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THE UNIVERSITY OF MELBOURNE SCHOOL OF CHEMISTRY SEMESTER 2 EXAMINATION, 2016 SUBJECT: CHEMISTRY 2, CHEM10004 Student Number: ___________________________ Exam Duration: 3 hours

Reading Time: 15 minutes

This paper has 22 pages. Authorized materials: Unassembled molecular model kits. Non-programmable, non-graphical calculators. Note:

Calculators are permitted in accordance with the rules of the Faculty of Science. They may be used for the processing of numerical information only. They must not have been programmed nor should they store additional information. Calculators will be randomly checked during the course of the examination.

Instructions to Invigilators: Students will attempt Section A on the examination paper itself. For Section A, students must also enter their answers on the computer scan sheet provided. Please remind students to leave the exam paper and the scan sheet on their desk for collection at the end of the examination. A 14-page script book is required for Section B of the paper. Instructions to Students: This assessment consists of two sections, Section A and Section B. Section A carries one half of the total marks available while Section B carries the remaining half. It is suggested that you spend equal time on each section. The marks available for each question are proportional to the suggested completion times given at the end of each question. You must answer Section A on the paper itself and also enter your answers on the computer scan sheet provided. Answer Section B in the examination script book provided. A table of selected physical constants, useful quantities and conversion factors is given in Appendix 1 and a table of standard reduction potentials is given in Appendix 2. Please ensure that the exam paper, the scan sheet and the script book used to answer Section B are all left on your desk at the end of the examination.

Paper to be held by Baillieu Library - YES

© 2016, The University of Melbourne

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© 2016, The University of Melbourne

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SECTION A The suggested time for this section is 1.5 hours. Note that a table of selected physical constants etc. are given in Appendix 1, and standard reduction potentials are given in Appendix 2. Your answers to this section of the examination must be circled on this examination script, which must be handed in at the end of the examination period. You must also show your answers to this section, together with your student number, on the computer scan sheet provided. Please enter your student enrolment number in the spaces provided. In addition, ensure that your student enrolment number is recorded on each page of Section A.

The following scheme is referred to in questions A1 – A4. O HN

NH2

O CH3

step 1

HN

O CH3

HN

CH3

step 2

aniline

NO2

OH paracetamol

Question A1. Part of a synthesis of the analgesic compound, paracetamol, is given above. The most appropriate reagent to effect the transformation depicted in step 1 shown above is: A.

acetic acid (ethanoic acid)

B.

ethyl acetate (ethyl ethanoate)

C.

acetic anhydride (ethanoic anhydride)

D.

acetone (propanone)

E.

None of the above. (3 minutes)

© 2016, The University of Melbourne

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CHEM10004 Semester 2, 2016

Question A2. The type of reaction shown in step 1 of the scheme shown above is: A.

an SN2 reaction

B.

an E1 reaction

C.

a nucleophilic addition reaction

D.

a nucleophilic addition/elimination reaction

E.

None of the above. (2 minutes)

Question A3. The most appropriate reagent to effect the transformation depicted in step 2 of the sequence depicted above is: A.

NO2 gas

B.

HNO3

C.

HNO3/H2SO4

D.

NO3

E.

None of the above. (3 minutes)

Question A4. The type of reaction shown in step 2 of the scheme shown above is: A.

a nucleophilic aromatic substitution

B.

an electrophilic aromatic substitution

C.

a nucleophilic addition/elimination reaction

D.

an electrophilic elimination reaction

E.

None of the above. (2 minutes)

© 2016, The University of Melbourne

Page 4 of 22

CHEM10004 Semester 2, 2016

Student enrolment number....................................

Question A5. Benzyl acetate, CH3CO2CH2C6H5, gives the characteristic flowery aroma to jasmine. Which sequence of reagents provides a plausible series of steps for the synthesis of benzyl acetate from benzyl bromide (C6H5CH2Br):

A

C6H5CH2Br

B

C6H5CH2Br

C

C6H5CH2Br

D

C6H5CH2Br

E

C6H5CH2Br

NaOH(aq)

C2H5COCl

NaOH(aq)

CH3CH2OH, H+

NaOH(aq)

CH3CH2Cl

NaOH(aq)

KMnO4

NaOH(aq)

CH3COCl

CH3CH2OH, H+

(3 minutes)

Question A6. Which one of the compounds listed below would be expected to react the fastest in an SN2 reaction with sodium bromide? A.

methanol

B.

2-iodobutane

C.

2-methyl-2-iodobutane

D.

sodium iodide

E.

None of the above would react with sodium bromide. (3 minutes)

© 2016, The University of Melbourne

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CHEM10004 Semester 2, 2016

Question A7. OH

Cl HCl

Which one of the following mechanisms most correctly describes the transformation depicted above? H Cl

OH2

OH

A.

Cl

H

B.

Cl

OH2

OH

Cl

H Cl

OH2

OH

C.

Cl

H

D.

Cl

OH2

OH

Cl

(4 minutes)

Question A8. Identify the best leaving group from the following chemical species (A-D). (pKa values of conjugate acids: H2O, 15.7; CH3NH2, 32; CH3CO2H, 4.7; C6H5OH, 10) O

O H3C

A.

NH

H3C

O

B.

OH

C.

D. (2 minutes)

© 2016, The University of Melbourne

Page 6 of 22

CHEM10004 Semester 2, 2016

Student enrolment number....................................

Question A9. Which one of the following is the most stable carbocation?

A.

B.

C.

D.

E.

(3 minutes)

Question A10. When treated with sodium hydroxide, the alkyl chloride shown below gives five possible elimination products (1-5).

NaOH

Cl alkyl chloride

+

1

+

+

2

3

+

4

5

Which product(s) constitute the major species formed? A. 1

B. 2 and 3

C. 4

D.

4 and 5

E. 5 (3 minutes)

Question A11. In a photoelectric effect experiment, what is the velocity of an electron emitted from a caesium (Cs) surface (Ebind = 206 kJ mol-1) by a photon with wavelength of 215 nm? A.

1.13 ´ 106 m s-1

B.

5.20 ´ 103 m s-1

C.

3.00 ´ 108 m s-1

D.

7.03 ´ 106 m s-1

E.

2.44 ´ 105 m s-1 (3 minutes)

© 2016, The University of Melbourne

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CHEM10004 Semester 2, 2016

Question A12. What is the De Broglie wavelength of an electron, photoemitted from a metal surface with a kinetic energy of 1.0233 × 10-19 J? A.

7.3 ´ 10-10 m

B.

1.2 ´ 10-10 m

C.

0.3 ´ 10-10 m

D.

1.53 ´ 10-9 m

E.

7.2 ´ 10-9 m (3 minutes)

Question A13. Which one of the following set of quantum numbers does NOT represent a valid solution of the Schrödinger equation for the hydrogen atom? n

l

ml

ms

A.

5

3

-2

-½

B.

3

0

0

-½

C.

3

3

-1

+½

D.

1

0

0

+½

E.

2

1

0

+½ (2 minutes)

Question A14. Which one of the following set of quantum numbers is associated to a 3d atomic orbital? n

l

ml

ms

A.

5

2

0

-½

B.

3

0

0

-½

C.

3

2

2

+½

D.

3

1

-1

-½

E.

4

2

1

+½ (2 minutes)

© 2016, The University of Melbourne

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CHEM10004 Semester 2, 2016

Student enrolment number....................................

Question A15. Which one of the following electron configurations corresponds to the ground state of the transition metal element chromium? A.

[Ar] 4s2 3d4

B.

[Ar] 4s0 3d6

C.

[Ar] 4s3 3d3

D.

[Ar] 4s1 3d5

E.

[Ar] 4s2 3d5 (2 minutes)

Question A16. Why is the ground state electron configuration of Li, 1s22s1 and not 1s22p1? A.

Because in the H atom energy spectrum, 2s orbitals have lower energy than 2p orbitals.

B.

Because of Hund’s rule.

C.

Because of the Pauli exclusion principle.

D.

Because the repulsion between the core 1s electrons and the valence electron in the n=2 shell (shielding effect) is reduced by the penetrating character of a 2s orbital.

E.

Because the 2p orbital is more penetrating than the 2s orbital. (2 minutes)

Question A17. The kinetics of oxidation of bromide by bromate in acidic solution: BrO3− + 5Br− + 6H+ ® 3Br2 + 3H2O has a rate law that is given by kobs[BrO3 − ] [Br− ] [H+]2. If an experiment is carried out in a highly acidic solution with a large excess of bromide over bromate, the observed changes in bromine concentration with time are likely to conform to an integrated rate equation which is: A. zeroeth order B.

first order

C.

second order

D.

third order

E.

fourth order (2 minutes) © 2016, The University of Melbourne

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CHEM10004 Semester 2, 2016

Question A18. The hydrolysis of sucrose to glucose and fructose is described by the reaction below: C12H22O11 + H2O

® C6H12O6 + C6H12O11

The activation energy for this reaction is 108 kJ mol-1. If at 35 oC, k for this reaction is 6.2 × 10-5 s-1, what is the rate constant, k, at 45 oC closest to? A.

9.7 x 10-5 s-1

B.

0.7 x 10-4 s-1

C.

1.7 x 10-4 s-1

D.

2.3 x 10-4 s-1

E.

3.2 x 10-4 s-1 (3 minutes)

Question A19. The reduction of NO to N2 by hydrogen is proposed to have a mechanism involving the following elementary steps: 2NO ® N2O2 N2O2 + H2 ® N2O + H2O N2O + H2 ® N2 + H2O In the overall stoichiometric reaction, at any time t, A.

d[NO]/dt = d[H2O]/dt = 2d[N2]/dt

B.

d[N2O]/dt = d[N2]/dt = −d[H2]/dt

C.

d[H2O]/dt = d[N2]/dt = d[N2O2]/dt

D.

d[NO]/dt = d[N2]/dt = d[N2O]/dt

E.

d[NO]/dt = −2d[N2]/dt = d[H2]/dt (3 minutes)

© 2016, The University of Melbourne

Page 10 of 22

CHEM10004 Semester 2, 2016

Student enrolment number....................................

Question A20. The formation of gaseous HBr from hydrogen and bromine is proposed to occur via the mechanism, which is given below:

Which one of the following statements is TRUE? A.

The steps leading to HBr as product, are chain termination steps.

B.

Bromine molecules are chain carriers.

C.

Bromine atoms are chain carriers, but hydrogen molecules are not.

D.

Hydrogen atoms are chain carriers and so are bromine atoms.

E.

There are two chain termination steps in the scheme shown here. (3 minutes)

Question A21. The following concentration/time data were determined at 120 oC for the breakdown of benzoyl peroxide, a radical initiator in some free radical polymerisation chain reactions. Time (min) [Benzoyl peroxide] × 102 (M)

0

15

30

45

60

75

2.19

1.53

1.09

0.77

0.54

0.38

The rate constant for this reaction is: A.

1.38 min-1

B.

0.032 min-1

C.

5.3 x 10-4 s-1

D.

3.8 x 10-4 s-1

E.

Cannot be determined from this data. (3 minutes)

© 2016, The University of Melbourne

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CHEM10004 Semester 2, 2016

Use the Table of standard reduction potentials in Appendix 2 to assist you in answering Questions A22 and A25. Question A22. Which one of the following statements is TRUE? A.

Ag spontaneously reduces Cl2 and Cl2 spontaneously oxidises F−.

B.

Cl2 spontaneously reduces Cu and Zn spontaneously reduces Cu.

C.

Zn2+ spontaneously oxidises Fe and Zn spontaneously reduces Mn2+.

D.

F2 is a stronger oxidising agent than Cl2 and Fe is a stronger reducing agent than Zn.

E.

Ag is a stronger reducing agent than Cl− and Mn2+ is a stronger oxidising agent than Na+. (3 minutes)

The following diagram is to be used to answer questions A23 to A24. The LEFT half cell has a 1 M solution of silver nitrate (AgNO3) in water. The RIGHT half cell has a solution formed by adding silver sulfate (Ag2SO4) to water.

V Ag electrode

Ag electrode

+

+

[Ag ]=1.00 M

[Ag ]= ? M Ag SO 2

4

Ag2SO4, Ksp = 2.0´10-5 Question A23. Which one of the following statements concerning the Galvanic cell shown above is TRUE? A.

The LEFT Ag electrode is the anode and electrons flow from LEFT to RIGHT.

B.

The LEFT Ag electrode is the anode and electrons flow from RIGHT to LEFT.

C.

The RIGHT Ag electrode is the anode and electrons flow from LEFT to RIGHT.

D.

The RIGHT Ag electrode is the anode and electrons flow from RIGHT to LEFT.

E.

Neither electrode acts as the anode because Ecell = 0 V. (2 minutes) © 2016, The University of Melbourne

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CHEM10004 Semester 2, 2016

Student enrolment number....................................

Question A24. Which one of the following changes will lead to the LARGEST increase in Ecell? A.

Lowering the concentration of Ag+ in the LEFT half cell and raising the concentration of SO42- in the RIGHT half cell.

B.

Lowering the concentration of Ag+ in the LEFT half cell and lowering the concentration of SO42- in the RIGHT half cell.

C.

Raising the concentration of Ag+ in the LEFT half cell and raising the concentration of SO42- in the RIGHT half cell.

D.

Raising the concentration of Ag+ in the LEFT half cell and lowering the concentration of SO42- in the RIGHT half cell.

E.

Doubling the size of the electrodes. (2 minutes)

Question A25. By considering the standard reduction potentials given in Appendix 2, decide which of the following metals could be used as a sacrificial coating to protect nickel metal, Ni(s)? A. Cu

B. Mg

C. Ag

D. Sn

E. Any of these metals. (2 minutes)

Question A26. Which one of the following only includes the transition metals in common oxidation states (i.e. oxidation states observed for the ions in aqueous solution in the presence of dioxygen)? A.

VV, CrVI and MnIII

B.

VIV, CrII and TiII

C.

CrIII, MnII and FeIII

D.

TiIII, VII, and MnII

E.

FeIV, CoII and CuIII (3 minutes)

© 2016, The University of Melbourne

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CHEM10004 Semester 2, 2016

Question A27. Which one of the following cations would generate solutions with the HIGHEST acidity (i.e. lowest pKa)? A. Fe3+

B. Ca2+

C. Na+

D. Cu2+

E. All cations have the same pKa. (2 minutes)

Question A28. Which one of the following statements is INCORRECT? A.

Enterobactin is a good ligand for iron.

B.

The crystal field stabilisation energy for low spin octahedral Fe2+ is -2.4Do + 2P.

C.

The compounds cis- and trans-[PtCl2(NH3)2] have identical anti-cancer properties.

D.

Porphyrin is a tetradentate ligand.

E.

Iron is typically in the +3 oxidation state at the surface of lakes/the ocean. (3 minutes)

Question A29. Which one of the following statements is INCORRECT? A.

Copper is important in a number of metalloenzymes.

B.

Cyanide is a stronger field ligand than bromide.

C.

The coordination complex [MnO4]− has a tetrahedral coordination geometry.

D.

Amino acids can be ligands for transition metals.

E.

Mn2+ complexes often have a magnetic moment, µ, of 6.9 BM. (3 minutes)

Question A30. Which one of the following ions is most likely to undergo a Jahn-Teller tetragonal elongation? A.

Cu+

B.

Mn7+

C.

Cr2+

D.

Ti4+

E.

Zn2+ (2 minutes)

© 2016, The University of Melbourne

Page 14 of 22

CHEM10004 Semester 2, 2016

Student enrolment number....................................

Question A31. Which one of the following combinations gives the most likely numbers of unpaired electrons for cobalt(II) complexes? A.

0 and 1

B.

0 and 3