowed down significantly,
then increase the voltage on the controller to 30 volts.
6. At a temperature just above 62°C, change the receiving flask from the 50 mL to the 25 mL RBF.
Make sure you did not loosen any glass joints.
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7. Increase the voltage on the temperature controller to 35 volts. Measure the volume of Fraction 1
using your graduated cylinder.
8. When the temperature reaches 90°C, turn off the heat, lower the heating mantle and let the
apparatus cool to room temperature (~25°C). Allow the water to run continuously through the
condenser during the cooling process.
9. Measure and record the volumes of the remaining 2 fractions that were collected.
10. Discard Fractions #1 and #2 in the organic solvent waste container. Fraction #3, which is only
water, can be discarded in the sink.
Unknown Analysis
NOTE! All glasswares MUST be completely dry
11. Obtain 20 mL of an unknown acetone-water solution from your instructor (DO NOT add any
additional water). Using simple distillation, determine the amount of acetone present in the
unknown sample. Use the 50 mL RBF as the distilling flask and the 25 mL RBF as the receiving
flask.
12. Set the temperature controller to 25 volts. When the temperature is just above 62°C, turn off the
heat, lower the heating mantle and allow the apparatus to cool to room temperature. Measure
and record the volume of the liquid in the 25 mL RBF. Discard this fraction in the organic solvent
waste container. The residual liquid in the 50 mL RBF can be discarded in the sink.
13. Discard all used boiling chips in the trash can, NOT the sink.
Post-Laboratory Questions
1. What is the reason for performing a distillation? (2 points)
2. Why is it necessary to add a boiling chip to the distilling flask? (2 points)
3. Cooling water usually enters the condenser from the LOWER spout and exits from the UPPER
spout. Explain the implications if water entered from the upper spout and exited from the lower
spout of the condenser. (4 points)
4. What is a good distillation rate? (2 points) What observation is necessary to indicate when a
distillation is complete? In other words, how do you know when to stop distilling? (2 points)
5. Why must the thermometer be positioned such that bulb is situated just below the sidearm of the
3-way connecting tube? (3 points)
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Distillation: Separation of an Acetone-Water Solution
REPORT SHEET
NAME
DATE
LAB DAY
TIME
Standard Sample
Fraction #
Boiling point range
1
56 – 62 °C
2
63 – 90 °C
3
91 – 100 °C
Volume Collected (mL)
Starting volume
mL
Total volume of all 3 Fractions collected
mL
%-Recovered
%
Unknown Sample
Starting volume
mL
Volume of acetone collected between 56-62 °C
mL
%-Acetone in unknown solution
CHE 1121 Lab Manual
%
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Page 28
Resolution of Racemic Phenylsuccinic Acid
Chemical Reaction
H
(S-PSA)-(L-Pro)2
O
HO
insoluble salt
H
OH
O
(R,S)-(+/-)-Phenylsuccinic acid
optically inactive
+
N
H
HCl
HO
O
OH
O
(S)-(+)-Phenylsuccinic acid
COOH
optically active
L-(-)-Proline
(R-PSA)-(L-Pro)
Chiral resolving agent
soluble salt
Introduction
Chiral compounds arise when a carbon atom is bonded to four different atoms or groups. These
atoms or groups can be bonded to the carbon atom in two different orientations in a 3-dimensional
space resulting in the formation of isomers called stereoisomers.
Enantiomers are stereoisomers that are non-superimposable mirror images of each other. They have
identical chemical and physical properties, i.e., solubility, density, polarity, boiling point, melting point,
etc. As a result, a pair of enantiomers cannot be physically separated from each other using
conventional methods.
Chemically, however, enantiomers react with compounds called chiral resolving agents (CRA) at
different rates. This chemical reaction is called resolution, which allows for the separation of a pair of
enantiomers. Resolution via salt formation will be the method demonstrated in this experiment. This
method was first accomplished in 1853 by the father of stereochemistry, Louis Pasteur.
The resolution of enantiomers is an extremely valuable method employed in the separation of chiral
drugs. FDA regulations require pharmaceutical companies to test each isomer of a chiral drug for its
therapeutic effect as well as for any toxicity. For example, with Ibuprofen (Motrin®, Advil®), the
S-enantiomer has all the anti-inflammatory activity, while the R-enantiomer is pharmacologically
inactive. With Citalopram (Celexa®), the S-enantiomer (Lexapro®) contains all the anti-depressant
effect, while the R-enantiomer antagonizes (inhibits) the anti-depressant activity of the S-isomer.
Esomeprazole (Nexium®), the S-enantiomer of omeprazole, is a proton-pump inhibitor that decreases
the production of gastric acid in the stomach. R-omeprazole, on the other hand, is pharmacologically
inactive.
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CHIRAL DRUGS
H CH3
OH
H CH3
OH
O
O
(S)-(+)-Ibuprofen
(R)-(-)-Ibuprofen
F
F
N
N
O
O
N
N
(S)-(+)-Citalopram
H
N
(R)-(-)-Citalopram
H
N
O
S
N
O
O
O
S
N
O
O
(S)-(-)-Omeprazole
(R)-(+)-Omeprazole
In this experiment, racemic phenylsuccinic acid (RS-PSA) will be resolved using L-(-)-proline (L-Pro) as
the chiral resolving agent. A racemic mixture is a compound containing equal amounts of a pair of
enantiomers.
When RS-PSA (an acid) reacts with L-proline (a base), two diasteroemeric salts form, namely the
(S-PSA)-(L-Pro)2 and the (R-PSA)-(L-Pro), respectively. Diastereomers are stereoisomers that are nonsuperimposable non-mirror images of each other. In comparison to enantiomers, diastereomers have
different physical properties, i.e., solubility, density, etc.
The two diasteroemeric salts have different solubilities in the reaction solvent, 2-propanol. The
(S-PSA)-(L-Pro)2 salt is insoluble in 2-propanol and precipitates out of the solution. This salt can then
be isolated by filtration. On the other hand, the (R-PSA)-(L-Pro) salt is soluble in 2-propanol and is
present in the filtrate (liquid) after the filtration. The optically active S-(+)-PSA enantiomer is then
liberated from its proline-salt by the addition of hydrochloric acid.
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Optical rotation is a physical property of chiral compounds (enantiomers and diastereomers) that is
measured using an instrument called a polarimeter. The polarimeter functions by converting
unpolarized light (light that travels in all different planes or directions) into a light that travels in only
one plane, which is called plane-polarized light. Enantiomers rotate plane-polarized light in equal, but
opposite directions. The unit for rotation is degrees (°) and the magnitude for rotation is denoted by
the prefixes (+) and (-). For example, if one enantiomer has a rotation of +10 °, the other enantiomer
will have a rotation of -10°. Compounds that exhibit an optical rotation are said to be “optically
active.”
Racemic mixtures (or racemates) contain 50% of the (+)-enantiomer and 50% of the (-)-enantiomer.
Since the rotations of each enantiomer cancel each other, the net rotation for a racemic compound is
0°. A racemic compound, is therefore, said to be “optically inactive.”
When a solution containing a chiral compound is placed in the path of the plane-polarized light, the
light gets rotated by a certain angle called the angle of rotation (aobs). From the angle of rotation and
the concentration of the sample, the specific rotation ([a]D) of the chiral compound can then be
calculated using the equation
[] =
obs
l c
where l is the length of the polarimeter cell (sample holder) expressed in units of decimeters (dm) and
c is the concentration of the sample expressed in units of g/mL.
If the specific rotation for a pure enantiomer ([a]max) is known, the %-optical purity of the resolved
enantiomer can be determined using the equation
%-Optical purity =
[]
[]m ax
x 100%
In this experiment, you will use a polarimeter to measure the angle of rotation for the optically active
S-(+)-phenylsuccinic acid enantiomer. You will then calculate its specific rotation and %-optical purity.
CHE 1121 Lab Manual
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SAFETY PRECAUTIONS
1. Safety goggles and lab coats must be worn at all times while an experiment is in progress.
2. 2-Propanol and acetone are flammable solvents! Never leave it in an open container close to any
heat source.
3. 6M Hydrochloric acid is corrosive and can cause burns to the skin and eyes. Remove any jewelry
before obtaining HCl. Handle with extreme care, and wash/rinse hands thoroughly after handling
it.
4. Apply a sufficient amount of grease to the reflux condenser.
5. Clamp the filter flask to a ring stand when vacuum filtering.
6. No chemicals can be disposed in the sink. Always discard the chemical in its appropriate waste
container. If unsure, consult your instructor.
7. Always use a “HOT-HAND” to handle extremely hot glasswares.
Materials Required
CHEMICALS
1. Racemic Phenylsuccinic acid
2. L-(-)-Proline
3. 2-Propanol
4. Acetone
5. 6M Hydrochloric acid (HCl)
CHE 1121 Lab Manual
EQUIPMENT
Reflux apparatus
• 100 mL RBF
• Reflux condenser
Stirrer
• Magnetic stirrer
• Stir bar
Filtration apparatus
• Buchner funnel
• Filter adapter
• 250 mL Filter flask
• Filter paper
Heat source
• Heating mantle
• Temperature controller
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Page 32
Procedure
Top of condenser
remains open
NOTE! All equipment must be clean and dry up to Step #5
1. On a weighing boat, measure 1.94 g of racemic
phenylsuccinic acid and 1.15 g of L-(-)-proline. Transfer
both solids to a clean, dry 100 mL RBF using a powder
funnel.
Water out
Reflux Condenser
2. Add 40 mL of 2-propanol (solvent) to the 100 mL RBF and
obtain a stir bar from your instructor.
3. Set-up a reflux apparatus (see Figure) and have your
instructor approve it. Reflux the reaction mixture with a
heating mantle and temperature controller (35 volts) for
25 minutes. A good reflux rate is 1-2 drops per second.
Water in
100 mL RBF
Stir Bar
4. After 25 minutes, shut off the heat, set aside the heating
mantle and air cool the RBF until it reaches room
temperature (takes ~10-15 minutes). Do not disassemble
the apparatus; allow the water to run through the
condenser and continue stirring. A white precipitate
should form as the flask is cooling.
Heating Mantle
Magnetic Stirrer
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5. Vacuum filter (Figure 3) the mixture in the RBF using clean, dry filtration apparatus. Mat the filter
paper down with 2-3 mL of 2-propanol. Remove any residual solid from the RBF by rinsing it twice
with 5 mL of 2-propanol. Consult your instructor if there is still residual solid in the RBF before
proceeding.
Buchner
Funnel
Clamp flask to
ring stand
Attach one end of the rubber tubing
to the filter spout here and
the other end of the tubing
to the yellow vacuum line
Filter Flask
Figure 3. Vacuum filtration apparatus
6. Once all the solid has been transferred to the buchner funnel, with the vacuum on, pour 10 mL of
acetone over the solid to remove any unreacted Proline. Leave the vacuum on for 5 minutes.
7. Transfer the solid to a large filter paper and dry it by pressing down with another large piece of
filter paper to absorb any solvent. Then use a spatula to break up the solid and allow it to “air dry”
for 5 minutes.
HAZARDOUS WASTE
•
Discard the filtrate from the filter flask in the ORGANIC solvent waste
container.
8. Transfer the solid to a clean 100 mL beaker and cool it an ice-water bath. Slowly, with stirring, add
10 mL of 6M HCl and stir for 2-3 minutes. A white precipitate should form. Consult your
instructor if there is no precipitate.
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9. Vacuum filter the mixture using clean filtration apparatus (does not have to be dry). Mat down the
filter paper with some distilled water. Use the filtrate to remove the residual solid from the
beaker.
Stirring rod OR spatula
solid
precipitate
Filtrate
10. With the vacuum on, pour 15 mL of ice-cold water (from your ice-water bath) over the solid to
remove any HCl.
HAZARDOUS WASTE
•
Discard the filtrate from the filter flask in the aqueous ACID waste
container.
11. Transfer the solid to a clean, dry 150 mL beaker and store it in your drawer uncovered until the
next lab period.
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Next Lab Period
12. Obtain the actual yield of your (S)-(+)-PSA as directed by your instructor and calculate the percent
yield.
13. Your instructor will show you how to use the polarimeter to measure the optical rotation of your
(S)-(+)-PSA. Calculate the specific rotation [] and %-optical purity (%-OP) using the formulas
shown on the report sheet.
Post-Laboratory Questions
1. Why was it necessary for the reflux apparatus to be completely dry for this reaction? (2 points)
2. Define enantiomers. (1 point)
3. What specific physical property allows you to distinguish between a pair of enantiomers?
(2 points)
4. Provide a brief explanation as to why a racemic mixture is optically inactive. (2 points)
5. In this experiment, racemic ()-phenylsuccinic acid was resolved to obtain pure (S)-(+)phenylsuccinic acid. Which enantiomer is present in the filtrate from Step #5? (2 points)
OH
L-(-)-Menthol
6. How many chiral centers are present in the structure of L-(-) menthol? (1 point) How many
stereoisomers are possible for this compound? (1 point)
7. A 5.0 g sample of L-(-)-menthol was dissolved in 25.0 mL of ethyl alcohol. The sample was then
placed in a 2-dm polarimeter cell. The observed rotation of the sample was -5.0°. Calculate
(a) the specific rotation ([a]) of the sample, and (b) the %-optical purity ([a]max = -51.0°).
(4 points)
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Resolution of Racemic Phenylsuccinic Acid
REPORT SHEET
YOUR NAME
PARTNER'S NAME
DATE
LAB DAY
TIME
Chemical Reaction
H
(S-PSA)-(L-Pro)2
O
HO
+
N
H
O
(R,S)-(+/-)-Phenylsuccinic acid
optically inactive
O
HO
insoluble salt
H
OH
HCl
OH
O
(S)-(+)-Phenylsuccinic acid
COOH
optically active
L-(-)-Proline
(R-PSA)-(L-Pro)
Chiral resolving agent
soluble salt
Results
Actual Yield of (S)-(+)-PSA
Theoretical Yield of (S)-(+)-PSA
g
Percent Yield
g
%
Optical Rotation
Observed rotation, 

Specific rotation, []

%-Optical purity
%
[] =
CHE 1121 Lab Manual
Concentration
g/mL, acetone
([]max = + 171 )
obs
%-Optical purity =
l c
SPRING 2018
[]
[]m ax
x 100%
Page 37
Synthesis of tert-Butyl Chloride (2-Chloro-2-methylpropane)
Chemical Reaction
+
OH
tert-Butyl alcohol
(2-Methylpropan-2-ol)
MM 74.12 g/mol
conc.
HCl
Cl
25 oC
MM 36.46 g/mol
+
H 2O
tert-Butyl chloride
(2-Chloro-2-methylpropane)
MM 92.57 g/mol
Introduction
Alkyl halides are organic compounds denoted by the general structure R-X where X can be Cl, Br or I.
Free-radical halogenation is one method that can be used to synthesize alkyl halides where an alkane
is reacted with a halogen in its elemental state (X 2 = Cl2, Br2, I2). The general reaction for the freeradical halogenation is:
R H
+
hv or
X2
R X
+ H X
The drawback of the above reaction is that alkanes are extremely flammable while the halogens are
highly corrosive and toxic.
Another method that is safer and is used to synthesize alkyl halides is the reaction of alcohols (R-OH)
with concentrated hydrohalic acids (H-X). The general reaction is:
R OH +
H X
R X
+
H 2O
In this experiment, the alkyl halide, tert-butyl chloride, will be synthesized by reacting tert-butyl
alcohol (a 3° alcohol) with concentrated hydrochloric acid (HCl). The advantage of this reaction is that
it is instantaneous at room temperature where tert-butyl chloride is formed immediately upon
combining both reagents.
This reaction is an example of a nucleophilic sustitution reaction that follows an S N1 mechanism. This
is a two-step reaction that first involves the formation of a tertiary carbocation intermediate followed
by a nucleophilic attack by the chloride anion in the second step yielding the alkyl halide product.
This reaction will be performed in a separatory funnel where an upper layer of the tert-butyl chloride
will form. The product will be isolated using the extraction technique followed by drying the organic
liquid with anhydrous sodium sulfate (a drying agent). The crude (impure) tert-butyl chloride will then
be purified by performing a fractional distillation.
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SAFETY PRECAUTIONS
1. Safety goggles and lab coats must be worn at all times while an experiment is in progress.
2. Handle concentrated HCl with extreme care. Read the safety precautions on Page #38.
3. Apply a sufficient amount of grease to the joints of the distillation apparatus. Never leave your
distillation unattended.
4. No chemicals can be disposed in the sink. Always discard the chemical in its appropriate waste
container. If unsure, consult your instructor.
5. Always use a “HOT-HAND” to handle extremely hot glasswares.
6. Discard all used boiling chips in the trash can, NOT the sink!!
Materials Required
CHEMICALS
EQUIPMENT
Extraction apparatus
1. tert-Butyl alcohol
• Separatory funnel
• Hollow stopper
2. Concentrated Hydrochloric acid (HCl) • Small iron ring
3. Saturated Sodium bicarbonate
(NaHCO3)
4. Sodium sulfate
CHE 1121 Lab Manual
Heat source
• Heating mantle
• Temperature controller
Other
• Boiling chips
SPRING 2018
Distillation apparatus
• 50 mL RBF
• 25 mL RBF
• 3-Way connecting tube
• Vacuum connecting tube
• Distillation condenser
• Thermometer
• Thermometer-adapter
Page 39
Procedure
1. To your separatory funnel, add 10 mL (7.75 g) of tert-butyl alcohol and 25 mL of concentrated
hydrochloric acid. To calculate the mass of HCl, use the volume of HCl (25 mL) and its molarity
(12.4M) to first obtain moles of HCl. Then use its molar mass (36.46 g/mol) to convert moles to
grams of HCl.
SAFETY PRECAUTION
Concentrated Hydrochloric acid (HCl) is extremely corrosive if it comes in
contact with skin. Safety goggles and lab coats must be worn at all times.
Handle HCl with extreme care. All jewelry, watches, rings, bracelets, etc must
be removed prior to handling it as HCl fumes (gas) from the chemical can react
with the metal. Rinse hands thoroughly with water after handling the acid.
2. Gently swirl the contents of the separatory funnel for ~30 seconds and then stopper it with a
hollow stopper. Invert and vent the separatory funnel by opening the stopcock to release the
pressure. Make sure you hold the hollow stopper in place when you invert the funnel. Repeat the
shaking, inverting, and releasing the pressure, slowly at first. As the pressure decreases, gradually
increase the shaking.
3. Once the pressure has subsided, clamp the stoppered funnel to a ring stand and let it stand until
both layers are clear (Figure 4). This will take 20-30 minutes. During this time, the student should
set-up the distillation apparatus used later in this experiment.
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Organic layer
Aqueous layer
Figure 4. Extraction apparatus
4. When both layers are clear, drain and discard the lower aqueous layer in the acid/base waste
container.
5. Add 10 mL of saturated sodium bicarbonate solution to the upper organic layer in the separatory
funnel. CAUTION! Carbon dioxide (CO2) gas will be generated, which will build up a lot of
pressure. First, gently swirl the funnel unstoppered for ~ 30 seconds. Then stopper the funnel,
invert and vent it. Continue inverting and venting until no more pressure is formed.
6. Clamp the separatory funnel and let the two layers separate. Drain and discard the lower aqueous
layer in the acid/base waste container.
7. Add 10 mL of distilled water to the upper organic layer, stopper, invert and vent the funnel. Let
the two layers separate, then drain and discard the lower aqueous layer in the acid/base waste
container.
8. Transfer the upper tert-butyl chloride layer to a clean, dry 125 mL Erlenmeyer flask and dry it with
anhydrous sodium sulfate (Na2SO4).
9. Using your long stem funnel with a very small piece of glass wool, decant the tert-butyl chloride
into a clean, dry 50 mL RBF.
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10. Set up an unpacked column distillation apparatus (Figure 5) using the 25 mL RBF as the receiving
flask, which must be cooled in a beaker of ice-water. Purify the tert-butyl chloride by distilling it to
a temperature of 52C or until no more distillate drips into the 25 mL RBF. Set the temperature
controller to 35 volts.
Thermometer
Attach Keck clips at these two joints
Thermometer
adapter
Condenser
3-way connecting tube
Water
out
Vacuum
connecting tube
Water
in
Receiving flask
Beaker of ice/water
cooling flask if necessary
Distilling flask
Boiling chip
X
Heating mantle
Figure 5. Unpacked-column distillation apparatus
11. Pure tert-butyl chloride is a clear, colorless liquid. If your product is cloudy, dry it with sodium
sulfate before handing it in to your instructor.
Post-Laboratory Questions
1. Why is it better to use concentrated HCl instead of dilute HCl in this reaction? (3 points)
2. Why was saturated sodium bicarbonate added to the separatory funnel in Step #5? (2 points)
3. Why was it necessary to use anhydrous sodium sulfate in Step #8? (2 points)
4. Butan-2-ol is reacted with concentrated HI. Draw the structure and write the name of the final
product. (8 points)
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Synthesis of tert-Butyl Chloride
REPORT SHEET
Chemical Reaction
OH
tert-Butyl alcohol
(2-Methylpropan-2-ol)
MM 74.12 g/mol
Name of
Reactant
Mass of
Reactant (g)
+
conc.
HCl
Cl
25 oC
MM 36.46 g/mol
Molar Mass
(g/mol)
+
H 2O
tert-Butyl chloride
(2-Chloro-2-methylpropane)
MM 92.57 g/mol
Moles of
Reactant
Mole
Ratio
P
R
Moles of
Product
Molar Mass
(g/mol)
Name of Product
Theoretical Yield Calculation
Lowest Moles of Product
x
MM of Product
=
g
Results
Actual Yield
CHE 1121 Lab Manual
g
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Percent Yield
%
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Synthesis of 2-Methylbut-2-ene
Chemical Reaction
OH
H 2SO4
+
+
2-Methylbutan-2-ol
2-Methylbut-2-e ne
2-Methylbut-1-e ne
MM 88.15 g/mol
MM 70.13 g/mol
MM 70.13 g/mol
Major
product
H 2O
Minor
product
Introduction
Alkenes are organic compounds called unsaturated hydrocarbons containing a carbon-carbon double
bond (C=C) in their molecular structure. In this experiment, we will be synthesizing an alkene by the
acid-catalyzed dehydration of an alcohol.
The relative reactivity of alcohols in this kind of reactions is 3° > 2° > 1°. A strong mineral acid such as
sulfuric or phosphoric acid is used as the acid catalyst. Hydrohalic acids (HCl, HBr, HI) cannot be used
to catalyze this reaction as they will promote a substitution reaction to form alkyl halides instead of
alkenes.
In this experiment, the alkene, 2-methylbut-2-ene will be synthesized by the sulfuric acid-catalyzed
dehydration of 2-methylbutan-2-ol (a 3° alcohol). Since the acid is catalyzing the removal of a water
molecule from the alcohol, this type of reaction is called an elimination reaction that specifically
follows an E1 mechanism. Similar to an SN1 mechanism, the E1 reaction also occurs in two-steps where
a carbocation intermediate is first formed followed by the abstraction of a proton adjacent to the
carbocation.
From the above reaction, we can seen that two structural isomers of 2-methylbutene are formed,
namely, 2-methylbut-2-ene and 2-methylbut-1-ene. Using Zaitsev’s rule, we can predict which of
these two alkenes is the major and which one is a minor product. Zaitsev’s rule states that the more
highly substituted alkene will be the major product as it is more stable. When comparing the two
structural isomers of 2-methylbutene, the major product is 2-methylbut-2-ene because it is a
trisubstituted alkene while 2-methylbut-1-ene is the minor product since it is disubstituted.
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A disadvantage of the above reaction is that it is reversible, which means that the reactants and
products exist in a state of equilibrium. Once the alkene product is formed, it can react with sulfuric
acid and water to re-form the alcohol. This reversible reaction is called ‘hydration.’ To prevent the
reverse reaction from occurring, we can apply Le Chatelier’s principle to favor the equilibrium reaction
towards the formation of the alkene product. During the reaction, the alkene product is separated
from the reaction mixture by performing a distillation since it has a lower boiling point than the
starting alcohol.
SAFETY PRECAUTIONS
1. Safety goggles and lab coats must be worn at all times while an experiment is in progress.
2. 2-Methylbutan-2-ol and 2-methylbut-2-ene are flammable liquids. Never leave it in an open
container close to any heat source.
3. Sulfuric acid and sodium hydroxide are corrosive! Handle these chemicals with extreme care.
Wash/rinse hands after use.
4. Apply a sufficient amount of grease to all the joints of the distillation apparatus. Never leave
your distillation unattended.
5. No chemicals can be disposed in the sink. Always discard the chemical in its appropriate waste
container. If unsure, consult your instructor.
6. Always use a “HOT-HAND” to handle extremely hot glasswares.
7. Discard all used boiling chips in the trash can, NOT the sink!!
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Materials Required
CHEMICALS
1. 2-Methylbutan-2-ol
(tert-Amyl alcohol)
2. 34% Sulfuric acid (H2SO4)
3. 10% Sodium hydroxide
(NaOH)
4. Anhydrous Sodium sulfate
EQUIPMENT
Distillation apparatus (Step #1)
• 100 mL RBF
• 50 mL RBF
• 3-way connecting tube
• Vacuum connecting tube
• Distillation condenser
• Hollow stopper
Distillation apparatus (Step #9)
• 50 mL RBF
• 25 mL RBF
• 3-way connecting tube
• Vacuum connecting tube
• Distillation condenser
• Thermometer
• Thermometer adapter
Heat source
• Heating mantle
• Temperature controller
Extraction apparatus
• Separatory funnel
• Hollow stoppered
• Small iron ring
Other
• Boiling chips
Procedure
1. Set-up a simple distillation using the 100 mL RBF as the distilling flask and the 50 mL RBF as the
receiving flask cooled in a beaker of ice-water. Substitute the hollow stopper in place of the
thermometer/thermometer adapter in the set-up. None of the equipment has to be dry.
2. Add 20 mL of a 34% sulfuric acid solution to a 125 mL Erlenmeyer flask and cool it in a beaker of
ice-water.
3. While the Erlenmeyer flask is cooled in the ice-water bath, slowly add 10 mL (8.05 g) of
2-methylbutan-2-ol (tert-amyl alcohol).
4. Using a long stem funnel, transfer the contents of the Erlenmeyer flask to the 100 mL RBF of the
distillation set-up.
5. Using a heating mantle and temperature controller (30 volts), distill the 2-methylbut-2-ene
product until no more liquid drips into the receiving flask, which takes ~10-20 minutes. There will
be liquid left in the 100 mL RBF, which is water and excess sulfuric acid.
HAZARDOUS WASTE
•
CHE 1121 Lab Manual
Discard the contents of the 100 mL RBF in the aqueous ACID-BASE waste
container.
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6. Transfer the contents of the 50 mL RBF to a clean separatory funnel and add 5 mL of 10% NaOH
solution. Swirl the unstoppered funnel for ~ 30 seconds. Place the hollow stopper on the funnel
and shake it with frequent venting.
7. Clamp the separatory funnel to a ring stand and let the two layers separate. Drain and discard the
lower aqueous layer in the aqueous acid-base waste container.
8. Transfer the upper organic layer into a clean, dry 125 mL Erlenmeyer flask. Cork and cool the flask
in an ice-water bath. Dry the product with anhydrous sodium sulfate.
9. Set-up a simple distillation using a clean, dry 50 mL RBF as the distilling flask and a clean, dry
25 mL RBF as the receiving flask that is cooled in a beaker of ice-water. Add 1 boiling chip to the
distilling flask.
10. Decant the dried organic liquid through a long stem funnel containing a small piece of glass wool
into the distilling flask. Using the heating mantle and temperature controller (30 volts), collect the
pure butene product up to a temperature of 43°C.
11. Hand in the product today as directed by your instructor.
Post–Laboratory Questions
1. What role does sulfuric acid play in this reaction? (2 points)
2. Briefly explain why 2-methylbut-2-ene is considered the “major” product in this reaction.
(3 points)
3. What is the reason for using 10% NaOH in Step #6? (2 points)
4. Draw the structures of the major and minor products formed when 1-methylcyclopentanol
undergoes dehydration in the presence of sulfuric acid. (8 points)
H 3C OH
H 2SO4
+
1-Methylcyclopentanol
Major product
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Minor product
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Synthesis of 2-Methylbut-2-ene
REPORT SHEET
Chemical Reaction
OH
H 2SO4
+
+
2-Methylbutan-2-ol
2-Methylbut-2-e ne
2-Methylbut-1-e ne
MM 88.15 g/mol
MM 70.13 g/mol
MM 70.13 g/mol
Major
product
Name of
Reactant
Mass of
Reactant (g)
Molar Mass
(g/mol)
H 2O
Minor
product
Moles of
Reactant
Mole
Ratio
P
R
Moles of
Product
Molar Mass
(g/mol)
Name of Product
Theoretical Yield Calculation
Lowest Moles of Product
x
MM of Product
=
g
Results
Actual Yield
CHE 1121 Lab Manual
g
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Percent Yield
%
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