Preparatory Problems"Bonding the World with Chemistry"
49th INTERNATIONAL CHEMISTRY OLYMPIAD
Nakhon Pathom, THAILAND

Preparatory problems: 49th IChO, Thailand, 20171

Preface
On behalf of the scientific committee, I am delighted to provide Preparatory Problems forthe 49th International Chemistry Olympiad. The aim of these problems is to facilitate thepreparation of participants. We intended to prepare problems to cover wide range of challenging
topics in modern chemistry that could be solved by applying fundamental chemical principles
covered in high school level along with six topics of advanced difficulty. These advanced topics
are listed explicitly under “Topics of Advanced Difficulty” and their applications are demonstrated
in the tasks. We expect the participants to be familiar with these topics.
The problems listed in this book consisted of 33 theoretical and 5 practical tasks. We hope
you find these tasks useful to prepare for the competition. The official solutions are only available
to the mentors of each country in May 2017. The Preparatory Problems with Solutions will be
published later on our IChO 2017 website. We welcome any comments, corrections or questions
about the problems to icho2017@mahidol.ac.th.
We also would like to take this opportunity to welcome you to Thailand. The International
Chemistry Olympiad is a venue for scholarly gathering and certainly will keep the participants
intellectually intrigued and inspired. We hope you will enjoy not only a challenging chemistrycompetition but also great and memorable experiences of Thai cultures. We look forward to seeing
you in Thailand.

Acknowledgements
I would like to express my deep gratitude to all the authors for their dedication and effort
in contributing to the Preparatory Problems as well as the members of the International Steering
Committee for valuable comments and suggestions. I also highly appreciate The Institute for the
Promotion of Teaching Science and Technology (IPST) in collaboration with the Faculty of
Science, Mahidol University, for facilitating meetings for members of Scientific Committee.

Piniti Ratananukul
Chair–Scientific Committee
Bangkok, 31 January 2017

Preparatory problems: 49th IChO, Thailand, 20172

Table of Contents
Page
Task Authors

4

Constants and Formulae

5

Periodic Table

6

Characteristic 1H and 13C NMR Chemical Shifts

7

IR Absorption Frequencies Table

8

Fields of Advanced Difficulty

10

Task lists

11

Theoretical Tasks

13

Practical Tasks

45

Appendices58

Preparatory problems: 49th IChO, Thailand, 20173

Task Authors
Chair of Scientific Committee
Piniti Ratananukul

POSN

Advisory Committee
Orn-anong Arqueropanyo
Laddawan Pdungsap
Yenchai Somvichian
Sunanta Vibuljan
Prapin Wilairat

Chiang Mai University
Mahidol University
POSN
Mahidol University
Mahidol University

Contributing Authors
Pongsaton Amornpitoksuk
Radchada Buntem
Chutima Jiarpinitnun
Kritsana Jitmanee
Tinakorn Kanyanee
Duangjai Nacapricha
Suwat Nanan
Paiboon Ngernmeesri
Pasit Pakawatpanurut
Shuleewan Rajviroongit
Nuanlaor Ratanawimarnwong
Yupaporn Sameenoi
Anchalee Samphao
Preeyanuch Sangtrirutnugul
Atitaya Siripinyanond
Ekasith Somsook
Panida Surawatanawong
Akapong Suwattanamala
Jonggol Tantirungrotechai
Yuthana Tantirungrotechai
Saowapak Teerasong
Tienthong ThongpanchangCharnsak Thongsornkleeb

Preparatory problems: 49th IChO, Thailand, 2017

Prince of Songkla University
Silpakorn University
Mahidol University
Chiang Mai University
Chiang Mai University
Mahidol University
Khon Kaen University
Kasetsart University
Mahidol University
Mahidol University
Srinakharinwirot University
Burapha University
Ubon Ratchathani University
Mahidol University
Mahidol University
Mahidol University
Mahidol University
Burapha University
Mahidol University
Thammasat University
King Mongkut's Institute of Technology,
Ladkrabang
Mahidol University
Chulabhorn Graduate Institute4Constants and Formulae
Avogadro's constant, NA = 6.0221×1023 mol–1
Boltzmann constant, kB = 1.3807×10–23 J K–1
Universal gas constant, R = 8.3145 J K–1 mol–1 = 0.08205 atm L K–1 mol–1
Speed of light, c = 2.9979×108 m s–1
Planck's constant, h = 6.6261×10–34 J s
Faraday constant, F = 9.64853399×104 C
Mass of electron, me = 9.10938215×10–31 kg
Standard pressure, P = 1 bar = 105 Pa
Atmospheric pressure, Patm = 1.01325×105 Pa = 760 mmHg = 760 torr
Zero of the Celsius scale, 273.15 K
1 picometer (pm) = 10–12 m; 1 Å = 10-10 m; nanometer (nm) = 10–9 m
1 eV = 1.6 × 10-19 J
1 amu = 1.66053904 × 10-27 kg
Ideal gas equation: PV = nRT
Enthalpy:

H = U – PV

Gibbs free energy:

G = H – TSG  G o  RT ln Qo
G o   RT ln K  nFEcell

Entropy change:

S 

q rev
, where qrev is heat for the reversible process
TVS  nR ln 2 (for isothermal expansion of an ideal gas)
V1

Nernst equation:

C
o RT
EE 
ln ox
nF CredEnergy of a photon:

E

hc



I
Lambert-Beer law: A  log 0  bC
I

Integrated rate law
Zero order[A]  [A] 0  kt

Second order

1
1

 kt
[A] [A] 0

First orderln [A]  ln [A] 0  kt

Arrhenius equationk  Ae  Ea / RT

Preparatory problems: 49th IChO, Thailand, 20175

Periodic table of elements

Preparatory problems: 49th IChO, Thailand, 2017

6

Characteristic 1H NMR Chemical Shifts
Type of Hydrogen(R=Alkyl, Ar=Aryl)

Chemical Shift(ppm)

Type of Hydrogen(R=Alkyl, Ar=Aryl)

Chemical Shift(ppm)(CH3)4Si

0 (by definition)

RCH3

0.9

RCH=O

9.5-10.1

RCH2R

1.2-1.4

RCOOH'

10-13

R3CH

1.4-1.7

RCOCH3

2.1-2.3

RCH2I

3.2-3.3

RCOCH2R

2.2-2.6

RCH2Br

3.4-3.5

RCOOCH3

3.7-3.9

RCH2Cl3.6-3.8

RCOOCH2R

4.1-4.7

RCH2F

4.4-4.5

R2C=CRCHR2

1.6-2.6

RCH2NH2

2.3-2.9

R2C=CH2

4.6-5.0

RCH2OH

3.4-4.0

R2C=CHR

5.0-5.7

RCH2OR

3.3-4.0RC≡CH

2.0-3.0

RCH2CH2OR

1.5-1.6

ArCH3

2.2-2.5

R2NH

0.5-5.0

ArCH2R

2.3-2.8

ROH

0.5-6.0ArH

6.5-8.5

Characteristic 13C NMR Chemical Shifts
Type of Carbon(R=Alkyl, Ar=Aryl)

Chemical Shift(ppm)

Type of Carbon(R=Alkyl, Ar=Aryl)

Chemical Shift
(ppm)

RCH3

10-25

RC(triplebond)CR

65-85

RCH2R

20-35

RCH=CHR

120-140

R3CH

25-35

ArylC

120-140

RCH2COR

35-50

RCOOR

160-180

RCH2Br25-35

RCONR2(amide)165-180

RCH2Cl

40-45

RCOOH

175-185

RCH2NH2

30-65

RCHO

190-205

RCH2OH

60-70

RCOR

200-215

RCH2OR

65-70

Adapted from RSC E-learning website.

Preparatory problems: 49th IChO, Thailand, 2017

7

IR Absorption Frequencies Table
FunctionalGroup
Alcohol
O-H
O-H
C-O

Characteristic IR Absorption Frequencies of Organic Functional Groups
Characteristic Absorptions
Type of Vibration
Intensity(cm-1)(stretch, H-bonded)

3200-3600

strong, broad(stretch, free)

3500-3700

strong, sharp(stretch)

1050-1150

strongC-H

stretch2850-3000

strong-C-H

bending

1350-1480

variable=C-H

stretch3010-3100

medium=C-H

bending675-1000

strong

C=C

stretch1620-1680

variable

C-F

stretch1000-1400

strongC-Cl

stretch600-800

strongC-Br

stretch500-600

strongC-I

stretch500

strongstretch3300

strong,sharp

stretch2100-2260

variable, not present in symmetricalalkynesN-H

stretch3300-3500

medium (primary amines have two bands;
secondary have one band, often very
weak)

C-N

stretch1080-1360

medium-weakN-Hbending

1600

mediumC-Hstretch3000-3100

mediumC=C

stretch1400-1600

medium-weak, multiple bands

AlkaneAlkeneAlkyl Halide

AlkyneC-H

Amine

Aromatic

Analysis of C-H out-of-plane bending can often distinguish substitution patterns
Carbonyl
C=O

stretch1670-1820

strong(conjugation moves absorptions to lower wave numbers)
Ether
C-O

stretch1000-1300 (1070-1150)

Preparatory problems: 49th IChO, Thailand, 2017strong8

NitrileCN

stretch2210-2260

mediumstretch1515-1560 & 1345-1385

strong, two bands

Nitro
N-O

IR Absorption Frequencies of Functional Groups Containing a Carbonyl (C=O)
Functional
Characteristic Absorptions
Type of Vibration
IntensityGroup(cm-1)
Carbonyl
C=O

stretch1670-1820

strong(conjugation moves absorptions to lower wave numbers)
Acid
C=O

stretch1700-1725

strongO-H

stretch2500-3300

strong, very broad

C-O

stretch1210-1320

strong

C=O

stretch1740-1720

strong=C-H

stretch2820-2850 & 2720-2750

medium, two peaks

C=O

stretch1640-1690

strongN-H

stretch3100-3500

unsubstituted have two bands

N-H

bending1550-1640

stretch1800-1830 & 1740-1775

two bands

C=O

stretch1735-1750

strongC-O

stretch1000-1300

two bands or morestretch1705-1725

strongcyclicstretch3-membered - 1850
4-membered - 1780
5-membered - 1745
6-membered - 1715
7-membered - 1705

strong,-unsaturated

stretch1665-1685

strongaryl ketone

stretch1680-1700

strongAldehyde

Amide

Anhydride
C=O
Ester

Ketoneacyclic

Data from http://www2.ups.edu/faculty/hanson/Spectroscopy/IR/IRfrequencies.html

Preparatory problems: 49th IChO, Thailand, 20179

Fields of Advanced Difficulty
Theoretical
1. Solid state and coordination chemistry (crystal structures, crystal field theory, andisomerism of inorganic complexes)
2. Thermodynamics (gases, liquid mixing, temperature dependence of equilibrium constant,electromotive force, and Gibbs free energy)
3. Electrochemistry and electrochemical analysis (amperometry and conductometry)
4. Kinetics (adsorption on solid catalyst, Arrhenius equation, and Integrated rate law)
5. Organic chemistry (stereoisomerism, simple stereocontrolled organic transformations,[4+2]-cycloaddition, and [3,3]-sigmatropic rearrangement)
6. Spectroscopy (Students are expected to relate simple organic structures with their
1

H-NMR, 13C-NMR, or IR data.)

Practical
1. Use of spectrophotometer
2. Basic techniques in organic synthesis (recrystallization and TLC, following the described
procedures)

Notes:
1. Although a few examples in the preparatory problems are related to biomolecules,
students are not expected to cover any biochemistry or carbohydrate chemistry as advanced topics.
2. Students are not required to use Microsoft Excel or any related computer software during
the exam.
3. Students are not expected to determine melting points in the exam.

Preparatory problems: 49th IChO, Thailand, 201710

Task lists
Theoretical partPage

Task 1. Dimerization of Acetic Acid

13

Task 2. Solubility of Calcite

13

Task 3. Expansion of Ideal Gas and Thermodynamics of Liquid Mixing

13

Task 4. Vibrational Frequency of a Diatomic Molecule

14

Task 5. Water-gas-shift Reaction

14

Task 6. Camphor in Benzene

15

Task 7. Gas and Liquid

16

Task 8. Decomposition of Nitrous Oxide

16

Task 9. Avogadro’s Number

17

Task 10. Buffer from Biological Acid: Lysine

18

Task 11. Amperometric Titration: Titration of Pb2+ with Cr2O72-

19

Task 12. Conductometric Titration

20

Task 13. Titration of Cu and Zn in Metal Alloy

21

Task 14. Spectrophotometric Determination of Iron

21

Task 15. Basic Electrochemistry24

Task 16. Calculation of Concentration

24

Task 17. Small Molecule Activation by Frustrated Lewis Pairs

25

Task 18. Silver Iodide

26

Task 19. Perovskite Structure

27

Task 20. Quantum Numbers and Atomic Orbitals

28

Preparatory problems: 49th IChO, Thailand, 201711

Task 21. Radioactivity of Iodine and Nuclear Equations

29

Task 22. Structure and Chemistry of Sodium Chloride

29

Task 23. Natural Chelator from Shrimp Shell

31

Task 24. Compound Identification and Related Chemistry33

Task 25. Isomerism of Octahedral Fe Complexes

34

Task 26. Stoichiometry and Structure Determination

34

Task 27. Atropine

35

Task 28. Synthesis of Building Blocks for Fluorescent Markers

37

Task 29. Synthesis towards Anatoxin-a

38

Task 30. Total Synthesis of Illudin C

39

Task 31. Total Synthesis of -Opioid Receptor (MOR) Agonists

39

Task 32. Pericyclic Reaction

41

Task 33. Stereoisomers without Stereocenter

43

Practical Part

Page

Task P1. Quantitative Determination of Ascorbic Acid and Citric Acid in
Beverages

46

Task P2. Spectrophotometric Determination of Chromium and Manganese

49

Task P3. Synthesis of “Ferrocenated” Iron Oxide Nanoparticles and Their
Activities in the Decolorization of Methylene Blue

52

Task P4. Synthesis of Aspirin

54

Task P5. Synthesis of Benzopinacolone

56

Preparatory problems: 49th IChO, Thailand, 201712

Part I: Theoretical Tasks
Task 1. Dimerization of Acetic Acid
Ethanoic acid or acetic acid (CH3COOH) is partially dimerized into dimers in the vapor
phase. At a total pressure of 0.200 atm, ethanoic acid is 92.0% dimerized at 298 K. By increasing
the temperature to 318 K, the degree of dimerization is lowered, with Kp = 37.3.
1.1) Calculate the enthalpy and the entropy changes for the reaction, assuming that ΔHoand ΔSo do not vary with temperature.
1.2) Applying the Le Chatelier’s principle, an increase of pressure should (select one
correct answer)⃝ favor the dimerization.
⃝ not favor the dimerization.
1.3) Continued from question 1.2, the extent of dimerization (select one correct answer)⃝ decreases with increasing the temperature.
⃝ increases with increasing the temperature.

Task 2. Solubility of Calcite
Calcite is a stable form of calcium carbonate (CaCO3). The solubility product (Ksp) is
decreased with increasing temperature; Ksp are 9.50 × 10-9 and 2.30 × 10-9 at 0 C and 50 C,
respectively. Estimate the enthalpy change for the solubility process of calcite.

Task 3. Expansion of Ideal Gas and Thermodynamics of Liquid Mixing
3.1) A quantity of 0.10 mol of an ideal gas A initially at 22.2 oC is expanded from0.200 dm3 to 2.42 dm3. Calculate the values of work (w), heat (q), internal energy change (U),
entropy change of the system (Ssys), entropy change of the surroundings (Ssurr), and total entropychange (Suniv) if the process is carried out isothermally and irreversibly against an externalpressure of 1.00 atm.
3.2) If 3.00 mol of A is condensed into liquid state and is mixed with 5.00 mol of liquid B,
calculate the changes in entropy and Gibbs free energy upon such mixing at 25.0 C. This mixture
can be assumed to be ideal.

Preparatory problems: 49th IChO, Thailand, 201713

Task 4. Vibrational Frequency of a Diatomic Molecule
For the vibrational motion of a diatomic molecule using a harmonic oscillator model, theallowed vibrational energy levels can be described as 1
E    h 2;   0, 1, 2, ...

where υ is the vibrational quantum number and ν is the vibrational frequency. The vibrationalfrequency represented by the harmonic oscillator model is

 

1

k

2



, where k is the force constant and μ is the reduced mass.

For molecule CX, where X is an unknown atom, the vibrational absorption energy fromvibrational ground state to the first vibrational excited state is 2170.0 cm-1 and the force constantis 1.903 × 103 kg s-2.
4.1) Find the reduced mass of CX in amu.

4.2) What is atom X?
Task 5. Water-gas-shift Reaction
In a drive toward cleaner energy production, fuel cell holds great promise because of its
capability of generating electricity directly from chemical reactions with environmentally-benign
byproducts. In particular, for hydrogen fuel cell, the only waste produced by the device is justwater.
In order to use fuel cell at an industrial scale, continuous production of hydrogen that
directly feeds into a fuel cell module is required. One option to mass produce hydrogen for thispurpose is the conversion of hydrocarbon fuel using hot steam. However, this kind of reaction
often leads to mixed products that consist of H2, CO2, and CO. Moreover, CO is not only hazardous
to human health, but it also degrades fuel cell’s active material. The reversible water-gas-shift(WGS) reaction, CO + H2O ⇌ CO2 + H2, provides one method of converting toxic CO into CO2
and useful H2. The efficiency of this reaction strongly depends on the solid catalyst used.

5.1) In one process, an equimolar mixture of CO and steam is continuously passed to a
WGS reactor containing catalyst at atmospheric pressure and 0 °C. Assuming that the catalyst is
95.0% efficient in converting the reactants into the products and that the reaction in the reactor isapproximately at equilibrium in this condition, estimate the free energy change for this reaction?

Preparatory problems: 49th IChO, Thailand, 2017145.2) Now assume that a large surface of catalyst is initially available to reacting molecules,
and the rate of reaction is measured immediately at the onset of the reaction. Below are the initialrates measured at different initial pressures of CO and H2O.
dPH 2
PH 2O , atm
PCO , atm
Trial
, atm s-1
dt
1

0.10

0.90

4.0 × 10-4

2

0.15

0.85

5.6 × 10-4

3

0.25

0.75

8.2 × 10-4

4

0.28

0.72

X

What is X?
5.3) In another condition where the pressure of hydrogen is found to be 0.50 atm,

 dPH 2dt
= 3.0 × 10 atm s . According to the information given in questions 5.1, 5.2, and this question,
estimate the rate of hydrogen production when the pressures in the reactor of CO, H 2O, CO2, andH2 are 0.14, 0.14, 0.36, and 0.36 atm, respectively. (Give your answer to three significant figures.)-7-15.4) Calculate the Gibbs free energy change for the conditions described in question 5.3.
5.5) Surface coverage, θ, is an important kinetics parameter, especially for reactions on
solid surfaces. It can be defined as the number of adsorbed molecules on a surface divided by the
total number of adsorbing sites on that surface. For WGS, after the adsorption of CO and H2O on
the catalyst’s surface, a carbonyl intermediate can be formed, which then dissociates to give
surface-bound CO2 and H atom. If the carbon dioxide is produced at a rate of
1.0 × 1011 molecules s-1 cm-2 with associated rate constant of 2.0 × 1012 molecules s-1 cm-2,
what is the value of θ for this intermediate?
Task 6. Camphor in Benzene
The vapor pressure of pure benzene (C6H6) is 100 torr at 26.1 oC. Calculate the vapor
pressure and the freezing point of a solution containing 24.6 g of camphor (C10H16O) dissolved in
100 cm3 of benzene. The density of benzene is 0.877 g cm-3. The freezing point and the cryoscopic
constant (Kf) of pure benzene are 5.50 oC and 5.12 oC kg mol-1, respectively.

Preparatory problems: 49th IChO, Thailand, 201715

Task 7. Gas and Liquid7.1) At temperatures above the boiling point, A behaves like an ideal gas. In a hypotheticalsituation, Jacques Charles performed an experiment about the volume-temperature relationshipand obtained the following result (which is not necessarily drawn to scale):

What is the volume of A at 100 oC?

7.2) At equilibrium, the vapor pressures above liquids B and C are 100.1 kPa and60.4 kPa, respectively. The two liquids B and C are mixed thoroughly at 298 K. What is the vapor
pressure above a mixture containing 3 mol B and 4 mol C?

7.3) What are the mole fractions of B and C above the mixture explained in question 7.2?

Task 8. Decomposition of Nitrous Oxide
Nitrous oxide decomposes exothermically into nitrogen and oxygen, at a temperature of
approximately 565 °C.
2N2O  2N2(g) + O2(g)This reaction follows the second-order kinetics when carried out entirely in the gas phase.
8.1) If the reaction is initiated with [N2O] equal to 0.108 mol dm-3, what will its
concentration be after 1250 s have elapsed at 565 °C? The rate constant for the second orderdecomposition of N2O is 1.10 × 10-3 dm3 mol-1 s-1 at this temperature.
8.2) The activation energy for the second order reaction at 565 °C is 234 kJ mol-1. What is
the rate constant for the reaction at 600 oC?

Preparatory problems: 49th IChO, Thailand, 201716

Task 9. Avogadro’s Number
An internationally accepted procedure is as follows.
We start with a “perfect” sphere of pure 28Si isotope. The weight of this sphere is W g. The
volume V of the sphere is found from the accurate measurement of the diameter of the sphere. The
unit cell of a crystal of silicon is a “diamond cubic lattice”, i.e. a face-centered unit cell but with
4 Si atoms inside the cube. The length of the unit cell can be determined precisely from X-ray
crystallographic measurements of a single crystal of 28Si isotope.
The experimental data are as follow:
Weight of sphere, W: 1000.064 543(15) g
Volume of sphere: 431.049 110(10) cm3
Length of unit cell, α: 543.099 619(20) pm
Atomic weight of 28Si, A: 27.976 970 029(23) g mol-1
Number of Si atoms in unit cell, n:9.1) Write down the equation for calculating Avogadro’s number NA in terms of theparameters.

9.2) How many silicon atoms are in the unit cell?

9.3) Calculate Avogadro’s number using the above data. Give answer to 7 significant
figures.

Preparatory problems: 49th IChO, Thailand, 201717

Task 10. Buffer from Biological Acid: Lysine
Acid Dissociation Constants
10.1)
Name

Carboxylic acid pKa

Ammonium pKa

Substituent pKa

Lysine

2.16

9.06

10.54

One of essential amino acids, lysine, is normally depicted using the molecular structure
below: Note that the amine group on the left is part of the substituent group. Is lysine likely toexist in this form when dissolved in neutral aqueous solution? If not, write the correct form.

10.2) Draw the molecular structures for dominant forms of lysine that are present inaqueous solution and arrange them in order from the most acidic form to the most basic form. Use
Na+ or Cl- to balance the charge. Label each structure with the name of the compound.

10.3) To prepare buffer solution, you start with the most acidic form of lysine that has theconcentration of 0.100 mol dm-3 with the volume of 100 cm3. How many cm3 of 0.500 mol dm-3
KOH should you add to obtain a pH of 9.5?
10.4) Dissolve 5.00 g of the neutral zwitterion form of lysine in 100.0 cm3 of pure water.
Determine pH of the solution once equilibrium is reached.

10.5) Determine the equilibrium concentrations of all other forms of lysine present in thesolution prepared in question 10.4.

Preparatory problems: 49th IChO, Thailand, 201718

Task 11. Amperometric Titration: Titration of Pb2+ with Cr2O72Amperometry is one of the sensitive electroanalytical methods used for quantitative
determination of electroactive species. A working electrode is held at a certain voltage (vsreference electrode) that is suitable for oxidation or reduction of an analyte. The analyte will beoxidized or reduced at the surface of the working electrode and the current passing through thiselectrode is measured. This current is directly proportional to the concentration of analyte and isused for quantitative purpose. It can be used for detection of titration end-point. In this example
amperometric detection was used for monitoring a titration progress. 20-cm3 of lead (II) ion
solution was titrated with 0.0020 mol dm-3 potassium dichromate solution. A dropping mercury
electrode (DME) was used as a working electrode and the potential of -0.8 V (vs SCE, saturated
calomel electrode) was applied to this electrode for enabling the reduction of lead (II) ion anddichromate ion with potassium nitrate as supporting electrolyte. The current-volume of titrant data
are shown in Table 1.
Reference: Vogel’s Textbook of Quantitative Chemical Analysis, 5th edition, John Wiley & Sons,
New York, pp630.
Table 1. Titration data
Volume of 0.0020 mol dm-3
dichromate (cm3)Current (microampere)

0.00

9.8

2.00

8.0

4.00

6.0

6.00

4.0

8.00

2.2

10.00

3.5

12.00

5.5

14.00

7.6

16.00

9.5

11.1) Plot the titration curve and find the titration end point. (The point where the change
in the slope of titration curve occurs)11.2) Write the titration reaction.
11.3) Calculate the concentration of lead (II).

Preparatory problems: 49th IChO, Thailand, 201719

Task 12. Conductometric Titration
Conductivity detector is an electrochemical technique which applies alternating current(AC) signal to two identical electrodes. The applied AC signal induces ions to move in solution
and switching of polarity of the AC voltage avoids electrolytic reaction at the electrode. As a result,the mobility of ions in solution relates to the conductivity of ions in solution. Conductivity probe
was used in acid-base titration of 25.00 cm3 HCl vs 0.100 mol dm-3 NaOH. The conductivity signal
was recorded during NaOH addition. The conductometric titration setup is shown in Fig 1. Whenstandard NaOH solution was dropped under gravity force to the titration cell at 3 drops per second
and the conductivity value from conductometer recorded, the plot of conductivity of solution vstitration time is shown in Fig 2.

HCl vs NaOH
4000

Conductometer

RecorderHCl

Conductivity probe
Magnetic
stirrer

Fig 1. Conductometric titration setup.

Conductivity, uS/cm

NaOH
3000

2000

1000

0
0

50

100

150

200

250

300

350

400

Titration time, second

Fig 2. Plot of conductivity of an initial 25.00 cm3
HCl vs titration time.

12.1) Explain why the slope of titration curve before and after the turning point is different.

12.2) Calculate the concentration of HCl, if the volume of NaOH of each drop is0.029 cm3 and the turning point is at 108 second.

Preparatory problems: 49th IChO, Thailand, 201720

Task 13. Titration of Cu and Zn in Metal Alloy
A metal alloy which contains mainly Cu and Zn was analyzed for its metal content.
An alloy sample of 2.300 g was placed in a 250 cm3 erlenmeyer flask. To this flask,
5.00 cm3 of mixed acid (concentrated nitric acid and concentrated hydrochloric acid) was addedin a fume hood for dissolution of the alloy. The resulting solution was transferred quantitatively
into 250 cm3 volumetric flask and adjusted to volume with deionized water.
A 25.00 cm3 aliquot of sample solution was adjusted to pH 5.5 and titrated with
0.100 mol dm-3 EDTA solution using 1-(2-pyridinezao)-2-naphthol or PAN as indicator. The
indicator changed color when 33.40 cm3 0.100 mol dm-3 EDTA was added to the sample solution.
Another 25.00 cm3 aliquot of sample solution was adjusted to neutral pH and mixed withexcess KI. The mixture was then filtered and the resulting solution was titrated against
0.100 mol dm-3 sodium thiosulfate using starch solution as indicator. The titration required
29.35 cm3 sodium thiosulfate to reach the endpoint. Note: KSP(CuI) = 1.1 x 10-1213.1) Write the oxidative dissolution reaction(s) of an alloy with nitric acid andhydrochloric acid.
13.2) Determine the %w/w of Cu and Zn in alloy.

Task 14. Spectrophotometric Determination of Iron
To study in vitro gastric digestion of iron, the following procedure is carried out.
Dried and homogeneously ground supplement tablet of 0.4215 g is accurately weighed, mixed
with 10 cm3 of water, adjusted to pH 2.0 with 6 mol dm-3 HCl, 0.375 cm3 of pepsin solution(16% w/v) added, and adjusted to 12.50 cm3 with 0.01 mol dm-3 HCl. This mixture wasquantitatively transferred into a dialysis bag of a fixed volume, which is further immersed for
2 hours in a 20.00 cm3 solution containing 0.01 mol dm-3 HCl. Iron released by gastric digestion
is dialyzed until the concentration of iron inside and outside the dialysis bag are equal.

Preparatory problems: 49th IChO, Thailand, 201721

0.01 mol dm-3 HCl of 20.00 cm3

Magnetic stirrer

Dialysis bag
Dried sample of 0.4215 g, mixed with 10 cm3 of water, adjusted
to pH 2.0 with 6 mol dm-3 HCl, added with 0.375 cm3 of pepsin
solution, and adjusted to 12.50 cm3 using with 0.01 mol dm-3 HCl

To determine the gastric digestible iron from the supplement tablet, colorimetricmeasurement after complex formation between ferrous ion (M) and complexing agent (L) is
carried out at pH 5.0. The resulting ML3 complex exhibits light absorption at 520 nm, whereas M
and L do not absorb light at this particular wavelength. Within the visible wavelength region,
ferrous ion (M) does not absorb light, the complex ML absorbs light at X nm with the molar
absorptivity of 50 L mol-1 cm-1, and the complex ML2 absorbs light at Y nm with the molar
absorptivity of 200 L mol-1 cm-1.

14.1) The stepwise constants, K1, K2 and K3 , refer to the formation of the complexes one
step at a time.
(i) At equilibrium, the absorbance of the solution (in 1.0-cm cuvette) at X nm is0.400. This solution also contains 1 x 10-5 mol dm-3 of M and 2 x 10-6 mol dm-3 of L. Calculate
the stepwise formation constant of ML (K1).
(ii) Then, L is added into the solution. At equilibrium, the absorbance of thesolution (in 1.0-cm cuvette) at Y nm is 0.400. This solution also contains 2 x 10-6 mol dm-3 of ML
and 2 x 10-4 mol dm-3 of L. Calculate the stepwise formation constant of ML2 (K2).

Preparatory problems: 49th IChO, Thailand, 201722

(iii) In an excess of L, all of iron is in the form of ML3.
Consider the following table:[M], mol dm-3

[L], mol dm-3

Abs (at 520 nm), pathlength (b) = 1 cm

6.25 x 10-5

2.20 x 10-20.750

3.25 x 10-5

9.25 x 10-5

0.360a) Calculate the molar absorptivity (Ɛ) of ML3 complexb) Calculate the overall formation constant (Kf) of ML3 complexc) Calculate the stepwise formation constant (K3) of the complex

14.2) The CHN analysis shows that the complexing agent (L) contains 80% C,
4.44% H, and 15.56% N. The molar mass of this compound is 180 g. Determine the molecular
formula of L.

14.3) The Fe2+ complexes, ML, ML2 and ML3, adopt the octahedral structure (assume
perfect octahedral geometry for each isomer of these three complexes). Sketch the d-orbital
splitting diagram for ML3. Draw all possible isomers of Fe2+ complexes. Order the magnitudes ofo (crystal field splitting) of these three complexes and explain.(Spectrochemical series:
I-< Br-<Cl-≈ SCN-< F- ≈ urea < ONO-≈ OH-< H2O < NCS-< pyridine ≈ NH3< en < bipy <o-phen< NO2-< CN-≈ CO)

14.4) To determine the dialyzable iron concentration (iron outside the dialysis bag),5.00 cm3 of the solution outside the dialysis bag is added with a reducing agent to ensure that allof dissolved iron is in the ferrous ion form. Then, the solution is adjusted to the suitable pH,
followed by addition of excess amount of complexing agent (L) and deionized water added tomake up the volume to 50.00 cm3 in a volumetric flask. The absorbance measured at 520 nm is0.550. Calculate the concentration of dialyzable iron (in unit of mg dm-3).

14.5) Presume all of the iron in the supplement tablet is completely digestible in the gastriccondition. Determine in mg the iron in 1.0000 g of supplement tablet.

Preparatory problems: 49th IChO, Thailand, 201723

Task 15. Basic Electrochemistry
Consider the following electrochemical cell:Pt(s)MnO4- (0.00100 mol dm-3), Mn2+(0.00200 mol dm-3), pH=3.00 ∥ Ce4+(0.0100 mol dm-3),
Ce3+(0.0100 mol dm-3)Pt(s)The relevant reduction half-reactions are:Ce4+ + e- ⟶ Ce3+

Eo = 1.70 V

MnO4- + 8H+ + 5e- ⟶ Mn2+ + 4H2O

Eo = 1.507 V

15.1) Write a balanced net reaction for this cell and determine the values of Eocell and K forthe net reaction.
15.2) How many Coulombs of electron charge are transferred when 5.0 mg of Ce4+ are
consumed in the reaction from question 15.1?

15.3) Determine the cell potential for the electrochemical cell shown in the cell diagram.

Task 16. Calculation of Concentration
16.1) What is the concentration of Cu (in mol dm-3) prepared by mixing CuCl2 1.345 gwith 50.00 cm3 of CuSO4 31.9 g dm-3 and adjusting the volume to 500 cm3 by 0.01 mol dm-3 HCl?
16.2) Calculate whether or not a precipitate will form if 25.00 cm3 aliquot of the resulting
solution in 16.1 is adjusted to pH 8.0 with NaOH and the final volume is 100.0 cm3.
Note: KSP(Cu(OH)2) = 4.8 x 10-20

Preparatory problems: 49th IChO, Thailand, 201724

Task 17. Small Molecule Activation by Frustrated Lewis Pairs
Electron acceptors and electron donors are usually called Lewis acids and Lewis bases,
respectively.
17.1) Trispentafluorophenylborane is a well-known Lewis acid for the polymerization of
olefin. Propose a reaction to prepare trispentafluorophenyborane from boron trichloride andbromopentafluorobenzene.

17.2) The steric hindrance precludes the formation of classical bonds between Lewis acidand Lewis base. Propose a structure of Frustrated Lewis Pairs from the reaction of B(C 6F5)3 andPH(t-Bu)2 if a zwitterion product is only obtained. (See Reference: Welch, G. C.; Juan, R. R. S.;
Masuda, J. D.; Stephan, D. W. Science 2006, 314, 1124-1126.)17.3) Propose a reaction between the obtained zwitterion in 17.2 and Me2SiHCl.
17.4) Show the structure of the product obtained from the B(C6F5)3 and P(t-Bu)3 underhydrogen gas atmosphere.
17.5) If HD is used instead of dihydrogen gas, write down all possible products.
17.6) Only one product is obtained from the reaction of B(C6F5)3 and P(t-Bu)3 underethylene gas atmosphere. Draw its structure.
17.7) Draw the structure of the product if the reaction of the isolated product from 17.6 iscarried out under nitric oxide gas atmosphere.
17.8) Only one product is obtained from the reaction of B(C6F5)3 and P(t-Bu)3 under carbon
dioxide gas atmosphere. Draw its structure.

Preparatory problems: 49th IChO, Thailand, 201725

Task 18. Silver Iodide
The crystalline structure of -AgI is similar to that of ice, allowing it to induce freezingby the process known as heterogeneous nucleation (cloud seeding). -AgI is a bright yellow solidand has the wurtzite structure.
18.1) When the solid silver iodide is exposed to sunlight, it will darken rapidly. What is
the oxidation state of silver in the darkened solid?
18.2) What is the solubility trend in AgF, AgCl, AgBr, AgI?
18.3) Consider:(a) Ag+ (aq) + e– ⟶ Ag (s)(b) AgI (s)Eo = +0.80 V

Ag+ (aq) + I– (aq)(c) Ag+ (aq) + 3 I– (aq)

[AgI3]2– (aq)Ksp = 8.51 x 10-17
K = 1014

From the given information, find the standard reduction potential of [AgI3]2–.
18.4) The salt [PPh3Me]2[AgI3] contains a triiodoargentate(I) ion [AgI3]2– withapproximate trigonal planar geometry. (See reference: Bowmaker, G. A.; Camus, A.; Skelton, B.
W.; White, A. H. J. Chem. Soc., Dalton Trans., 1990, 727-731.) The structure of [AgI3]2– is shown
below. Draw the crystal field splitting diagram for the d orbitals of silver and fill in all appropriate
electrons.

Preparatory problems: 49th IChO, Thailand, 201726

Task 19. Perovskite Structure
A mineral perovskite crystallizes in the cubic unit cell in which Ca2+ and O2– ions constitutea ccp arrangement and Ti4+ ion occupies an interstitial hole as shown here.

Ca2+
Ti4+

O2-

19.1) Based on the unit cell above, what is the empirical formula of perovskite?

19.2) Name types of interstitial holes present in the ccp unit cell. How many holes are there,
for each type, within the unit cell?

19.3) From your answer in 19.2, which type of interstitial hole is occupied by Ti4+ ion?

Preparatory problems: 49th IChO, Thailand, 201727

Task 20. Quantum Numbers and Atomic Orbitals
20.1) Each of the following sets of quantum numbers is not permissible for an orbital.
Why?

(i)
(ii)
(iii)

n
1
3
2

l
1
1
-1

ml
0
-2
0

ms
+1/2
-1/2
+1/2

20.2) Give the notation for the subshells denoted by the following quantum numbers.
(i) n = 6, l = 2(ii) n = 4, l = 3(iii) n = 6, l = 1

20.3) What is the number of different orbitals in each of the following subshells?
(i) 3d(ii) n = 5, l = 3(iii) n = 3, l = 0

Preparatory problems: 49th IChO, Thailand, 201728

Task 21. Radioactivity of Iodine and Nuclear Equations
21.1) The half-life of I-131 is 8 days. If a freshly prepared solution of I-131 has aconcentration of 0.1 mol dm-3,(i) what will be the concentration of I-131 after 2 half-lives?
(ii) what will be the concentration of I-131 after 40 days?

21.2) Identify X in each of the following nuclear equations:(i) X  147N +  38
18Ar + X

(ii)

38
19K

(iii)

55
26Fe

+ −10𝑒  X4(iv) X  234
90Th + 2He+ X  146C + 11H

(v)

14
7N

(vi)

110𝑚
47Ag 

(vii)

1
0n

136
1
+ 235
92U  53I + X + 4 0n(viii)

2
1H+ 31H  X + 10n

X + 

Task 22. Structure and Chemistry of Sodium Chloride
22.1) The unit cell of NaCl is shown below:(i) What is the coordination number of Na+ and Cl-?
(ii)What is the number of formula units in the unit cell?
(iii) If the length of the unit cell of NaCl is 560 pm and the mass of NaCl is
58.5 g mol-1, what is the density of NaCl?

Preparatory problems: 49th IChO, Thailand, 201729

22.2) NaCl can be prepared by a reaction between Na(s) and Cl2(g):Na(s) + 1/2Cl2(g)  NaCl

Hformation = -411 kJ(i) What are the values of n and l for the valence electrons of a Na atom?
(ii) Compare the size of Na vs. Cl and Na+ vs. Cl-.
(iii) Draw the Lewis structure of Cl2.
(iv) Calculate the lattice energy of NaCl.
where Hsublimation for Na = 107 kJ mol-1, IE1 for Na = 496 kJ mol-1,
ClCl dissociation = 244 kJ mol-1, Electron Affinity of Cl = -349 kJ mol-122.3) Chemistry of NaCl:(i) Write the reaction between NaCl(aq) and Br2(l).
(ii) Write the ionic equation between NaCl(aq) and AgNO3(aq).
(iii) What is the flame color when NaCl is placed in the flame?

Preparatory problems: 49th IChO, Thailand, 201730

Task 23. Natural Chelator from Shrimp Shell
Chitosan is a linear polysaccharide composed of β-(1-4)-linked D-glucosamine(deacetylated unit) and N-acetyl-D-glucosamine (acetylated unit). It is made by treating the chitin
shells of shrimp or other crustaceans with a strong base, like sodium hydroxide. The deacetylationof chitin by a strong base yields partially-acetylated chitosan as shown below:

Chitosan can be used for a variety of purposes like helping plants to fight off fungal
infections, preventing spoilage in wine, helping deliver drugs through the skin, being applied toreduce bleeding, and as an antibacterial agent. In the environmental aspect, chitosan can be used
as an effective metal ion adsorbent. The adsorption capacities of chitosan for Cu(II), Hg(II), Pb(II)and Zn(II) are 79.94, 109.55, 37.2, 47.15 mg (g chitosan)-1, respectively.

23.1) Suggest the preferred binding sites in completely-deacetylated chitosan for metal ion.

The selectivity of chitosan towards Pb2+ can be increased by modification with CS2 yielding
partially modified chitosan (PMCS) as in the structure below:

Preparatory problems: 49th IChO, Thailand, 201731

The absorption capacity toward Pb2+ was increased from 37.2 to 156.0 mg g-1 chitosan(Wang, N.; Zheng, P.; Ma, X. Powder Technol. 2016, 301, 1-9.)23.2) Suggest the most preferred site(s) in chitosan for Pb2+ and draw the bond(s) between
that preferred site(s) and Pb2+. Explain the increase in absorption capacity of PMCS toward Pb2+.
To increase the sensitivity of the chitosan toward metal ion, the dye like meso-tetra(pcarboxyphenyl)porphyrin is chemically bonded with chitosan matrix. After the two acidic protons
are removed, the four nitrogen atoms will bind with metal ion. The two axial sites of the metal ion
normally bind with water molecules yielding the octahedral complex. Each metal ion gives
characteristic absorption maximum in the visible range.

23.3) Suggest the bonds between meso-tetra(p-carboxyphenyl)porphyrin and chitosan if aweak protonic acid is used as a catalyst.

23.4) If Fe2+ is being adsorbed by the chitosan-porphyrin adsorbent, draw the structure of
the complex and predict the approximate d-orbital splitting in the proposed complex.

Preparatory problems: 49th IChO, Thailand, 201732

Task 24. Compound Identification and Related Chemistry
A reaction between M and Cl2 gives the only product MxCly. The following results are
obtained under various conditions:

M (mol)Cl2 (mol)

Product (g)

0.20

0.80

26.7

0.30

0.70

40.0

0.40

0.60

53.3

0.50

0.50

44.4

0.60

0.40

35.6

0.70

0.30

26.7

0.80

0.20

17.8

24.1) What is the chemical formula of MxCly? Identify M.

24.2) Write balanced chemical equations of:(i) complete hydrolysis of MxCly(ii) MxCly + H2SO4

24.3) At certain temperatures, MxCly exists in equilibrium as a dimer:

Draw a chemical structure of the dimer.

Preparatory problems: 49th IChO, Thailand, 201733

Task 25. Isomerism of Octahedral Fe Complexes
Fe(N,N')2Cl2 has an octahedral structure featuring two bidentate, neutral -iminopyridine(N,N') ligands, whose structure is shown below.

25.1) Draw all possible isomers of Fe(N,N')2Cl2.

25.2) Which isomers of Fe(N,N')2Cl2 are optically active?

Task 26. Stoichiometry and Structure Determination
Compound A consists only of three elements C, H, and O. Under standard conditions, A
is a yellow solid with molar mass of 166.2 g mo1-1. By weight, A has 28.9% O and 65.0% C.

26.1) Determine chemical formula of A.

26.2) A contains a phenol functional group with intramolecular hydrogen bonding. The 1H and13
C{1H} NMR spectra of A in CDCl3 are shown below. Based on your answer in 26.1, draw achemical structure of A, and show the intramolecular hydrogen bond(s).

*NMR data were obtained from Sigma-aldrich.com.

Preparatory problems: 49th IChO, Thailand, 201734

26.3) From the reaction scheme below, draw chemical structures of X, Y, and Z.

2

A +

H 2N

NH 2

-2Y

X

Cu(OOCCH3) 2Z- 2 CH3COOH

Task 27. Atropine
Atropine is an organic compound used to treat certain types of nerve agent and pesticide
poisonings. This compound can be synthesized from tropine and tropic acid in one step.
27.1) Tropine can be prepared as shown in the diagram below. The first step of this
synthesis is “double Mannich reaction” (Robinson, 1917).
Write down the structural formulae of compounds A and B.

27.2) Tropic acid can be prepared from the reaction of acetophenone and HCN followedby hydrolysis, elimination, addition and nucleophilic substitution (Mackenzie and Ward, 1919). In
this synthesis, it should be noted that the electrophilic addition by HCl did not follow
Markovnikov's Rule, and the anti-Markovnikov product (E) was obtained.
Tropic acid (F) can also be prepared in only three steps from ethyl 2-bromo-2phenylacetate and paraformaldehyde (Pernot, 1950). NMR data of tropic acid (F) are provided
below.
H NMR (400 MHz, CDCl3) δ 3.76-3.83 (2H, m), 4.80 (1H, dd, J = 8.1 Hz), 7.21-7.30 (5H,m) and 2 broad peaks at ~5 ppm and ~12 ppm.
1

C NMR (100 MHz, CD3OD) δ 55.9, 65.1, 128.5, 129.2, 129.7, 137.9, 176.1

13

Write down the structural formulae of compounds C-G in the diagram below.

Preparatory problems: 49th IChO, Thailand, 201735

27.3) When tropine was combined with tropic acid under acidic conditions, atropine wasproduced. Write down the structural formula of atropine.

27.4) Predict the major products of the reactions shown below. 13C NMR spectrum ofcompound I shows nine signals in the range of 0-80 ppm, four signals in the range of120-140 ppm, and one signal at 155 ppm. 13C NMR spectrum of compound J shows eight signals
in the range of 0-80 ppm and one signal at 155 ppm. 13C NMR spectrum of compound K shows
seven signals in the range of 0-80 ppm and four signals in the range of 120-140 ppm.

Preparatory problems: 49th IChO, Thailand, 201736

Task 28. Synthesis of Building Blocks for Fluorescent Markers
Carboxy-functionalized fluorescein dyes, which have been employed as importantconjugated fluorescent markers of biologically active compounds, can be synthesized based on the
improved synthetic route developed by M.H. Lyttle and co-workers (Lyttle, M. H.; Carter, T. G.;
and Cook, R. M. Org. Proc. Res. Dev. 2001, 5, 45–49). In these synthetic sequences, two different
precursors (C and I) were required and they were synthesized as followed.

Identify compounds A-I.

Preparatory problems: 49th IChO, Thailand, 201737

Task 29. Synthesis towards Anatoxin-a
Anatoxin-a (I) is a secondary amine alkaloid with acute neurotoxicity that can cause deathby respiratory paralysis. This compound is produced by several different genera of cyanobacteria
found all over the world. In 2004, Jehrod B. Brenneman and Stephen F. Martin reported a concise
synthesis of anatoxin-a from commercially available D-methyl pyroglutamate, which wasconverted to compound A. Write down the structural formulae of compounds B, C, F, H and I in
the boxes provided.

Preparatory problems: 49th IChO, Thailand, 201738

Task 30. Total Synthesis of Illudin C
During the synthesis of sesquiterpene ()-illudin C, R. L. Funk required the building block
C which could be prepared based on the short synthesis shown below (Aungst, Jr., R. A.;
Chan, C.; Funk, R. L. Org. Lett. 2001, 3, 2611–2613.) Compound C was then carried on in thesynthesis as shown. Provide the correct structures of A, B, C and D.

Task 31. Total Synthesis of -Opioid Receptor (MOR) Agonists
In the studies of pain management, -opioid receptor has been an important protein target
in the central nervous system which interacts with specific small molecules and may therefore
alleviate pain in patients. In studying this target, one needs to have access to these compounds.
Nature has been a major source of these small compounds which may be used in the research. In
addition to the parent compounds in plants which are known to reduce pain, synthetic derivatives
are also equally important for the study. In a recent pharmacological evaluation of the synthetic
mitragynine and derivatives, the principle alkaloids found in the Southeast Asian plant Mitragyna
speciosa (known as Kratom in Thailand), by Sames and co-workers (Kruegel, A. C.;
Gassaway, M. M.; Kapoor, A.; Váradi, A.; Majumdar, S. Filizola, M.; Javitch, J. A.; andSames, D. J. Am. Chem. Soc. 2016, 138, 6754–6764), the materials for the evaluation wereaccessed via total synthesis. The brief synthesis is illustrated in the scheme below.

Preparatory problems: 49th IChO, Thailand, 201739

31.1) Draw the correct structure of compound A.
31.2) Identify the structures of compounds B-D with correct stereochemistry.

Preparatory problems: 49th IChO, Thailand, 201740

Task 32. Pericyclic Reaction
32.1) A series of pericyclic reaction can be used to construct complex organic molecular
structure in a stereocontrolled manner. For example, Moore, et al. (J. Org. Chem. 1998, 63,6905.) reported the synthesis of triquinane derivatives from the corresponding cyclobutenone asshown in scheme below.

Propose structures of intermediates A and B.

32.2) In the synthesis of prostaglandin, Corey, et al. (J. Am. Chem. Soc. 1969, 91, 5675.)
used cycloaddition reaction as a key step along with a series of straightforward chemicaltransformations to set up stereochemistry at the periphery of cyclopentyl structure as shown inscheme below.

Preparatory problems: 49th IChO, Thailand, 201741

(i) Identify structures of compounds C-G with correct relative stereochemistry.
(ii) There is a carbon, labeled with an asterisk in compound 3. Indicate the positionof this labeled carbon in either compound 1 or 2 by placing an asterisk on the carbon in the given
structure.

(iii) If a student synthesizes compound 3 from compounds 1 and 2 by following thesynthetic scheme above, how many possible stereoisomers of compound 3 can the student obtain?

Preparatory problems: 49th IChO, Thailand, 201742

32.3) 1,3-Dipolar cycloaddition is a powerful tool for the construction of heterocyclic
structure. For example, upon heating, compound H undergoes intramolecular [4+2]-cycloaddition
to yield compound I. Reduction of a weak N-O bond of compound I by catalytic hydrogenation
gave product J.

(i) Propose structures of compounds I and J.
(ii) If a racemic mixture of H is used in the reaction, write all possible stereoisomer(s)of products J.

Task 33. Stereoisomers without Stereocenter
Axial chirality refers to stereoisomerism of a special case of chirality in which a molecule
does not possess a stereogenic center but an axis of chirality. An axis of chirality is defined as an
axis about which a set of substituents is held in a spatial arrangement that is not superimposable
on its mirror image.
Two necessary preconditions for axial chirality are:i. A rotationally stable axis
ii. Presence of different substituents on both sides of the axis
Axial chirality is most commonly observed in atropisomeric biaryl compounds wherein therotation about the aryl-aryl bond is restricted, for example, biphenyl, binaphthyls. Certain allene
compounds also display axial chirality.
33.1) From the given structures, draw 3-D structure and the corresponding mirror image ofthe given compounds. Use plane of symmetry to determine whether they are chiral or achiral.
(i)

(ii)

Preparatory problems: 49th IChO, Thailand, 201743

(iii)(iv)33.2) Enantiomers of medium ring trans-cycloalkenes exist. For example, transcyclooctene can be resolved and its enantiomers are stable at room temperature. On the other
hand, trans-cyclononene has also been resolved but it racemizes with a half-life of 4 min. at 0oC.
(i) Draw mirror images of the given structures of trans-cyclooctene and transcyclononene.

(ii) Why does trans-cyclononone racemize faster than trans-cyclooctene?

Preparatory problems: 49th IChO, Thailand, 201744

Part 2. Practical Tasks
The safety rules and regulations
Regulations of the International Chemistry Olympiad (IChO)
Safety1. During the experimental part, the competitors must wear laboratory coats and eye
protection. The competitors are expected to bring their own laboratory coats. Other means ofprotection for laboratory work are provided by the organizer.
2. When handling liquids, each student must be provided with a pipette ball or filler.
Pipetting by mouth is strictly forbidden.
3. The use of acutely toxic substances (GHS hazard statement H300, H310, H330) is
strictly forbidden. The use of toxic substances is not recommended, but may be allowed if special
precautions are taken. Substances with GHS hazard statements H340, H350, H360 (provenmutagens, carcinogens, and teratogens) must not be used under any circumstances (seeAppendix B for definitions of these categories).
4. Detailed recommendations involving students’ safety and the handling and disposal ofchemicals can be found in Appendices A 1, A 2, and B.
Appendix A 1: Safety Rules for Students in the laboratory.
Appendix A 2: Safety Rules and Recommendations for the Host Country of the IChO.
Appendix B contains a reference to the hazard symbols and statements of the Globally
Harmonized System of Classification of Chemicals (GHS), the use of which is expected in labelingand classifying materials used at the IChO.

Preparatory problems: 49th IChO, Thailand, 201745

Task P1. Quantitative Determination of Ascorbic Acid and Citric Acid in Beverages
The weather in Thailand is generally hot and humid which may cause discomfort andfatigue. Therefore drinking of water or beverage is optional choice to refresh and reduce anappetite. There are various brands of drink available in the markets. The main components in thebeverage are sweetener, organic acid, minerals as well as color and flavor. These components
basically improve the taste and texture.
In this task, you will determine the amount of ascorbic acid (C6H8O6) and citric acid
(C3H5O(COOH)3) that are in a beverage sample by two titrations.
A) Determination of ascorbic acid by redox titrationB) Determination of total acid content by acid-base titration
Source: S. B. Sigmann and D. E. Wheeler, J. Chem. Educ., 2004, 81, 1479.
Chemicals
0.001 mol dm-3 KIO3
1 mol dm-3 HCl
0.5% w/v starch solution
0.1 mol dm-3 NaOH*
0.5% w/w phenolphthalein indicator
KI
Sample (containing 1.28x10-3 mol dm-3 ascorbic acid and 6.76x10-2 mol dm-3 citric acid)
Glasswares
2 burets
50 cm3 -volumetric pipet
10 cm3 -volumetric pipet
pipet bulb
6 Erlenmeyer flasks* This solution must be standardized. Use potassium hydrogen phthalate, KHP for the
standardization.

Preparatory problems: 49th IChO, Thailand, 201746A) Determination of ascorbic acid by redox titration
1. Fill a buret with 0.001 mol dm-3 KIO3
2. Pipet a 50.00 cm3 aliquot of sample solution and quantitatively transfer it to an Erlenmeyer
flask. Add 1 gram of KI, 5 cm3 of 1 M HCl and 3 cm3 of 0.5 % starch solution to the flask.
3. Titrate with 0.001 mol dm-3 KIO3 immediately.
4. Endpoint is marked by the appearance of the blue starch–I3−complex.
5. Repeat with two additional 50.00 cm3 aliquots.

The amount of ascorbic acid is determined by titration with KIO3. The reaction equations areshown as equations (1) – (4).
IO3- + 5I- + 6H+

3I2 + 3H2O

(1)

C6H8O6 + I2

C6H6O6 + 2H+ + 2I-(2)

I2 + I-

I3-(3)

I3- + starchstarch - I3- complex(4)(blue)(i) Fill the data in the Table.
Titration no.

1

2

3

Initial reading of the burette, cm3
Final reading of the burette, cm3
Consumed KIO3 volume, cm3(ii) Calculate mg of ascorbic acid per 100 cm3 of sample.

Preparatory problems: 49th IChO, Thailand, 201747B) Determination of total acid content by acid-base titration
1. Pipet a 10.00 cm3 aliquot of the sample solution and quantitatively transfer it to Erlenmeyer
flask.
2. Add 2-3 drops of phenolphthalein indicator to the flask.
3. Slowly add NaOH from the buret to the flask.
4. At the endpoint, color of the indicator will change from colorless to pink.
5. Repeat with two additional 10.00 cm3 aliquots.

Titration with NaOH therefore determines the amount of total acid in the sample. The reaction
equations are shown as equations (5) – (6).

C6H8O6 + NaOH
C3H5O(COOH)3 + 3NaOH

C6H7O6Na + H2O(5)

C3H5O(COO)3Na3 + 3H2O

(6)(i) Fill the below Table
Titration no.

1

2

3

Initial reading of the buret, cm3
Final reading of the buret, cm3
Consumed base volume, cm3(ii) Calculate number of moles of reacted hydroxide

The amount of citric acid determined by difference as shown below.
moles NaOH neutralized (total acid) - moles NaOH neutralized (ascorbic acid)= moles NaOH neutralized (citric acid)(iii) Calculate grams of citric acid per 100 cm3 of sample

Preparatory problems: 49th IChO, Thailand, 201748

Task P2. Spectrophotometric Determination of Chromium and Manganese
According to Beer’s law, the net absorbance is an additive of each solute, provided there
is no reaction between the two solutes.
λ1
A total A λX1  A Yλ1

λ2
A total A λX2  A Yλ 2

where Atotalλ1 and Atotal λ2 are the net measured absorbances at λ1 and λ2 respectively, andA X and A Y are the absorbances of the two solutes.

Chemicals
0.5 mol dm-3 H2SO4
0.01 mol dm-3KMnO4
0.01 mol dm-3K2Cr2O7
Instrument
Visible Spectrophotometer
Glasswares
2.00 cm3 measuring pipet (2)10.00 cm3 measuring pipet (2)50.00 cm3 volumetric flask (13)pipet bulbA) Determination of molar absorption coefficients of KMnO4 and K2Cr2O7
1. Prepare standard KMnO4 solutions of 0.5 x 10-4, 1.0 x 10-4, 2.0 x 10-4, 5.0 x 10-4 mol dm-3
in 0.5 mol dm-3 H2SO4 by appropriate dilution from standard 0.01mol dm-3 KMnO4 solution to
the final volume of 50.00 cm3 in volumetric flask.
2. Prepare standard K2Cr2O7 solutions of 2.0 x 10-4, 3.0 x 10-4, 4.0 x 10-4, 6.0 x 10-4 mol dm-3
in 0.5 mol dm-3 H2SO4 by appropriate dilution from standard 0.01 mol dm-3 K2Cr2O7 solution
to the final volume of 50.00 cm3 in volumetric flask.

Preparatory problems: 49th IChO, Thailand, 201749

3. Record the absorbance values of all solutions at 440 and 545 nm
KMnO4(mol dm-3)

Absorbance(A)(at 440 nm)

Absorbance(A)(at 545 nm)

Molar absorption
coefficient(at 440 nm)

Molar absorption
coefficient(at 545 nm)

Molar absorption
coefficient(at 440 nm)

Molar absorption
coefficient(at 545 nm)

0.5 x 10-4
1.0 x 10-4
2.0 x 10-4
5.0 x 10-4
Molar absorption coefficient (average)

K2Cr2O7(mol dm-3)

Absorbance(A)(at 440 nm)

Absorbance(A)(at 545 nm)

2.0 x 10-4
3.0 x 10-4
4.0 x 10-4
6.0 x 10-4
Molar absorption coefficient (average)B) Determination the concentrations of KMnO4 and K2Cr2O7 in solution mixture
1. Prepare a solution containing 5.0 cm3 of KMnO4 0.5 x 10-4 mol dm-3 and 5.0 cm3 of
K2Cr2O7 6.0 x 10-4 mol dm-3 (Solution A)
2. Prepare a solution containing 5.0 cm3 of KMnO4 2.5 x 10-4 mol dm-3 and 5.0 cm3 of
K2Cr2O7 4.0 x 10-4 mol dm-3 (Solution B)
3. Prepare a solution containing 5.0 cm3 of KMnO4 5.0 x 10-4 mol dm-3 and 5.0 cm3 of
K2Cr2O7 2.0 x 10-4 mol dm-3 (Solution C)
4. Record the absorbance values of all solutions at 440 and 545 nm
Solution

Absorbance(A)(at 440 nm)

Absorbance(A)(at 545 nm)

A
BC

Preparatory problems: 49th IChO, Thailand, 201750

Calculate the concentration of KMnO4 and K2Cr2O7 in each solution (from the experimental
absorbance values)
Solution

KMnO4(mol dm-3)% error

K2Cr2O7(mol dm-3)% errorA
B
C

Preparatory problems: 49th IChO, Thailand, 201751

Task P3. Synthesis of “Ferrocenated” Iron Oxide Nanoparticles and Their Activities in the
Decolorization of Methylene Blue
Ferrocenated compounds are a mixture containing ferrocene, iron oxide, andcyclopentadienyl radical. The preparation of ferrocenated compounds can be done by thedecomposition of ferrocenium in basic condition. Cyclopentadienyl radical in ferrocenatedcompounds is an active specie to generate reactive oxygen species for the decolorization of
methylene blue.
In this task, you will:Perform the synthesis of ferrocenated iron oxide nanoparticles by coprecipitation.
Perform the decolorization of methylene blue by ferrocenated iron oxide, and follow
reaction by spectrophotometric analysis.

Chemicals
Ferric chloride hexahydrate (FeCl3∙6H2O)
Ferrous chloride tetrahydrate (FeCl2∙4H2O)
Ferrocene
Concentrated sulfuric acid

De-ionized water
Sodium hydroxide
Barium chloride
Methylene blue

Glasswares
Round-bottomed flask, 250 cm3
Beaker, 100 cm3
Erlenmeyer flask, 250 cm3
Graduated cylinder, 10 cm3
Test tubes
Magnetic bars
Evaporation dishAluminum foil

Beaker, 25 cm3
Beaker, 250 cm3
Volumetric flask, 250 cm3
Graduated cylinder, 100 cm3
Pasteur pipets and rubber bulb
Stirring rods
Centrifuge tubes

Instruments
Stirrer
pH meterOven

Preparatory problems: 49th IChO, Thailand, 2017

4-digit balanceCentrifuge
Visible Spectrophotometer

52

Synthesis of ferrocenated iron oxide nanoparticles
1. Add concentrated sulfuric acid (0.5 cm3) to ferrocene (6.84 g) to yield aferrocenium solution. Do this experiment in a fume hood.
2. Add the ferrocenium solution to water (5 cm3) and stir for 30 minutes.
3. Prepare a mixed solution of ferrous chloride tetrahydrate (1.55 g) and ferric chloride
hexahydrate (4.15 g) in de-ionized water (80 cm3).
4. Add the mixed solution into the blue solution of ferrocenium and then stir for
1 hour.
5. Add a saturated NaOH solution slowly until the pH of solution is 12.
6. Collect the orange precipitate by centrifugation at 4500 rpm for 20 minutes.
7. Wash the precipitate with de-ionized water. Be sure that sulfate ion is completely
washed by checking with BaCl2 solution.
8. Dry orange solid at 100 °C for 1 hour. Record the weight and calculate the yield of
the ferrocenated iron oxide.
Decolorization of methylene blue
1. Prepare a solution of methylene blue (9.9710-6 mol dm-3).
2. Add 100 cm3 of methylene blue in a 250 cm3-Erlenmeyer flask which is wrappedwith aluminum foil. Keep this flask in a dark box while stirring.
3. Add the prepared orange solid (0.100 g) into the solution of methylene blue.
4. Collect 3 cm3 of the mixture at every 5 minutes.
5. Centrifuge the mixture at 4500 rpm for 3 minutes.
6. Take the clear supernatant for spectrophotometric analysis.
7. Plot a graph between the absorbance at a specific wavelength and reaction time.
You may prepare iron oxide by repeating the above experiments without the addition
ferrocene and perform the decolorization of methylene blue for comparison with ferrocenated ironoxide.

Preparatory problems: 49th IChO, Thailand, 201753

Task P4. Synthesis of Aspirin
Aspirin or acetylsalicylic acid (ASA) is a well-known medication for the treatment of pain,
fever, and inflammation. It is a nonsteroidal anti-inflammatory drug (NSAID). Aspirin irreversibly
inhibits COX enzyme results in the decrease in the production of prostaglandins andthromboxanes, the key molecules that affect various physiological responses includingtransmission of pain, regulation of inflammation and fever, as well as aggregation of platelets.
In this task, you will:
Perform the synthesis of acetylsalicylic acid via the esterification of salicylic acid with acetic
anhydride.
Calculate % yield of the purified product.
Perform thin layer chromatography analysis.
Chemicals
Acetic anhydride
Concentrated H2SO4 (18 mol dm-3)
Distilled Water
Ethanol

Ethyl acetate
HexaneIce (for an ice bath)
Salicylic acid

Glasswares
Beaker, 100 cm3
Buchner funnel
Crystallizing dish (for a hot water bath and an ice bath)
Erlenmeyer flasks, 125 cm3 and 250 cm3
Filter paper
Graduated cylinder, 25 cm3
Pasteur pipet and rubber bulb
Stirring rod
SpatulaSuction flask
Capillary tube for TLC
TLC plate on aluminum foil or glass supports and TLC jar
Instruments
Analytical balance ( 0.0001 g)
Hotplate
Water aspirator or vacuum pumpStand and clamps

Preparatory problems: 49th IChO, Thailand, 201754

Procedure:
1. Weigh out 5.00 g of salicylic acid. Transfer this to a 125 cm3 Erlenmeyer flask. Record
the mass.
2. In the hood, add 7.0 cm3 of acetic anhydride to the flask contained salicylic acid.
3. Carefully add 8 drops of concentrated sulfuric acid (18 mol dm-3) to the reaction flask.
4. Assemble a hot water bath using a beaker and a hotplate.
5. Place the flask in the water bath and heat. After the water begins to boil, heat for an
additional 15 minutes.
6. Allow the reaction flask to cool down for few minutes.
7. Carefully add 15.0 cm3 of room temperature water to the flask. Swirl the flask to mix thecontents.
8. Place the reaction flask in an ice bath. Let it cool down until the crystallization of the
product completes (approx. 15 minutes). If crystals do not appear, scratch the walls of the flaskwith a stirring rod to induce crystallization.
9. Collect the solid product by vacuum filtration using a Buchner funnel.
10. Transfer the solid product from the Buchner funnel to a 250 cm3 Erlenmeyer flask.
Recrystallize the crude product with ethanol and water.
Recrystallization Protocol: Add preheated ethanol until the product is all dissolved. While heating thesolution, add water dropwise and swirl. Keep adding water until the solution becomes cloudy. To the cloudy
solution, hot ethanol is added dropwise until the solution becomes clear. Remove the flask from heating
and allow the solution to cool down undisturbed to the room temperature. Crystals should form. Chill theflask containing crystals in an ice-water bath to complete crystallization.

11. Collect the crystalline product using by vacuum filtration using a Buchner funnel.
12. Dry the product. Record weight and determine % yield
13. Perform thin layer chromatography (TLC) to determine the purity of the purified
product.

Preparatory problems: 49th IChO, Thailand, 201755

Task P5. Synthesis of Benzopinacolone
The pinacol–pinacolone rearrangement can be used to convert 1,2-diol to carbonylcompound. The reaction takes place under acidic conditions. In this experiment, benzopinacol
could be transformed to benzopinacolone via acid-catalyzed carbocation rearrangement.

In this task, you will:
Perform the acid catalyzed pinacol–pinacolone rearrangement.
Calculate % yield of the purified product.
ChemicalsBenzopinacol
Ethyl acetate
Glacial acetic acid
HexaneIodineIce (for an ice bath)
Silicone oil or alike for oil bath
Glasswares
Beaker, 600 cm3
Buchner funnel
Erlenmeyer flask, 125 cm3
Filter paper
Ice bath
Graduated cylinder, 25 cm3Magnetic bar or boiling chip

Round-bottomed flask , 100 cm3
Reflux condenser
Stirring rod
Suction flask
Oil bath
SpatulaPasteur pipette and rubber bulb

Instruments
Analytical balance ( 0.0001 g)
Hotplate stirrer
Water aspirator or vacuum pumpStand and clamps

Preparatory problems: 49th IChO, Thailand, 201756

Procedure:
1. Place 25 cm3 of glacial acetic acid and 0.1 g of iodine in a 100 cm3 round-bottomed flask
equipped with a reflux condenser.
2. Add 0.015 mol of benzopinacol. (Benzopinacol could be prepared from photochemical
reaction of benzophenone and isopropyl alcohol, see appendix C.)
3. Reflux the solution for 10 minutes in a hot oil bath.
4. Cool the reaction mixture to room temperature.
5. Collect the solid by vacuum filtration using Buchner funnel. Record the mass of crude
product.
6. Recrystallize the crude product with the mixture of ethyl acetate and hexane (Therecrystallization protocol is similar to that described in Task P4).
7. Collect the crystals by vacuum filtration using Buchner funnel. Record the mass ofrecrystallized product.
8. Determine the yield of the product.

Preparatory problems: 49th IChO, Thailand, 201757

APPENDICESAPPENDIX A
A1: SAFETY RULES FOR STUDENTS IN THE LABORATORY
All students of chemistry must recognize that hazardous materials cannot be completely
avoided. Chemists must learn to handle all materials in an appropriate fashion. While it is notexpected that all students participating in the International Chemistry Olympiad know the hazardsof every chemical, the organizers of the competition will assume that all participating students
know the basic safety procedures. For example, the organizers will assume that students know thateating, drinking or smoking in the laboratory or tasting a chemical is strictly forbidden.
In addition to the common-sense safety considerations to which students should have beenpreviously exposed, some specific rules, listed below, must also be followed during the Olympiad.
If any question arises concerning safety procedures during the practical exam, the student should
not hesitate to ask the nearest supervisor for direction.
Rules regarding personal protection
1. Eye protection must be worn in the laboratories at all times. If the student wears contactlenses, full protection goggles must also be worn. Eye protection will be provided by the hostcountry.
2. A laboratory coat is required. Each student will supply this item for himself/herself.
3. Long pants and closed-toed shoes are recommended for individual safety. Long hair andloose clothing should be confined.
4. Pipetting by mouth is strictly forbidden. Each student must be provided with pipette bulb
or pipette filler.
Rules for Handling Materials
1. Specific instructions for handling hazardous materials will be included by the hostcountry in the procedures of the practical exam. All potentially dangerous materials will be labeledusing the GHS symbols. Each student is responsible for recognizing these symbols and knowing
their meaning (see Appendix B).
2. Do not indiscriminately dispose chemicals in the sink. Follow all disposal rules provided
by the host country.
A2: SAFETY RULES AND RECOMMENDATIONS FOR THE HOST COUNTRY OF
THE INTERNATIONAL CHEMISTRY OLYMPIAD
Certainly it can be assumed that all students participating in the IChO have at least modest
experience with safety laboratory procedures. However, it is the responsibility of the International
Jury and the organizing country to be sure that the welfare of the students is carefully considered.

Preparatory problems: 49th IChO, Thailand, 201758

Reference to the Safety Rules for Students in the Laboratory will show that the students carry someof the burden for their own safety. Other safety matters will vary from year to year, depending onpractical tasks. The organizers of these tasks for the host country are therefore assigned
responsibility in the areas listed below. The organizers are advised to carefully test the practicaltasks in advance to ensure the safety of the experiments. This can best be accomplished by having
students of ability similar to that of IChO participants carry out the testing.
APPENDIX B
HAZARD WARNING SYMBOLS AND HAZARD DESIGNATIONS
Chemicals used in the IChO laboratory experiments need to be labeled according to the
Globally Harmonized System of Labelling of Chemicals (GHS) standard developed by the United
Nations. The organizing country should use the locally legislated GHS system (pictograms, hazard
statements, etc.) if it exists. If such rules do not exist, the original GHS directives(http://www.unece.org/trans/danger/publi/ghs/ghs_welcome_e.html) and the GHS compliant
documentation by the chemical providers should be used.

Preparatory problems: 49th IChO, Thailand, 2017

59

APPENDIX C
Synthesis of benzopinacol
Org. Synth. 1934, 14, 8.
DOI: 10.15227/orgsyn.014.0008

Procedure
A mixture of 150 g (0.82 mol) of benzophenone, 1 drop of glacial acetic acid, and 665 g (850 cm3,
11 mol) of isopropyl alcohol in a 1L round-bottomed flask is warmed to 45 °C. The flask is closedwith a tight cork firmly wired or tied in place, and is supported in an inverted position ina tripod and exposed to direct sunlight. After 3-5 hours under the sunlight, crystals of benzopinacol
should be observed; after 8-10 days of exposure to the sunlight (See Note), the crystalsof benzopinacol should be completely formed. Chill the reaction flask containing crystals in theice bath to complete crystallization. The crystalline product is collected by vacuum filtration,filtered using Buchner funnel. The crystalline product is washed with a small quantity of isopropyl
alcohol, and allowed to air dry. The product should be sufficiently pure for most purposes. It may
be crystallized by dissolving it in hot benzene, filtering, and adding 400 cm3 of hot ligroin(b.p. 90–100 °C) to the hot filtrate. After cooling in ice and filtering there is obtained
129–130 g of purified product.

Note:
About 5 days of bright sunlight exposure are required to complete the reduction. The reaction canbe interrupted at any time, the crystals filtered, and the filtrate then exposed further.

Preparatory problems: 49th IChO, Thailand, 201760