O-Chem Lab Final
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)
What controls which ionized fragments reach the detector at a given time? a) mass analyzer b) gravity wells c) power supply d) ionization source
a) mass analyzer
What is an electron-poor or electron-withdrawing species called? a) α-halogen b) stereoisomer c) nucleophobe d) electrophile
d) electrophile
A= 0.7, B= 0.8 , C= 0.5 , D= 0.3 Which statements about the retardation factor values in the table are CORRECT? i. Compound A is more polar than compound B. ii. Compound C is less polar than compound D. iii. Compound C is less attracted to the stationary phase than compound B.
(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 of the mixture times the components mole fraction. 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) they are immiscible
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)
In the boiling point diagram shown, what does the top dashed line represent?
Dew Point
What allows the mobile phase to move up the TLC plate? a) Capillary action b) Gravity c) Evaporation d) Pressurization
a) Capillary action
A _____ funnel is best for liquid-liquid extraction?
buchner
Rf equation
distance moved by substance/distance moved by solvent
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 of the following methods can be used to detect the solute spots on the TLC plate? i. Putting the plate under a UV lamp ii. Placing the plate inside a jar with iodine iii. 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)
A chemist separates three unknown compounds with TLC using a silica-gel stationary phase. Which option lists these compounds from the most polar to the least?
A>C>B>D
True/False: The temperature as which a pure liquid boils never changes.
False
Which of the following does NOT decrease the rate of SN2 reactions? a) Decreased bond strength between the leaving group and the α-carbon. b) Steric hindrance at the α-carbon. c) Using polar protic solvents. d) Steric hindrance at the β-carbon.
a) Decreased bond strength between the leaving group and the α-carbon.
Which of the following calculations determines the percent recovery? a) Dividing the mass of recrystallized product by the mass of starting materials and multiplying the result by 100. b) Dividing the mass of starting materials by the mass of recrystallized product and multiplying the result by 100. c) Dividing the mass of impurities by the mass of the recrystallized product and multiplying the results by 1/100. d) Multiplying the mass of recrystallized product and the mass of starting materials and dividing the results by 1/100.
a) Dividing the mass of recrystallized product by the mass of starting materials and multiplying the result by 100.
The fluid that is collected at the bottom of a vacuum filtration is called a(n) ___________. a) Filtrate b) Efflux c) Solute d) Supernatant
a) Filtrate
Which of the following statements about a silica gel-based stationary phase is CORRECT? a) It is extremely polar. b) It is slightly polar. c) It is extremely nonpolar. d) It is slightly nonpolar.
a) It is extremely polar.
How is the retardation factor of an organic compound calculated in TLC? a) It is the distance traveled by the solute divided by the distance traveled by the mobile phase. b) It is the distance traveled by the mobile phase divided by the length of the TLC plate. c) It is the distance traveled by the solute in an organic solvent divided by the distance traveled by the solute in water. d) It is the distance traveled by the solute divided by the length of the TLC plate.
a) It is the distance traveled by the solute divided by the distance traveled by the mobile phase.
What should NOT be considered when trying to prevent bumping? a) Magnetic fields b) The reduced pressure in the flask c) Water bath temperature d) Flask rotation speed
a) Magnetic fields
The formation of the first crystals during recrystallization is called: a) Nucleation b) Filtration c) Purification d) Agitation
a) Nucleation
Which statement about the rate of cooling during recrystallization is correct? a) Rapid cooling allows more nucleation sites and smaller crystals. b) Rapid cooling allows less nucleation sites and smaller crystals. c) Rapid cooling allows more nucleation sites and larger crystals. d) Rapid cooling allows less nucleation sites and larger crystals.
a) Rapid cooling allows more nucleation sites and smaller crystals.
How do you prepare a Grignard reagent? a) React an organohalide with magnesium metal. b) React a carbonyl-containing compound with an organohalide. c) Mix an organohalide with molten magnesium. d) React a carbonyl-containing compound with magnesium metal.
a) React an organohalide with magnesium metal.
Which of the following does NOT affect which IR frequencies a bond can absorb? a) Relative location of the bond to the IR source. b) Bond properties, such as length and strength. c) The atoms connected by the bond. d) The vibrational modes available to the bond.
a) Relative location of the bond to the IR source.
A scientist wants to purify compound (i) from a mixture that she suspects to be contaminated by compounds (ii) and (iii). She adds 100 mL of boiling water to 0.4 g of mixture. Which of the following is the correct sequence of crystallization (Water solubility characteristics of each compound are listed in the table)? a) Remove (iii) with hot filtering then remove (i) by filtering at room temperature. b) Remove (ii) with hot filtering, remove (iii) by filtering at room temperature. c) Remove (i) with hot filtering, remove (iii) by filtering at room temperature. d) Remove (i) with hot filtering, remove (ii) by filtering at room temperature.
a) Remove (iii) with hot filtering then remove (i) by filtering at room temperature.
Tea is an example of: a) Solid-liquid Extraction b) Liquid-liquid Extraction c) Hot gravity filtration d) None of these
a) Solid-liquid Extraction
Which of the following statements is NOT correct? a) Some extremely nonpolar substances may have Rf values above 1. b) The more polar a substance, the lower is its Rf value. c) For effective separation, Rf values should differ by 0.3-0.7 d) Less-polar substances travel faster than more polar substances.
a) Some extremely nonpolar substances may have Rf values above 1.
For a solvent to be used to crystallize a compound, which of the following characteristics are ideal? a) The compound should be insoluble in the solvent at room temperature but soluble at high temperatures. b) The compound should be soluble in the solvent at room temperature but insoluble at high temperatures. c) The compound should be soluble in the solvent between 0C and 100C. d) The compound should be partially soluble in the solvent at room temperature and less soluble at high temperatures.
a) The compound should be insoluble in the solvent at room temperature but soluble at high temperatures.
Following steam distillation and extraction, the organic phase containing the essential oils of interest is treated with magnesium sulfate. Why is this treatment necessary? a) The magnesium sulfate takes up excess water to become a hydrated compound, removing water contamination. b) The magnesium sulfate reacts with non-volatile components and removes them from the product. c) The magnesium sulfate is added as preservative to stabilize the essential oils. d) None of these are correct.
a) The magnesium sulfate takes up excess water to become a hydrated compound, removing water contamination.
Vapor pressure is defined as:__? a) The pressure exerted by the gaseous phase in contact with the liquid or solid phase of a substance in a closed system b) The gravitational force exerted on the liquid phase of a substance c) The pressure exerted by the gaseous phase in contact with the liquid or solid phase of a substance in an open system d) The partial pressure of each gaseous component in a closed system
a) 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? a) The separation of compounds is preserved. b) The flow is frequently halted to let the compounds diffuse in the column. c) Column chromatography uses so much solvent that you can never collect it all at once. d) It gives you something to do while you wait.
a) The separation of compounds is preserved.
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? a) The student will recover mostly caffeine and very little benzoic acid. b) The student will recover mostly benzoic acid and very little caffeine. c) The sodium hydroxide will react with the caffeine to form a side product. d) The sodium hydroxide will react with the benzoic acid, allowing benzoic acid to partition into the aqueous phase.
a) The student will recover mostly caffeine and very little benzoic acid.
What is the definition of the dew point? a) The temperature at which vapor starts to condense. b) The temperature at which liquid starts to vaporize. c) The temperature at which liquid starts to freeze. d) None of these statements are correct.
a) The temperature at which vapor starts to condense.
What is the definition of vapor pressure? a) The total pressure of a vapor in equilibrium with its condensed phase. b) The total pressure of a liquid in equilibrium with its condensed phase. c) The pressure of one component in the mixture. d) None of these options are correct.
a) The total pressure of a vapor in equilibrium with its condensed phase.
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? a) There was no vacuum seal between the Buchner funnel and the flask. b) The vacuum source wasn't powerful enough. c) His vacuum tubing was too long. d) He didn't use the correct sized vacuum flask.
a) There was no vacuum seal between the Buchner funnel and the flask.
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? a) To dissolve and remove any remaining sodium benzoate. b) To unclog the pores of the Buchner funnel. c) To keep the benzoic acid solids from drying. d) To help build bigger benzoic acid crystals.
a) To dissolve and remove any remaining sodium benzoate.
Why are the 'peaks' upside-down in an IR transmittance spectrum? a) Transmittance decreases when the sample absorbs more light. b) IR spectrometers are conventionally used upside-down. c) The x-axis is in reciprocal units. d) IR radiation has longer wavelengths than visible light.
a) Transmittance decreases when the sample absorbs more light.
What should you do before baking the column and setting up the autosampler? a) Turn on the flow of inert carrier gas. b) Inject the sample. c) Ignite the FID flame. d) Zero the chromatogram baseline.
a) Turn on the flow of inert carrier gas.
What is the first step of manually loading and injecting a sample? a) Turn the injector handle to 'Load'. b) Inject the sample into the septum port. c) Turn the injector handle to 'Inject'. d) Stop the solvent pump.
a) Turn the injector handle to 'Load'.
Why is it important to vent the separatory flask after every mixing step? a) Venting prevents a build-up of vapor pressure caused by agitation of the organic solvent. b) Oxygen is required for the successful separation of phases. c) Venting releases trapped air bubbles in the solution that would otherwise disrupt the separation of the two phases. d) Gaseous products formed by the reaction of the two solvents would build up if not released.
a) Venting prevents a build-up of vapor pressure caused by agitation of the organic solvent.
Compounds that interact WEAKLY with the stationary phase... a) elute faster. b) elute slower. c) will never elute. d) react with the stationary phase.
a) elute faster.
A theoretical plate is... a) equivalent to one vaporization-condensation cycle, or one simple distillation. b) the adaptor connecting the fractionating column to the condenser. c) the best estimate of the size of the plate you will need for your cell plating experiment. d) equivalent to one bead.
a) equivalent to one vaporization-condensation cycle, or one simple distillation.
Preparatory HPLC is used to... a) purify compounds. b) analyze compounds. c) decompose compounds. d) dissolve compounds.
a) purify compounds.
In the micro method for boiling point determination, the boiling point is recorded _____ a) when liquid goes back into the glass capillary after gas has been escaping from it b) after gas has been bubbling out of the glass capillary for awhile c) when the liquid changes color d) 5 minutes after liquid goes back into the glass capillary the liquid cools to room temperature
a) when liquid goes back into the glass capillary after gas has been escaping from it
Which labware are used to assemble a gravity filtration setup? a)Conical funnel, filter paper, Erlenmeyer flask b) Büchner funnel, filter paper, Erlenmeyer flask c) Büchner funnel, filter paper, round-bottom flask d) Conical funnel, filter paper, Büchner flask
a)Conical funnel, filter paper, Erlenmeyer flask
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? a) 2.915 M b) 4.58 M c) 4.77 M d) There is not enough information.
b) 4.58 M
What is bumping? a) The solvent comes to a constant, controlled boil. b) A large pocket of solvent vapor rapidly forms, displacing the surrounding liquid. c) The solute precipitates from the concentrated solution and rattles around the flask. d) The solvent rapidly freezes.
b) A large pocket of solvent vapor rapidly forms, displacing the surrounding liquid.
How can you avoid air bubbles creating voids in the stationary phase and destabilizing the detector readings? a) Periodically disconnect the column to let out air bubbles. b) Always degas solvents and carbonated samples. c) Always perform HPLC in a vacuum. d) Feed the waste lines back into the solvent bottles so the solvent will never run dry.
b) Always degas solvents and carbonated samples.
A student wants to separate a mixture of two compounds into its components based on their differences in solubility in water. Both compound A and compound B dissolve in boiling water. Compound A starts recrystallizing at 82 °C, whereas compound B recrystallizes around 35 °C. Which experimental time point is ideal to separate the compounds? a) Filter at (i) using boiling water b) Filter at (ii) using 50°C water c) Filter at (ii) using 82°C water d) Filter at (iii) using 35°C water
b) Filter at (ii) using 50°C water
How does steam distillation differ from fractional distillation? a) Fractional distillation can be used to isolate highly volatile organic compounds, whereas steam distillation is used for solutions that are mostly aqueous. b) Fractional distillation is used for miscible liquids, whereas steam distillation can be used for immiscible liquids. c) Steam distillation requires bringing the solution to the boiling point of the most volatile component, whereas fractional distillation requires a gradient of temperatures to separate out compounds. d) Steam distillation does not require a condenser, whereas fractional distillation does.
b) Fractional distillation is used for miscible liquids, whereas steam distillation can be used for immiscible liquids.
How does the composition of the distillate change over the course of a distillation? a) It begins rich with the less volatile phase, and ends rich with the more volatile phase. b) It begins rich with the more volatile phase, and ends rich with the less volatile phase. c) It does not change during the distillation. d) It begins rich with water, and ends rich with the more volatile phase.
b) It begins rich with the more volatile phase, and ends rich with the less volatile phase.
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? a) It won't change because the Rf value of a compound is always the same. b) It will be larger than 0.5. c) It will be smaller than 0.5 d) More information is needed to determine whether Rf value would change.
b) It will be larger than 0.5.
Which of the following statements about TLC is correct? a) More polar solutes will have greater attraction to the stationary phase and travel further. b) More polar solutes will have greater attraction to the stationary phase and travel less. c) More polar solutes will be less attracted to the stationary phase and travel further. d) More polar solutes will be less attracted to the stationary phase and travel less.
b) More polar solutes will have greater attraction to the stationary phase and travel less.
Which of the following statements is NOT CORRECT about extractions? a) Liquid-liquid extractions are performed in a separatory funnel. b) Only liquid phase solutes can be extracted. c) The solute and solvent(s) being used should be unreactive. d) In a solvent pair, the two solvents should have different densities.
b) Only liquid phase solutes can be extracted.
Why does scratching the bottom of a flask encourage crystallization? a) The mechanical force of scratching is used by nearby solute molecules to attract molecules alike. b) Scratching the bottom produces a non-smooth surface, ideal for crystal nuclei to form. c) Stirring the solution while scratching the bottom of the flask cools the solution further. d) Scratching the bottom of the flask increases the available surface area of the flask.
b) Scratching the bottom produces a non-smooth surface, ideal for crystal nuclei to form.
What occurs in an SN2 reaction? a) Slow departure of the leaving group, then nucleophilic attack on the carbocation. b) Slow nucleophilic back-attack on the α-carbon, then fast departure of the leaving group. c) Fast electrophilic back-attack on the α-carbon, then slow departure of the leaving group. d) Fast departure of the α-carbon, then nucleophilic back-attack on the leaving group.
b) Slow nucleophilic back-attack on the α-carbon, then fast departure of the leaving group.
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? a) Student A and Student B will both extract the same yield of essential oils from the mint leaves. b) Student A may have a higher yield of the correct volatile organic oils than Student B. c) Student B may have a higher yield of the correct volatile organic oils than Student A. d) Student B distilled a greater amount than Student A.
b) Student A may have a higher yield of the correct volatile organic oils than Student B.
What is the solid phase in thin-layer chromatography? a) Glass capillary b) TLC plate c) Ruler d) Solute
b) TLC plate
When a mixture first reaches its boiling point, what component transitions to vapor first? a) The component with the higher boiling point. b) The component with the lower boiling point. c) The component with the higher molecular weight. d) The component with the lower density.
b) The component with the lower boiling point.
Which of the following statements regarding the partition coefficient is correct? a) The partition coefficient is found by dividing the concentration of the solute in the aqueous phase by the concentration of the solute in the organic phase. b) The higher the partition coefficient of a solute, the less likely it is to partition into the aqueous phase. c) The lower the partition coefficient of a solute, the more likely it is to partition into the organic phase. d) None of these are correct.
b) The higher the partition coefficient of a solute, the less likely it is to partition into the aqueous phase.
What effect does an impurity have on the melting point of a solid? a) The melting point becomes the same as the boiling point. b) The melting point range broadens and the melting point is lowered. c) The melting point range narrows to less than 0.1 °C of variation. d) The melting point range narrows and the melting point is raised.
b) The melting point range broadens and the melting point is lowered.
What information does the splitting pattern of a peak provide? a) The concentration of the sample b) The number of and distance to nearby NMR-active nu c) The number of nuclei represented by the peak d) The name of the compound
b) The number of and distance to nearby NMR-active nu
What information does the area under a 1 H NMR peak provide? a) How long it took to acquire the spectrum b) The number of protons represented by the peak c) The number of and distance to nearby NMR-active nuclei d) The number of 13C, 19F, and 31P nuclei in the molecule
b) The number of protons represented by the peak
When setting up the distillation setup, which port on the condenser serves as the water inlet? a) The port closest to the round-bottom flask. b) The port furthest from the round-bottom flask. c) It depends on the mixture being distilled. d) It makes no difference.
b) The port furthest from the round-bottom flask.
Which of the following statements about the solvent used in column chromatography is CORRECT? a) The solvent is known as the stationary phase. b) The solvent is known as the mobile phase. c) The solvent reacts with the stationary phase to form the column. d) None of these are correct.
b) 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? a) All three compounds were very nonpolar and didn't stick to the stationary phase. b) The solvent wasn't polar enough. c) The UV lamp was broken. d) The polarity of the solvent was very different from the polarities of all three compounds.
b) 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? a) The student did not add enough acid during the acid-base extraction portion of the experiment. b) The student did not properly dissolve the starting material in the dichloromethane. c) The student started with too much starting material. d) The student should have used a base instead of an acid during the acid-base extraction step.
b) The student did not properly dissolve the starting material in the dichloromethane.
When should you NOT use simple distillation? a) Two liquids with boiling points more than 30 °C apart. b) Two liquids with boiling points less than 30 °C apart. c) One of the liquids is non-volatile. d) The liquid has no more than 10% liquid contaminants.
b) Two liquids with boiling points less than 30 °C apart.
The setup in the image represents which of the following methods? a) Gravity filtration b) Vacuum filtration c) Multilayer filtration d) Density filtration
b) Vacuum filtration
At what point is it time to end a distillation procedure? a) When the round-bottom flask is completely dry. b) When there is a thin film of liquid left in the round-bottom flask. c) When drops of liquid begin to collect on the thermometer. d) When the solution in the round-bottom flask begins to boil.
b) When there is a thin film of liquid left in the round-bottom flask.
Uneven flow through a column... a) separates compounds very well. b) can cause poor separation of compounds. c) never affects compound separation. d) makes the solvent a stronger eluent.
b) can cause poor separation of compounds.
Retention time is... a) how long it takes to inject the analyte. b) how long the analyte is in the column. c) how long it takes for the analyte to reach the column. d) how long it takes to combust the analyte.
b) how long the analyte is in the column.
What is an electron-rich or electron-donating species called? a) electrofull b) nucleophile c) carbocation d) steric hindrance
b) nucleophile
Rf is the characteristic ratio of the distance a compound traveled up a TLC plate to... a) the distance the reference spot traveled up the plate. b) the distance the solvent traveled up the plate. c) the total length of the TLC plate. d) the distance between the spot starting point and the bottom of the TLC plate.
b) the distance the solvent traveled up the plate.
If the impurities are less soluble in the recrystallization solvent than the solute... a) they do not matter. b) the impurities can be removed by hot filtration before proceeding with recrystallization. c) the impurities can easily be washed away after recrystallization. d) they cannot be removed.
b) the impurities can be removed by hot filtration before proceeding with recrystallization.
For a pure compound, the melting point is the thermodynamic condition where... a) the gas and plasma phases coexist. b) the solid and liquid phases coexist. c) only the liquid phase exists. d) the solid and gas phases coexist.
b) the solid and liquid phases coexist.
What should you avoid allowing into the reaction mixture when preparing and using a Grignard reagent? a) magnesium b) water c) organic solvents d) organohalides
b) water
If N is the number of atoms in a molecule, how many vibrational modes does a nonlinear molecule have? a) 3N b) 7N + 20 c) 3N − 6 d) 3 - 8N
c) 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) A mixture of dimethyl sulfoxide and hexane will form a biphasic system with hexane on the top and dimethyl sulfoxide on the bottom. b) A mixture of toluene and dimethylformamide will form a homogenous solution. c) A mixture of toluene and DMF will form a biphasic system with toluene on top and DMF on the bottom. d) A mixture of 1-butanol and water will form a diphasic system with 1-butanol on top and water on the bottom.
c) A mixture of toluene and DMF will form a biphasic system with toluene on top and DMF on the bottom.
What may cause molecules to vibrate? a) Earthquakes b) Eager anticipation. c) Absorbing IR radiation. d) Loud music.
c) Absorbing IR radiation.
Which type of solvent movement is essential for a TLC analysis? a) Gravitational pull b) Evaporation through the stationary phase c) Capillary movement d) Pull by an electrical current
c) Capillary movement
Which of the following methods is the BEST way to separate mixtures on a microscale? a) Rotary evaporation b) Fractional distillation c) Column chromatography d) Liquid-liquid extraction
c) Column chromatography
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? a) Volatile organic compounds can be extracted with organic solvents and then boiling the solvent away. b) Steam distillation is used to extract volatile organic compounds because steam is less harsh compared to organic solvent. c) Fractional distillation cannot be used to extract volatile organic compounds because high temperatures may decompose or change the compound into something else. d) None of these are true about volatile organic compounds.
c) Fractional distillation cannot be used to extract volatile organic compounds because high temperatures may decompose or change the compound into something else.
What is in a fractionating column? a) Collected fractions. b) Silica gel. c) Glass or plastic beads. d) Liquid nitrogen.
c) Glass or plastic beads.
Which of the following is NOT a component of a TLC system? a) Stationary phase b) Solute c) Heating filament d) Development solvent
c) Heating filament
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: a) Size b) Charge c) Hydrophobicity d) Polarity
c) Hydrophobicity
Which of the following is NOT a property that can be used to separate and purify mixtures? a) Polarity b) Size c) Hygroscopicity d) Hydrophobicity
c) Hygroscopicity
Under which condition can we separate impurities before recrystallizing the compound to be purified? a) If the impurities are soluble in the solvent at room temperature. b) If we agitate the solution to separate the impurities from the compound. c) If the impurities are insoluble in the hot solvent. d) We cannot separate impurities before recrystallizing the compound.
c) If the impurities are insoluble in the hot solvent.
Why is the water reservoir important in steam distillation? a) It keeps the organic compounds in solution. b) It maintains a vapor equilibrium with the volatile organic compounds. c) It lowers the boiling temperature of the mixture, allowing for extraction of organic compounds below their boiling point. d) It prevents organic compounds from decomposing during the distillation process by providing a protective layer of water molecules that dissipate the heat.
c) It lowers the boiling temperature of the mixture, allowing for extraction of organic compounds below their boiling point.
How full should the round-bottomed flask be? a) Three-quarters full b) Filled to the neck c) Less than half full d) Empty
c) Less than half full
What could a wide peak near 3300 cm-1 indicate? a) C=O stretching b) C=C stretching c) O-H or N-H stretching d) C-O stretching
c) O-H or N-H stretching
In a TLC setup, the distance a solute molecule travels on the stationary phase depends mainly on its ______________ . a) Size b) Shape c) Polarity d) Purity
c) Polarity
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? a) Charge b) Hydrophobicity c) Size d) Polarity
c) Size
Liquid-liquid extractions are based on which of the following properties of a solute? a) Density b) Intermolecular forces c) Solubility d) Molecular weight
c) Solubility
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? a) Deuterated solvents are much less toxic than proteated solvents. b) Compounds are always more stable in deuterated solvents. c) The 1 H signal from a proteated solvent would overwhelm the sample signals. d) Organic solvent vapors never mix with deuterated solvents.
c) The 1 H signal from a proteated solvent would overwhelm the sample signals.
Which of the following statements is TRUE about a fast-moving band moving through a chromatography column from a heterogenous mixture? a) The band has the strongest interactions with the stationary phase. b) The band has the lowest molecular mass compared to the rest of the mixture. c) The band has the weakest interactions with the stationary phase. d) None of the statements are correct.
c) The band has the weakest interactions with the stationary phase.
Which of the following statements about immiscible mixtures is TRUE? a) The partial pressure of each component is dependent on the other components. b) Organic compounds with similar polarities form immiscible mixtures. c) The boiling point of the mixture is lower than the boiling point of any of the components. d) Boiling occurs when the mixture pressure exceeds atmospheric pressure.
c) The boiling point of the mixture is lower than the boiling point of any of the components.
Which of the statements BEST describes this visual of a mixture of diethyl ether and water (yellow on top and blue on bottom)? a) The volatile organic compounds are located at the interface of the two liquid phases. b) This is a solid-liquid extraction. c) The phase on top is the organic phase and contains the volatile organic compounds. d) The phase on the bottom is the organic phase and contains the volatile organic compounds.
c) The phase on top is the organic phase and contains the volatile organic compounds.
Which statement about recrystallization is correct? a) It is the only way to remove impurities from a product. b) It requires dissolving the impure product in a lot of solvent. c) The solubility of the product typically increases in solvents that are heated. d) Crystallization is always a spontaneous event.
c) The solubility of the product typically increases in solvents that are heated.
The top of the mobile phase, is called: a) The immersion point b) The mobility line c) The solvent front d) The retardation factor
c) The solvent front
Which of these is NOT true of a good recrystallization solvent? a) The compound is insoluble in the solvent when it is cold. b) The solvent boiling temperature is at least 40 °C. c) The solvent has many impurities. d) The compound is soluble in the solvent when it is hot.
c) The solvent has many impurities.
What is the definition of partial pressure? a) The total vapor pressure of a mixture. b) The atmospheric pressure. c) The vapor pressure of one component in a mixture. d) The total pressure of the liquid.
c) The vapor pressure of one component in a mixture
What happens to the vapor in a fractionating column? a) The vapor condenses and drips back into the column, with no vapor reaching the top of the column. b) The vapor passes the beads and does not condense until it reaches the condenser. c) The vapor repeatedly condenses on and evaporates from the beads, allowing more volatile liquids to reach the top of the column faster. d) The vapor adsorbs to the beads, which are collected in portions to preserve the separation of compounds.
c) The vapor repeatedly condenses on and evaporates from the beads, allowing more volatile liquids to reach the top of the column faster.
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? a) There will be more crystals and they will be larger. b) There will be more crystals but they will be smaller. c) There will be fewer crystals but they will be larger. d) There will be fewer crystals and they will be smaller.
c) There will be fewer crystals but they will be larger.
Which of the following statements BEST describes the liquid in the highlighted area (round flask attached at end) from a steam distillation of essential oils from a fruit? a) The liquid is pure essential oils. b) The liquid is the non-volatile components of the fruit. c) This liquid requires further extraction to isolate the essential oils. d) The liquid is at the same temperature as the sample in the larger flask.
c) This liquid requires further extraction to isolate the essential oils.
How can you monitor the progress of a Grignard reaction? a) Use TLC to monitor the concentration of magnesium metal. b) Titrate the reaction mixture with nitric acid. c) Use TLC to monitor the consumption of the carbonyl-containing compound. d) Add water and see if the mixture reacts with it.
c) Use TLC to monitor the consumption of the carbonyl-containing compound.
What is the mobile phase in gas chromatography? a) Solution-state sample and liquid solvent. b) Vaporized sample and liquid solvent. c) Vaporized sample and inert carrier gas. d) Solution-state sample and inert carrier gas.
c) Vaporized sample and inert carrier gas.
How are components separated using distillation? a) When heated, the substance with the higher boiling point is vaporized first, and then it is condensed and collected. b) When heated, the substance with the higher boiling point is vaporized first, and then it is released as vapor. c) When heated, the substance with the lower boiling point is vaporized first, then it is condensed and collected. d) When heated, the substance with the lower boiling point is vaporized first, and then it is released as vapor.
c) When heated, the substance with the lower boiling point is vaporized first, then it is condensed and collected.
When should you reduce the melting point apparatus heating rate to 1 °C/min? a) Long after the sample is completely molten. b) When the sample starts melting. c) When the sample temperature is close to the expected melting point. d) When the sample is completely molten.
c) When the sample temperature is close to the expected melting point.
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 fraction. What should your next step be? a) You should load more of the sample into the column and reduce the rate of fraction collection. b) You should use a longer column to allow for better separation of bands and increase the amount of sample loaded into the column. c) You should try using two solvents with different polarity. d) You should dilute the fractions with more solvent before loading them into the column.
c) You should try using two solvents with different polarity.
A Grignard reaction is the reaction between a Grignard reagent and... a) an inorganic salt. b) a pure metal. c) a carbonyl-containing compound. d) a pure halide.
c) a carbonyl-containing compound.
Solvents that interact WEAKLY with the stationary phase... a) are strong eluents. b) always have a low boiling point. c) are weak eluents. d) never have a low boiling point.
c) are weak eluents.
For good separation, the mobile phase should be... a) as polar as possible. b) as acidic as possible. c) as nonpolar as possible. d) as viscous as possible.
c) as nonpolar as possible.
How are ions separated in mass spectrometry? a) mass-to-volume ratio b) volume-to-charge ratio c) mass-to-charge ratio d) positive-to-negative ratio
c) mass-to-charge ratio
What can you use to prevent peak broadening of less polar compounds and improve peak separation? a) autosampler b) calibration curve c) mobile phase gradient d) degassing
c) mobile phase gradient
What can be lost if molecule fragmentation is too great? a) efficient molecule ionization b) system power c) molecular structure information d) ion acceleration
c) molecular structure information
Pa = (Xa)(Poa), Pb = (Xb)(Pob) Which of the following statements about the formula is NOT correct? a) pA* is the vapor pressure of pure substance A. b) pB is the partial pressure of substance B in a miscible solution. c) xA is the number of moles of substance A. d) In a solution composed of substance A and B, the sum of xA and xB must equal 1.
c) xA is the number of moles of substance A.
What is the product of a Grignard reaction? a) A 2° or 3° amine with the nitrogen bound to the R group from the Grignard reagent. b) A six-membered ring. c) An ester that incorporates the R group from the Grignard reagent. d) A 2° or 3° alcohol with the α-carbon bound to the R group from the Grignard reagent.
d) A 2° or 3° alcohol with the α-carbon bound to the R group from the Grignard reagent.
What should an ICP-MS standard test solution contain? a) A set of elemental standards with masses that do not overlap with the expected analyte mass range. b) Pure water only. c) A solution of the analyte. d) A set of elemental standards spanning the expected mass range of the analyte solution.
d) A set of elemental standards spanning the expected mass range of the analyte solution.
After you determine the boiling point of an organic liquid, what do you do with the waste. a) Pour it down the drain b) Put it back in the bottle that you got it from c) Drink it d) Add the liquid to halogenated or non-halogenated waste depending on its composition e) Save it for next lab
d) Add the liquid to halogenated or non-halogenated waste depending on its composition
A student assembles a silica gel column to separate green dye, following the same procedure outlined in this lab. As the dye runs the column, the student notices streaking lines of dye being left behind as the band moves down the column. Which of the following statements is correct about the phenomenon observed? a) The stationary phase was not properly packed. b) A channel is present in the stationary phase. c) Air bubbles or dry patches are present in the column. d) All of these statements are correct.
d) All of these statements are correct.
What can you use to predict the number of theoretical plates you need for your distillation? a) Distillation curve b) Tauc plot c) Dowsing rod d) Boiling point composition curve
d) Boiling point composition curve
Compound A is more volatile than Compound B. Which of the following statements about the relationship between A and B is CORRECT? a) Compound A has a higher boiling point than Compound B. b) A mixture of Compound A and Compound B will require a higher temperature to boil than either compound individually. c) Compound B has a lower melting temperature than Compound A. d) Compound A has a higher vapor pressure than Compound B.
d) Compound A has a higher vapor pressure than Compound B.
What is the primary use of a rotary evaporator? a) Collecting solids at the bottom of a flask b) Mixing solutions together c) Running a reaction at a constant temperature d) Drying and purifying samples
d) Drying and purifying samples
Which of these affects the chemical shift of a nucleus relative to a standard? a) Magnetic strength of the instrument b) The weather c) Instrument software d) Electrons of nearby atoms
d) Electrons of nearby atoms
Which of the following will not encourage crystallization? a) Adding a seed crystal b) Scratching the bottom of the flask c) Agitating the solution d) Further increasing the temperature of the solution
d) Further increasing the temperature of the solution
Which of the following is was not used in any of the videos for determination of boiling point? a) Glass Capillary b) Thermometer c) Test Tube d) Heating Mantle e) Ring Stand
d) Heating Mantle
Why must the FID always be hotter than the GC column? a) Keeping the GC column warm.Keeping the GC column warm. b) Inducing condensation. c) Burning off the carrier gas. d) Preventing condensation.
d) Preventing condensation.
What is recrystallization used for? a) Depositing thin films. b) Degassing a solution. c) Performing a solvent-free reaction. d) Purifying solid compounds.
d) Purifying solid compounds.
A biochemist receives a patient sample that is thought 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? a) Thin layer chromatography b) Ion exchange chromatography c) Affinity chromatography d) Size exclusion chromatography
d) Size exclusion chromatography
What occurs in an SN1 reaction? a) Slow nucleophilic back-attack on the α-carbon, then fast departure of the leaving group. b) Fast nucleophilic attack on either side of the α-carbon, then slow departure of the leaving group. c) Fast departure of the leaving group, then electrophilic attack on either side on the remaining carbocation. d) Slow departure of the leaving group, then nucleophilic attack on either side of the remaining carbocation.
d) Slow departure of the leaving group, then nucleophilic attack on either side of the remaining carbocation.
What is important to consider when choosing solvents? a) Solid phase density b) Solvent and solute color c) Weight of the collection flask d) Solvent and solute polarity
d) Solvent and solute polarity
Which of the following is NOT true of reverse-phase HPLC? a) Compounds are eluted in order of decreasing polarity. b) The mobile phase is usually a mixture of water and an organic solvent. c) The stationary phase is usually silica beads with a hydrophobic coating. d) Solvents are never degassed to ensure that there are a lot of gas bubbles in the mobile phase.
d) Solvents are never degassed to ensure that there are a lot of gas bubbles in the mobile phase.
How should you start putting the system under vacuum? a) Start at a very high vacuum so the solvent is removed quickly. b) Start the vacuum at the same setting as the last person who used it, no matter what. c) Start at a very low vacuum and do not increase the vacuum strength for any reason. d) Start with a low vacuum and increase the vacuum strength as needed until solvent begins condensing in the trap or the solution starts bubbling.
d) Start with a low vacuum and increase the vacuum strength as needed until solvent begins condensing in the trap or the solution starts bubbling.
Which of the following statements regarding acid-base extractions is NOT correct? a) To extract a basic organic compound, acid is added to form water-soluble ions that will partition into the aqueous phase. b) Acid-base extractions require a significant difference in the solubility of the organic compound with its conjugate salt in the aqueous phase. c) To extract an organic compound that can donate hydrogens, a base is added to allow the salt to partition into the aqueous phase. d) The addition of an acid or base disrupts the organic phase, allowing the organic compound to become more soluble in water.
d) The addition of an acid or base disrupts the organic phase, allowing the organic compound to become more soluble in water.
Which of these is NOT required for a two-solvent system? a) A solvent in which the solute is highly soluble. b) The two solvents are miscible. c) A solvent in which the solute is less soluble. d) The two solvents are an acid-base pair.
d) The two solvents are an acid-base pair.
When should you record the temperature in a melting point test? a) When the sample is half-melted and when the sample is completely molten. b) Only when the sample is completely molten. c) Only when the sample starts melting. d) When the sample starts melting and when the sample is completely molten.
d) When the sample starts melting and when the sample is completely molten.
To improve separation on the plate, the spot should be... a) as large as possible. b) easy to visualize. c) applied with enough force to chip the surface of the plate. d) as small as possible.
d) as small as possible.
NMR spectroscopy CANNOT provide information about... a) reaction progress. b) purity. c) structure. d) color.
d) color.
Which of the following is NOT part of a mass spectrometer? a) mass analyzer b) ionization source c) detector d) fusion generator
d) fusion generator
What is used to hold the sample in a melting point apparatus? a) Erlenmeyer flask b) weigh boat c) filter paper d) glass capillary
d) glass capillary
The dimensions of an FID peak are proportional to the... a) retention time of the analyte corresponding to that peak. b) temperature of the hydrogen flame. c) flow rate of the carrier gas. d) mass of carbon in the analyte corresponding to that peak.
d) mass of carbon in the analyte corresponding to that peak.
For a pure liquid, the boiling point is the thermodynamic condition where... a)the solid and liquid phases coexist. b) only the liquid phase exists. c) the gas and plasma phases coexist. d) the vapor pressure of the liquid is equal to the atmospheric pressure
d) the vapor pressure of the liquid is equal to the atmospheric pressure