Organic Chemistry I Lab Final

What should NOT be considered when trying to prevent bumping?

magnetic fields

The following image displays the boiling points of compounds i, ii, and iii in solution. The thermometer represents the current temperature of the solution.

Compound i is the most volatile component of the solution.

NMR spectroscopy CANNOT provide information about...

...color.

For a pure compound, the melting point is the thermodynamic condition where...

...the solid and liquid phases coexist.

For a pure liquid, the boiling point is the thermodynamic condition where...

...the vapor pressure of the liquid is equal to the atmospheric pressure.

If N is the number of atoms in a molecule, how many vibrational modes does a nonlinear molecule have?

3N - 6

Which of the following statements regarding solvent pairs is NOT correct? The density of hexane is 0.659 g/mL and the density of DMF is 0.944 g/mL.

A mixture of toluene and DMF will form a biphasic system with toluene on top and DMF on the bottom.

Which of the following calculations determines the percent recovery?

Dividing the mass of recrystallized product by the mass of starting materials and multiplying the result by 100.

Essential oils in fruits and plants provide the familiar scents associated with them. As volatile organic compounds, they readily enter the gaseous phase at room temperature. Which of the following statements about volatile organic compounds is TRUE?

Fractional distillation cannot be used to extract volatile organic compounds because high temperatures may decompose or change the compound into something else.

How does the composition of the distillate change over the course of a distillation?

It begins rich with the more volatile phase, and ends rich with the less volatile phase.

What is the purpose of the highlighted equipment in the steam distillation setup? (distillation flask)

It is a water reservoir.

Which of the following statements about a silica gel-based stationary phase is CORRECT?

It is extremely polar.

How is the retardation factor of an organic compound calculated in TLC?

It is the distance traveled by the solute divided by the distance traveled by the mobile phase.

Why is the water reservoir important in steam distillation?

It lowers the boiling temperature of the mixture, allowing for extraction of organic compounds below their boiling point.

A compound has a retardation factor of 0.5 in a TLC setup when run with a 30:70 acetone:hexane mixture. What would happen to the retardation factor if the solvent is changed to 50:50 acetone:hexane mixture?

It will be larger than 0.5.

Which of the following statements about TLC is correct?

More polar solutes will have greater attraction to the stationary phase and travel less.

What could a wide peak near 3300 cm indicate?

O-H or N-H stretching

Which of the following statements is NOT CORRECT about extractions?

Only liquid phase solutes can be extracted.

Which statement about the rate of cooling during recrystallization is correct?

Rapid cooling allows more nucleation sites and smaller crystals.

How do you prepare a Grignard reagent?

React an organohalide with magnesium metal

What is the solid phase in thin-layer chromatography?

TLC plate

Why is it preferable to use deuterated solvents (i.e. CDCl 3) rather than regular proteated solvents (i.e. CHCl 3) in 1 H NMR samples?

The 1 H signal from a proteated solvent would overwhelm the sample signals.

Which of the following statements regarding acid-base extractions is NOT correct?

The addition of an acid or base disrupts the organic phase, allowing the organic compound to become more soluble in water.

Which of the following statements is TRUE about a fast-moving band moving through a chromatography column from a heterogeneous mixture?

The band has the weakest interactions with the stationary phase.

Which of the following statements about immiscible mixtures is TRUE?

The boiling point of the mixture is lower than the boiling point of any of the components.

For a solvent to be used to crystallize a compound, which of the following characteristics are ideal?

The compound should be insoluble in the solvent at room temperature but soluble at high temperatures.

Which of the following statements regarding the partition coefficient is correct?

The higher the partition coefficient of a solute, the less likely it is to partition into the aqueous phase.

Following steam distillation and extraction, the organic phase containing the essential oils of interest is treated with magnesium sulfate. Why is this treatment necessary?

The magnesium sulfate takes up excess water to become a hydrated compound, removing water contamination.

Vapor pressure is defined as:__?

The pressure exerted by the gaseous phase in contact with the liquid or solid phase of a substance in a closed system.

Why is the eluate collected in fractions?

The separation of compounds is preserved.

Which statement about recrystallization is correct?

The solubility of the product typically increases in solvents that are heated.

Which of these is NOT true of a good recrystallization solvent? The compound is insoluble in the solvent when it is cold.

The solvent has many impurities.

Which of the following statements about the solvent used in column chromatography is CORRECT?

The solvent is known as the mobile phase.

A student ran a TLC experiment with three different compounds. None of the compounds moved far enough to determine Rf values. Which of the following is the MOST LIKELY cause of immobility of the compounds?

The solvent wasn't polar enough.

A student extracted cellulose, caffeine, and benzoic acid from a mixture of the three. They recovered a large amount of cellulose but very little caffeine and benzoic acid. What is the MOST LIKELY experimental cause?

The student did not properly dissolve the starting material in the dichloromethane.

A student prepares a solvent of benzene and water for use in liquid-liquid extraction of a branched long-chain fatty acid in an aqueous solution. Based on the table and the supplied image, which phase should the student move forward with?

The student should move forward with the top blue phase as this is the organic phase that contains her product.

A fellow undergraduate student is performing an acid-base extraction with a solution of dichloromethane containing caffeine and benzoic acid. Confident that they remember the next step, the student adds 3 M sodium hydroxide to their organic mixture. Which of the following is the MOST LIKELY experimental outcome?

The student will recover mostly caffeine and very little benzoic acid.

Which of these is NOT required for a two-solvent system?

The two solvents are an acid-base pair.

What happens to the vapor in a fractionating column?

The vapor repeatedly condenses on and evaporates from the beads, allowing more volatile liquids to reach the top of the column faster.

A student set up a vacuum filtration system by placing a Büchner funnel directly over a vacuum flask with a sidearm. He then connected the sidearm to the vacuum via vacuum tubing. Next, he placed a filter paper inside the funnel, turned the vacuum on and wetted the filter paper. When he finally poured the solution to be filtered, the filtrate dripped very slowly and then stopped. When he looked around, he saw that the filtrates in other students' setup quickly collected at the bottom. What is the most likely explanation for the failure of his setup?

There was no vacuum seal between the Buchner funnel and the flask.

An entrepreneur designed a 'build-your-own-crystals' kit to be used in elementary school classrooms. When she demonstrated her product to a focus group of educators, she was asked what would happen to the crystals if they cooled the solvent slowly instead of using an ice bath. Which answer is correct?

There will be fewer crystals but they will be larger.

Why are the 'peaks' upside-down in an IR transmittance spectrum?

Transmittance decreases when the sample absorbs more light.

What should you do before baking the column and setting up the autosampler?

Turn on the flow of inert carrier gas.

What is the first step of manually loading and injecting a sample?

Turn the injector handle to 'Load'.

How are components separated using distillation?

When heated, the substance with the lower boiling point is vaporized first, then it is condensed and collected.

When should you record the temperature in a melting point test?

When the sample starts melting and when the sample is completely molten.

A Grignard reaction is the reaction between a Grignard reagent and...

a carbonyl-containing compound

What should an ICP-MS standard test solution contain?

a set of elemental standards spanning the expected mass range of the analyte solution

What may cause molecules to vibrate?

absorbing IR radiation

Solvents that interact WEAKLY with the stationary phase...

are weak eluents

For good separation, the mobile phase should be...

as nonpolar as possible.

What can you use to predict the number of theoretical plates you need for your distillation?

boiling point composition curve

Which of the following statements about the solvent in a TLC setup is/are correct?i. Two solvents are sometimes combined to achieve the desired polarity.ii. The development solvent is usually less polar than the stationary phase.

both i and ii

Uneven flow through a column...

can cause poor separation of compounds.

Retention time is...

how long the analyte is in the column.

Which of the following is NOT a property that can be used to separate and purify mixtures?

hygroscopicity

Under which condition can we separate impurities before recrystallizing the compound to be purified?

if the impurities are insoluble in the hot solvent

What can you use to prevent peak broadening of less polar compounds and improve peak separation?

mobile phase gradient

What can be lost if molecule fragmentation is too great?

molecular structure information

What is the first step of crystallization?

nucelation

The formation of the first crystals during recrystallization is called _________.

nucleation

What is an electron-rich or electron-donating species called?

nucleophile

Preparatory HPLC is used to...

purify compounds.

One popular product that is used in water purification is a filtration straw. The straw passively removes particulates from contaminated water as the consumer sucks up water. What property is this product MOST LIKELY using to remove particulates from contaminated water?

size

A tea bag is an example of:

solid-liquid extraction

Liquid-liquid extractions are based on which of the following properties of a solute?

solubility

When should you NOT use simple distillation?

two liquids with boiling points less than 30 C apart

What is the mobile phase in gas chromatography?

vaporized sample and inert carrier gas

What should you avoid allowing into the reaction mixture when preparing and using a Grignard reagent?

water

If the partition coefficient of benzoic acid in a benzene-water biphasic system is 0.636, how much benzoic acid is present in the aqueous phase if a 7.5 M benzoic acid solution has mixed at a 1:1 ratio with benzene?

4.58 M

What is the product of a Grignard reaction?

A 2° or 3° alcohol with the α-carbon bound to the R group from the Grignard reagent

What is bumping?

A large pocket of solvent vapor rapidly forms, displacing the surrounding liquid.

After you determine the boiling point of an organic liquid, what do you do with the waste?

Add the liquid to halogenated or non-halogenated waste depending on its composition.

Compound A is more volatile than Compound B. Which of the following statements about the relationship between A and B is CORRECT?

Compound A has a higher vapor pressure than Compound B.

The temperature at which a pure liquid boils never changes.

False

How does steam distillation differ from fractional distillation?

Fractional distillation is used for miscible liquids, whereas steam distillation can be used for immiscible liquids.

Why does scratching the bottom of a flask encourage crystallization?

Scratching the bottom produces a non-smooth surface, ideal for crystal nuclei to form.

What occurs in an SN1 reaction?

Slow departure of the leaving group, then nucleophilic attack on either side of the remaining carbocation.

What occurs in an SN2 reaction?

Slow nucleophilic back-attack on the a-carbon, then fast departure of the leaving group.

Which of the following is NOT true of reverse-phase HPLC?

Solvents are never degassed to ensure that there are a lot of gas bubbles in the mobile phase.

Which of the following statements is NOT correct?

Some extremely nonpolar substances may have Rf values above 1.

How should you start putting the system under vacuum?

Start with a low vacuum and increase the vacuum strength as needed until solvent begins condensing in the trap or the solution starts bubbling.

Two undergraduate students are attempting to extract the essential oils found in mint leaves. Each student correctly assembles a steam distillation apparatus to extract the essential oils. Student A allows the water rate to be replenished at the same rate as the distillation. Student B attempts to speed up the rate of distillation by increasing the temperature and decreasing the rate of water replenishment. Which of the following statements BEST describes the likely experimental outcome?

Student A may have a higher yield of the correct volatile organic oils than Student B.

What effect does an impurity have on the melting point of a solid?

The melting point range broadens and the melting point is lowered.

Which of the statements BEST describes this visual of a mixture of diethyl ether and water?

The phase on top is the organic phase and contains the volatile organic compounds.

A student mixes their aqueous reaction mixture with acetone to perform a liquid-liquid extraction. After shaking the mixture in a separatory funnel and allowing the mixture to settle, which of the following is the expected experimental outcome?

There are no phases present, only one homogenous solution.

Which of the following statements BEST describes the liquid in the highlighted area from a steam distillation of essential oils from a fruit? (round-bottomed flask)

This liquid requires further extraction to isolate the essential oils from a fruit.

How can you monitor the progress of a Grignard reaction?

Use TLC to monitor the consumption of the carbonyl-containing compound.

Why is it important to vent the separatory flask after every mixing step?

Venting prevents a build-up of vapor pressure caused by agitation of the organic solvent.

When should you reduce the melting point apparatus heating rate to 1 C/min?

When the sample temperature is close to the expected melting point.

At what point is it time to end a distillation procedure?

When there is a thin film of liquid left in the round-bottom flask

You are tasked with separating a mixture containing multiple dyes, each with different polarities and hydrophobicity. You first separate fractions using their hydrophobicity, identifying two fractions. You have reason to believe that these fractions still contain 2 or more dyes in them. You prepare a silica gel column and run the first fraction through, using water as the solvent. This fails to further separate the fractions. What should your next step be?

You should try using two solvents with different polarity.

How can you avoid air bubbles creating voids in the stationary phase and destabilizing the detector readings?

always degas solvents and carbonated samples

To improve separation on the plate, the spot should be...

as small as possible.

What allows the mobile phase to move up the TLC plate?

capillary action

Which type of solvent movement is essential for a TLC analysis?

capillary movement

Which of the following methods is the BEST way to separate mixtures on a microscale?

column chromatography

Which labware are used to assemble a gravity filtration setup?

conical funnel, filter paper, Erlenmeyer flask

Which of the following does NOT decrease the rate of SN2 reactions?

decreased bond strength between the leaving group and the a-carbon

What is the primary use of a rotary evaporator?

drying and purifying samples

Which of these affects the chemical shift of a nucleus relative to a standard?

electrons of nearby atoms

What is an electron-poor or electron-withdrawing species called?

electrophile

Compounds that interact WEAKLY with the stationary phase...

elute faster

A theoretical plate is...

equivalent to one vaporization-condensation cycle, or one simple distillation.

The fluid that is collected at the bottom of this setup is called a(n) ___________.

filtrate

Which of the following will not encourage crystallization?

further increasing the temperature of the solution

Which of the following is NOT part of a mass spectrometer?

fusion generator

What is used to hold the sample in a melting point apparatus?

glass capillary

What is in a fractionating column?

glass or plastic beads

Which of the following is NOT a component of a TLC system?

heating filament

Which of the following was not used in any of the videos for determination of boiling point?

heating mantle

You are a laboratory technician interning at a major forensic science institution. You are tasked with separating an unknown mixture containing different organic compounds. Your supervisor has mentioned that the components in this mixture seem to be immiscible in water. The best way to separate these organic compounds is by:

hydrophobicity

When does boiling occur? i. when the energy gained by a liquid overcomes the intermolecular interactions in the liquid phase ii. when the total vapor pressure of the substance is equal to the atmospheric pressure iii. when the total vapor pressure of the substance is less than the atmospheric pressure

i and ii

Which impurities tend to separate in a recrystallization experiment? i. Impurities that are insoluble in the solvent at high temperatures ii. Impurities that are soluble in the solvent at room temperature

i and ii

Which of the following methods can be used to detect the solute spots on the TLC plate?i. Putting the plate under a UV lampii. Placing the plate inside a jar with iodineiii. Feeling the deposited crystals on the plate with fingertips

i and ii

Which of the following statements about the bubble point is correct? i. The bubble point is the temperature at which the first bubble of vapor starts to form. ii. For a pure liquid, the boiling point and bubble point are the same. iii. For a miscible mixture, the boiling point of the mixture and the bubble points of each component are the same.

i and ii

Which statements about crystallization are correct? (i) Crystallization can happen spontaneously. (ii) Providing a growth surface encourages crystallization. (iii) Rate of cooling does not affect crystallization.

i and ii

Silica gel is a form of silicon dioxide. Listed below are the different intermolecular forces. Which of these BEST describes the major contributors of interactions that can occur between a compound and silica gel? i. dipole-dipole interactions ii. covalent bonding iii. hydrogen bonding iv. ionic bonding

i and iii

Which of the following statements must be true about the solutes found in the hot water of this brewing teacup? i. These solutes are water-soluble. ii. These solutes must be essential oils from the tea leaves. iii. These solutes have a high solubility in aqueous solutions.

i and iii

Which of the following statements about miscible liquids is correct? i. The components form a homogeneous solution. ii. The partial pressure of each component is the vapor pressure. iii. Each component has its own vapor pressure.

i, ii, and iii

A student prepares the following solvent pairs, labeled i-iv. Which of these are appropriate for liquid-liquid extraction? i. Acetone mixed with dimethylformamide ii. Dimethyl sulfoxide mixed with hexane iii. Toluene mixed with water iv. Benzene mixed with hexane

ii and iii

How full should the round-bottomed flask be?

less than half full

What controls which ionized fragments reach the detector at a given time?

mass analyzer

The dimensions of an FID peak are proportional to the...

mass of carbon in the analyte corresponding to that peak.

How are ions separated in mass spectrometry?

mass-to-charge ratio

In a TLC setup, the distance a solute molecule travels on the stationary phase depends mainly on its ______________ .

polarity

Why must the FID always be hotter than the GC column?

preventing condensation

What is recrystallization used for?

purifying solid compounds

Which of the following does NOT affect which IR frequencies a bond can absorb?

relative location of the bond to the IR source

A biochemist receives a patient sample that is though to contain a prion, a pathogenic protein product caused by the misfolding of a host/native protein. The hydrophobicity, charge, and polarity are similar to the host proteins, but the misfolded protein has a different structure than the native protein. Which of the following chromatography techniques is the BEST method to isolate the prion?

size exclusion chromatography

What is important to consider when choosing solvents?

solvent and solute polarity

When a mixture first reaches its boiling point, what component transitions to vapor first?

the component with the lower boiling point

In the boiling point diagram shown, what does the top dashed line represent?

the dew point

Rf is the characteristic ratio of the distance a compound traveled up a TLC plate to...

the distance the solvent traveled up the plate.

If the impurities are less soluble in the recrystallization solvent than the solute...

the impurities can be removed by hot filtration before proceeding with recrystallization.

What information does the splitting pattern of a peak provide?

the number of and distance to nearby NMR-active nu

What information does the area under a 1 H NMR peak provide?

the number of protons represented by the peak

When setting up the distillation setup, which port on the condenser serves as the water inlet?

the port furthest from the round-bottom flask

The arrow points to the top of the mobile phase, which is called ____.

the solvent front

What is the definition of the dew point?

the temperature at which vapor starts to condense

What is the definition of vapor pressure?

the total pressure of a vapor in equilibrium with its condensed phase

What is the definition of partial pressure?

the vapor pressure of one component in a mixture

A student synthesized benzoic acid by reacting sodium benzoate and hydrochloric acid in deionized water and vacuum filtered his product. Why did he pour the remaining deionized water over the benzoic acid solids on filter paper inside the Büchner funnel?

to dissolve and remove any remaining sodium benzoate

In the micro method for boiling point determination, the boiling point is recorded _____.

when the liquid goes back into the glass capillary after gas has been escaping from it

Which of the following statements about the formula is NOT correct?

xA is the number of moles of substance A