TAMU CHEM 237 Lab Final Review
10. Consider the following reaction: What type of mechanism is this? a. SN1 c. E1 e. cannot be determined b. SN2 d. E2
A
12. Which structures below depict limonene and eugenol?
A
15. In attempting to recrystallize impure benzoic acid, it was found that the benzoic acid formed a layer of oil on top of the recrystallizing solvent as the solution cooled. How could this problem be solved? a. Reheat the solution to completely dissolve the oil, add a small portion of hot solvent, and allow the solution to cool slowly. b. Reheat the solution, and then quickly place the hot solution in an ice bath to induce crystallization. c. Add NaOH to make the solution basic, and then allow the solution to cool slowly. d. Add HCl to acidify the solution, and then allow the solution to cool slowly in an ice bath. e. Add an organic solvent to help dissolve the oil, reheat the solution for a few minutes, and then allow it to cool.
A
17 13. If you have a sample that is known to be either adipic acid or acetanilide, what is a quick way to distinguish the two? a. Determine the solubility of each in sodium bicarbonate b. Perform a mixed melting point with the two substances c. Spot all three on a TLC plate and elute it d. Perform the bromine test e. Perform a GC analysis with both
A
17 16. What is the chemical formula of the precipitate formed in the Baeyer's test? a. MnO2 d. MnCl2 b. MnO e. KMnO4 c. K2MnO4
A
17 17. What effect on the rate of an SN1 type reaction would there be if you doubled the concentration of the nucleophile? a. it would have no effect on the rate b. stop the reaction completely c. increase the rate by a factor of 2 d. increase the rate by a factor of 4 e. decrease the rate by a factor of 2
A
17 19. In normal phase thin layer chromatography, the stationary phase is: a. polar b. nonpolar c. apolar d. similar in properties to derivatized silica gel e. is a derivative of cellulose
A
17 20. What is the volume range of a typical injection for the Preparative Gas Chromatography experiment? a. 25 - 100 µL b. 0.25 - 0.50 mL c. 500 - 700 µL d. 1.0 - 2.0 mL e. 5 - 10 mL
A
17 27. The distillate collected whilst dehydrating cyclohexanol is an azeotropic mixture of cyclohexene and water. What is the composition ratio of cyclohexene to water? a. 90:10 b. 25:75 c. 60:40 d. 20:80 e. 75:25
A
17 30. Steam distillation is useful for isolating compounds that: a. are water immiscible with low vapor pressure at room temperature b. are water soluble and have a high vapor pressure at room temperature c. are high melting solids d. are water soluble e. have high viscosity
A
17 39. What observation would be most conclusive in determining that the following compound was successfully oxidized to it carbonyl product? a. IR band at 1710 cm-1 b. Product with a higher boiling point than starting alcohol c. Presence of IR band at 3500 cm-1 d. Double bonds in 2680 and 2830 cm-1 region of IR spectrum e. Oxidation of this tertiary alcohol is not possible
A
17 40. For the following reaction, the starting material weighs 3.00 g and the final product weighs 2.00 g. What is the percent yield for this reaction? Cyclohexanol (100 g /mol) + H+ -> Cyclohexene (82 g/mol) + H2O a. 81.3% b. 54.7% c. 66.7% d. 76.9% e. 100%
A
17 41. Which of the following items is not true of the mini-column used in the phase transfer catalysis? a. Any leftover starting material eluted off the column before the product. b. The column contains silica gel like the particles on the TLC plate, only larger in particle size. c. The naphthyl ether product elutes out first. d. The column is used as a purification technique. e. Methylene chloride was the mobile phase in the column.
A
17. Preparative gas chromatography would be the best method for: a. the separation of 0.5 g of a mixture of two liquids (bp 150 C and 160 C). b. the separation of 30 mL of a mixture of two liquids (bp 136 C and 162 C). c. the separation of the -naphthol ether from the starting materials and catalyst used in the synthesis of allyl--naphthyl ether. d. the purification of a high molecular weight protein. e. the separation of a solution of a liquid (bp 150 C) and a solid (mp 200 C).
A
20. In an SN2 reaction, if the concentration of the nucleophile is doubled, the rate of the reaction will: a. be doubled b. be halved c. remain the same d. be quadrupled e. decrease by a factor of ten
A
24. Use the following IR spectrum to determine which compound is present in the sample.
A
32. Which of the following molecules are expected to be sp3 hybridized at all multi-bonded atoms? a. A, B, C c. B, C e. A, B, C, D b. A, C d. B, C, D
A
37. In the dehydration of cyclohexanol experiment, there is a possibility that the intermediate cyclohexyl cation (carbonium ion) might undergo a condensation reaction with a starting cyclohexanol molecule to produce dicyclohexyl ether as a byproduct (see reaction below). If this condensation reaction had taken place during your experiment and gave you a mixture of cyclohexene and dicyclohexyl ether in 8:1 mole ratio as a result, what would be the percent yield of cyclohexene, considering all of cyclohexanol was converted to these two products? a. 80% c. 20% e. 100% b. 89% d. 11%
A
6. In the Who Has My Compound? experiment (among other experiments) you performed thin layer chromatography on a number of compounds and used the Rf values to help determine who else had the same compound as you had. Based on the structures of the following molecules, which would you expect to have the lowest Rf value when run in 50/50 EtOAc and Hexanes.
A
9. Select the proper set of reagents to complete the following two reactions: a. 1. reaction with sodium borohydride 2. reaction with HOCl b. 1. reaction with sodium hypochlorite 2. reaction with sodium borohydride c. 1. oxidation with NaBH4 2. reduction with NaOCl d. 1. reaction with sodium borohydride 2. oxidation with Tollens' reagent e. 1. acid catalyzed condensation with water 2. based catalyzed dehydration
A
1. Considering the reaction of 2A + 3B goes to 1C + 3D, with molecular weights being 150, 200, 200, and 233 for A, B, C and D respectively, what would the theoretical yield for C be if you started with an excess of B and 75 grams of A. a. 25g c. 75g e. 175g b. 50g d. 100g
B
17 10. Which of the structures shown below would exhibit the lowest IR energy absorption for the carbonyl functionality?
B
17 11. Arrange the following substituted cyclohexanes in order of increasing total steric strain (lowest strain energy first). You may need to see Table below.
B
17 14. Why is it important not to distill a flask/vial to dryness? a. the product will polymerize b. the residue in the flask could explode c. the glass will melt d. the heating mantle might catch fire e. the boiling chips will melt and contaminate the product
B
17 23. Infrared spectroscopy may be used to distinguish a primary amine from a secondary amine because: a. Secondary amines do not show N-H absorption in the 3400-3100 cm-1 region. b. Primary amines show two absorptions at 3400-3100 cm-1 and secondary amines show only one absorption at 3400-3100 cm-1 . c. Secondary amines show no absorptions at 3400-3100 cm-1 and primary amines show one absorption at 3400-3100 cm-1 . d. Primary amines do not show N-H absorptions in the 3400-3100 cm-1 . e. Primary amines show one absorption at 3400-3100 cm-1 and secondary amines show two absorptions at 3400-3100 cm-1 .
B
17 26. Which of the following functional groups has sp hybridization? a. Alkene b. Alkyne c. Alcohol d. Amine e. None of the above
B
17 28. In the solvolysis reaction of 1-chloro-1-phenylethane what is the nucleophile? a. 1-phenyl-1-chloroethane b. water c. H3O+ d. -OH e. all of these
B
17 44. In a distillation, one vaporization and condensation step is usually called a(n): a. azeotrope b. theoretical plate c. eutectic d. reflux ratio e. retention
B
17 46. Which compound below would you expect to have a greater than zero dipole moment?
B
17 47. Which of the following statements is false for recrystallization as a method for purification of organic compounds? a. Low solubility of the compound at low temperatures minimizes the amount of the purified compound that will be lost during recrystallization. b. If the impurities are soluble, they may be removed by filtration at high temperatures. c. Scratching the side of the beaker with a stirring rod may induce crystallization. d. Recrystallization is often used to purify solids. e. A good recrystallization solvent should be reasonably volatile.
B
17 48. In the Who Has My Compound experiment, which technique did you not use to determine your compound? a. melting point determination b. boiling point determination c. solubility in sodium bicarbonate d. thin layer chromatography e. all of the above were used
B
21. An example of sp2 hybridization on the central atom is:
B
27. Why would an organic substance dissolve in a basic sodium bicarbonate solution which is mostly water? a. The compound is conjugated b. The compound reacts to make a charged compound c. The compound is basic d. The compounds melting point is high e. The compound is a liquid
B
28. Common TLC stationary phases include all of the following except: a. Silica gel b. Calcium chloride c. Alumina d. Microcrystalline cellulose e. All of the above
B
41. Which of the following compounds undergoes a SN1 solvolysis reaction with the highest rate?
B
43. In the natural product isolation experiment, which of the following statements is false? a. Some common classes of natural products are terpenes, steroids, acetogenins, and alkaloids. b. Eugenol and limonene are a steroid and a terpene, respectively. c. Eugenol reacts with ferric chloride to give colored complexes. d. The Baeyer test for limonene is positive. e. The bromine test for limonene is positive.
B
45. In an acid/base extraction of p-toluidine and benzoic acid, which of the following would you expect to find in the aqueous layer after addition of NaOH?
B
5. Which of the following is not a criterion for the selection of a good recrystallization solvent? a. ability to dissolve the solute at elevated temperature b. low volatility c. boiling points below the melting point of the solute d. poor ability to dissolve the solute at low temperatures e. low toxicity
B
50. The product of the following reaction with sodium hypochlorite and acetic acid is:
B
8. What change in naphthol's structure upon forming naphthyl ether will allow you to determine if the reaction is complete by IR? a. loss of C-O stretch b. loss of O-H stretch c. gain of C-Br bend d. gain of N-H stretch e. IR cannot be used to monitor the progress of a reaction
B
14. Rank the following conformations of 2-methylbutane in the increasing order of energy strain a. I, II, III, IV b. I, II and III, IV c. II and III, I, IV d. IV, I, II and III e. II and III, IV, I
C
17 1. Volatile organic compounds should: a. be handled carefully to avoid explosions b. not be kept in closed containers c. be transferred in the hood d. be handled only with polystyrene gloves e. all of these
C
17 15. Which reagent is not an oxidizing agent? a. NaOCl b. KMnO4 c. H2O d. K2Cr2O7 e. CrO3
C
17 18. Compounds such as -pinene and (+)-limonene are members of the class of natural products known as: a. acetogenins b. steroids c. terpenes d. alkaloids e. carbohydrates
C
17 24. The computer calculated that the local minimum for the gauche butane conformation had a dihedral angle of: a. 0 b. 60 c. 65 d. 90 e. 180
C
17 3. A positive bromine test indicates the presence of what? a. phenols b. ketones c. carbon-carbon double bonds d. aromatic rings e. carboxylic acids
C
17 31. Which statement is true about thin layer chromatography? a. In liquid chromatography, the stationary phase is a liquid. b. Silica gel is a nonpolar material. c. The solvent moves through the stationary phase by capillary action. d. The polar solvent, derivatized silica gel system is called normal phase chromatography. e. If a compound is present in the silica gel that absorbs ultraviolet light, the area containing the compound will show up as a light spot under a UV lamp.
C
17 33. In simple distillation, the temperature frequently drops after the main fractions have distilled because: a. too much vapor and condensate are present in the head to keep the thermometer bulb hot b. impurities begin to distill c. not enough vapor and condensate are present in the head to keep the thermometer bulb hot d. uncondensed vapor is being carried through the condenser e. the thermometer is positioned incorrectly
C
17 36. Which of the following is the most polar compound? a. acetone b. acetic acid c. water d. toluene e. cyclohexane
C
17 37. If you take the melting point of an impure substance, the observed melting point range will be ______ relative to the melting point range observed for the pure substance. a. higher and broader b. higher and narrower c. lower and broader d. lower and narrower e. neither higher nor lower, but broader
C
17 5. A phenol (ArOH) that is deprotonated by NaOH will become _______. a. ArNa b. ArO+ c. ArO- Na+ d. Sodium hydroxide is not a powerful enough base to deprotonate a phenol e. NaOH is not acidic enough to deprotonate a phenol
C
19. In the oxidation of cyclohexanol to cyclohexanone with bleach solution, the oxidation state of what element is reduced? a. Cr b. hydrogen c. Cl d. O (of hypochlorous acid) e. C (attached to C=O of acetic acid)
C
26. In IR what kind of absorption can help you identify the cyclohexene formation for certain? a. increase of a broad band around 3200-3600 cm-1 b. decrease of peaks around 2850-2960 cm-1 c. presence of a peak around 1650 cm-1 and 3010-3100 cm-1 d. decrease of peaks around 1050-1300 cm-1 e. presence of a peak around 3300 cm-1
C
31. For a first order reaction, the specific rate constant is found by which of the following techniques? a. the slope of a line found by plotting ln([A]t/[A]o) versus the concentration of A b. the slope of a line found by plotting ln([A]t/[A]o) versus time c. the slope of a line found by plotting ln([A]o/[A]t) versus time d. solve this equation for k ln([A]o/[A]t) = kt e. solve this equation for k ln([A]t/[A]o) = kt
C
35. According to the Merck Index, the amount of solvent necessary to dissolve 1.0 g of mnitrobenzoic acid is: water - 146 mL, ethanol - 3 mL, chloroform - 220 mL, ether - 4.5 mL, acetone - 2.5 mL. Why wouldn't acetone be the best solvent to extract m-nitrobenzoic acid from water? a. The acid is not soluble enough in acetone. b. The acid is more soluble in water than in acetone. c. Acetone is soluble in water. d. 2.5 mL of acetone is not enough to do an extraction. e. Acetone has a lower density than water.
C
40. Which of the compounds below could be used as a phase transfer catalyst for a reaction of naphtholate anion with an alkyl halide?
C
42. What is the predicted hybridization of the oxygen in ethanol? a. sp b. sp2 c. sp3 d. s e. none of the above
C
44. A nonvolatile impurity dissolved in a liquid: a. raises the boiling point and the vapor pressure b. lowers the boiling point and the vapor pressure c. raises the boiling point and lowers the vapor pressure d. lowers the boiling point and raises the vapor pressure e. has no effect on the boiling point or the vapor pressure
C
46. Which of the following is a limitation to recrystallization? a. The solvent needs to dissolve the desired compound at low temperatures, but not at high temperatures b. The desired compound needs to be a liquid c. Some product will be lost d. b and c e. none of the above
C
47. Which of the following alcohols will have the highest and lowest E1 dehydration rate?
C
11. Which structure(s) represent an alcohol?
D
17 2. Which chemical was used to destroy excess oxidant in the oxidation of a 2° alcohol experiment? a. HOCl b. NaHCO2 c. HCl d. NaHSO3 e. Na2CO3
D
17 21. Which of the following statements about gas chromatography is true? a. Doubling the column length doubles the separation. b. Increasing temperature increases the retention time. c. Compounds with lower boiling points always elute first. d. Polar compounds are retained more by polar columns. e. Retention time is related to the percent composition.
D
17 32. Which of the following does not influence the separation of a mixture of compounds in gas chromatography? a. sample injection volume b. temperature at which the gas chromatography will be carried out c. the number of theoretical plates in the column d. the densities of the compounds in the sample e. polar interactions between the compounds and the liquid stationary phase
D
17 34. To separate two compounds by liquid-liquid extraction, the compounds must a. have a wide separation of boiling points. b. be slightly soluble at low temperature and highly soluble at elevated temperatures. c. have a lower boiling point than the solvent. d. be distributed unevenly between the two immiscible liquids. e. both be thermally stable and be reasonable volatile.
D
17 4. In the kinetics experiment, two different solvent mixtures were used. One mixture was 50% water-50% ethanol, the other was 60% water-40% ethanol. What would you predict about the rates in the two solvent mixtures? a. The rates would be the same. SN1 reactions are unaffected by the solvent. b. The rates would be the same. Both solvent mixtures have equal polarity. c. The rate in the 60% water-40% ethanol mixture would be faster because the solvent better stabilizes the anion. d. The rate in the 60% water-40% ethanol mixture would be faster because the solvent better stabilizes the cation. e. The rates would be the same. Both solvent mixtures have equal density.
D
17 43. In gas chromatography, the efficiency of separation does not depend on the: a. column operating temperature b. nature of the stationary phase c. column length d. type of detector used e. rate of gas flow
D
17 45. A mixture of benzoic acid, benzyl chloride and cyclohexyl amine is dissolved in dichloromethane. The solution is extracted with dilute aqueous HCl and the layers separated. The dichloromethane layer contains: 1. cyclohexyl amine 2. benzoic acid 3. benzyl chloride a. 1 only b. 2 only c. 3 only d. 2 and 3 e. 1 and 3
D
17 50. Which of the following would not be a role of the phase transfer catalyst? a. increases the yield of the desired product b. changes the solubility of the reactant ion c. allows both of the reactants to be solvated in the organic solvent d. aids in the separation of the products of the reaction e. promotes the reaction by pairing the hydrophillic ion with a hydrophobic counter ion
D
17 7. Which statement(s) below are advantages for the purification of compounds by preparative GC versus distillation? a. You may be able to separate different compounds which have exactly the same boiling point. b. You can isolate a compound at temperatures well below its boiling point once it has been vaporized. c. Some compounds which cannot survive the extended heating necessary for distillation may be stable enough to purify by GC. d. all of the above e. none of the above
D
17 9. You have carried out a synthesis and the pot contains your product (a liquid which you plan to distill) and one impurity. You will have to carry out a fractional distillation in order to recover the product in good purity if the impurity is: a. insoluble in the product b. immiscible with the product c. greater than 10% of the total volume in the pot d. soluble in the product and volatile e. all of these would require fractional distillation
D
18. Which statement is false for the phase transfer catalysis experiment? a. Preparation of a naphthyl ether is an example of an SN2 substitution b. Naphtholate anion is water soluble but practically insoluble in organic solvent c. Allyl bromide is organic soluble but water insoluble d. The role of the phase transfer catalyst, benzyltri-n-butyl ammonium chloride is to carry the naphtholate anion into the water e. The phase transfer catalyst is a quaternary ammonium salt
D
2. Steam distillation is a good method for the isolation of high boiling compounds because the vapor pressure for an immiscible mixture is equal to the _________ of the two compounds' vapor pressures. a. quotient b. product c. difference d. sum e. square
D
22. Which of the following statements is true? a. As the atmospheric pressure is reduced, the boiling point is raised. b. As the atmospheric pressure is raised, the vapor pressure of a liquid is lowered. c. As the atmospheric pressure is reduced, the vapor pressure of a liquid is lowered. d. As the temperature of a liquid increases, the vapor pressure increases. e. As the temperature of a liquid is reduced, the boiling point is raised.
D
3. What characteristic bond stretching does an aldehyde have in its IR spectrum that makes it easy to differentiate it from a ketone, a carboxylic acid, or an amide? a. an N-H stretch at 3300 cm-1 b. a C=O stretch at approximately 1700 cm-1 c. an O-H stretch at approximately 3300 cm-1 d. a C-H stretch at approximately 2700 cm-1 e. a C-H stretch at approximately 3100 cm-1
D
30. What product(s) can be prepared through the oxidation of primary alcohols? a. ketones b. aldehydes and ketones c. ketones and carboxylic acids d. aldehydes and carboxylic acids e. carboxylic acids
D
34. Upon simple distillation a mixture of CH3CH2OH and H2O distills at a constant boiling point and with a constant composition. This mixture is called a(n): a. liquid crystal c. polymorph e. hydrate b. eutectic mixture d. azeotrope
D
36. Which structure below will have the highest strain energy when calculated by molecular mechanics?
D
38. When you tested mixture melting point temperatures in the lab, your records showed that: a. the melting point of your unknown compound will not change no matter what you are mixing it with, so the melting point range will stay always narrowed and not depressed. b. the melting point of your unknown compound will be lower and the range broader if you mixed it with an organic compound different from your unknown. c. organic compounds and insoluble inorganic compounds that do not mix when melted give a melting range that is sharp even though there are inorganic impurities in the sample. d. b and c only e. a and c only
D
7. There is a maximum quantity of sample that should be injected for preparative gas chromatography separations. This maximum quantity is determined by: a. how much the column is cooled by large injections. b. the change in retention times caused by large injections. c. the tendency of compounds to decompose when large injections are made. d. loss of resolution (separation) with increasing injection size. e. the fact that the detector is damaged by large injections
D
13. How does a change in dipole moment effect IR absorption? a. A vibration causing a change in dipole moment will not be observed in the IR spectrum. b. Dipole moments have nothing to do with IR absorption. c. Small changes in dipole moment cause strong absorption in the IR spectrum. d. Large changes in dipole moment are unrecognizable in an IR spectrum. e. Bond stretching, causing a change in dipole moment, results in an IR absorption peak.
E
16. Which of the following statements best describes a eutectic mixture? a. The composition of mixture in exact 1:1 ratio b. The composition of components that never dissolves in on another c. The composition of mixtures of two elements that make highest possible melting point d. The composition of mixture of organic and inorganic sand in 4:1 ratio. e. The composition of mixtures of two elements that makes a lowest possible melting point
E
17 12. Which one of the following statements would not be desired in a good recrystallization solvent? a. A large amount of the desired compound dissolves at a temperature near the boiling point of the recrystallization solvent. b. Impurities are very insoluble in the recrystallization solvent. c. Impurities are highly soluble in the recrystallization solvent at all temperatures. d. The solvent is nonflammable. e. The recrystallization solvent is nonvolatile.
E
17 22. To form a salt of an amine, R-NH2, you must add which reagent? a. hexene b. NaOH c. magnesium sulfate d. NaCl e. HCl
E
17 25. In the recrystallization of acetanilide, you were asked to allow the hot solution to cool slowly to form crystals. What happens if the solution is cooled rapidly? a. the solvent evaporates. b. large crystals form which turn to oil. c. small pure crystals form. d. the crystals redissolve into the solution. e. small crystals form and adsorb impurities.
E
17 29. In the phase transfer catalysis experiment, the role of benzyltri-n-butylammonium chloride is a. to carry the chloride ion into the organic phase so the naphtholate anion is free to react. b. to lower the pH of the aqueous layer by removing OH-. c. to carry the allyl bromide to the aqueous layer so it can react with the naphtholate anion. d. to remove the allyl-2-naphyl ether from the reaction mixture while it is being formed so it is not able to undergo further reactions. e. to carry the naphtholate anion to the organic phase
E
17 35. The IR spectra of a compound reveals absorptions around 3400 cm-1 and 1600 cm-1 . Which of the following could be the compound?
E
17 38. Based on VSEPR theory, what is the hybridization of the nitrogen atom and the approximate bond angles around nitrogen in methylamine, CH3NH2? a. sp and 120 b. sp and 180 c. sp2 and 109.5 d. sp2 and 120 e. sp3 and 109.5
E
17 42. In TLC, a Rf value is: a. the distance a compound has moved b. the ratio of the distance the solvent moved divided by the distance the compound moved c. unaffected by the absorbent used d. the difference between the distance that the compound moved and the distance the solvent moved e. the ratio of the distance the compound moved divided by the distance the solvent moved
E
17 49. Which of these statements about the column with a typical GC is false? a. The typical column of a GC is constructed of a long, coiled tube. b. The column is contained in an oven. c. Longer columns give better resolution or separation. d. Column contains an inert, powdered solid. e. Column contents are volatile
E
17 6. When hexane was used as the solvent for your Analgesics TLC lab, why didn't the spots move? a. Hexane isn't able to move up the plate as efficiently as a more polar solvent b. Hexane has a lower vapor pressure than the other solvents used c. Hexane reacts with the silica and ruins the plate d. Hexane reacts with the analgesics and makes them too dense to travel up the plate e. Hexane is not able to disrupt the polar-polar interactions between the analgesics and the silica gel
E
17 8. Which of the following statements about gas chromatography is false? a. Increasing the sample volume may decrease resolution. b. An inert gas such as helium or nitrogen is used as the mobile phase. c. The number of theoretical plates is directly proportional to column length. d. Smaller particle size produces a higher number of plates. e. If the stationary phase is polymeric alcohol, a non polar compound would move more slowly than a polar compound with the same boiling point.
E
23. If two compounds are close in boiling points, which might be a good technique to separate them? a. Simple Distillation because it offers a high number of theoretical plates. b. Simple Distillation because it offers a low number of theoretical plates. c. Gas Chromatography because it separates compounds based on molecular weight. d. Both Simple Distillation and Gas Chromatography are valid techniques. e. Gas Chromatography because it can separate compounds based on polarity.
E
25. In considering rotation about the C2-C3 bond of butane, how many conformations are encountered? a. one c. three e. an infinite number b. two d. six
E
29. Which of the following is not true about phase transfer catalysts? a. They are applied to heterogeneous organic reactions b. They can change the solubility of the reagents c. Quaternary ammonium salts can be used as phase transfer catalyst d. They are soluble in organic solvents e. They are insoluble in water
E
33. In a Gas Chromatograph, the liquid adsorbed on to the column packing is usually referred to as: a. the mobile phase b. the solid phase c. the straight phase d. the chromatographic phase e. the stationary phase
E
39. In a thin layer chromatography experiment, a sample was spotted 1.0 cm from the bottom of a plate that was 10 cm long. When developed, the solvent was allowed to rise 9 cm above the bottom edge. Two spots were observed which had moved 3 cm and 5 cm from the point of origin. Their respective Rf values are: (Hint: draw the TLC plate) a. 0.30 and 0.50 c. 3.0 and 5.00 e. 0.38 and 0.63 b. 0.33 and 0.55 d. 0.40 and 0.60
E
4. A dichloromethane solution contains three compounds; A, B, and C. When this dichloromethane solution is extracted with aqueous sodium hydroxide, one obtains a basic aqueous solution of Compound A and a dichloromethane solution of compounds B and C. If this latter dichloromethane solution containing B and C is extracted with aqueous hydrochloric acid, one obtains an acidic aqueous solution containing the salt of compound B and a dichloromethane solution containing compound C. Of the following, Compound B is most probably: a. pentane b. benzoic acid c. naphthalene d. sodium sulfate e. benzocaine
E
48. What are the two main properties of compounds necessary to do a successful gas chromatography? a. Thermal stability and miscibility d. Thermal stability and immiscibility b. Thermal instability and volatility e. Thermal stability and volatility c. Volatility and miscibility
E
49. In a thin layer chromatography experiment, a compound is found to have an Rf close to unity (1.0). The spot for this compound on a TLC plate is most likely to appear: a. at the starting point b. slightly above the solvent front c. slightly above the starting point d. midway between the starting point and the solvent front e. slightly below the solvent front
E