CH342
Fall 2011
Lab package
Sample Theoretical and Percent Yield calculations:
OH
H3C
Cl
CH2CH3
+ Conc. HCl
CH3
+
H2O
CH3
2-Methyl-2-butanol
10.0 mL
Density = 0.805 g/mL
CH2CH3
H3C
2-Chloro-2-methylbutane
10.0 mL
12.1 molar
8.0 grams isolated
1
Write a balanced chemical equation for the reaction. Without this, the calculation is
impossible. Most of the time, this is in the lab book or the lab handout. In the sample
equation, one 2-methyi-2-butanol + one HCI gives one 2-chloro-2-methylbutane.
2.
Find the reactants. Solvents and catalysts do not influence the yield.
3.
Obtain or calculate the molecular weights of each reactant. 2-methyl-2-butanol has 5
carbons, 1 oxygen, and 12 hydrogens. Its molecular weight would be (5 x 12.01) + (1 x 16.00)
+ (12 x 1.008) = 60.05 + 16.00+12.10 = 88.15. 2-chloro-2-methyibutane is 60.05+16.00+35.45
= 106.59. HCl is 36.46, but we won't actually need this.
4.
Calculate the number of moles of each reactant. If we have grams, we just divide the
grams used by the molecular weight (which has units of grams/mole). For 2-methyl-2butanol, this is a little more difficult, since we are given mLs of 2-methyl-2-butanol. We need
to use the density (which is in grams/mL) to get the grams of 2-methyl-2-butanol. From the
Aldrich Catalog, the density of 2-methyl-2-butanol is 0.805. Therefore, 10.0 mL 2-methyl-2butanol x 0.805 g 2-methyl-2-butanol/niL = 8.05 g 2-methyl-2-butanol. 8.05 g 2-methyl-2butanol I 88.15 g 2-methyl-2-butanol I mole = .0913 moles 2-methyl-2-butanol. For conc. HCI,
we are given molarity, which is in moles/L, so all we have to do is multiply 12.1 moles/L x
.0100 L = .121 moles HCl.
5.
Find the limiting reagent. In our equation, one HCl + one 2-methyl-2-butanol give one
2-chloro-2-methylbutane. Therefore, whichever reagent has the fewest number of moles will
control how much product is formed. We have 0.121 moles of HCl and 0.0913 moles of 2methyl-2-butanol. Since we have less 2-methyl-2-butanol than HCI, 2-methyl-2-butanol is the
limiting reagent, and we can form only 0.0913 moles of 2-chloro-2-methylbutane.
6.
Calculate the theoretical yield of product. The molecular weight of 2-chloro-2methylbutane is 106.59. So, 0.0913 moles of 2-chloro-2-methylbutane x 106.59 g 2-chloro-2methylbutanelmole =9.73 grams 2-chloro-2-methylbutane. This is our theoretical yield.
7.
Percent yield is what proportion of the theoretical yield we actually make. If we had
produced 8.00 grams of 2-chloro-2-methylbutane when we actually did the reaction, then
the percent yield is 100% X 8.00g/9.73g = 82.2%.
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CH342
Fall 2011
Lab package
Report format for Learning Basic Operations: The Effect of pH on a Food Preservative
1.
Title Page (Attach a separate Title page to your report)
A short descriptive title of the lab exercise.
Date the experiment was performed.
Course and section numbers.
Name(s)
2.
Body of the report
a.
Amount of sodium benzoate used (gm)
b.
Amount of sodium benzoate used (moles)____________________
c.
Amount of 3M HCl used (ml)
d.
Amount of 3M HCl used (moles)
e.
Limiting reagent
____________________
f.
Theoretical yield of benzoic acid (gm)
____________________
g.
Actual yield of benzoic acid (gm)
____________________
h.
Percent yield (Show calculation)
____________________
___________________
____________________
____________________
Show calculations for Theoretical yield and percent yields here. Indicate the Limiting
Reagent in this reaction.
3.
Exercises
Do Exercises 1 and 4 on page 47. If more space needed, use separate papers and attach
them to this report.
Report Format for
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CH342
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Lab package
Separating the Components of Panacetin.
Recrystallization and Melting Point
Measurement: Identifying the Components of Panacetin
1. Title Page (Attach a separate Title page to your report)
A short descriptive title of the lab exercise.
Dates the experiment was performed.
Course and section numbers.
Name(s)
2. Body of the report (start a new page)
Panacetin sample number _______________
Statement of the problem
Weight of initial panacetin sample
_______________________
Weight of sucrose collected
_______________________
Weight of aspirin collected
_______________________
Melting point range of aspirin
_______________________
Weight of unknown compound isolated in Expt. 2 _____________
Weight of recrystallized unknown compound in Expt. 3._________
Melting point range of recrystallized unknown compound _______
Mixture melting point ranges of the unknown compound with acetanilide ________
Mixture melting point ranges of the unknown compound with phenacetin ________
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CH342
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Lab package
Percent recoveries of sucrose, aspirin and your unknown (divide the weight of each solid by
answer in c.,  100%). Show your calculations.
A final conclusion, supported by evidence, about identity of the unknown compound.
3.
Exercises
Do Exercises 1 and 5 on page 54, and Exercise 1 on page 60. Use separate papers to write
answer the exercises and attach them to this report.
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INTRODUCTION TO THIN LAYER CHROMATOGRAPHY (TLC)
In this experiment, you will be identifying an unknown compound by TLC. Your unknown
may have impurities added to it, including benzoic acid. Since the unknowns and benzoic
acid all show up under UV light, we can easily detect them with TLC.
Procedure:
Obtain a TLC plate, and draw a light pencil line across the width of the plate, about 1 cm
from the edge. Place 5 light “tic marks” on the line, approximately equally spaced.
In separate test-tubes, dissolve tiny amounts of your unknown in about 1 mL of acetone.
Using one of the spotting capillary tube, spot a tiny drop of the acetone solution of your
unknown on the first from the left “tic-mark” - you may want to practice spotting on a paper
towel or tissue, to make small spots. Allow it to dry, and then check the plate under a shortwave UV light, to see if you have a visible spot. If not, spot your solution again on the same
“tic-mark”. Do not spot any more times than needed - too much material may give results
that are hard to interpret! After you have your samples spotted, take your plate to the
standards in the hood, and spot benzoic acid on the second from the left “tic-mark”, three
possible unknowns on the third, fourth and fifth “tic-mark”s. Keep track of which possible
unknown spotted where. Do not get the spotting capillaries for the standards contaminated!
Check the spots under the UV light, to see if they are all visible.
To prepare a developing chamber, obtain a piece of 11 cm filter paper, and fold it about 1
inch from the edge, to obtain a flat edge. Place the filter paper, flat edge down, in your 250
mL beaker. Obtain 15 mL of the TLC solvent, and pour it into the beaker, swirling the beaker
to wet the filter paper with the solvent.
Carefully place the TLC plate in the developing chamber, spotted side down, trying not to
splash the solvent on the plate. The level of solvent must be below the pencil line. Cover
the beaker with a watch glass. The solvent will rise up through the stationary phase on the
plate. When the solvent has risen to 1-2 cm from the top of the plate, remove the plate, and
draw a light pencil line across the plate, at the level to which the solvent rose. Allow the
solvent to evaporate (waving the plate in the air will speed this up), and then look at the
plate under the UV light. Circle all of the spots.
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Fall 2011
Lab package
TLC Plate
TLC Developing Chamber
Pencil line 1 cm
from the end
Watch Glass
400 mL Beaker
TLC plate
Folded piece of
11 cm Filter paper
Level of solvent below
line of spots
“Tic marks”
A developed plate may look like this:
Y
X
You will identify the components of your unknown tablet by comparing the amounts the
components traveled up the plate with the amounts the standards traveled. These amounts
are reported as Rf (retention factor) values.
X
Distance the spot traveled
Rf = --- = -----------------------------------Y Distance the solvent traveled
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Lab package
Measure the distance a spot moves from the center of the spot. Separate Rf values are
calculated for each of the spots. Since the spots for the materials in the samples and in the
standards are different sizes and shapes, they may have slightly different Rf values.
Cleaning Up
When you are finished with the experiment, pour the TLC solvent in the “Recovered TLC
Solvent” container. The filter paper may be thrown away in the trash can. Used spotting
capillaries should be placed in the “Clean Broken Glass” container. Your acetone solutions
you used to spot with may be flushed down the sink with lots of water.
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CH342
Fall 2011
Lab package
Report format for Identification of the Unknown Compound by Thin Layer Chromatography
1.
Title Page (Attach a separate Title page to your report)
a.
b.
c.
d.
A short descriptive title of the lab exercise.
Dates the experiment was performed.
Course and section numbers.
Name(s)
2.
Body of the report (start a new page)
a.
Unknown compound number _____________
b.
Calculate Rf values (Show your work below) of each of the spots on your TLC plate
(Attach TLC plate to this report).
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3.
Questions
(a)
What is the identity of your unknown solid? Explicitly explain your choice using the
data you acquired.
(b)
If your unknown compound and more than one of the possible unknowns produce
similar Rf values when a 1:1 mixture of ethyl acetate and hexane is used to develop your TLC
plate, how could you modify the TLC experiment so you can determine which one was your
unknown? Explain your reasoning.
(c)
Is it possible to have Rf greater than 1 for a compound? Justify your choice.
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CH342
Fall 2011
Lab package
Report format for Purification of an Unknown Compound by Recrystallization
1.
Title Page (Attach a separate Title page to your report)
A short descriptive title of the lab exercise.
Dates the experiment was performed.
Course and section numbers.
Name(s)
2.
Body of the report
Unknown compound number ________________
Results of solubility tests in the different solvents. Summarize the results in a neat table.
Solvent
Solubility Result
Best recrystallization solvent found – explain
Weight of compound used for recrystallization __________________________
Melting point range of unknown before recrystallization. ___________________
Weight of recrystallized unknown compound ____________________________
Melting point range of recrystallized unknown compound __________________
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Fall 2011
Lab package
Calculate Rf value for all spots appeared on your TLC plate under UV light (Attach your TLC
plate to your lab report)
Calculate the percent recovery of the unknown. Show your work.
3. Questions
(a)
What is the identity of your unknown solid? Explicitly explain your choice using the
data you acquired (mp, TLC etc)
(b)
How do you know if the compound you recrystallized is pure? Explain.
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CH342
Fall 2011
Lab package
Report format for Fractional Distillation
1.
Title Page (Attach a separate Title page to your report)
A short descriptive title of the lab exercise.
Course and section numbers.
Dates the experiment was performed.
Name(s)
2.
Body of the report
You will receive your GC results either in the lab, or you can pick them up from your
instructor later. We have a thermal conductivity (TC) detector on our GC. Use the correction
factor for the TC detector to convert the peak areas to relative masses. Calculate the
percentage by mass of cyclohexane and toluene in each fraction. Plot the component masses
for each fraction on the y-axis as a function of the boiling temperature, using the midpoints
of the appropriate boiling ranges on the x-axis: use different symbols for the different
components. Draw a smooth curve connecting the points for cyclohexane, and another one
for toluene: do not merely “connect the dots.” Turn in your gas chromatograms with your
report.
3.
Questions on page 84
Exercises 1
Exercise 2
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Fractional Distillation Apparatus
Water Out (to sink!)
Water In
Rubber Band
Thermowell
Transformer
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CH342
Fall 2011
Lab package
Report Format for Preparations of Synthetic Banana Oil
1. Title Page (Attach a separate Title page to your report)
a.
b.
c.
d.
A short descriptive title of the lab exercise.
Course and section numbers.
Dates the experiment was performed.
Name(s)
2. Body of the report
a. Observations made during the reaction, and their meanings, if possible.
b. Weight of product isolated _____________________________
c. Boiling point range of product __________________________
d. Calculations of grams and moles of reactants. Show your work.
e. Calculations of theoretical and percent yields. Show your work.
f.
List your GC results in a tabular manner.
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Lab package
Peak#
RT
Area
3. Exercises on page 78
Exercises 2
Exercise 4
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% Area
CH342
Fall 2011
Lab package
Banana Oil Gas Chromatogram
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Lab package
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Fall 2011
Lab package
Report Format for Dehydration of Methylcyclohexanols
Only collect 1 fraction of distillate, not two!
1.
Title Page (Attach a separate Title page to your report)
A descriptive title with between 15-25 words.
Course and section numbers.
Dates the experiment was performed.
Names.
2.
Body of the report
Observations made during the reaction, and their meanings, if possible.
Weight of product isolated ________________________________
Boiling point range of product _____________________________
Calculations of grams and moles of reactants. Show your work.
Calculations of theoretical and percent yields of total methylcyclohexenes. Show your work.
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Lab package
List your GC results.
Your instructor will give you copy of IR and NMR of methylcyclohexanol and dehydration
product(s) of methylcyclohexanol. Label all significant peaks on the IR and NMR spectra and
attach the spectra to the report. Using IR and NMR result interpret success of your
dehydration experiment carried out in the lab.
3.
Questions on page 197
Exercises 2
Exercises 3
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CH342
Fall 2011
Lab package
Oxidation of an Unknown Alcohol with Jones Reagent in Aqueous Media and on Silica Gel
Support
In this lab you will oxidize isoborneol using two different methods and compare the results.
These two methods are (a) classical Jones oxidation method and (b) a method developed by
Dr. Mohammed Ali and his students in this department that utilizes silica gel supported Jones
reagent.
A. Preparation of Silica Gel Supported Jones Reagent.
Weigh 4.0 gram of silica gel in a 50 mL round bottom flask. Add 1.5 mL of chromic acid (8M)
to the flask drop by drop with stirring (use magnetic stirrer) using a syringe. Continue stirring
until a free flowing orange solid is obtained. Your silica gel supported chromic acid is now
ready for next step.
B. Oxidation of an Unknown Alcohol with Jones Reagent in Acetone.
Note: Jones reagent and methylene chloride are toxic. Follow safety procedure outlined by
the instructor.
Weigh 1.5g of your unknown alcohol in a 250 mL Erlenmeyer flask. Add 50 mL of acetone to
the flask and stir the content of the flask until solid dissolved. Add Jones reagent (8M) drop
by drop with stirring until the characteristic orange color of the Jones reagent persist for
several minutes (will require 3-4 mL of Jones reagent). Decant the acetone layer into
another Erlenmeyer flask and rinse the green residue of the original flask with about 5 mL of
acetone. Add the rinse to the acetone decant. If the color of the Jones reagent is visible in
the acetone solution, add methanol drop by drop with stirring until the orange color
disappear. Transfer the content of the flask into a 100 mL round bottom flask and remove
the acetone using a rotary evaporator. Dissolve the residue in the flask in 10 mL of
methylene chloride and transfer the solution into a 125 mL separatory funnel. Rinse the
round bottom flask with a small amount of methylene chloride and add the rinse to the
separatory funnel. Add 10 mL of a dilute sodium bicarbonate solution to the separatory
funnel, stopper, and shake the funnel for a minute with periodically venting the pressure.
Set the funnel on an iron ring and wait until the two layers separates in the funnel. Drain
the bottom methylene chloride layer into an Erlenmeyer flask, save it and then discard the
top aqueous layer. Return the methylene chloride solution back into the separatory funnel
and shake it with a 10 mL of brine (saturated aqueous NaCl solution). Drain the bottom layer
into a dry Erlenmeyer flask and add 2-3 spatula full of anhydrous sodium sulfate drying
agent. Stopper the flask and wait for five minutes. Filter the solution through a funnel with a
cotton plug. Rinse the drying agent with small amount of methylene chloride and add the
rinse to the funnel. Transfer the filtrate into a 100 mL round bottom flask and remove the
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solvent using rotary evaporator. Determine the yield of the crude product. Determine purity
of the crude product by TLC.
C.
Oxidation of an Unknown Alcohol with Jones Reagent supported on silica gel.
Weigh 5.0 g of silica gel supported Jones reagent (0.4 mL of Jones reagent/g of silica
gel) in a 125 mL Erlenmeyer flask. Add 20 mL of methylene chloride to the flask. Gently stir
the content of the flask using a magnetic stirrer. Dissolve 1.5g of your unknown alcohol in
about 5 mL of methylene chloride in a separate flask and add this solution to the Erlenmeyer
flask containing the silica gel supported Jones reagent with stirring. Monitor the reaction by
TLC. After the reaction is over, suction filter the reaction mixture and wash the solid with
about 60 mL of methylene chloride. Transfer the methylene chloride solution into a 100 mL
round bottom flask and remove the solvent using rotary evaporator. Weigh the product and
determine the yield of the crude product. Determine purity of the crude product by TLC.
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Lab package
Oxidation of alcohol lab report
Names _______________________
______________________________
Date of Expt. ____________
Section ___________
Data Table
Procedure
Amounts of
the
Alcohol used
(g)
Amounts of # of mmoles Product Yield %
Jones
of
(mg)
Recovery
Reagent
Jones
used (mL)
reagent used
B
C
Questions
1.
Which of the methods (B or C) is easier to carry out? Why?
2.
Which method (B or C) produced higher yield? Suggest where loses might have
occurred in the low yielding method.
3.
Which of the two methods (B or C) has less potential to expose the person
carrying out Jones oxidation reaction to the harmful reagents? Justify your answer.
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4.
Which of the two procedures will you apply for alcohol oxidation in general? Why?
5.
Collect IR spectra of your product from both procedures. Assign the significant peaks
on the NMR (provided) and IR spectra and attach them to your lab report.
6. Was the oxidation of unknown alcohol complete in both the procedures? Justify your
answer in terms of spectral data.
7. Suggest identity of your starting unknown alcohol using NMR data provided. Justify your
choice.
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