Ochem Final Practice TEST 2 PDF

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CHEMISTRY 237 FINAL EXAMINATION SPRING 2018 TEST FORM A

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Chemistry 237 – Spring 2018

Final Examination – Form A

Ch Choos oos oose e tthe he m most ost co corr rr rrect ect an answ sw swer: er: (4 poi points nts each) 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 d. 100g 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 e. square 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 e. a C-H stretch at approximately 3100 cm-1 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

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 c. boiling points below the melting point of the solute d. poor ability to dissolve the solute at low temperatures e. low toxicity

Form A – Page 3

Chemistry 237 – Spring 2018

Final Examination – Form 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. d.

b.

e.

Impossible to tell

c.

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. e. the fact that the detector is damaged by large injections. 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 c. gain of C-Br bend d. gain of N-H stretch e. IR cannot be used to monitor the progress of a reaction

Form A – Page 4

Chemistry 237 – Spring 2018

Final Examination – Form A

9. Select the proper set of reagents to complete the following two reactions:

b. c. d. e.

1. reaction with sodium hypochlorite 1. oxidation with NaBH4 1. reaction with sodium borohydride 1. acid catalyzed condensation with water

2. reaction with sodium borohydride 2. reduction with NaOCl 2. oxidation with Tollens’ reagent 2. based catalyzed dehydration

10. Consider the following reaction:

What type of mechanism is this? b.

c. d.

SN2

E1 E2

e.

cannot be determined

11. Which structure(s) represent an alcohol? a.

CH3 CH2 OH

O

b. H

C

OH OH

c.

CH3 CH2 CH2 CH2 CHCH3

.

e.

a, b, and c

Form A – Page 5

Chemistry 237 – Spring 2018

Final Examination – Form A

12. Which structures below depict limonene and eugenol? .

b.

c.

d.

e.

None of the above

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. . 14. Rank the following conformations of 2-methylbutane in the increasing order of energy strain

I

II

III

IV

a. I, II, III, IV b. I, II and III, IV d. IV, I, II and III e. II and III, IV, I

Form A – Page 6

Chemistry 237 – Spring 2018

Final Examination – Form 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?

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. 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.

17. Preparative gas chromatography would be the best method for: 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). 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. e. The phase transfer catalyst is a quaternary ammonium salt 19. In the oxidation of cyclohexanol to cyclohexanone with bleach solution, the oxidation state of what element is reduced? a. Cr b. hydrogen d. O (of hypochlorous acid) e. C (attached to C=O of acetic acid)

Form A – Page 7

Chemistry 237 – Spring 2018

Final Examination – Form A

20. In an SN2 reaction, if the concentration of the nucleophile is doubled, the rate of the reaction will: b. c. d. e.

be halved remain the same be quadrupled decrease by a factor of ten

21. An example of sp2 hybridization on the central atom is:

a.

c.

e.

both a and b

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. e. As the temperature of a liquid is reduced, the boiling point is raised. 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.

Form A – Page 8

Chemistry 237 – Spring 2018

Final Examination – Form A

24. Use the following IR spectrum to determine which compound is present in the sample.

c.

b.

e.

d.

25. In considering rotation about the C2-C3 bond of butane, how many conformations are encountered? a. one c. three b. two d. six 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 d. decrease of peaks around 1050-1300 cm-1 e. presence of a peak around 3300 cm-1

Form A – Page 9

Chemistry 237 – Spring 2018

Final Examination – Form A

27. Why would an organic substance dissolve in a basic sodium bicarbonate solution which is mostly water? a. The compound is conjugated c. The compound is basic d. The compounds melting point is high e. The compound is a liquid 28. Common TLC stationary phases include all of the following except: a. Silica gel c. Alumina d. Microcrystalline cellulose e. All of the above 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

30. What product(s) can be prepared through the oxidation of primary alcohols? a. ketones b. aldehydes and ketones c. ketones and carboxylic acids e. carboxylic acids 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 d. solve this equation for k ln([A]o/[A]t) = kt e. solve this equation for k ln([A]t/[A]o) = kt

Form A – Page 10

Chemistry 237 – Spring 2018

Final Examination – Form A

32. Which of the following molecules are expected to be sp3 hybridized at all multi-bonded atoms?

A

b.

A, C

B

C c. d.

B, C B, C, D

D e.

A, B, C, D

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

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 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. d. 2.5 mL of acetone is not enough to do an extraction. e. Acetone has a lower density than water.

Form A – Page 11

Chemistry 237 – Spring 2018

Final Examination – Form A

36. Which structure below will have the highest strain energy when calculated by molecular mechanics?

a.

b.

e.

c.

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?

b.

89%

c. d.

20% 11%

e.

100%

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. e. a and c only

Form A – Page 12

Chemistry 237 – Spring 2018

Final Examination – Form A

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 b. 0.33 and 0.55 d. 0.40 and 0.60 40. Which of the compounds below could be used as a phase transfer catalyst for a reaction of naphtholate anion with an alkyl halide? a.

b.

d. e.

41. Which of the following compounds undergoes a SN1 solvolysis reaction with the highest rate?

a.

d.

e.

c.

Form A – Page 13

Chemistry 237 – Spring 2018

Final Examination – Form A

42. What is the predicted hybridization of the oxygen in ethanol? a. sp b. sp2 d. s e. none of the above 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. 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. 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 d. lowers the boiling point and raises the vapor pressure e. has no effect on the boiling point or the vapor pressure 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? a.

d.

e. Na+

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 d. b and c e. none of the above

Form A – Page 14

Chemistry 237 – Spring 2018

Final Examination – Form A

47. Which of the following alcohols will have the highest and lowest E1 dehydration rate? I.

III.

II.

IV.

a. b.

highest IV and lowest I highest II and lowest III

V.

e. d.

highest V and lowest IV

highest III and lowest I

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 c. Volatility and miscibility 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

50. The product of the following reaction with sodium hypochlorite and acetic acid is:

a.

d.

e.

c.

Form A – Page 15

Chemistry 237 – Spring 2018

Final Examination – Form A

Form A – Page 16...