CHEM 237

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Which of the following is true of lab report due dates and the submission location?

-Due dates for lab reports are found on the syllabus. -Lab reports are to be placed in one of the organic labs report cabinets in the slot labelled with your TA\’s name on it.

Which of the following statements are examples of academic misconduct?

-Observing your lab partner copying answers or duplicating lab reports and keeping this action to yourself. -Attempting to receive credit for work performed by another, including papers obtained fully or in part from individuals or other sources. -Acquiring answers for any assigned work from any unauthorized source.

Which of the following are true statements which apply when using weigh boats in laboratory?

-In some cases, the weigh boat will be use by all students -The weigh boat must be tared before adding new material. -A paper towel should not be used to transfer product out of a weigh boat. – The balances in lab can be zeroed out with a weigh boat on the balance. -Plastic weigh boats can help prevent spillage when weighing liquids into a beaker.

Label the following statements as true or false:
1. If a student is asked to weigh out 3.0 g of a material, anything between 2.8 g and around 3.1 g will work fine.
2. If a student is asked for an arbitrary volume of 10 mL, then they must measure to precisely 10 mL.
3. For an ice bath, only use ice alone to assist in an even cooling and temperature transfer.
4. When assembling your apparatus, always start from the bottom up when using clamps.
5. Never grease the joints on common glassware setups.

1. T 2. F 3. F 4. T 5. F

Label the following statements as true or false.
1. The term reflux means heating a liquid to boiling and condensing the vapors back into the flask.
2. For the condenser, the bottom tube should be connected to the water source, the upper tube placed into the drain.
3. Regardless of the setup of the reflux apparatus, if liquid is circulated through a condenser, the cold water (inlet) should be directed at the top first.
4. One should allow the apparatus to completely cool before disassembling.
5. One should never use boiling chips to moderate reflux and prevent bumping.

1. T 2.T 3.F 4.T 5.F

How can a student know how much drying agent to use?

If the drying agent swirls, the student has added enough. If all of the drying agent stays clumped together, the student needs to add a little more drying agent to the sample.

Label the following statements as true or false.
1. If a student needs to heat things over 100 °C, then one should use a heating mantle.
2.Magnetic stirrers provide sufficient agitation to prevent bumping.
3. Heating mantles should be plugged directly into an alternating current outlet.
4. Never drop a magnetic stir bar into a flask. Instead, tip the flask sideways and slide the stir bar in.
5. For maximum agitation potential, use stir bars and boiling chips together.

1.T 2.T 3.F 4.T 5.F

When keeping a laboraory notebook, a student should always:

-mark out any unused portion of the page to indicate the conclusion of the day\’s work if there is no additional work to be done with the experiment. -write on the numbered, duplicated notebook pages that are included in the back of the lab manual.

Consider the reaction of 3.9 g cyclohexanol and an acid catalyst to yield 2.8 g cyclohexene. The molar mass of cyclohexanol is 100.16 g/mol and the molar mass of cyclohexene is 82.14 g/mol. Calculate the theoretical yield.

3.2 g

Consider the reaction of 3.0 g cyclohexanol and an acid catalyst to yield 2.0 g cyclohexene. The molar mass of cyclohexanol is 100.16 g/mol and the molar mass of cyclohexene is 82.14 g/mol. Calculate the percent yield.

81%

Label the following statements as true or false:
1. No sandals or other open toed shoes allowed.
2. Shorts and skirts, as long as they are below the knee, are acceptable for laboratory.
3. You will be required to wear long pants in the laboratory at all times.
4. Sandals and open toed shoes are permitted as long as you wear socks underneath.
5. Long unrestrained hair is not permitted.
6. Wear enclosed safety goggles at all times in the lab.
7. Safety glasses are allowed in place of goggles if you do not wear contacts.
8. Loose-fitting or baggy clothing is not allowed in the laboratory.

1. T 2. F 3. T 4. T 5. T 6. T 7. F 8. T

Which of the following are appropriate attire for the chemistry laboratory?

-enclose safety goggles -nitrile resistant gloves

In the laboratory, what should a student be able to locate at all times?

-fire extinguishers -eyewash stations -safety shower -laboratory exits

What situations should students report to their Teaching Assistant immediately?

-if there is a fire in the laboratory -if there is a chemical spill

What safety rules apply to the organic chemistry laboratory?

-Keep all backpacks and coats off the floor and out of the aisles. -Follow the experimental procedures given. No unauthorized experiments. -Wear proper clothing at all times. -Do not conduct any experimental procedures unless the Teaching Assistant is present.

If a student spills a chemical on their skin or clothing, what should they do?

-Inform their Teaching Assistant immediately. -Wash with soap and water immediately.

At the end of an experiment, a student has an unused portion of reagent. Where should he or she place it?

– See if anyone else doing the experiment needs some of the reagent. – In the properly marked waste conainer

What should a student do if there is a fire in the laboratory?

Do not panic, evaluate the situation, and then alert your TA for help.

Match the type of fire with the method used to extinguish it.
1. Small fire contained completely with a beaker.
2. Fire confined to small portion of clothing.
3. The entire room is on fire.
4. A large portion of your clothes is on fire.

1. Cover the flame with a watch glass or hard-back book. 2. Pat the fire out. 3. Sound the fire alarm and evacuate the building. 4. Use the safety shower or fire blanket.

What does the term CARCINOGEN mean?

A substance or agent capable of causing or producing cancer in mammals.

During Thin Layer Chromatography, what method is typically used to apply the dilute sample of solution to a TLC plate?

a thin glass spotter or capillary tube

During the developing of a TLC plate, it is common to place a cover on the chromatography chamber and have a piece of moist filter paper line the walls of the TLC chamber. Why is the moist filter paper in the TLC chamber of importance during thin-layer chromatography?

– to prevent evaporation from the TLC plate during development -To ensure that the air in the chamber is saturated with solvent vapor.

Label the following statements concerning TLC as true or false.
1. Use a pencil or pen to mark the position of a spot on the TLC plate.
2. Spot the plate on the dull, not shiny side of the plate.
3. Only touch the edges of the plate.
4. Mark the plate after applying the sample.
5. Spots should be 1 to 2 mm in diameter.

1. F 2. T 3. T 4. F 5. T

The retention factor, or Rf, is a number that describes the position of a spot on a chromatography plate relative to the position of the solvent on the chromatography plate. What are the minimum and maximum values of Rf?

0 and 1.

The image below shows thin-layer chromatography results for two samples, A and B. Calculate the Rf values for both samples. Distances from the origin to the center of each sample and the distance from the origin to the solvent front have been provided.
Distance to center of sample A= 2.8 cm
Distance to center of sample B= 4.2 cm
Distance from origin to solvent front= 6.8 cm

0.4,0.6

List the 7 procedural steps, from start to finish, that are required to form a thin layer chromatographic separation.

1. Add just enough developing solvent to cover the bottom 3 mm of the TLC chamber. Cover with a watch glass. 2. Make a pencil mark on the TLC plate 10 mm from the bottom. 3. Use a capillary to deliver a 2 mm diameter spot onto the pencil mark. 4. Stand the TLC plate upright in the chamber, and replace the lid. 5. Remove the TLC plate when solvent is near the top of the plate and mark the solvent front with a pencil before the TLC plate dries. 6. Mark the outline of the spots on the plate with a pencil. Unless the spots are colored, some visualization method will be needed. 7. Measure the distance that the spot and the solvent have moved.

What are true statements which apply to TLC?

-The solvent level should be below the spots. -Do not allow the edges of the plate to touch the filter paper. -Do not allow the solvent front to get 5 to 10 mm from the top of the plate. -When the solvent front has reached the correct height, remove from the chamber and immediately draw a line at the new solvent front. -TLC data is interpreted in terms of Rf values.

Label the following statements as true or false.
1. Rf is dependent on polarity.
2. Polar compounds will have higher Rf values than nonpolar compounds under the same developing conditions.
3.Rf values should be kept in the range of 0.2 to 0.8 for the most effective separation when more than one compound is present in the sample.
4. The less polar the solvent, the higher the Rf values.

1. T 2. F 3.T 4.T

Label the following statements as either true or false:
1. The distance the spot moved is where the spot started to where it ended up.
2. The Rf value is defined as the ratio between the distance the spot moved and the distance the solvent moved.
3. Rf is not depenent on polarity.
4. The distance the solvent moved is where the spot started to where the solvent front ended up.
5. Polar compounds will have higher Rf values than nonpolar compounds uner the same developing conditions.

1.T 2.T 3.F 4.T 5.F

How would the melting point range of a pure organic material be changed if there was a tiny shard of broken glass inside the melting point capillary?

The melting range would not be affected.

What is a eutectic?

The composition of a mixture of 2 components that generates the lowest possible melting point.

List the 7 procedural steps that are required to perform an accurate melting point determination.

1. Press the open end of a capillary tube into the solid sample. 2. Invert the tube and tap gently to move the solid to the bottom of the capillary. 3. Place the loaded tube into the hole inthe melting point apparatus, and heat at 10 degrees per minute. 4. Observe the material through the complete melting process to get a rough estimate of the melting range. 5. Turn off and allow to cool by 15 degrees. 6. Replace the existing tube with a new sample. 7. Heat at 2 degrees/minute through the expected range.

Why is it good practice to perform a mixed melting point determination at two different ratios of unknown to known materials in the melting point capillary?

Because it is possible that one particular combination of materials generates a eutectic.

Which of the following statements about melting point determination are true?

-The melting point is a physical measure of the forces holding the material into its crystal lattice. -The lower limit of the melting temperature range occurs when the first crystal starts to melt. -The upper limit of the melting temperature range occurs when the last remaining crystal melts.

During a melting point determination, it is normal to first take a rapid rough measurement followed by a slower more accurate measurement. Why is it important to allow the Mel-Temp to cool 15°C before placing the second capillary tube in, and to set the voltage generate 1°-2°C temperature increase per minute?

A rapid temperature increase will give a melting point range that is too high.

When comparing melting temperature ranges of pure and impure samples, which of the following statements describes the melting temperature range of an impure sample? Select all answers that apply.

The melting temperature range of an impure sample is lower than that of a pure sample. The melting temperature range of a pure sample is narrower than that of an impure sample.

Mixture melting point determination, solubility tests, and thin layer chromatography can be used to assess the purity and identity of a substance. Drag and drop each of the chemical wastes generated in this reaction into the appropriate container.
1. used melting point capillaries
2. contaminated paper towels
3. sodium bicarbonate solution
4. TLC solvent

1. broken glass 2. solid waste 3. aqueous waste 4. non-chlorinated organic waste

There are four major methods of purification in the chemistry laboratory. Which of the following techniques are included in the four most common methods for separation and purification?

-distillation -chromatography -extraction

When is recrystallization not a suitable method to purify an organic material?

When the organic material is not a solid.

Which is less soluble in hot water, a compound with a single benzylic ring(Salicylic acid) or a compound wih two rings (2-naphthol)?

2-naphthol

Which of the following are requirements for a suitable solvent when performing recrystallization?

-The solvent should not dissolve the compound when cold. -The solvent should either dissolve the impurities at all temperatures or not at all.

During the recrystallization of a solid, the sample is dissolved in hot solvent then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. What is the purpose of the initial hot vacuum filtration in the recrystallization process?

To remove insoluble solid impurities.

To remove insoluble solid impurities.

During the recrystallization of a solid, the sample is dissolved in hot solvent then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. What effect will result if the filtrate solution is cooled too rapidly?

Small impure crystals will form.

Recrystallization is a common laboratory method to purify solids by dissolving them in hot solvent, filtering while hot, then allowing the filtrate to cool so that crystals form. Use the pop-up menus to label the following statements about the practical aspects of recrystallization as either True or False.
1. Use clamps to secure the filter flask to avoid tipping and unnecessary exposure to hot liquids or the solute.
2. Recrystallization requires the material that is to be purified be a solid.
3. For hot vacuum filtration, the filter paper should be completely dry when pouring the hot solution into the Buchner funnel to filter.
4. Recrystallization is the process of dissolving a solid material into a suitable solvent or mixture of solvents and allowing the material to crystallize from this solution.
5. For recrystallization, rapid cooling gives the best crystals.

1. T 2. T 3. F 4. T 5. F

The solubility of acetanilide is 18.5 g in 100 mL of methanol at 0 °C, and 59.2 g in 100 mL of methanol at 60 °C. What is the maximum percent recovery that can be achieved for the recrystallization of acetanilide from methanol?

68.75%

A student was given a sample of crude acetanilide to recrystallize. The initial mass of the the crude acetanilide was 166 mg. The mass after recrystallization was 125 mg. Calculate the percent recovery from recrystallization.

75.3%

List the procedural steps, from start to finish, that are required in the recrystallization of acetanilide.

1. Place the finely divided mixture and a boiling chip into an Erlenmeyer flask on a steam bath. 2. Add the minimum amount of hot water to dissolve the solid. 3. Rapidly filter the hot solution through a pre-warmed funnel. 4. Wash the filter with hot solvent and transfer the filtrate to a clean flask. 5. Allow the filtrate to cool slowly, then cool in an ice bath to form precipitation. 6. Vacuum filter the cold suspension. 7. Air dry the purified solid on the filter.

Acetanilide was recrystallized from the minimum amount of hot water, and collected by vacuum filtration. Identify where the waste generated by this process should go.
1. filtrate
2. filter paper
3. rinse acetone
4. melting point capillary

1. aqueous waste 2. solid waste 3. non-chlorinated organic waste 4. broken glass

During the recrystallization of an impure solid sample of acetanilide, the sample is dissolved in hot water then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. Which of the following actions will increase the percent recovery of the acetanide solute?

After the first filtration, place the solution an ice-water bath for about 10 minutes.

During the recrystallization of an impure solid sample of acetanilide, the sample is dissolved in hot water then filtered while hot. The filtrate is allowed to cool and the mixture is filtered a second time. What should a student do if they observe an oil forming as the solution cools?

-Add a small amount of additional water to the flask containing the oil. -Once the oil has dissolved, allow the solution to cool slowly. -Reheat the solution gently until the oil dissolves.

The gauche conformation of butane occurs when the dihedral angle between the C1-C2 bond and the C3-C4 bond is 60°. There is steric strain in the molecule because of the proximity of the two methyl groups. Would the magnitude of this steric strain increase or decrease if the dihedral angle was increased from 60° to 65°?

The magnitude of steric strain will decrease because the groups are moving further apart.

The gauche conformation of butane occurs when the dihedral angle between the C1-C2 bond and the C3-C4 bond is 60°. There is steric strain in the molecule because of the proximity of the two methyl groups. Would the steric strain in this molecule increase or decrease if the C1-C2-C3 bond angle (and the C2-C3-C4 bond angle) was increased to more than 109.5° ?

Steric strain will decrease because groups are moving further apart.

The gauche conformation of butane occurs when the dihedral angle between the C1-C2 bond and the C3-C4 bond is 60°. There is steric strain in the molecule because of the proximity of the two methyl groups. When you consider that E(strain) = E(stretch) E(angle) E(torsion) E(steric), would E(torsion) increase or decrease when the dihedral angle of gauche butane is increased from 60° to 65° ?

Torsional strain increases.

Infrared spectra are recorded using an ATR detector. What does ATR stand for?

Attenuated Total Reflectance

In which of the following ways is the use of an infrared spectrophotometer fitted with an ATR sample advantageous over a beam-through-sample spectrophotometer? Select all answers that apply.

-The ATR crystal is not degraded by the presence of water. The same ATR sample holder may be used for liquid samples and solid samples.

What region of an infrared spectrum is most useful for distinguishing between isomers that contain the same functional group?

1400-400 cm-1

The infrared spectrum displays the wavelengths at which specific functional groups absorb energy. Match the functional group to the region of the spectrum that it is most likely to absorb energy.
1. O-H alcohol
2. C=O aldehyde
3. C=C alkene

1. 4000-3000 cm-1 2. 1800-1640 cm-1 3. 1600 cm-1

Which of the following statements about IR is not true?

Infrared spectroscopy can be used ot analyze almost any kind of sample.

How are molecules ranked in terms of their carbonyl stretching frequency in the infared spectrum?

The more carbons a molecule has, the greater its carbonyl stretching frequency.

What error is induced if the bulb of the thermometer, or the thermocouple, is too high in the distillation apparatus?

The recorded boiling point will be lower than actual because the bulb is not exposed to the hot vapor.

A mixture of hexane and octane were separated by a simple distillation and then tested for purity using gas chromatography. Identify where the waste generated by this process should go.
1. used kimwipe
2. hexane
3. octane
4. pasteur pipet
5. rinse acetone

1. solid waste 2,3. non-chlorinated organic waste 4. pasteur pipet 5. rinse acetone

Which of the following statements about the collection of a GC trace is true?

-The staitonary phase is a very high-boiling liquid absorbed onto fire brick. -The amount of sample detecte is proportional to the peak area.

Which of the following statements describe why moisture must be excluded from any sample injected into the G.C. Select all answers that apply.

-Water is very slow to elute from the column. -Water contains dissolved salts that can degrade the column.

Label the following statements as either true or false in relation to theoretical plates in a GC column.
1. The rate of heating affects the number of theoretical plates in the column.
4. Increasing the length of the column and packing the column with glass beads or rings are methods that produce more theoretical plates.
5. Rapid heating can drive heated vapor up the column, preventing the formation of an equilibrium that allows the lower boiling component to separate. As a result, this will increase the number of theoretical plates and increase the separation.

1. T 4. T 5. F

Which of the following statements are true concerning azeotropes?

-An unknown liquid that boils at a constan temperaure could be an azeotrope. -The boiling point of an azeotrope is lower than either of the pure substance it is composed of.

A mixture of two miscible volatile liquids is distilled. Which of the following statements are true concerning the boiling point of the distillate?

-The temperature range should start being recorded from when the liquid first starts to boil. -The temperature range should be recorded until right before the dramatic drop in temperaure. -If the range is within 2 degrees C, then the distillate can be considered pure.

Which of the following statements best describes density?

The ratio of a substance’s mass to its volume, measured in g/mL and also equivalent tog/cm3.

Does density always increase as molar mass increases?

No.

During a solvent extraction, a student lost track of which layer was the aqueous layer and which was the organic layer. What simple, non-destructive test could be used ot determine which layer was which?

Add a little distilled water ot see which layer the water adds to.

The solubility data table shows that both benzoic acid and benzocaine are significantly more soluble in ethanol than they are in water. Why is ethanol not a suitable solvent for the solvent extraction of benzoic acid and benzocaine from aqueous solution?

Ethanol is miscible in water.

During a solvent extraction between water and an immiscible solvent, a student has two layers in their separatory funnel and then shakes it. A single, milky liquid develops and no real sign of any layers are visible. What has occurred and what should the student do?

-an emulsion has formed. -First, add a small quantity of water. If that does not work, then add solvent.

To get effective mixing in a separatory funnel, then combined level of liquids should not exceed:

Higher than the widest part of the separatory funnel.

Label the following statements concerning the care and use of a separatory funnel as either true or false.
1. The first step in utilizing a separatory funnel is t omake sure the funnel stopcock is closed and then carefully pour the liquid to be extracted into the funnel.
2.The stopcock can be used to vent excess pressure if either of the liquids are warm to the touch and has a low boiling point.
3. Students should throw away the first layer and acid washes.
4.Hold your thumb firmly over the hole in the top of the funnel during shaking.
5. If one is going to re-extract the upper layer with another volume of liquid, the upper layer can be left in the separatory funnel and fresh solvent added to the funnel.

1. T 2. T 3.F 4. F 5. T

Eugenol, the essential oil found in cloves, is insoluble in water. The alcohol group in eugenol is dramatically more acidic than regular straight-chain alcohols. How could eugenol be separated from a mixture of other non-acidic molecules?

Dissolve the mixture in dichloromethane, shake with sodium hydroxide, collect the aqueous layer, and reacidify to force precipitation of the eugenol.

List the procedural steps, from start to finish, that are required to perform a chemically active solvent extraction of a three-component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolvved in dichloromethane.

1. Dissolve the solid three-component mixture in dichloromethane and place in a separatory funnel. 2. Add water to dissolve the brown emulsion between the layers. 3. Separate and collect the aqueous layer in a flask, then add base. 4. Place the dichloromethane layer back in the separatory funnel and extract it with 3 M NaOH. Allow layers to settle. 5. Add water to disolve the white gel-like emulsion. 6. Separate and collect the aqueous layer in a flask, and add acid. 7. Collect and dry the solids in both Erlenmeyer flasks by filtration.

Match the procedural step for its purpose for the chemically active solvent extraction of a three-component mixture composed of benzoic acid, benzocaine, and a neutral organic molecule all dissolved in dichloromethane.
1. To recover a mixture in case a stopcock leaks
2. To dissolve the emulsion due to the benzocaine salt exceeding its solubility.
3. To precipitate the benzocaine.
4. To handle the separatory funnel properly.

1. Place a beaker below the separatory funnel. 2. Add water to the separatory funnel that contains an acidified three-component mixture in dichloromethane. 3. Add base to the aqueous acidic layer mixture. 4. Cradle the inverted separatory funnel in the palm of the hand and hold the stopper between the fingers of the same hand.

A mixture of benzoic acid and benzocaine in dichloromethane solution were separated by solvent extraction first with sodium hydroxide, and then with hydrochloric acid. Which container should the chemical waste go to?

Aqueous Waste: sodium hydroxide solution, hydrochloric acid solution Solid Waste: used pH paper, benzoic acid Chlorinated Organic Waste: dichloromethane Non-Chlorinated Organic Waste: rinse acetone

How is it possible to separate two liquids with the exact same boiling point by gas chromatography (GC) when it cannot be done by fractional distillation?

The use of a polar GC column will separate the liquids based on differences in polar interactions and volatility.

The carrier gas in a GC separation is usually an inert gas such as nitrogen, helium, or argon, but can also be hydrogen. What are the pros and cons of using hydrogen as a carrier gas in a GC separation?

Pros: -Cheaper than helium -Can be generated at the GC instead of from gas tanks -Greater difference in mass b/w carrier gas and sample than nitrogen Cons: -Explosion hazard

A 0.7 mL mixture of pentanol and heptanol are separated and collected using preparative gas chromatography on a GC fitted with a polar column and a TCD detector. During the separation, why are the injection port and detector heated to a higher temperature than the column? Select all that apply.

-The wire in the thermal conductivity detector needs to be cooled by the eluent in order to register a signal. -A heated injector creates flash vaporization which allows separation at temperatures lower than the boiling point of the sample.

What effect would each of the following changes to the conditions of a GC separation have on the retention time for a sample.
1. The amount of sample injected is doubled.
2. The carrier gas flow is increased.
3. The column temperature is decreased.

1. Retention time increases. 2. Retention time decreases. 3. Retention time increases.

List the procedural steps, from start to finish, that are required to separate and collect a two-liquid mixture using preparative gas chromatography.

1. Collect a vial of unknown mixture. Record its number and letter. 2. Inject te mixture into the numbered Prep GC instrument that matches the number on your sample vial. 3. Slip a collection tube over the lower exit ort of the Prep GC just after the first fraction begins to elute. 4. Remove the collection tube when the first peak is almost finished. 5. Add another collection tube, and take a center cut for next fraction. 6. Transfer the samples to conical sample vials by connecting the vials to collecting tubes. 7. Centrifuge both vials to collect the samples. Cap the vials.

Match the procedural step to its purpose for the separation and collection of a two-component liquid mixture by preparative gas chromatography.

1. To avoid the introduction of a spurious peak into the GC trace … do not rinse the syringe with acetone, rinse it with sample instead. 2. To avoid dangerous vibration due to imbalance … vials are placed into the centrfuge in pairs, 180 degrees apart. 3. To avoid loss of sample … the detector fitted to the Prep GC is a TCD not a FID. 4. To preserve the purity of the sample because there is a lag between being detected and being eluted … wait for the second peak to be on the rise before beginning its collection.

A student is comparing two samples of crystalline organic solids. A TLC analysis shows a single spot for each sample and the co-spot with the same Rf value. Which of the following would provide the most conclusive evidence that the two samples are the same compound?

Perform a mixture melting point.

The active ingredients in an over the counter analgesic pill were separated by TLC on silica, using a solvent system of hexanes and ethyl acetate. Identify where the waste generated by this process should go.

Solid Waste: TLC plate Non-Chlorinated Organic Waste: hexane, ethyl acetate, rinse acetone Broken glass: spotting capillary

Label the following statements as either true or false.
1. Silica is toxic.
2. Hexane is flammable.
3. Ethyl acetate is flammable.
4. Acetone is flammable.
5. It is acceptable to handle TLC plates with bare hands.

1. F 2. T 3. T 4. T 5. F

An over the counter headache pill was crushed, extracted into ethanol / dichloromethane, and then analyzed by TLC on silica using ethyl acetate as an eluent. The pill was shown to contain: acetaminophen, aspirin, and ibuprofen.
Which is the least polar molecule?
Rank the molecules interms of their Rf (highest to lowest).

ibuprofen ibuprofen, aspirin, acetaminophen

The suggested procedure for spotting a sample on a TLC plate involves transferring a droplet of concentrated solution from a capillary onto the plate, allowing it to dry, then repeating the process over the existing spot. Why is it advised to spot multiple times? Select all answers that apply.

The higher compound concentration facilitates visualization. To achieve a high concentration of sample in a small spot.

In regard to the TLC plate you will be using in lab, which statement is FALSE?

The mobile phase is more polar than the stationary phase.

For a successful TLC experiment, you need to pay attention to the details. From the list of instructions and tips below, select the correct items.

-Use a micropipet or glass capillar to put a small amount of the sample solution on the starting line. -The solvent level in the chamber should be lower than the starting line where you spot the samples. -Use only a plain pencil to draw a starting line and mark the compounds\’ spots. Never use a pen or marker! -Cover the developing chamber with a watch glass. -Once the solvent front is getting close to the top of the plate, remove the plate and mark the solvent front. -Do not disturb the developing chamber, do not move it or carry around. -Do not permit the solvent to rise to the very top of the TLC plate.

Limonene and eugenol are natural products . Drag and drop the labels that describe these two essential oils into the appropriate boxes below their structures. Not all labels will be used.

Eugenol: acetyl coenzyme A precursor, acetogenin Limonene: isopentyl diphosphate precursor, terpene

Eugenol, the essential oil found in cloves, can be isolated by steam distillation because it is insoluble in water and has a much higher boiling point than water. Use data from the table to calculate the temperature at which a mixture of eugenol and water will boil.
What temperature will a mixture of eugenol and water boil at?

Slightly less than 100 degrees C.

What is the equation relating volume and mole fraction?

volume1 = (mole fraction1 x molar mass1)/(density1)

Under the reaction of limonen with excess Br2, what mecanism is in effect?

electrophilic addition

Both Br2 and HCl undergo electrophilic addition to alkenes. Why is Br2 used as a test for unsaturation instead of HCl?

The reaction with bromine can be followed because of a visible loss of color.

Which of the following is an indication of a positive test for the permanganate test (Baeyer\’s test)?

-A brown precipitate of manganese dioxide is formed. -The deep purple color of the reagent disappears.

List the procedural steps, from start to finish, that are required to perform an extraction of eugenol from a solution of clove oil in dichloromethane.

1. Place the dichloromethane solution of clove oil into a separatory funnel. 2. Add sodium hydroxide solution. Separate and collect the aqueous layer. 3. Acidify the aqueous layer with hydrochloric acid. 4. Extract the acidic solution into dichloromethane. Collect the organic layer. 5. Dry the dichloromethane solution over calcium chloride. 6. Remove the dichloromethane solvent by microdistillation. 7. Collect and weigh the residue of pure eugenol.

List the procedural steps, from start to finish, that are required to perform a steam distillation of limonene from orange peel.

1. Place citrus peel into a preweighed round bottom flask. 2. Add water until the level is past the midpoint of the flask. 3. Attach a ondenser and receiving flask with greased joints, then distill the mixture. 4. Add ethyl acetate to the receiving flask to extract the droplets of oil. 5. Separate the layers, and dry the organic layer over calcium chloride. 6. Filter off the drying agent, and then remove the ethyl acetate solvent by microdistillation. 7. Collect and weigh the residue of pure limonene.

Natural products can be extracted into organic solvent. For example, limonene can be extracted from the largely-aqueous distillate of a steam distillation of orange peel by ethyl acetate, and eugenol can be extracted from aqueous solution into dichloromethane. In the two solvent systems of water/ethyl acetate and water/dichloromethane, which are the top and which are the bottom layers?

water/ethyl acetate: top = ethyl acetate; bottom = water water/dichloromethane: top = water; bottom = dichloromethane

List the procedural steps, from start to finish, that are required to convert 2-naphthol and allyl bromide into allyl 2-naphthyl ether.

1. Fit a conical vial with a stirring vane and add 2-naphthol, allyl bromide, and benzyltriammonium chloride in dichloromethane. 2. Add sodium hydroxide to the reaction flask. 3. Cover the reaction vial and stir. 4. Periodically, stop the stirring, allow the layers to settle, and spot the organic layer on a TLC plate. 5. Remove the bottom layer and dry over calcium chloride. 6. Run the reaction solution through a silica chromatography column. 7. Evaporate the dichloromethane solvent to dryness.

Match the procedural step to its purpose by dragging each step in the written procedure for the reaction of 2-naphthol with allyl bromide and a phase transfer catalyst in strong base into the appropriate box.
1. The non-polar ether product can be separated from the polar by-products.
2. Dissolved water is removed from the reaction mixture.
3. To avoid making the reaction mix become a emulsion …
4. Dichloromethane solvent is highly volatile.
5. The time for the reaction to go to completion is kept under an hour.

1. The contents of the reaction flask were passed through a column of silica. 2. Enough calcium chloride to cover half the bottom of the flask was added. 3. The reaction was stirred at a moderate, not rapid, pace. 4. The reaction vial was stoppered before it was stirred. 5. Allyl bromide was used in excess.

The Williamson ether synthesis between 2-naphthol and allyl bromide in the presence of strong base and benzyltriphenylammonium chloride as a phase transfer catalyst in dichloromethane solution is known to proceed in reasonable yield. The need for a phase transfer catalyst would be removed if a polar aprotic solvent such as DMSO were used as a reaction solvent. Why is DMSO not used as a solvent for this reaction?

Because of risks associated with toxicity.

The Williamson ether synthesis between 2-naphthol and allyl bromide in the presence of strong base and benzyltriphenylammonium chloride as a phase transfer catalyst in dichloromethane solution is known to proceed in reasonable yield.
Why will the reaction fail to work if the solvent is switched to ethanol while retaining the same reactants, phase transfer catalyst, and base?

Because the base would deprotonate alcohol and create a second nucleophile.

In the reaction to produce allyl 2-naphthyl ether, 2-naphthol is first reacted with aqueous sodium hydroxide to make sodium 2-naphtholate, which then goes on to react with allyl bromide and benzyltributylammonium chloride phase transfer catalyst, with dichloromethane as a solvent. The boxes in the diagram represent the layers inside the reaction flask part-way to completion. Place the labels in the appropriate box. (If a molecule has significant solubility in both layers, it may be used more than once).

AQUEOUS LAYER: (top) -water -sodium 2-naphtholate -sodium hydroxide -benzyltributylammonium chloride ORGANIC LAYER: (bottom) -dichloromethane -allyl bromide -allyl naphthyl ether -benzyltributylammonium chloride

A Williamson ether synthesis between 2-naphthol and allyl bromide is performed in the presence of a phase transfer catalyst and strong base in dichloromethane solution. The reaction mix contains: unreacted allyl bromide, unreacted 2-naphthol, benzyltributylammonium chloride, allyl naphthyl ether, and dichloromethane. The reaction mix is passed through a silica gel mini column. What are the components of the mixture that elute from the column?

dichloromethane allyl naphthyl ether

Label the following as either true or false.
1. NaOH can cause severe damage to the skin and eyes
2. Lachrymators like allyl bromide are specifically dangerous because of their explosion hazard.
3. The primary risk associate with dichloromethane is its flammability.
4. Unused allyl bromide can be disposed of in the aqueous waste.
5. Gloves and goggles are not required when handling sodium hydroxide.

1. T 2. F 3. F 4. F 5. F

What is the relationship between substitution and carbocation stability?

The more substituted a carbocation, the more stable it is.

For SN1 solvolysis of t-butyl chloride, rank the solvents from fastest reaction to slowest reaction.

-water -formic acid -methaol -ethanol -acetone -acetic acid

1-chloro-1-phenylethane undergoes solvolysis in water by an SN1 mechanism to make 1-phenylethanol.
The reaction is followed with bromothymol blue indicator and an aliquot of sodium hydroxide base. Which of the following statements about the reaction are true?

Carbocations are stabilized by protic solvents like water. The first step is the slowest because a bond is being broken. The reaction can be followed because acid is produced as a product. The reaction follows first order kinetics because there is one reactant in the rate determining step.

List the procedural steps, from start to finish, that are required to convert 1-chloro-1-phenylethane into 1-phenylethanol via SN1 solvolysis in water.

1. Add a few drops of bromothymol blue to a stirred solution of ethanol and water. 2. Add sodium hydroxide solution from a burette. 3. Add alkyl halide and start the timer. 4. Record the time it takes for the solution to turn green. 5. Repeat the process of adding aliquots of measured base, annd recording the time taken for a color change. 6. Heat on a steam bath above 50 degrees Celsius for 20 minutes. 7. Titrate the contents of the flask against NaOH, and record the volume.

The slow step in the conversion of alcohol to an alkyl halide by an SN1 mechanism is the loss of water from the protonated alcohol to form the carbocation intermediate.
Rank the following molecules in terms of their rate of reaction, fastest at the top.

1. 1-methylcyclohexanol 2. cyclohexanol 3. 1-hexanol

In the presence of hydrochloric acid, 3,7-dimethyl-3-octanol is converted to 3-chloro-3,7-dimethyloctane via an SN1 mechanism. SN1 and E1 mechanisms are usually in competition with each other. Why, in this case, is the elimination product not observed?

The alkene formed by any E1 reaction would react with HCl to form the same product as the substitution reaction

List the procedural steps, from start to finish, that are required to convert of 3,7-dimethyl-3-octanol to 3-chloro-3,7-dimethyloctane using hydrochloric acid in an SN1 reaction.

1. Add concentrated hydrochloric acid to alcohol in an Erlenmeyer flask. 2. Add a stir bar and stir the solution for 20 minutes. 3. Occasionally rinse the sides of the flask with an aqueous layer. 4. Transfer the mixture to a test tube and remove the lower aqueous layer. 5. Wash the organic layer with saturated sodium chloride solution followed by sodium carbonate solution. 6. Dry the organic layer over sodium chloride. 7. Filter the dried organic material into a clean pre-weighed vial.

Match the procedural step to its purpose by dragging each step in the written procedure for the SN1 conversion of 3,7-dimethy-3-octanol to 3-chloro-3,7-dimethyloctane by hydrochloric acid, with characterization test with silver nitrate solution.
1. To make the polar impurities less soluble in the organic layer.
2. To test for free chloride ions; an indication of a tertiary/benzylic carbocation.
3. To gently neutralize the acidic reaction.
4. To exclude water from the product and push the equilibrium to the right.

1. The organic layer was shaken with saturated sodium chloride solution. 2. A few drops of silver nitrate solution were added to the organic product 3. The organic layer was shaken with sodium bicarbonate solution. 4. The reaction was performed in concentrated hydrochloric acid, in which the organic halide is not soluble.

In regards to the E2 mechanism, rank the leaving groups in order of increasing reaction rate.

R-F, R-Cl, R-Br, R-I

List the procedural steps, from start to finish, that are required to perform a dehydrohalogenation of 3-chloro-3,7-dimethyloctane by ethanolic potassium hydroxide. All steps must be used.

1. Add 3-chloro-3,7-dimethloctane and ethanolic potassium hydroxide to a roun-bottom flask containing boiling chips. 2. Attach a claisen head and an air condenser with greased joints. 3. Heat under reflux on a heating mantle for twenty minutes. 4. Cool, and pour the reaction contents into a test tube containing water. 5. Transfer the organic layer into another test tube and wash with water three times. 6. Dry the organic layer over calcium chloride in a sample vial. 7. ilter the product through a cotton plug into a pre-weighed vial.

In order to perform a bromine test on a compound, it must be treated with a dilute solution of bromine. Which of the followingresults will indicate the presence of an alkene.

The reddish color of the bromine will disappear.

Which of the following are commonly used oxidizing agents? Select all that apply.

chromic acid sodium dichromate

Compared to the dichromate oxidizing agents, hypochlorous acid (prepared from household bleach) is …

-safe -environmentally sound -inexpensive

Sodium hypochlorite and glacial acetic acid combine to make hypochlorous acid. Hypochlorous acid oxidizes cyclohexanol to cycylohexanone. At the end of te reaction, any excess hypochorous acid must be neutralized. How is the neutralization of HOCl accomplished?

Add sodium bisulfite, NaHSO3.

List the procedural steps, from start to finish, that are required to convert cyclohexanol to cyclohexanone.

1. Mix cycylohexanol and acetic acid in an Erlenmeyer flask 2. Add bleach dropwise into the flask. 3. Maintain the reaction temperature between 40 and 45 on a steam bath. 4. Remove unused bleach wih sodium bisulite solution. 5. Add drops of 6M NaOH until solution is pH 6. Place reaction in separatory funnel, extract with dichloromethane. 7. Dry the dichloromethane layer over potassium carbonate. 8. Decant from the potassium carbonate and collect by distillation.

Match the procedural step to its purpose by dragging each step in the written procedure for the oxidation of cyclohexanol to cyclohexanone into the appropriate box.
1. Generate the oxidizing agent.
2. Destroy the oxidizing agent.
3. Test for the presence of oxidizing agent.
4. Control the rate of reaction.
5. Dry the reaction produt.

1. Add bleach dropwise into a flask containing acetic acid. 2. Add sodium bisulfite solution. 3. Touch a drop of the reaction mix onto a piece of KI-starch paper. 4. Place the reaction flask in an ice-water bath. 5. Combine the organic layers over anhydrous potassium carbonate.

Cyclohexanol is converted to cyclohexanone by hypochlorous acid. Excess hypochlorous acid is removed by adding sodium bisulfite. The aqueous reaction mixture is then saturated with sodium chloride and placed in a separatory funnel with methylene chloride (dichloromethane). The boxes in the diagram represent the layers of the separatory funnel. Place the labels in the appropriate box.

AQUEOUS LAYER: (top) -water -sodium chloride ORGANIC LAYER: (bottom) -methylene chloride -cyclohexanone

Label the following statements as true or false.
1. Hypochlorous acid is an oxidizing agent.
2. Concentrated acid is corrosive.
3. Methylene chloride is flammable.
4. Methylene chloride is a probably human carcinogen.
5. Pipets that contain only water can be disposed of in the trash.

1. T 2. T 3. F 4. T 5. F

Cyclohexanol is oxidized by a mixture of sodium hypochlorite and acetic acid. The solution is treated with sodium bisulfite and sodium hydroxide, before the product is extracted into dichloromethane. The organic layer was dried over potassium carbonate, decanted, and the product was obtained when the solvent was evaporated.

aqueous waste/sink: aqueoous layer after extraction solid waste: potassium carbonate, potassium iodide/starch strip chlorinated organic waste: dichloromethane non-chlorinated organic waste: cyclohexanone product

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