th

40 International
Chemistry Olympiad

Theoretical Problems

17 July 2008
Budapest, Hungary

40th International Chemistry Olympiad

Theoretical Problems

Instructions• Write your name and code on each page.
• You have 5 hours to work on the problems. Begin only when the START command isgiven.
• Use only the pen and calculator provided.
• All results must be written in the appropriate boxes. Anything written elsewhere will
not be graded. Use the reverse of the sheets if you need scratch paper.
• Write relevant calculations in the appropriate boxes when necessary. If you provide
only correct end results for complicated problems, you receive no score.
• When you have finished the examination, you must put your papers into the envelope
provided. Do not seal the envelope.
• You must stop your work immediately when the STOP command is given. A delay indoing this by 3 minutes may lead to cancellation of your exam.
• Do not leave your seat until permitted by the supervisors.
• This examination has 26 pages.
• The official English version of this examination is available on request only forclarification.

Official English version

2

40th International Chemistry Olympiad

Theoretical Problems

Constants and Formulae
Avogadro
constant:

NA = 6.022·1023 mol–1

Ideal gas equation:

pV = nRT

Gas constant:

R = 8.314 J K–1 mol–1

Gibbs energy:

G = H – TS

Faraday constant:

F = 96485 C mol–1o
Δr G o = −RT ln K = −nFEcell

Planck constant:h = 6.626·10–34 J s

Nernst equation:

E = Eo +Speed of light:

c = 3.000·108 m s–1

Energy of a photon:

E=

RT coxln
zF credhc

λIZero of the Celsius
A = log 0 = ε cl273.15 K
Lambert-Beer law:scale:
I
In equilibrium constant calculations all concentrations are referenced to a standard
concentration of 1 mol/dm3. Consider all gases ideal throughout the exam.

Periodic table with relative atomic masses
1

18

1

2

H

He

1.008

2

13

14

15

16

17

4.003

3

4

5

6

7

8

9

10

Li

Be

B

C

N

O

F

Ne

6.94

9.01

10.81

12.01

14.01

16.00

19.00

20.18

11

12

13

14

15

16

17

18

Na Mg

Al

Si

P

S

Cl

Ar
39.95

22.99

24.30

3

4

5

6

7

8

9

10

11

12

26.98

28.09

30.97

32.06

35.45

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

K

Ca Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga Ge

As

Se

Br

Kr
83.80

39.10

40.08 44.96 47.87

50.94

52.00

54.94

55.85

58.93

58.69

63.55

65.38

69.72

72.64

74.92

78.96

79.90

37

38

39

40

41

42

43

44

45

46

47

48

49

50

51

52

53

54

Rb

Sr

Y

Zr

Nb Mo

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Xe

85.47

87.62 88.91 91.22

92.91

95.96

-

55

56

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

Cs

Ba

Hf

Ta

W

Re

Os

Ir

Pt

Au

Hg

Tl

Pb

Bi

Po

At

Rn

-

-

-

132.91 137.33
87

Fr
-

88

5771

Ra 89103-

101.07 102.91 106.42 107.87 112.41 114.82 118.71 121.76 127.60 126.90 131.29

178.49 180.95 183.84 186.21 190.23 192.22 195.08 196.97 200.59 204.38 207.2 208.98
104

105

106

107

108

109

110

111

Rf

Db

Sg

Bh

Hs

Mt

Ds

Rg

-

-

-

-

-

-

-

-

61

62

57

58

59

60

63

64

65

66

67

68

69

70

71

La

Ce

Pr

Nd Pm Sm Eu

Gd

Tb

Dy

Ho

Er

Tm Yb

Lu

138.91 140.12 140.91 144.24-

150.36 151.96 157.25 158.93 162.50 164.93 167.26 168.93 173.05 174.97

89

90

91

92

93

94

97

98

99

102

103

Ac

Th

Pa

U

Np

Pu Am Cm Bk

Cf

Es Fm Md No

Lr-

232.04 231.04 238.03

Official English version

-

-

95
-

96
-

-

-

-

100
-

101
-

-

-

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Problem 1

6% of the total

1a 1b 1c 1d Task 1
4 2 8 8 22
The label on a bottle containing a dilute aqueous solution of an acid became damaged.
Only its concentration was readable. A pH meter was nearby, and a quick measurement
showed that the hydrogen ion concentration is equal to the value on the label.
a)Give the formulae of four acids that could have been in the solution if the pH changed
one unit after a tenfold dilution.

b)

Could it be possible that the dilute solution contained sulfuric acid?
Sulfuric acid: pKa2 = 1.99
YesNo

If yes, calculate the pH (or at least try to estimate it) and show your work.

pH:

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c)

Code: XXX-

Could it be possible that the solution contained acetic acid?
Acetic acid:Yes

pKa = 4.76

No

If yes, calculate the pH (or at least try to estimate it) and show your work.

pH:

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Could it be possible that the solution contained EDTA (ethylene diamino tetraaceticacid)? You may use reasonable approximations.
EDTA: pKa1 = 1.70, pKa2 = 2.60, pKa3 = 6.30, pKa4 = 10.60
YesNo

If yes, calculate the concentration.

cEDTA:

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Problem 2

7% of the total

Task 218
Determine the structure of the compounds A-H (stereochemistry is not expected), basedon the information given in the following reaction scheme:AradicalPdCB+ 5 H2( C10H18 ) oxidation(C10H18O)

ZnCl2
− H2O

D
1. O3

450°C

2. Zn/H+

Pd/C, 350°C
H− H2O, − 8 H

1. Pd/H2G

2. NaBH4F

Na2CO3, Δ− H2OE

Hints:• A is a well-known aromatic hydrocarbon.
• A hexane solution of C reacts with sodium (gas evolution can be observed), but C
does not react with chromic acid.
•13

C NMR spectroscopy shows that D and E contain only two kinds of CH2 groups.

• When a solution of E is heated with sodium carbonate an unstable intermediate
forms at first, which gives F on dehydration.
A

B

C

D

H

G

F

E

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Problem 3

6% of the total

3a 3b 3c Task 3
4 8 2 14
Vinpocetine (Cavinton®, Calan®) is one of the best selling original drugs developed in
Hungary. Its preparation relies on a natural precursor, (+)-vincamine (C21H26 N2O3), which
is isolated from the vine plant, vinca minor. The transformation of (+)-vincamine tovinpocetine is achieved in two steps depicted below.

H
N
HO
H3CO2CN

cat. conc. H2SO4
CH2Cl2

1. NaOH
2. C2H5Br
A

C2H5OHB (Vinpocetine)

C2H5

Vincamine1
All compounds (A to F) are enantiomerically pure compounds.
• The elementary composition of A is: C 74.97%, H 7.19%, N 8.33%, O 9.55%.
• B has 3 other stereoisomers.

a)A

Propose structures for the intermediate A and vinpocetine (B).
B

A study of the metabolism of any drug forms a substantial part of its documentation. There
are four major metabolites each formed from vinpocetine (B): C and D are formed inhydrolysis or hydration reactions, while E and F are oxidation products.

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Hints:• The acidity of the metabolites decreases in the order C >> E >> D. F does notcontain an acidic hydrogen.
• C and E each have 3 other stereoisomers, while D and F each have 7 otherstereoisomers.
• F is a pentacyclic zwitterion and it has the same elementary analysis as E:
C 72.11%, H 7.15%, N 7.64%, O 13.10%.
• The formation of E from B follows an electrophilic pattern.
• The formation of D from B is both regio- and stereoselective.

b)

Propose one possible structure for each of the metabolites C, D, E and F!

C

D

E

F

c)

Draw a resonance structure for B that explains the regioselective formation of D andthe absence of the alternate regioisomer in particular.

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Problem 4

6% of the total

4a 4b 4c 4d 4e Task 4
6 2 6 8 6 28

A major transformation route for oxiranes (epoxides) is ring opening. This may be
accomplished in various ways.
On acid catalysis the reactions proceed through cation-like (carbenium ion-like) species.
For substituted oxiranes the direction of ring opening (which C–O bond is cleaved)
depends on the stability of the intermediate carbenium ion. The more stable theintermediate carbenium ion the more probable its formation. However, an open carbenium
ion (with a planar structure) only forms if it is tertiary, benzylic or allylic.
On base catalysis the sterically less hindered C–O bond is cleaved predominantly.
Keep stereochemistry in mind throughout the whole problem. To depict stereochemistrybond symbols and nothing else where necessary.
use only thea)Draw the structure of the reactant and the predominant products when 2,2-dimethyloxirane (1,2-epoxy-2-methylpropane) reacts with methanol at low temperatures,catalysed by(i) sulfuric acid(ii) NaOCH3.
2,2-dimethyloxiraneb)

H+

NaOCH3

CH3OH

CH3OH

Draw the structure of the predominant product when the epoxide ring of the following
leukotriene derivative is opened with a thiolate (RS–).
O
COOCH3
H3C

CH3

1. RSH3C

2. H+

Different porous acidic aluminosilicates can also be used to catalyse the transformation ofalkyl oxiranes. In addition to ring opening, cyclic dimerisation is found to be the main
reaction pathway producing mainly 1,4-dioxane derivatives (six-membered saturated rings
with two oxygen atoms in positions 1,4).
40th IChO Theoretical Problems, Official English version

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Name:c)

Draw the structure(s) of the most probable 1,4-dioxane derivative(s) when thestarting compound is (S)-2-methyloxirane ((S)-1,2-epoxypropane). Give the structureof the reactant as well.

(S)-2-methyloxiraned)Code: XXX-

product

Draw the structure(s) of the substituted 1,4-dioxane(s) when the epoxide reacting is(R)-1,2-epoxy-2-methylbutane ((R)-2-ethyl-2-methyloxirane). Give the structure of thereactant as well.

(R)-1,2-epoxy-2-methylbutane:e)Give the structure(s) of the substituted 1,4-dioxane(s) when this reaction is carriedout with racemic 1,2-epoxy-2-methylbutane (2-ethyl-2-methyloxirane).

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Problem 5

7% of the total

5a 5b Task 5
67 33 100A and B are white crystalline substances. Both are highly soluble in water and can bemoderately heated (up to 200 °C) without change but both decompose at higher
temperatures. If an aqueous solution of 20.00 g A (which is slightly basic, pH ≈ 8.5-9) is
added to an aqueous solution of 11.52 g B (which is slightly acidic, pH ≈ 4.5-5) a white
precipitate C forms that weighs 20.35 g after filtering, washing and drying. The filtrate is
essentially neutral and gives a brown colour reaction with an acidified KI solution. Whenboiled, the filtrate evaporates without the appearance of any residue.
The white solid D can be prepared by the heating of A in the absence of air. The
exothermic reaction of D with water gives a colourless solution. This solution, if kept in an
open container, slowly precipitates a white solid E and leaves water. Upon prolonged
exposure to air at room temperature, solid D is transformed into E as well. However,heating D in air at 500 °C produces a different white substance F, which is barely soluble
in water and has a mass of only 85.8% of the E formed from the same amount of D. F
gives a brown colour reaction with an acidified solution of KI.
E can be converted back into D but ignition above 1400 °C is required for this purpose.
The reaction of B and D in water forms the precipitate C and is accompanied by acharacteristic odour.
a)b)Give the formulae of the substances A - F
A

B

C

D

E

F

Write balanced equations for all the reactions mentioned. (The equation for thethermal decomposition of B is not required.)

Equations:40th IChO Theoretical Problems, Official English version

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Problem 6

Code: XXX-

7% of the total

6a 6b 6c 6d 6e 6f 6g Task 6
3 5 3 6 6 12 10 45

A feathery, greenish solid precipitate can be observed if chlorine gas is bubbled into waterclose to its freezing point. Similar precipitates form with other gases such as methane andnoble gases. These materials are interesting because vast quantities of the so-called
methane-hydrates are supposed to exist in nature (comparable in quantity with othernatural gas deposits).
These precipitates all have related structures. The molecules of water just above its
freezing point form a hydrogen-bonded structure. The gas molecules stabilize thisframework by filling in the rather large cavities in the water structure forming clathrates.
The crystals of chlorine and methane clathrates have the same structure. Their main
characteristics are dodecahedra formed from 20 water molecules. The unit cell of thecrystal can be thought as a body-centered cubic arrangement built from thesedodecahedra which are almost spherical objects. The dodecahedra are connected via
additional water molecules located on the faces of the unit cell. Two water molecules canbe found on each face of the unit cell. The unit cell has an edge dimension of 1.182 nm.
There are two types of cavities in this structure. One is the internal space in thedodecahedra (A). These are somewhat smaller than the other type of voids (B), of which
there are 6 for each unit cell.
a)

How many type A cavities can be found in a unit cell?

b)

How many water molecules are there in a unit cell?

c)

If all cavities contain a guest molecule, what is the ratio of the number of water to thenumber of guest molecules?

d)Methane hydrate is formed with the structure in c) at temperatures between 0-10 °C.
What is the density of the clathrate?

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Density:e)

The density of chlorine hydrate is 1.26 g/cm3. What is the ratio of the number of waterand guest molecules in the crystal?

Ratio:
Which cavities are likely to be filled in a perfect chlorine hydrate crystal? Mark one or more.
Some A

Some B

All A

All B

Covalent radii reflect atomic distances when the atoms are covalently bonded. Nonbonded
or van der Waals radii give a measure of the atomic size when they are not bonded
covalently (modeled as hard spheres).
Atom Covalent radius (pm) Nonbonded radius (pm)
H
37
120
C
77
185
O
73
140
Cl
99
180

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Based on the covalent and nonbonded radii of these atoms estimate lower andupper bounds for the average radii of the cavities where possible. Show your reasoning.

< r (A) << r(B)Let us consider the following processesg)

H2O(l) → H2O(s)(1)

x CH4(g) + H2O (l)→ xCH4.1H2O(clathrate)(2)

What are the signs of the following molar quantities referring to these reactions in thegiven direction at 4 °C? Mark with a –, 0 or +.
sign
ΔGm(1)
ΔGm(2)
ΔHm(1)
ΔHm(2)
ΔSm(1)
ΔSm(2)
ΔSm(2) – ΔSm(1)ΔHm(2) – ΔHm(1)40th IChO Theoretical Problems, Official English version

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Problem 7

Code: XXX-

8% of the total

7a 7b 7c 7d 7e 7f 7g 7h Task 7
2 1 4 2 8 5 8 12 42
The dithionate ion (S2O62−) is a rather inert inorganic ion. It can be prepared by bubbling
sulphur-dioxide continously into ice-cooled water to which manganese dioxide is added insmall increments. Dithionate and sulphate ions are formed under these circumstances.
a)

Write the balanced chemical equations for the two reactions.

After the reaction is complete, Ba(OH)2 is added to the mixture until the sulphate ions are
fully precipitated. This is followed by the addition of Na2CO3.
b)

Write the balanced equation for the reaction that takes place upon addition of
Na2CO3.

Sodium dithionate is then crystallized by evaporating some of the solvent. The prepared
crystals dissolve readily in water and do not give a precipitate with BaCl2 solution. Whenthe solid is heated and maintained at 130 °C, 14.88 % weight loss is observed. The
resulting white powder dissolves in water and does not give a precipitate with BaCl2
solution. When another sample of the original crystals is kept at 300 °C for a few hours,
41.34 % weight loss occurs. The resulting white powder dissolves in water and gives awhite precipitate with BaCl2 solution.
c)Give the composition of the prepared crystals and write balanced equations for thetwo processes that occur during heating.

Formula:Equation (130 °C):
Equation (300 °C):

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Although dithionate ion is a fairly good reducing agent thermodynamically, it does not reactwith oxidants in solution at room temperature. At 75 °C, however, it can be oxidized inacidic solutions. A series of kinetic experiments were carried out with bromine as anoxidant.
d)Write the balanced chemical equation for the reaction between bromine anddithionate ion.

The initial rates (v0) of the reaction were determined in a number of experiments at 75 °C.
[Br2]0[Na2S2O6]0[H+]0v0(mmol/dm3) (mol/dm3) (mol/dm3) (nmol dm–3s−1)
0.500
0.0500
0.500
640
0.500
0.0400
0.500
511
0.500
0.0300
0.500
387
0.500
0.0200
0.500
252
0.500
0.0100
0.500
129
0.400
0.0500
0.500
642
0.300
0.0500
0.500
635
0.200
0.0500
0.500
639
0.100
0.0500
0.500
641
0.500
0.0500
0.400
511
0.500
0.0500
0.300
383
0.500
0.0500
0.200
257
0.500
0.0500
0.100
128
e)

Determine the order of the reaction with respect to Br2, H+ and S2O62−, theexperimental rate equation, and the value and unit of the rate constant.

Reaction order for Br2:

for H+:

for S2O62−:

Experimental rate equation:k:

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In similar experiments, chlorine, bromate ion, hydrogen peroxide and chromate ion haveall been used as oxidizing agents at 75 °C. The rate equations for these processes areanalogous to the one observed with bromine, the units of all rate constants are the same,the values are 2.53·10−5 (Cl2), 2.60·10−5 (BrO3−), 2.56·10−5 (H2O2), and 2.54·10−5 (Cr2O72−).
Experiments were also carried out in acidic sodium dithionate solution without any
oxidizing agent. When following the processes by UV spectrophotometry, the slow
appearance of a new absorption band around 275 nm was observed. Although hydrogensulphate ion is a detectable product of the reaction, it does not absorb any light above 200
nm.
f)Give the formula of the major species causing the new absorption band and write thebalanced equation of the chemical reaction occurring in the absence of oxidants.

Species:
Reaction:An experiment was carried out to follow the absorbance at 275 nm with initialconcentrations: [Na2S2O6] = 0.0022 mol/dm3, [HClO4] = 0.70 mol/dm3, and the temperature
was 75 °C. A pseudo first-order kinetic curve was found with a half-life of 10 hours and 45
minutes.
g)

Calculate the rate constant of the reaction.

k:

Suggest a balanced chemical equation for the rate determining step of the reactions thatused an oxidizing agent.
Rate determining step:

When periodate ion (which is present as H4IO6− in aqueous solution) was used as anoxidant for dithionate ion, the two kinetic curves depicted in the graph were detected at
75 °C in the same experiment at two different wavelengths. The initial concentrations were
[H4IO6−] = 5.3·10−4 mol/dm3, [Na2S2O6] = 0.0519 mol/dm3, [HClO4] = 0.728 mol/dm3 At
465 nm, only I2 absorbs and its molar absorption coefficient is 715 dm3mol−1cm−1. At 350
nm, only I3− absorbs and its molar absorption coefficient is 11000 dm3mol−1cm−1. The
optical path length was 0.874 cm.

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0.20
0.18
0.16
0.14
0.12
A

465 nm
0.10
0.08
0.06
0.04
0.02

350 nm
0.00
0

200

400

600

800

1000

1200

1400

1600

1800

2000

2200

2400

time (s)h)

Write balanced chemical equations for the reactions that occur in the region where
the absorbance increases at 465 nm, and in the region where the absorbancedecreases at 465 nm.

Increase:
Decrease:
Calculate the expected time for the maximum absorbance of the kinetic curve measured at
465 nm.

tmax:
Estimate the expected ratio of the slopes of the increasing and decreasing regions in the
kinetic curve measured at 465 nm

Slope ratio:
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Problem 8

Code: XXX-

7 % of the total

8a 8b 8c 8d 8e 8f 8g 8h 8i Task 8
3 3 4 3 3 2 7 3 5 32
Ms. Z was a bright student, whose research project was to measure the complexation of
all lanthanide(III) ions with newly designed complexing ligands. One day she monitored theUV-vis absorption with Ce(III) and a particularly poor complexing ligand in a
spectrophotometer. She noticed that some small bubbles had formed in the closed cell by
the end of the 12-hour experiment. Soon she realized that the presence of the ligand is notnecessary to see the bubble formation, and continued her experiments with an acidified
CeCl3 solution. Bubble formation never occurred when she just kept the solution in the
spectrophotometer without turning on the instrument. Next, Ms. Z used a small quartz flask,in which she dipped a chloride ion selective electrode and could also withdraw samples
regularly for spectrophotometric measurements. She calibrated the chloride ion selective
electrode using two different NaCl solutions and obtained the following results:
cNaCl (mol/dm3) E (mV)
0.1000
26.9
1.000
−32.2

a)

Give a formula to calculate the chloride ion concentration of an unknown sample
based on the electrode voltage reading (E).

[Cl−] =
Ms. Z also determined the molar absorption coefficient for Ce3+ (ε = 35.2 dm3mol−1cm−1) at
295 nm, and, as a precaution, also for Ce4+ (ε = 3967 dm3mol−1cm−1).
b)Give a formula to calculate the Ce3+ concentration from an absorbance reading at
295 nm (A) measured in a solution containing CeCl3 (cuvette path length: 1.000 cm).

[Ce3+] =Ms. Z prepared a solution which contained 0.0100 mol/dm3 CeCl3 and 0.1050 mol/dm3 HCl,and began her experiment by turning on a quartz lamp. HCl does not absorb at 295 nm.
c)What were the expected initial absorbance and voltage readings?

A295nm=E=

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Before the quantitative experiment Ms. Z collected the gas formed into a carefully
neutralized solution of methyl orange (acid-base and redox indicator). Although she saw
bubbles going through the solution, the colour did not change or fade even after a day.
d)Give the formula of two gases, comprised of elements in the illuminated sample,
which could not be present given the results of this experiment.

During her quantitative experiment she recorded the absorbance and voltage values
regularly. The uncertainty of the spectophotometric measurements is ±0.002 and theaccuracy of the voltage measurements is ±0.3 mV.
time (min) 0
120
240
360
480
A295 nm0.3496 0.3488 0.3504 0.3489 0.3499
E (mV)
19.0
18.8
18.8
19.1
19.2
e)

Estimate the average rate of change in the concentrations of Ce3+, Cl−, and H+.

d[Ce3+]/dt =d[Cl–]/dt =d[H+]/dt =The following day, Ms. Z used an intense monochromatic light beam (254 nm) with anintensity of 0.0500 W. She passed this light through a 5-cm long quartz photoreactor filledwith the same acidic CeCl3 solution she had used before. She measured the molar
absorption coefficient for Ce3+ (ε = 2400 dm3mol−1cm−1) at 254 nm.
f)What percentage of the light is absorbed in this experimental setup?

The equipment allowed her to lead the gas first through a drying tube that removed tracesof water vapour and then into a closed chamber, whose volume was 68 cm3. The chamber
was equipped with a high-precision manometer and an igniter. She first filled the chamberwith dry argon to a pressure of 102165 Pa and then she turned on the lamp. In 18.00
hours, the pressure reached 114075 Pa. The temperature of the equipment was 22.0 °C.

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Code: XXX-

Estimate the amount of substance of the gas collected in the chamber.

ngas:

At this point, Ms. Z turned off the light and pressed the ignition button. When the chambercooled down to the initial temperature, the final pressure was 104740 Pa.
Suggest the formula(s) of the gas(es) formed and collected, and give the balanced
equation for the original chemical reaction taking place under illumination.

Gas(es):Reaction:h)What would be the final pressure after the ignition if the chamber was being filled for
24 hours before ignition?

p=i)

Estimate the quantum yield of product formation in the Ce(III) solution.

Quantum yield:
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Problem 96 % of the total

9a 9b 9c 9d Task 9
12 21 15 9 57
Thallium exists in two different oxidation states: Tl+ and Tl3+. Iodide ions can combine withiodine to form tri-iodide ions (I3–) in aquous solutions,
The standard redox potentials for some relevant reactions are:Tl+(aq) + e– → Tl(s)Eº1 = – 0.336 V
Tl3+(aq) + 3e– → Tl(s)Eº2 = + 0.728 V––
I2(s) + 2e 2I (aq) Eº3 = + 0.540 V
The equilibrium constant for the reaction I2(s) + I–(aq) → I3–(aq): K1 = 0.459.
Use T=25 °C throughout this problem.
a)Calculate the redox potential for the following reactions:Tl3+(aq) + 2 e– → Tl+(aq)Eº4

I3–(aq) +2 e– →3 I–(aq)

Eº5

Eº4 =

Eº5 =

b)

Write empirical formulae for all theoretically possible neutral compounds that containone thallium ion and any number of iodide and/or tri-iodide ion(s) as anion(s).

There is an empirical formula that could belong to two different compounds. Which one?

40th IChO Theoretical Problems, Official English version

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Based on the standard redox potentials, which of the two isomers mentioned above is thestable one at standard conditions? Write the chemical reaction for the isomerisation of theother isomer of thallium iodide.
More stable:
Isomerisation:
Complex formation can shift this equilibrium. The cumulative complex formation constantfor the reaction Tl3+ + 4I– → TlI4– is β4 = 1035.7
c)Write the reaction that takes place when a solution of the more stable isomer ofthallium iodide is treated with an excess of KI. Calculate the equilibrium constant forthis reaction.

Reaction:K2:

If the solution of the more stable isomer is treated with a strong basic reagent precipitationof a black substance can be observed. After the water content of the precipitate isremoved, the remaining material contains 89.5% thallium (by mass).
d)

What is the empirical formula of this compound? Show your calculations. Write abalanced equation for its formation.

40th IChO Theoretical Problems, Official English version

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Formula:Equation:40th IChO Theoretical Problems, Official English version

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