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ACS ORGANIC CHEMISTRY EXAM 2025/
SPRING-SUMMER QUESTIONS AND ANSWERS
GRADED A+
Why should you vent the separatory funnel periodically when preforming an extraction involving organic solvents?
Mixing increases the evaporation of volatile organic solvents creating pressure in the closed space of a separatory funnel.
How much anhydrous magnesium sulfate is required to dry a diethyl ether solution after preforming extractions involving water?
Enough such that some powder remains free flowing in solution with swirling without clumping.
Why is sodium benzoate more soluble in water than benzoic acid?
Sodium benzoate is more soluble in water than benzoic acid because sodium benzoate has an ionic bond, while benzoic acid has a hydrogen bond. Ionic bonds are more soluble in water than hydrogen bond.
Why is biphenyl more soluble in diethyl ether than water?
Biphenyl is more soluble in diethyl ether than water, because biphenyl is a non- polar compound, which furthermore makes it insoluble in water. Diethyl ether on the other hand is non-polar as well, which allows biphenyl to dissolve in it.
What solvent (diethyl ether or water) would glucose (shown below) be most soluble in? Briefly explain why?
Glucose would be most soluble in water because of its polarity. Diethyl ether is non-polar compound while glucose is a polar compound. According to the "like dissolves like" principle, glucose is unable to dissolve in diethyl ether.
Which has a higher vapor pressure hexane or nonane?
hexane
Which should have a higher boiling point hexane or nonane?
nonane
Simple distillation is more effective when there is a __ difference between the boiling points of the two compounds.
large
During the beginning of the distillation experiment (either simple or distillation), what compound in the starting water/methanol mixture predominates in the distillate? Briefly explain why.
During the beginning of the distillation experiment, methanol predominates in the distillate, because it has a lower boiling point than water. The boiling point for methanol is 64.7°C, while water has a boiling point of 100°C.
As the distillation continues eventually the observed temperature of the vapor will approach but never exceed 100oC (assuming there is nothing wrong with the thermometer, no bubbles in the alcohol column, etc.). Why is 100oC the upper limit observable in the experiment?
100°C is the upper limit observable in the experiment, because water has a boiling point of 100°C, making it the least volatile substance used in the experiment.
What species if formed when benzoic acid reacts with NaOH(aq)?
*Can't put on here because the question includes an image- refer to lab manual for full question and answer.
What is the density of water at room temperature in g/mL? Give just the number and not the unit.
Which layer will be the ether layer in a separatory funnel containing diethyl ether and a saturated aqueous solution of NaCl?
the top layer
Outline a procedure for separating anthracene and 4-chloroaniline (shown below) using extraction and possibly acid/base chemistry.
Step 1: Add 10% HCl and ether to both of the compounds. (this will make an organic and an aqueous layer)
Step 2: Separate the organic and aqueous layer into different containers and label them
Step 3: Evaporate the solvent from the organic layer, and from there you will get a pure compound (anthracene)
Step 4: add %10 NaOH and ether to the aqueous layer
Step 5: Separate the aqueous and organic layer once again
Step 6: Evaporate the solvent from the organic layer, and from there you will get a pure compound (4-chloroaniline)
What size filter paper should be used with a Hirsch funnel?
10 mm
Which of the following will be most soluble in hot water?
Why does the addition of water to the hot ethanol solution of hydrocarbon help increase crystal growth? Hint: Which solvent is the hydrocarbon more soluble in?
Due to the fact that hydrocarbon is not soluble in water, the addition of water speeds up the crystallization process. We watched this happen as crystals instantaneously formed once water was added. The water itself, removes the hydrocarbon from the solution, in order to form the crystals.
Why does ethanol have to be added to the hot water/carboxylic acid mixture to get all of the solid carboxylic acid to dissolve?
The addition of ethanol to the mixture of hot water/carboxylic acid, has the same effect as adding water to the ethanol. Carboxylic acid is not soluble in ethanol, but is soluble in hydrocarbon. By adding ethanol to the mixture, it increases the solubility of the carboxylic acid.
What affect on the melting point might be observed if the crystals of carboxylic acid are still wet when measuring the melting point of the sample.
If the crystals of the carboxylic acid were still wet when measuring the melting point of the sample, the solvent would still be partially present. This presence would reduce the melting point of our compounds, furthermore altering our data. And it broadens the range of the melting point.
Why should the vial of hot solution be allowed to cool to room temperature slowly during crystallization rather than putting it in an ice bath to speed the process?
The vial of the hot solution should be allowed to cool to room temperature slowly in order to reduce the possibility of obtaining impurities within the crystals formed.
Which layer will be the organic layer during the aqueous tea dichloromethane extraction process?
bottom layer
Which layer will the caffeine preferentially dissolve in during the aqueous tea dichloromethane extraction process?
the dichloromethane layer
A solution is considered dry (i.e., devoid of water) when which of the following cases is true?
After treatment with an anhydrous salt, the salt clumps together significantly but also has several crystals that do not clump with any other crystal.
When evaporating solvent from a solution by gently blowing compressed air on it, why is it helpful to warm the solution?
Evaporating solvent removes heat energy from the solution and container, cooling it in the process and decreasing the vapor pressure of the liquid. Warming the solution counters this.
of these impurities would throw off the melting point that was found. In order to get our isolated caffeine to exhibit a melting point closer to the literal value of 238 °C, we could recrystallize the caffeine which would remove transferred impurities that might of been picked up during the extraction of the caffeine.
How much solid material is needed to make the spotting solutions in this experiment?
a very small amount, enough to barely cover the tip of your spatula
What should be used to mark the silica gel on the TLC plate?
a pencil with a soft tip to avoid gouging the thin layer of silica gel thus preventing the solvent from traveling up the plate
What is the Rf value for a spot that travels 2.1 cm on a TLC plate when developed and the solvent traveled 7.2 cm?
What solvent is used to clean NaCl plates used in IR spectroscopy?
dichloromethane
What solvent is used to clean the diamond crystal of the ATR module used for collecting IR spectra of solids?
isopropanol
Where did you observe the O-H and/or C=O peaks (depending on which compound you used) in the IR spectrum of the compound for which you acquired a spectrum?
The IR spectrum of the compound I acquired, benzoic acid, had a peak at 1675.80, indicating a C=O peak, based on the fact that C=O peaks between 1800 and 1650.
AD
Are these consistent with those seen in the reference spectra (located in Experiment 5 folder on Blackboard) for the same compound?
The C=O peak seen in my IR spectrum is consistent with the C=O peak of the benzoic acid reference spectra. Both spectrums have at peak at approximately
Which of the three compounds has a O-H group and how do the O-H peak locations in the IR spectra compare?
Of the three IR spectra, the benzyl alcohol IR spectrum has a peak at approximately 3300, indicating an O-H group. Neither benzoic acid nor benzaldehyde have O-H groups, for they do not have peak between 3200 and 3600.
During the washing/extraction portions of product isolation, which layer has a higher density?
organic layer
Where should the solid from the initial reaction mixture that should have ended up in the bottom of your centrifuge tube be disposed?
halogenated waste
What is the theoretical yield of butan-2-one (shown) if 0.30 mL of butan-2-ol is treated with TEMPO and an excess of of TCCA and is completely oxidized? Your answer should be in grams and give only the number. Your answer should have at least 2 significant digits (2nd decimal place). * goes from 74.12 g/mol & 0. g/mL to 72.11 g/mol
What are the products (if any) of a reaction between each of the following compounds and TEMPO/TCCA in dichloromethane?
*can't include this question on the quizlet because it requires the image with it- refer to your lab report
AD
If the IR spectrum of a reaction product contains a broad peak near 3300 cm-1, what else could be present in the sample other than an alcohol?
If the IR spectrum of a reaction product contains a broad peak near 3300 cm^-1, then there could be an indication of an Alkyne, such as C-H in the sp hybridization, or an Amine group, such as N-H.
What compound (ketone, carboxylic acid, or alcohol) best matches the following IR spectrum? Explain your reasoning.
*refer to spectrum on lab report. The IR spectrum best matches a ketone. The reason being that there is a broad peak at ~ 1700 cm, which indicates a C=O group which is found in ketones. Although there is a peak at 3000, which corresponds with a C-H group, it is not as broad as the one found at ~1700, therefore not making the IR spectrum that of a carboxylic acid.
If a small amount of carboxylic acid is produced in the oxidation reaction of a primary alcohol with the TEMPO/TCCA, why would you not likely observe it in the IR spectrum of the product mixture? Hint: What aqueous solutions are used to extract the organic layer during the product isolation portion of the experiment?
If a small amount of carboxylic acid is produced in the oxidation reaction of a primary alcohol with the TEMPO/TCCA, you would not likely observe it because during the experiment, the organic layer was extracted with sodium carbonate. The amount of carboxylic acid produced would have formed a sodium carboxylate salt
What is the stationary phase in the column used for this course?
polymethylphenylsiloxane
What is typically the mobile phase in gas chromatography?
Typically, the mobile phase in gas chromatography is the phase in which the gas phase is carried through the column. The gas phase must be carried by a non reactive element such as helium and nitrogen.
What affect is expected for retention times in a gas chromatography experiment if the temperature of the column is reduced?
If the temperature of the column is reduced, the retention time should increase since temperature and retention time have an inverse relationship.
If a significant clog in a 30 m capillary column is so severe that it has to be trimmed to 20 m, how will this affect its ability to effectively separate mixtures of compounds?
If a significant clog in a 30 m capillary column is so severe that it had to be trimmed to 20 m, it's ability to effectively separate mixtures of compounds will decrease.
Why is CH2Cl2 the first peak observed in the gas chromatograms for this experiment?
CH2Cl2 has the lowest boiling point, therefore it is the first peak observed in the gas chromatograms for this experiment.
If a student submitted a sample of water for GC analysis because they were confused about what was their organic layer and what was their aqueous layer, would a solvent peak be observed in the gas chromatogram of the sample assuming it was analyzed? Remember our gas chromatograph uses a FID.
FID is a flame ionization detector, therefore if the water is not burned by the oxygen and hydrogen flames, then it will be not be seen in the solvent peak of the gas chromatograph.
What is the limiting reagent in this reaction?
acetaminophen
What is the role of potassium carbonate in this reaction?
base
What is the role of 2-butanone in this reaction?
solvent
Propose a synthesis of the following compound. Hint: Use a SN2 reaction.
- can not include this question in the quizlet due to the fact that the reaction has to be drawn out. Refer to the lab report for the answer.
What role does water play in the reaction with t-BuCl? Choose all that apply.
nucleophile
solvent
base
What role does the added NaOH(aq) play in the reactions for this experiment?
reactant with HCl(aq) produced from the reaction
What color is bromophenol blue under acidic conditions?
yellow
How many mL is 300 μL?
0.300 mL
If 3 mL of 0.1 M tBuCl in acetone is mixed with 0.9 mL of 0.1 M of NaOH and 6.1 mL of water and it takes 360 seconds for the color of the added bromophenol blue indicator to change from blue to yellow, what does this indicate?
It took 360 s for the reaction to be 30% complete
How would doubling the concentration of t-BuCl affect the rate of the reaction? Why?
Doubling the concentration of t-BuCl would double the rate of the reaction due to the fact that SN1 reaction rates are dependent on substrate concentrations, which in this case the substrate would be t-BuCl
How would doubling the concentration of NaOH(aq) used in this experiment affect the rate of the reaction? Why?
Doubling the concentration of NaOH(aq) would have no effect on the rate of the reaction. This is because, as stated above, SN1 reactions depend on substrates, and NaOH(aq) is not a substrate.
What would happen to the rate of the reaction if 9 mL of 0.0333 M t-BuCl in acetone and 1 mL of water were combined and mixed instead of the 3 mL of 0.1 M t-BuCl in acetone and 7 mL of water mixture used in this experiment? Why? (Hint: In addition to being a nucleophile, what other role does water have in this reaction?)
