Ochem lab Midterm

A neutral compound will react with an acid

False

After adding water to your extraction you should violently shake the centrifuge tube.

False

The mechanisms shown in the lab manual occur using a cis-alkene. In this lab, some students will use a trans-alkene. Each mechanism will result in the same product(s) whether using the cis- or trans-alkene.

False

You know you added enough sodium sulfate to your product when the sodium sulfate gets clumpy

False

Hydrogen bonding is an example of an intermolecular force that occurs in molecules that contain a hydrogen atom bonded to an electronegative atom such as oxygen, nitrogen, or fluorine.

H bonding

After spotting your compound on your TLC plate, placing it in the TLC chamber, and allowing the solvent to reach 1 cm below the top of the plate, you should remove your TLC plate from the chamber and mark the solvent front with a pencil. Why do you need to mark the solvent front?

In order to properly calculate Rf values

When spotting your compound on the TLC plate, you don't want to add too much of your sample. What would happen to your plate if you add too much?

It will streak across the plate

The pka of a protonated cyclohexyl amine is 10.7. At a pH of 2, the amine is still primarily protonated.

True

When two miscible solvents come into contact, they do not separate into two layers.

True

Configurational isomers can not interconvert rapidly and can be separated from each other.

can not

Alkyl branches off of a parent chain are named by replacing the -ane ending with _______.

-yl

Question 40.5 / 1 pts If the bromination of a symmetrical, cis-alkene (like cis-2-butene shown in your lab manual) proceeded through a syn-addition, [ Select ] different product(s) would be formed. The product(s) would be [ Select ] .

1 meso compounds

Your reaction is refluxing when the solvent is boiling and visibly recondensing back into the flask upon contact with the cooler surface of the water condenser. The height of the condensation ring should be __________ way up the condenser.

1/4 to 1/2 of the

Mixed melting point is a technique used to determine the identity of an unknown solid. 10% of a(n) [ Select ] ["known", "unknown"] compound is added to a(n) [ Select ] ["unknown", "known"] sample. If the melting point of the unknown solid by itself matches the mixed melting point, there is strong support that the unknown solid and the known solid are the same.

10% Known unknown

If the bromination of a symmetrical, cis-alkene (like cis-2-butene shown in your lab manual) proceeded through a bromonium ion intermediate, [ Select ] different product(s) would be formed. The product(s) would be [ Select ]

2 a pair of enantiomers

The following statements refer to the reaction procedure. Use the lines next to each statement to put the statements in the proper order (1 = first, 8 = last) (4 pts). 3 Remove the bottom acidic layer and place in a labeled beaker containing 20 mL of water. [ Select ] ["7", "6", "5", "2", "1", "4", "8", "3"] Wash the product in the sep. funnel two more times with 2 mL 5% aqueous sodium carbonate and then repeat washings 2 more times with 2 mL DI water. [ Select ] ["2", "5", "4", "6", "1", "3", "7", "8"] Allow product to dry 5‐10 minutes. [ Select ] ["3", "2", "1", "6", "8", "4", "7", "5"] After the reflux period, remove the apparatus from the heating mantle and cool. [ Select ] ["7", "5", "8", "4", "2", "1", "6", "3"] Add 2 mL of water to the separatory funnel containing your product and invert to mix layers. [ Select ] ["4", "7", "8", "5", "1", "2", "3", "6"] Add anhydrous sodium sulfate to your product. [ Select ] ["2", "4", "7", "8", "1", "5", "3", "6"] Transfer the contents of the round bottom to a separatory funnel. [ Select ] ["5", "4", "1", "8", "7", "2", "3", "6"] Remove the bottom product layer into a clean labeled beaker. Remove the remaining aqueous layer from the separatory funnel.

3 6 8 1 4 7 2 5

If the bromination of a symmetrical, cis-alkene (like cis-2-butene shown in your lab manual) proceeded through a carbocation intermediate, 2 different product(s) would be formed. The product(s) would be a pair of enantiomers .

3 a pair of entiomers and a meso compound

Use the dropdown boxes to put the following intermolecular forces in order from weakest (1) to strongest (4). Ionic Dipole-dipole van der Waals (also known as induced dipole-dipole) Hydrogen Bonding

4213

The following statements refer to the procedure for extraction of pigments from a spinach leaf. Use the lines next to each statement to put the statements in the proper order (1 = first, 8 = last) Add 4mL water to the centrifuge tube. Swirl gently. Wash the organic layer twice with water. Add anhydrous sodium sulfate. Swirl. Cut or tear the spinach leaf into small pieces and place the pieces in a mortar. Add 2 mL cold acetone. Add 4mL hexane to the tube containing the spinach and acetone. Shake the centrifuge tube. After 10 min, transfer solution to a test tube. Add 2 mL hexane to centrifuge tube. Decant hexane into test tube. 8 Evaporate the solvent using a pipette to bubble air gently. Stop evaporating when you have ~0.5mL left. 5 Remove and discard the bottom aqueous layer with a Pasteur pipette. Grind the spinach until a dark green liquid has developed. Transfer the mixture to a centrifuge tube.

46137852

The pKa of cyclohexyl amine is 10.7. This means that at a pH of 10.7, cyclohexyl amine is

50% protonated and 50% neutral

The following statements refer to the procedure for recrystallization of your solid. Choose the correct number that aligns with the order of the procedure Allow the filtrate to cool. Once at room temperature, place the flask in an ice bath for 5 min. Add hot water to the Erlenmeyer flask containing your unknown solid. Swirl. Continue adding water while swirling. Keep flask hot by periodically placing it onto the hot plate. Obtain a solid unknown sample from the bench and record the unknown number in your notebook. Weigh out approximately 0.8 g of your unknown solid. Record the mass of how much you weigh out. Add solid to Erlenmeyer flask. Filter your sample using the Buchner funnel. Discard the insoluble impurity. Place a 250 mL beaker containing water on your hot plate. Heat until near boiling. Use the Hirsch funnel to filter your sample. Wash your crystals with a small amount of cold water.

6402537

Which of the TLC solvents below is most polar?

80:20 Ethyl acetate:hexane

Melting is an process. Melting points are to impurities . The presence of an impurity will the melting point and the melting point

Answer 1:endothermic Answer 2:very sensitive Answer 3:decrease Answer 4:!widen

A solid is dissolved in a hot recrystallization solvent. As the solution cools, the solubility of the solute decreases . As the crystals grow, the impurities are excluded . It is important that recrystallization takes place slowly or impurities may become trapped in the lattice of the solid.

Answer 1:solubility Answer 2:decreases Answer 3:excluded Answer 4:slowly

If a compound does not appear visible to the naked eye, they can be visualized if they absorb The plates we use are coated in a fluorescent chemical. When a plate is exposed to ultraviolet light , the compounds will appear as spots because they the light.

Answer 1:ultraviolet light Answer 2:fluorescent Answer 3:ultraviolet light Answer 4:dark Answer 5:absorb

In your reflux apparatus, two pieces of rubber tubing will be hooked to the water condenser (shown in the picture below). The flow of water will go IN the condenser at the spot labeled B and the water will flow OUT of the condenser at the spot labeled A .

B A

Select all of the techniques you will use to characterize your alkyl halide product.

Belstein test density boiling point

Match the intensive properties you will be measuring to characterize your liquid unknown with the name(s) of the equipment/instrument you will use to obtain each measurement

Density = balence and auto pipette boiling point Buchi

Neutral compounds (compounds with no acidic or basic functional groups) are soluble in ether.

True

Recrystallization is the purification technique you will use during this lab to remove impurities from your solid unknown.

Recrystallization

Good leaving groups are weak bases.

weak

To measure boiling point of your liquid, you will add your sample to a clean, dry boiling point tube. You should have approximately 1 cm of liquid in the tube. What do you need to do to the sample before placing it in the instrument to measure boiling point?

Take a clean melting point tube and place it open side down in the liquid.

Select all of the examples of good TLC techniques

The TLC chamber should be left closed when developing a plate Spots on the spotting line should be small Solvent level in the TLC chamber should be below the spotting line

What is the purpose of adding sodium sulfate to your extraction?

To remove excess water from the reaction

When spotting your compound on the TLC plate, you don't want to add too little sample. What would happen if you add too little sample?

You won't be able to see your spots under UV

Prefixes di- tri, and tetra- are used in naming when

a group appears more than once

The S,S-isomer and R,R-isomer of the same compound are

a pair of enantiomers

A meso-compound must have: (select all that apply)

a plane of symmetry at least 2 chiral centers

If you are washing your product and you aren't sure which layer is the organic layer (the product) and which layer is the aqueous layer, what could you do to find out (without looking up density)?

add water to the separatory funnels

Halogenations are _________________ reactions.

addition

On a TLC plate, less polar substances generally remain closer to the spotting line than the more polar substances.

advance further up the plate

Which of the following does the lab manual discuss as examples of solid adsorbents used in liquid chromatography

alumina cellulose silica gel

In this lab, we will be using m-nitroaniline. m-Nitroaniline is

an amine

In this lab, we will be using benzoic acid. Benzoic acid is

an organic acid

Tailing on a TLC plate can result from

application of too much compound on the spotting line a compound slowly decomposing on the plate

In an SN2 reaction, bond breaking and bond forming are concerted, which means they occur at the same time .

at the same time

Acids will deprotonate to form salts of organic acids. These salts are soluble in

bases acids water

In a liquid-liquid extraction, an extracting solvent must:

be immiscible with the original solvent dissolve the solute better than the original solvent

Rf values are determined by measuring the distance from the spotting line to the center of the spot and dividing it by the distance traveled by the solvent.

center

Once you obtain your purified crystals, you will rinse them with

cold water

You will be given a solid unknown to characterize. Select all of the intensive properties you will measure to identify the unknown.

color melting point

When naming molecules, are used between numerals, and are used between numerals and letters.

commas hyphen

In the acid-base reaction shown, species C is the

conjugate base

A compound's Rf value isunder a precise set of conditions. An Rf value is calculated by dividing the by the

constant distance the compound traveled distance the solvent traveled

Constitutional isomers have the same atom connectivity, but the atoms are arranged differently in space.

constitutional isomers

For the flame test, you will drip a copper wire into your sample. When the wire with your sample is heated in the flame, a [ Select ] ["red", "blue", "green", "yellow"] flame indicates there is a [ Select ] ["alkene", "alkane", "halogen", "alcohol"] present.

copper green halogen

Pyridinium tribromide is ___________________(select all that apply). Avoid skin contact by wearing gloves.

corrosive a lachrymator

In a Newman projection, high-energy conformations exist when the bonds and atoms are in line with each other, also called eclipsed .

eclipsed

A molecule containing one chiral center exists as a pair of non-superimposable mirror images, or _______________.

enantiomers

If a substituent is axial and the structure undergoes a ring flip, the substituent would then be equatorial .

equatorial

A student is making TLC solvents using hexane and ethyl acetate. The student decides the solution being used is not polar enough. Which solvent does the student need to increase in the mixture?

ethyl acetate

1-bromobutane and 1-butanol are: (select all that apply)

flammable irritants

A chiral carbon is a carbon bonded to four different groups.

four

A good separation is achieved when each compound

has a different Rf value

The lower the compound's affinity for the solid phase relative to the liquid phase, the slower the compound will move through the adsorbent.

higher

During your recrystallization, you cool the filtrate containing your dissolved unknown to room temperature, then place it in an ice bath. What would happen if you placed your flask in the ice bath before the sample cools slowly to room temperature?

impurities may be trapped in the solid

Select all of the qualities of a good recrystallization solvent.

inexpensive nontoxic inert low boiling point

In liquid chromatography, components of a mixture are separated by partitioning between a moving liquid phase and a solid adsorbent.

liquid solid

The lower the pH, the higher the hydrogen ion concentration and the more acidic the solution.

lower more

When naming molecules, [ Select ]=are used between numerals, and [ Select ] are used between numerals and letters.

lowest alphabetical

Select all of the information you need to calculate percent recovery for you recrystallization.

mass of impure compound used mass of recrystallized compound

During this lab, you will characterize the product(s) obtained from the bromination of cis- or trans-stillbene. From the product(s) produced (meso-only, pair of enantiomers-only, or meso-compound and a pair of enantiomers) you will be able to disprove 2 of the 3 possible mechanisms. In order to tell which product(s) you obtained, you will use melting point .

melting point

"Oiling out" is a condition where the solid in the recrystallization solvent but does not

melts dissolve

Compounds that contain more than one chiral center and have an internal plane of symmetry are called

meso

Use the drop down boxes to put the reactivity of alkyl halides in order from most (1) to least (4) reactive. [ Select ] secondary [ Select ] primary [ Select ] methyl

methyl > primary > secondary > tertiary

Prefixes di- tri, and tetra- are used in naming when

molecular formula not identical

Reactions involving negatively charged nucleophiles occur [ Select ] ["more", "less"] rapidly in [ Select ] ["polar-aprotic", "nonpolar-aprotic", "polar-protic"] solvents such as DMSO.

more polar aprotic

To be chiral, a molecule (select all that apply):

must be non-superimposable may not contain mirror plane

In this lab, we will be using azobenzene. Azobenzene is

neither an amine nor an organic acid

If you add sodium sulfate to your product and after 5-10 min the solid is clumped, this indicates your sample is [ Select ] ["dry", "not dry"] and you should [ Select ] ["add more sodium sulfate", "proceed to characterize your product"]

not dry add more sodium sulfate

In an SN2 reaction, the nucleophile replaces the leaving group .

nucleophile leaving group

The SN2 reaction is a one -step reaction and the reaction rate depends on the concentration of the nucleophile .

one nucleophile and electrophile

In an SN2 reaction, the nucleophile approaches the carbon atom from the opposite side as the leaving group.

opposite

In the image below, species B is a(n) (Select all that apply!)

organic base amine

To name branched alkanes, you should begin by finding the longest carbon chain. This is the _______________ chain

parent

A straight-chain alkane with the molecular formula C5H12 is called

pentane

a carbocation is

planar

At a pH of 2, a carboxylic acid will be protonated

protanted

TLC is primarily a tool for rapid qualitative analysis.

qualitative

During the vacuum filtration to remove the insoluble impurity, the vacuum may cool the filter flask enough to cause the crystals to form. How does the lab manual tells you to fix this problem?

reheat the solution and transfer to a new flask

The hydroxide ion is a [ Select ] ["weak", "strong"] base, and therefore, a poor leaving group. By protonating the -OH group with the acid catalyst, you can convert it into [ Select ] ["peroxide", "water"] which is a better leaving group.

strong poor acid water

Stronger bases are better nucleophiles.

stronger

The pKa of benzoic acid is 4.17. The pKa of HCl is -7. This means that HCl is a stronger acid than benzoic acid.

stronger

In order for a liquid to boil, the system must overcome the forces holding molecules together. intermolecular forces translate to higher boiling points. When a substance is boiled, the This is an example of a PHYSICAL change, NOT a CHEMICAL change.

stronger intermolecular forces

In this reaction, __________________ acts as a catalyst.

sulfuric acid

What is TLC used for?

to get a rough estimate of the purity of a product to test the completeness of a reaction to identify a compound by comparing to a standard

What is the role of capillary action in TLC?

to move the liquid phase up the plate

After the reflux is over and you separate out your product, you wash it several times. What is the purpose of the washes?

to remove remaining acids and alcohol

In order to remove the insoluble solid impurity during your recrystallization, you will perform a vacuum filtration using a Hirsch funnel

vacuum filtration Hirsch funnel

During a halogenation reaction, a molecule of bromine adds to an alkene to produce a __________ dihalide, which is a compound with halogens bonded to adjacent carbons.

vicinal

All of the following are examples of intensive properties EXCEPT:

volume

The recrystallization solvent you will use for your solid unknown is:

water

In general, salts are soluble in and neutral (uncharged) organic molecules are soluble in

water organic solvents

Select all of the items you will need in order to assemble your reflux apparatus.

water condenser stir bar large o ring large screw cap with a hole round bottom flask

Water is an example of a [ Select ] ["weak", "strong"] base. This makes it a good leaving group, but a [ Select ] ["good", "poor"] nucleophile.

weak good poor

How do you know when you have added enough sodium sulfate to your extraction?

when it swirls freely