CH342
Fall 2011
Lab package
Sample Theoretical and Percent Yield calculations:
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-2-butanol, 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-2-butanol x 0.805 g 2-methyl-2-butanol/niL = 8.05 g 2-methyl-2-butanol. 8.05 g 2-methyl-2-butanol 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 2-methyl-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-2-methylbutane is 106.59. So, 0.0913 moles of 2-chloro-2-methylbutane x 106.59 g 2-chloro-2-methylbutanelmole =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%.
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
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 ______
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.
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 short-wave 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.
TLC Plate TLC Developing Chamber
A developed plate may look like this:
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
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.
Report format for Identification of the Unknown Compound by Thin Layer Chromatography
1. Title Page (Attach a separate Title page to your report)
a. A short descriptive title of the lab exercise.
b. Dates the experiment was performed.
c. Course and section numbers.
d. 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).
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.
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 ResultBest 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 ______
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.
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
Fractional Distillation Apparatus
Report Format for Preparations of Synthetic Banana Oil
1. Title Page (Attach a separate Title page to your report)
a. A short descriptive title of the lab exercise.
b. Course and section numbers.
c. Dates the experiment was performed.
d. 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.
Peak# / RT / Area / % Area3. Exercises on page 78
Exercises 2
Exercise 4
Banana Oil Gas Chromatogram
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.
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
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.