Code: XXX-01

48th International
Chemistry Olympiad

Practical Tasks
Part I.

26 July 2016
Tbilisi, Georgia
48th IChO Practical Tasks, Official English version

1

Code: XXX-01

Instructions

Begin only when the START command is given. The exam contains two parts. You
have 100 minutes to work on Part I (Task 1). After this you will have to leave thelab for 30 minutes.

Part I of the exam (Task 1) contains 5 pages, its answer sheets have 3 pages.



Follow the safety rules announced in the preparatory tasks. You get one warningfor violations. On the second warning you will get disqualified.



Wear your lab coat and safety goggles while in the lab. Ask your lab assistant for
the gloves of your size when you need them.

Use only the pen, marker pen and calculator provided. Do not write with themarker on paper; use it only to label glass or plastic labware.



Make sure that your student code is on every answer sheet.

All answers must be written in the appropriate boxes on the answer sheet.
Anything written elsewhere will not be graded. Use the reverse of the exam
sheets if you need scratch paper.

You have no access to sinks in the lab. You are provided with a sufficient quantityof labware. Only a few items need to be used again. Wash these carefully with anappropriate solvent into the waste container. Use the brush if needed. Distilledwater and paper tissues are freely available.

Liquid waste is to be put into the container labeled “LIQUID WASTE”. Do not put
rubbish (tissues, plastic, etc.) in this container, but into the waste baskets in thelab.

Chemicals and labware are not supposed to be refilled or replaced. Each such
incident (other than the first in the entire exam, which you will be allowed) will
result in the loss of 1 point from your 40 practical points.



Raise your hand if you have a safety question or you need a restroom break or
drinking water.

When you have finished this part of the examination, put your answer sheet into
the envelope provided and leave it on the table. Do not seal the envelope. You will
not have further access to the answer sheets from this part.



You must stop your work immediately when the STOP command is given. A delay
in doing this may lead to cancellation of your exam. Do not leave your place until
permitted by the lab assistants. You can keep the task text.

The official English version of this examination is available on request only forclarification.

48th IChO Practical Tasks, Official English version

2

Code: XXX-01

LabwareItem
Quantity
All tasks, on the table of common use
Latex gloves of different sizes, choose your size
General equipment for all tasks, for each student, on the table
Test tube rack (60 holes)
1
Paper tissue (can ask for extra)5
Permanent marker
1
Glass stirring rod, 20 cm
1
Polypropylene funnel, diam. 3.5 cm
1Soft plastic cup
3Strong plastic cup
1
All tasks, for each student in the soft plastic cup
Caps for polystyrene test tubes
22
Task 1, for each student, on the table
Rack for centrifuge tubes (21 holes)
1
3
Container with a screw cap for waste,1 dm , labeled “Liquid
1
Waste, Test 1”
Paper filters in zip-bag
5
Task 1, for each student, in the strong plastic cup
Pasteur pipettes
20
Task 1, for each student, in the 60-hole rack
Polystyrene test tubes, 10 cm335

48th IChO Practical Tasks, Official English version

3

Code: XXX-01

Chemicals
Name

State

Conc.

Q-ty

Placed inLabeledAll tasks, for each student, on the table
Wash bottle,
1 dm3
Task 1, for each student, on the table
Glass bottle with
HexaneLiquid25 cm3screw cap, 50 cm3
Amber plastic
Sodium3
Aqueous solution
1M
80 cm
bottle with screwhydroxide
cap, 125 cm3Glass bottle with
Nitric acid*
Aqueous solution
2M
150 cm3
dropper cap,
250 cm3
Task 1, for each student, in the 21-hole rack
Centrifuge tubes,
5 unknowns
Aqueous solution
45 cm350 cm3Centrifuge tube,
Silver nitrate
Aqueous solution
0.1 M
25 cm350 cm3
Aluminium
Centrifuge tube,
Aqueous solution
0.3 M
25 cm3sulfate50 cm3Centrifuge tube,
Barium nitrate Aqueous solution 0.25 M 25 cm350 cm3Iron(III)
Aqueous acidic
Centrifuge tube,
0.2 M
25 cm3nitrate(HNO3) solution
50 cm3
Potassium
Centrifuge tube,
Aqueous solution
0.1 M
25 cm3
iodide50 cm3
Potassium
Centrifuge tube,
Aqueous solution
0.1 M
25 cm3
iodate50 cm3Magnesium
Centrifuge tube,
Aqueous solution
0.2 M
25 cm3chloride
50 cm3
SodiumCentrifuge tube,
Aqueous solution
0.2 M
25 cm3
carbonate
50 cm3Centrifuge tube,
Sodium sulfite Aqueous solution
0.2 M
25 cm350 cm3Centrifuge tube,
Ammonia*
Aqueous solution
1M
25 cm350 cm3* Nitric acid and ammonia solutions are needed in a subsequent task.
Distilled water

Liquid-1 dm3

48th IChO Practical Tasks, Official English version

H2O dist.
HexaneNaOH
HNO3
Unknown
No ___AgNO3
Al2(SO4)3Ba(NO3)2
Fe(NO3)3
KI
KIO3
MgCl2
Na2CO3
Na2SO3NH3(aq)4

Code: XXX-01

Task 1
You have 10 different compounds dissolved in water in 5 unknown solutions. Each
numbered container contains two of the following compounds in aqueous solution(every compound is used, and each compound is used only once):
AgNO3, Al2(SO4)3, Ba(NO3)2, Fe(NO3)3, KI, KIO3, Na2CO3, Na2SO3, MgCl2, NH3
You are given HNO3 solution, NaOH solution, hexane and the aqueous solutions of the 10
pure compounds listed above.
You can use empty test tubes and any of the liquids provided (including the unknowns)
to identify the unknown samples. A funnel and filter paper can be used for separation.
Identify the compounds in the solutions 1-5. Give the number of the solution that
contains the individual compounds on the answer sheet. Indicate two
observations caused by a chemical reaction for each compound in yourunknown mixtures by giving the letter code of the appropriate observation(choose one or more from the list), and write appropriate balanced ionicequation(s) that explain the observation. At least one of the reactions has to be
specific for clearly identifying the compound from this selection of unknowns.
Note: After the STOP signal close all the centrifuge test tubes containing the unknown
mixtures with the blue caps labeled with the student code and leave these in the rack.

48th IChO Practical Tasks, Official English version

5

Code: XXX-01

48th International
Chemistry Olympiad

Practical Tasks Part I.
Answer Sheets

26 July 2016
Tbilisi, Georgia

48th IChO Practical Tasks, Official English version

1

Code: XXX-01

Task 17713% of the total
7

7

7

7

7

7

7

7

Sum: 70

Only fill out this table when you are ready with all your assignments. Use the following
observation codes:
A - Formation of white precipitate
B - Formation of colored precipitate(red, brown, yellow, black etc.)
C - Dissolution of precipitate
D - Color change in the solution
E - Formation of colored solution
CompoundNo. ofunknown

Formula ofreactionpartner(s)F - Brown color in the organic phase
G - Purple color in the organic phase
H - Formation of colored gas
I - Formation of colorless and odorless gas
J - Formation of colorless and odorous gas
K – Change in the color of precipitate
Observation
code(s)Balanced net ionic equation(s)NH3

Fe(NO3)3

Al2(SO4)3

AgNO3

KIO3

48th IChO Practical Tasks, Official English version

2

Code: XXX-01
CompoundNo. ofunknown

Formula ofreactionpartner(s)Observation
code(s)Balanced net ionic equation(s)Na2CO3

MgCl2

Na2SO3

Ba(NO3)2KI

Replacements:
Item

Quantity

Lab assistant’s
signature

48th IChO Practical Tasks, Official English version

Student’s
signature3

Code: XXX-01
5p for locating each compound, 1 p for each relevant equation. Altogether 10x7p.
Subpoints for 1p: 0.4p for correct observation with appropriate reagent(s); 0.6p for the
relevant balanced ionic equation (-0.1p for minor typos; maximum of -0.3p for poor
balancing; maximum of 0.3p for an equation in other than ionic form)
The unknowns are identical mixtures for every student in different order. Most are
mixed in 1:1 ratio by volume.
Characteristic reactions are marked with bold letters. One of these or equivalent has tobe shown on the answer sheet.
NH3
AgNO3, B)C)
Fe(NO3)3, B)
Al2(SO4)3, A)

2 Ag+ + 2 OH− = Ag2O + H2O (if Ag+ is not mixed with Fe3+)
Ag2O + H2O + 4 NH3 = 2 [Ag(NH3)2]+ + 2 OH− (if Ag+ is not with Fe3+)
Fe3+ + 3 OH−= Fe(OH)3
Al3+ + 3OH− = Al(OH)3 (or [Al(H2O)6]3+ + 3 OH− = Al(OH)3 + 6
H2O)
MgCl2, A)
Mg2+ + 2 OH− = Mg(OH)2
NaOH, J)
NH4+ + OH− = NH3 + H2O(KIO3) + AgNO3, C) AgIO3 + 2 NH3 = [Ag(NH3)2]+ + IO3−Fe(NO3)3
NaOH, B)
NH3, B)KI, D) or E)
MgCl2, E)

Fe3+ + 3 OH− = Fe(OH)3
Fe3+ + 3 OH− = Fe(OH)3
2 Fe3+ + 2 I− = 2 Fe2+ + I2
Fe3+ + Cl− = [FeCl]2+ (or Fe3+ + 3 Cl− = FeCl3 etc.)

Al2(SO4)3
NaOH, A)C)(NaOH +)
HNO3 A)
Ba(NO3)2, A)
Na2CO3, A)

Al3+ + 3 OH− = Al(OH)3 (or [Al(H2O)6]3+ + 3 OH− = Al(OH)3 + 6 H2O)
Al(OH)3 + OH− = [Al(OH)4]−[Al(OH)4]− + H+ = Al(OH)3 + H2O
Ba2+ + SO42− = BaSO4
Al3+ + 3 OH− = Al(OH)3 (or [Al(H2O)6]3+ + 3 OH− = Al(OH)3 + 6 H2O)

48th IChO Practical Tasks, Official English version

4

Code: XXX-01
AgNO3
NaOH, B)KI, B)
NH3, B)C)
MgCl2, A)
Na2CO3, A)
or B)
Na2SO3, A)C)
KIO3, A)

2 Ag+ + 2 OH− = Ag2O + H2O
Ag+ + I− = AgI
2 Ag+ + 2 OH− = Ag2O + H2O (if Ag+ is not mixed with Fe3+)
Ag2O + H2O + 4 NH3 = 2 [Ag(NH3)2]+ + 2 OH− (if Ag+ is not with Fe3+)
Ag+ + Cl− = AgCl
2 Ag+ + CO32− = Ag2CO3
2 Ag+ + SO32− = Ag2SO3
Ag2SO3 + 3 SO32− = 2 [Ag(SO3)2]3−
Ag+ + IO3- = AgIO3KIO3Na2SO3 + HNO3, B) or E)(+ hexane, G)
KI + HNO3, B) or E)(+ hexane, G)
AgNO3, A)
Ba(NO3)2, A)

5 SO32− + 2 IO3− + 2 H+ = I2 + 5 SO42− + H2O
5 I− + IO3− + 6 H+ = 3 I2 + 3 H2O
Ag+ + IO3− = AgIO3
Ba2+ + 2 IO3− = Ba(IO3)2

Na2CO3
HNO3, I)
Ba(NO3)2, A)+ HNO3, C), I)
AgNO3, A) or B)+ HNO3, C), I)
MgCl2, A)+ HNO3, C), I)

CO32− + 2 H+ = H2O + CO2
Ba2+ + CO32− = BaCO3
BaCO3 + 2 H+ = Ba2+ + H2O + CO2
2 Ag+ + CO32− = Ag2CO3
Ag2CO3 + 2 H+ = 2 Ag+ + H2O + CO2
Mg2+ + CO32− = MgCO3
MgCO3 + 2 H+ = Mg2+ + H2O + CO2

MgCl2
NaOH, A)
NH3, A)
AgNO3, A)
Na2CO3, A)
Fe(NO3)3, E)

Mg2+ + 2 OH− = Mg(OH)2
Mg2+ + 2 OH− = Mg(OH)2
Ag+ + Cl− = AgCl
Mg2+ + CO32− = MgCO3
Fe3+ + Cl− = [FeCl]2+ (or Fe3+ + 3 Cl− = FeCl3 etc.)

Na2SO3
HNO3, J
KIO3 + HNO3, B) or E)(+hexane, G)
Ba(NO3)2, A)+ HNO3, C)
AgNO3, A)C)
KI + KIO3 , D)

SO32− + 2 H+ = H2O + SO2
5 SO32− + 2 IO3− + 2 H+ = I2 + 5 SO42− + H2O
Ba2+ + SO32− = BaSO3
BaSO3 + 2 H+ = Ba2+ + SO2 + H2O
2 Ag+ + SO32− = Ag2SO3
Ag2SO3 + 3 SO32− = 2 [Ag(SO3)2]3−
I2 + SO32− + H2O = 2 I− + SO42− + 2 H+

48th IChO Practical Tasks, Official English version

5

Code: XXX-01
Ba(NO3)2
Al2(SO4)3, A)
KIO3, A)
Na2CO3, A)
Na2SO3, A)+ HNO3, C)

Ba2+ + SO42− = BaSO4
Ba2+ + 2 IO3− = Ba(IO3)2
Ba2+ + CO32− = BaCO3
Ba2+ + SO32− = BaSO3
BaSO3 + 2 H+ = Ba2+ + SO2 + H2O

KI
Fe(NO3)3, E) or D)
AgNO3, B)
KIO3, + HNO3, B) or E)(+hexane, G)

2 Fe3+ + 2 I− = 2 Fe2+ + I2
Ag+ + I− = AgI
5 I− + IO3− + 6 H+ = 3 I2 + 3 H2O

48th IChO Practical Tasks, Official English version

6

Code: XXX-01

48th International
Chemistry Olympiad

Practical Tasks
Part II.

26 July 2016
Tbilisi, Georgia

48th IChO Practical Tasks, Official English version

1

Code: XXX-01

Instructions
You have a 15 minute reading time before you start work. Begin reading only
when the START command is given.



Follow the safety rules announced in the preparatory tasks. You get one warningfor violations. On the second warning you will get disqualified.



Wear your lab coat and safety goggles while in the lab. Ask your lab assistant for
the gloves of your size when you need them.

Use only the pen, marker pen and calculator provided. Do not write with themarker on paper; use it only to label glass or plastic labware.



Make sure that your student code is on every answer sheet.

All answers must be written in the appropriate boxes on the answer sheet.
Anything written elsewhere will not be graded. Use the reverse of the exam
sheets if you need scratch paper.

You have no access to sinks in the lab. You are provided with a sufficient quantityof labware. Only a few items need to be used again. Wash these carefully withappropriate solvent into the waste container. Use the brush if needed. Distilledwater and paper tissues are freely available.

Liquid waste is to be put into the container labeled “LIQUID WASTE”. Do not put
rubbish (tissues, plastic, etc.) in this container, but into the waste baskets in thelab.

Chemicals and labware are not supposed to be refilled or replaced. Each such
incident (other than the first in the entire exam, which you will be allowed) will
result in the loss of 1 point from your 40 practical points.



Raise your hand if you have a safety question or you need a restroom break or
drinking water.

When you have finished the examination, put your answer sheet into theenvelope provided and leave it on the table. Do not seal the envelope.

You must stop your work immediately when the STOP command is given. A delay
in doing this may lead to cancellation of your exam. Do not leave your place until
permitted by the lab assistants. You can keep the task text.

The official English version of this examination is available on request only forclarification.

Instructions specific for Part II

The working time for Part II (Task 2 and 3) is 200 minutes.

Start Part II with Task 2. When you are ready to start with Task 3, tell the lab
assistant, and you will receive the chemicals and labware for Task 3. Reagents for
Task 2 will be taken away from you at this point.

Part II of the exam (Task 2-3) contains 10 pages, its answer sheets have 7 pages.



Ask the lab assistants when you need your alcohol lamp lighted. Heat only glass
test tubes. Close the alcohol lamp with the cap when finished.

48th IChO Practical Tasks, Official English version

2

Code: XXX-01

LabwareItem
Quantity
General equipment for all tasks, for each student, on the table
Test tube rack (60 holes)
1
Paper tissue
5
Permanent marker
1
Glass stirring rod, 20 cm
1
Polypropylene funnel, diam. 3.5 cm
1Soft plastic cups
3
Strong plastic cup
1Caps for polystyrene test tubes
22
Tasks 2 and 3, for each student, on the table
Container with a screw cap for waste,3 dm3, labeled “Liquid Waste,1
Tests 2&3”
Task 2, for each student, on the table
Storage box labeled “Task 2”
1
Laboratory stand with double burette clamp
1
Burette, 25.00 cm3
2
3
Graduated pipette, 10.0 cm
1
3
Graduated pipette, 1.00 cm
1
Bulb (Mohr) pipette, 10.00 cm3
1
3
Erlenmeyer flask, 100 cm
2
3
Graduated cylinder, 10.0 cm
2
Brush
1
Polypropylene funnel, 5.5 cm
1
Task 2, for each student, in the storage box “Task 2”
Polystyrene test tubes, 10 cm3
8
Pipette filler
1
Pasteur pipettes for indicators
2
Task 3, for each student, get from the lab assistants
Storage box labeled “Task 3”
1
Task 3, for each student, in the storage box “Task 3”
Polystyrene test tubes, 10 cm3
20
Alcohol lamp
1
Test tube holders, wooden
1
Glass test tubes
10
Pasteur pipettes
10Strong plastic cup
1

48th IChO Practical Tasks, Official English version

3

Code: XXX-01

Chemicals
Name

State

Conc.

Q-ty

Placed in

Task 2, for each student, on the table
Glass bottle
Aqueous
Nitric acid
2M-*
with dropper
solution
cap, 250 cm3
Task 2, for each student, in the storage box “Task 2”
Glass bottle
Water sample
Aqueous
To be
100 cm3
with screw
solutionsolutiondeterminedcap, 100 cm3
Glass bottle
SodiumAqueous
9 mg/dm3 in
3
50 cmwith screw
fluoride
solutionfluoridecap, 50 cm3
Zirconyl
Acidic0.055% ZrOCl2,
Glass bottle
3
Alizarinaqueous0.028%
10 cm
with screw
indicator
solutions
Alizarin Red S
cap, 25 cm3Glass bottle
SodiumAqueous0.0500 M
50 cm3
with screw
chloride
solution
cap, 50 cm3
Ammonium
AqueousGlass bottle,iron(III) sulfate
acidic20 g/dm3
10 cm315 cm3
dodecahydrate
solution
Amber glass
Aqueous
To be
3
Silver nitrate
200 cmbottle,solutiondetermined
250 cm3
See exact
Glass bottle
Ammonium
Aqueousconcentration 100 cm3with screw
thiocyanate
solutionon the label
cap, 100 cm3
Potassium
AqueousGlass bottle,
10%
5 cm3
chromate
solution
15 cm3
Task 3, for each student, on the table
Glass bottle
3
EthanolLiquid95 %150 cmwith dropper
cup, 250 cm3
Task 3, for each student, in the storage box “Task 3”
Organic
LiquidSyringes,
unknowns 1 to
0.5 cm3
2 cm3
8
Potassium
AqueousAmber glass
0.13 %
5 cm3
permanganate
solutionbottle, 50 cm3
Ammonium
2.0 M HNO3
HDPE bottle,
cerium(IV)aqueous28.6 %
5 cm3
30 cm3nitrate reagent
solution
Glass bottle,
Acetonitrile
Liquid45 cm350 cm348th IChO Practical Tasks, Official English version

Labeled

HNO3

Water
sampleF−, 9mg/dm3
Zirconyl
Alizarin
NaCl,
0.0500M
Fe3+ ind.
AgNO3
NH4SCN,X.XXXXM
K2CrO4C2H5OH

1 to 8KMnO4Ce(IV)
CH3CN

4

Code: XXX-01
Name
2,4-Dinitrophenylhydrazine
reagent

State
Sulfuric acidsolution inaqueousethanol

Conc.

Q-ty

Placed inLabeled3%

20 cm3

HDPE bottle,
30 cm3

DNPH

1 cm3

HDPE bottle,
30 cm3FeCl3

0.5 M HClaqueous2.5 %solution
Hydroxylamine
Ethanolic
0.5 Mhydrochloride
solution
SodiumAqueous6Mhydroxide
solution
Hydrochloric
Aqueous1Macidsolution*In the quantity left after doing Task 1.
Iron(III)
chloride

HDPE bottle,
30 cm3
HDPE bottle,
30 cm3
HDPE bottle,
30 cm310 cm35 cm325 cm3NH2OH
HCl
NaOH
HCl

Periodic table with relative atomic masses
1

18

1

H

2

1.008

2

13

14

15

16

17

3

4

5

6

7

8

9

9.01

10.81

12.01

14.01

16.00

19.00

20.18

11

12

13

14

15

16

17

18

22.99

24.30

3

4

5

6

7

8

9

10

11

12

26.98

28.09

30.97

32.06

35.45

39.95

19

20

21

22

23

24

25

26

27

28

29

30

31

32

33

34

35

36

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

72.63

74.92

78.97

79.90

37

38

41

42

43

44

45

46

47

48

50

51

52

53

85.47

87.62

91.22

92.91

95.95

-

101.1

102.9

106.4

107.9

112.4

114.8

118.7

121.8

127.6

126.9

131.3

55

56

72

73

74

75

76

77

78

79

80

81

82

83

84

85

86

132.9

137.3

178.5

180.9

183.8

186.2

190.2

192.2

195.1

197.0

200.6

204.4

87

88

104

105

106

107

108

109

110

111

112

113

-

-

-

-

-

-

-

-

-

-

-

57

58

59

60

61

62

63

64

65

138.9

140.1

140.9

144.2

-

150.4

152.0

157.3

89

90

91

92

93

94

95

96

-

232.0

231.0

-

-

-

-

-

K

Ca Sc Ti

Rb Sr

39

Y

88.91

40

Zr

Cs Ba 57-71 Hf
Fr-

Ra 89103-

V

Cr Mn Fe Co

Ni

W

Re Os

Ir

Pt

Si

P

O
S

Cu Zn Ga Ge As Se

Nb Mo Tc Ru Rh Pd Ag Cd
Ta

Al

N

Au Hg

49

In

Tl

Rf Db Sg Bh Hs Mt Ds Rg Cn Nh

Sn Sb Te
Pb

F

10

Be

Na Mg

C

4.003

Li

6.94

B

He

Cl

Br
I

Ne
Ar
Kr

83.80
54

Xe

207.2

Bi

209.0

Po

At Rn
-

-

114

115

116

117

118

-

Fl

Mc Lv
-

-

Ts Og
-

-

66

67

68

69

70

71

158.9

162.5

164.9

167.3

168.9

173.0

175.0

97

98

99

100

101

102

103

-

-

-

-

-

La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu

Ac Th PaU

238.0

Np Pu Am Cm Bk

48th IChO Practical Tasks, Official English version

Cf-

Es Fm Md No

Lr5

Code: XXX-01

Task 2
Determination of fluoride and chloride content in mineral water
Georgia is world famous for its splendid mineral waters. Many of these are used to curevarious diseases. Manufacturers have to carefully control the ionic composition of waters,
fluoride and chloride being among the most important ions.

Visual colorimetric detection of fluoride
The method of fluoride determination is based on the decrease in the color intensity ofzirconium(IV)-Alizarin Red S complex in the presence of fluoride ions due to formationof a more stable colorless complex. The equilibrium is achieved in about 20 minutes
after the reagent addition. The fluoride concentration is determined visually bycomparing the color developed in the sample with those in the calibration solutions.
Transfer 9.0 cm3 of mineral water from the sample into the plastic test tube labeled “X”.
Calculate how much of the 9.0 mg/dm3 standard fluoride solution you will need toprepare a set of calibration solutions with the following fluoride ion content: 0.0; 1.0;
2.0; 3.5; 5.0; 6.5; 8.0 mg/dm3 (calculate for 9.0 cm3 of each solution).
Using the 1.0 cm3 and 10.0 cm3 graduated pipettes, add thecalculated amounts of the standard fluoride solution to the testtubes, then add 1.0 cm3 of Zirconyl Alizarin indicator into each test
tube, and bring the volume in each calibration test tube to the 10.0
cm3 mark with distilled water (the mark is shown in the figure withthe arrow).

2.1.1.

Report the fluoride volumes used in your dilutions.

Mix the obtained solutions in the test tubes. Set the tube rack aside for at least 20
minutes.
2.1.2.

Compare the color of the sample and the calibration solutions looking on themfrom the top down and from the front. Select the concentration of the standard
that is closest to the fluoride concentration of the water sample.

Note: the rack with the test tubes will be photographed by the lab staff after the wholeexam is finished.

Standardization of silver nitrate solution by the Mohr method
Transfer 10.0 cm3 of the standard 0.0500 mol/dm3 NaCl solution into an Erlenmeyer
flask using the bulb (Mohr) pipette. Add approximately 20 cm3 of distilled water and
10 drops of 10% aqueous K2СгО4 solution.

48th IChO Practical Tasks, Official English version

6

Code: XXX-01
Fill a burette with the silver nitrate solution. Titrate the contents of the flask with thesilver nitrate solution while vigorously mixing the solution containing the precipitate
formed. The final titrant drops are added slowly with vigorous swirling of the flask. The
titration is complete when the faint color change visible on titrant addition does notdisappear in the pure yellow suspension. Take the final burette reading. Repeat thetitration as necessary.
2.2.1.

Report your volumes on the answer sheet.

2.2.2.

Write balanced chemical equations for the titration of NaCl with AgNO3 and forthe end-point indication reaction.

2.2.3.

Calculate the concentration of the AgNO3 solution from your measurement.

2.2.4.

The Mohr titration method requires a neutral medium. Write down equations
for the interfering reactions that take place at lower and at higher pH.

Chloride determination by the Volhard method
Wash the bulb (Mohr) pipette with distilled water. Wash the Erlenmeyer flasks first witha small portion of the ammonia solution left over from Task 1 to help removing thesilver salt precipitate and then with distilled water. (In case you used up all the ammonia
solution in the first task, you can get a refill without penalty.)
Transfer a 10.0 cm3 aliquot of the mineral water from the sample into an Erlenmeyer
flask using the bulb (Mohr) pipette. Add 5 cm3 of 2 mol/dm3 nitric acid using a
graduated cylinder. Add 20.00 cm3 of the silver nitrate solution from the burette and mix
well the suspension. Add appr. 2 cm3 of the indicator (Fe3+) solution with the Pasteur
pipette.
Fill the second burette with the standard ammonium thiocyanate solution (see the exact
concentration on the label). Titrate the suspension with this solution while vigorously
swirling. At the end point one drop produces a faint brown color that is stable even after
intense mixing. Take the final burette reading. Repeat the titration as necessary.
Note. The AgCl precipitate exchanges Cl− ions with SCN– ions from the solution. If you
titrate too slowly or with breaks, the brown color disappears with time, and too muchtitrant is spent for the titration. Therefore when approaching the endpoint you should
add the titrant at a constant slow rate swirling the flask constantly so that the suspension
would stay white. The appearance of faint brown color will mean reaching the endpoint.
2.3.1.

Report your volumes on the answer sheet.

2.3.2.

Write down balanced chemical equations for the back titration with NH4SCN
and that for the end-point indication reaction.

2.3.3.

Calculate the chloride concentration (in mg/dm3) in the water sample from yourmeasurements.

2.3.4.

If Br−, I−, and F− ions are present in the sample in addition to chloride, theconcentration of which ion(s) will contribute to the result of the Volhard
titration?

48th IChO Practical Tasks, Official English version

7

Code: XXX-01
2.3.5.

When trying to determine the concentration of Cl− in the presence of otherhalides, an analyst added some potassium iodate and sulfuric acid to the sample
and boiled the solution. Afterwards he reduced the excess of iodate to iodine byboiling the sample with phosphorous acid H3PO3. What interfering anions were
removed by this operation? Write the chemical equations for the reactions ofthese ions with iodate.

48th IChO Practical Tasks, Official English version

8

Code: XXX-01

Task 3
Identifying flavors and fragrances
Tourists coming to Georgia admire many specialties, local cuisine occupying one of the
top positions in the list of adventures. Excellent meat, fresh vegetables and greens, ripe
fruits, home-made jams… What else is needed to satisfy true gourmets? Of course,
unique flavors and fragrances!
You are given 8 samples of unknown organic compounds (labeled 1 to 8), which areindustrially used as flavors and fragrances. All samples are pure individual compounds.
Their possible structures are found among A-M given here.

The organic compounds in your unknown samples are readily soluble in ether, andinsoluble in dilute aqueous NaOH and HCl. These compounds, but the unknown No. 6.
are insoluble in water, the latter being slightly soluble (3.5 g/dm3).
3.1.

Perform test reactions described below to identify the samples 1-8. Indicate theresults of the tests by giving the Roman numeral of the appropriate observation(choose one or more from the list). Fill in all cells of the table. Use + and – toindicate positive and negative tests.

3.2.

Identify the unknowns based on the test results and the information given
above. Write the structure codes (of A to M) of the identified samples in theappropriate box.

Test procedures
KMnO4 test (Baeyer test)
Place appr. 1 cm3 of 95% ethanol in a plastic test tube and add 1 drop of an unknown.
Add 1 drop of KMnO4 solution and shake the mixture. Treat the test as positive if thepermanganate color disappears immediately after shaking.

48th IChO Practical Tasks, Official English version

9

Code: XXX-01
3.3.

Write the reaction scheme for a positive Baeyer test with one of the compounds
A-M.

Cerium(IV) nitrate test
Place 2 drops of the Ce(IV) reagent into a glass test tube, add 2 drops of acetonitrile andthen 2 drops of an unknown (the sequence is important!). Shake the mixture. In the caseof positive test the mixture color promptly changes from yellow to orange-red.
Note 1. Use only glass test tubes to perform the test. In case you need to wash the glass
test tubes, carefully choose the appropriate solvent. Use caps to prevent the strong odor.
Note 2. Comparison with blank (no unknown) and reference (with ethanol) tests is
recommended for adequate interpretation.
Note 3. Ce(IV) ions initially form brightly colored coordination compounds withalcohols. Complexes formed from primary or secondary alcohols react further (within
15 seconds to 1 hour) with the disappearance of the color.

2,4­dinitrophenylhydrazine (2,4-DNPH) test
Add only 1 drop of an unknown to 1 cm3 of 95% ethanol in a plastic test tube. Add 1 cm3of the DNPH reagent to the prepared solution. Shake the mixture and let it stand for
1-2 min. Observe formation of yellow to orange-red precipitate if the test is positive.
3.4.

Write the reaction scheme for a positive 2,4-DNPH test with one of thecompounds A-M.

Ferric hydroxamate test
Ask a lab assistant to light up your alcohol lamp. Mix 1 cm3 of 0.5 mol/dm3 ethanolichydroxylamine hydrochloride solution with 5 drops of 6 mol/dm3 sodium hydroxideaqueous solution in a glass test tube. Add 1 drop of an unknown and use the alcohol
lamp to heat the mixture to boiling while gently swirling the test tube to avoid splashesof the reaction mixture. Allow it to cool down slightly and add 2 cm3 of 1 mol/dm3 HCl
solution. Add 1 drop of 2.5% iron(III) chloride solution. Observe appearance of magenta
color if the test is positive. Close the alcohol lamp with the cap when finished.
Note 1. Use glass test tubes only to perform the test; use the test tube holder when
heating. In case you need to wash the glass test tubes, use an appropriate solvent.
Stopper the test tubes with a green cap after completing the test to prevent a strong
odor.
Note 2. Fe(III) ions form a colored 1:1 complex with hydroxamic acids (R-CO-NHOH).
3.5.

Write the reaction scheme for a positive ferric hydroxamate test with one of thecompounds A-M.

Note: After the STOP signal reattach the corresponding needles on the syringes with the
unknown compounds, and place them into the plastic cup and leave them on thetable.

48th IChO Practical Tasks, Official English version

10

Code: XXX-01

48th International
Chemistry Olympiad

Practical Part II.
Answer Sheets

26 July 2016
Tbilisi, Georgia

48th IChO Practical Tasks, Official English version

1

Code: XXX-01

Task 2

14% of the total

2.1.1 2.1.2 2.2.1 2.2.2 2.2.3 2.2.4 2.3.1 2.3.2 2.3.3 2.3.4 2.3.5 Sum
2
15
30
2
2
2
30
2
4
2
4
95

2.1.1.

Report the fluoride volumes used in your dilutions.
F− content (mg/dm3)
Calculated volume of
F− solution (cm3)2.1.2.

1.0

2.0

3.5

5.0

6.5

8.0

2p
Circle the concentration of the standard that is closest to the fluoride
concentration of the water sample.
15p, 5p for adjacent values.
F− content (mg/dm3)

2.2.1.

0.0

0.0

1.0

2.0

3.5

5.0

6.5

8.0

Report your titration volumes.
Titration no.

1

2

Initial burette reading, cm3
Final burette reading, cm3
Volume spent, cm3Your accepted volume, V1:
2.2.2.

cm3

30p on a sliding scale

Write a balanced chemical equation for the titration of NaCl with AgNO3 andthat for the end-point indication reaction.

Titration reaction:
Cl– + Ag+ ⟶ AgCl↓
CrO42–+ 2 Ag+ ⟶ Ag2CrO4↓
Indication reaction:
2p
2.2.3.

Calculate the concentration of the AgNO3 solution from your measurement.

Your work:c(Ag+) = c(Cl–)10.0 cm3 / V1c(Ag+):

2p

48th IChO Practical Tasks, Official English version

2

Code: XXX-01
2.2.4.

The Mohr titration method requires a neutral medium. Write equations for theinterfering reactions that take place at lower and at higher pH.

Low pH: 2 CrO42–+ 2 H+ ⟶ Cr2O72–+ H2O (dichromic or chromic acids also accepted),or Ag2CrO4 + H+  2Ag+ + HCrO4–
High pH: 2 Ag+ + 2 OH– ⟶ Ag2O + H2O
2p2p2.3.1.

Report your volumes on the answer sheet.
Titration no.

1

2

Initial burette reading, cm3
Final burette reading, cm3
Volume spent, cm3Your accepted volume, V2:
2.3.2.

cm3

30p on a sliding scale

Write a balanced chemical equation for the back titration with NH4SCN and thatfor the end-point indication reaction.

Titration reaction:
Ag+ + SCN– ⟶ AgSCN↓
SCN– + Fe3+ ⟶ Fe(SCN)2+ or analogous reaction
Indication reaction:
2p
2.3.3.

Calculate the chloride concentration (in mg/dm3) in the water sample from yourmeasurements.

Your work:c(Cl–) = [20.00 cm3 c(Ag+) − V2 c(SCN–)] M(Cl)/ 10.00 cm3
4p, 3p if in different unitc(Cl–):

mg/dm348th IChO Practical Tasks, Official English version

3

Code: XXX-01
2.3.4.

If Br−, I−, and F− ions are present in the sample in addition to chloride, theconcentration of which ion(s) will contribute to the result of the Volhard
titration? Tick the appropriate box(es).
 Br–

 I–

 F–

Br−, I−
2.3.5.

 none2p, 1p if 1 mistake committed

When trying to determine the concentration of Cl− in the presence of otherhalogens, an analyst added some potassium iodate and sulfuric acid to thesample and boiled the solution. Afterwards he reduced the excess of iodate toiodine by boiling the sample with phosphorous acid H3PO3. What interfering
anions were removed by this operation?
 Br–

 I–

 F–

 noneBr−, I−
2p
Write the reaction equations of these ions with iodate.
5I– + IO3– + 6H+  3I2 + 3H2O
10Br– + 2IO3– + 12H+  5Br2 + I2 + 6H2O (IBr also accepted)
2p

Replacements:
Item

Quantity

Lab assistant’s
signature

48th IChO Practical Tasks, Official English version

Student’s
signature4

Code: XXX-01

48th IChO Practical Tasks, Official English version

5

Code: XXX-01
Grading scheme for the titration results
Value (M.V.)A

B

Max grade

Masteryz

If A< Value < B, then Grade = Max grade
If Value < y, then Grade = 0, If Value > z, then Grade = 0
If y < Value < A, then Grade = Max grade  (Value – y)/(A – y)If B < Value < z, then Grade = Max grade  (z – Value)/(z – B)

Question M.V., mL

A, mL

В, mL

y, mL

z, mL

2.2.1.
2.3.1.

9.9
0.1

10.15
+0.3

9.8
0.3

10.4
+0.8

10.0
Theoretical values

48th IChO Practical Tasks, Official English version

Max
grade
30p
30p

6

Code: XXX-01

Task 3
3.1.
32

3.1.

13% of the total
3.2.
16

3.3.
4

3.4.
4

3.5.
4

Sum
60

Indicate the results and observations of tests by giving the Roman numerals of
the appropriate observations in the table. Fill in all cells of the table. Use + and –to indicate positive and negative tests. Choose one or more codes from the list
below.

I – Immediate disappearance of purple
color
II – Slow disappearance of purple color
III - Disappearance of yellow color
IV – Formation of a brown or black
precipitate
V - Formation of a white precipitate

VI - Formation of a yellow or orange-red
precipitate
VII - Appearance of orange or red color insolution
VIII - Appearance of magenta color
IX - The unknown compound is insoluble inethanol
X – no visible changes

Sample No.

1

2

3

4

5

6

7

8

Baeyer test result (+/–)

+

–

+

–

–

–

–

+

Baeyer test observations (I-X)

I,
IV

X

I,
IV

II,
IV

X

II,
IV

X

I,
IV

Ce(IV) nitrate test result (+/–)

+

+

–

–

–

–

–

–

Ce(IV) nitrate test observations (I-X)

VII

VII

III,
V

III

X

X
or
III

X

III

2,4-DNPH test result (+/–)

–

–

–

+

–

–

–

–

2,4-DNPH test observations (I-X)

X

X

X

VI

X

X

X

X

Fe(III) hydroxamate test result (+/–)

–

–

–

–

+

–

–

+

X

X
or
IX

VIII

Fe(III) hydroxamate test
observations (I-X)

X

X

X

48th IChO Practical Tasks, Official English version

X

VIII

7

Code: XXX-01
3.2.

Write the structure codes (of A to M) of the identified samples in theappropriate boxes when you are certain in your assignments.

Sample No.

1

2

3

4

5

6

7

8

Structure code

A

B

E

G

C

H

I

D

3.3.

Write the reaction scheme for a positive Baeyer test with one of the compounds
A-M.

KMnO4
OH

Or analogous
3.4.

OH
HO

- MnO2OH

4p

Write the reaction scheme for a positive 2,4-DNPH test with one of thecompounds A-M.

O
DNPH
N

H
N

NO2

NO2

4p
3.5.

Write the reaction scheme for a positive ferric hydroxamate test with one of thecompounds A-M.

NH2OH

O
O

Or analogous

O
N
H

OH

FeCl3

O
HN

FeCl2

O
magenta color

4p (any 1:1 hydroxamate – Fe(III) complex is acceptable)

48th IChO Practical Tasks, Official English version

8

Code: XXX-01
The problem can be approached in many ways. A systematic solution for one variant of
the unknown compounds encoding is given below (other variants are processedsimilarly).

Step 1. Solubility data analysis.
The data given allow excluding compounds K (presence of phenol-like moiety) and M(presence of azine nitrogen) soluble in aqueous NaOH and aqueous HCl, respectively.
Step 2. Tests for the functional groups.
2.1 Unsatured compounds excluding those aromatic give positive Baeyer test, and thosewith keto- or aldehyde group give positive 2,4­DNPH test
2.2 For avoiding mistakes in true-positive / false-positive interpretation the precise
description of true-positive tests is given in the test procedures.
2.3 The information given in the Notes after the test procedures CLEARLY indicates thefollowing prompts:
Note
Comparison with blank (no unknown) andreference (with ethanol) tests is
recommended for adequate interpretationof the test.
Brightly colored Ce(IV) coordination
compounds bearing Csp3-O→Ce(IV) moiety
have the formation constant in the range of
0.51 (MeOH, kinetically unstable) to 2.76
(t-BuOH, kinetically stable).
Brightly colored Fe(III)-hydroxamic acids
coordination compounds have theformation constants K1 ~ 42; K2 ~ 2.5; K3 ~1.2∙10−2 (for acetohydroxamate inethanol–water 1:1 mixture).

Prompt
The cerium(IV) nitrate test is one foralcohols
Red color appearing as a result of apositive cerium(IV) nitrate test candisappear due to further oxidation of
alcohols by Ce(IV) in the case of primaryand secondary alcohols
The ferric hydroxamate test is the one forthe compounds capable of forming thehydroxamic acids in the reaction with
NH2OH. ONLY ESTERS are appropriate
candidates for the positive test. Amides (J)do not afford hydroxamic acid under
NH2OH treatment, thus giving negative
test.

48th IChO Practical Tasks, Official English version

9

Code: XXX-01
The results of the experimental work can be summed up in the hereunder table.
# of sample

KMnO4

Ce(NH4)2(NO3)6

2,4­DNPH

1
2
3
4
5
6
7
8

+
–
+
–
–
–
–
+

+
+
–
–
–
–
–
–

–
–
–
+
–
–
–
–

FerricHydroxamate
Test
–
–
–
–
+
–
–
+

Analysis of the table allows unanimously identifying A, B, E, C, and G. L (Ferrichydroxamate and 2,4­DNPH), J (2,4-DNPH and Cerium(IV) nitrate test), and F (KMnO4 and2,4­DNPH tests) can be excluded from further consideration, since these provide for two
positive tests each.
#

Structure

1

OH
OH

2
3

KMnO4

Ce(NH4)2(NO3)6

2,4­DNPH

FerricHydroxamate
Test

+

+

–

–

–

+

–

–

+

–

–

–

–

–

+

–

–

–

–

+

–

–

–

–

–

–

–

–

+

–

–

+

O

4

5
6
7
8

O
O

?
?

O
O

Step 3. Choosing of right structures of the samples 6 and 7 based on additional data given.
Among all compounds in the list, only H and I cannot give any positive test, the attribution
requiring consideration of the solubility data. Sample 7 in the above table is soluble inether only (attributed as I), whereas Sample 6 is partially soluble in water (attributed as
H).

48th IChO Practical Tasks, Official English version

10

Code: XXX-01
The final assignment is given below.
SampleNo
Structure
code

1

2

3

4

5

6

7

8

A

B

E

G

C

H

I

D

1 points for each test (1p  4 tests  8 unknowns=32p)
2 points for each correct assignment (2p 8 unknowns=16p)

48th IChO Practical Tasks, Official English version

11

Code: XXX-01

Appendix A
Hazard codes, provided by Globally Harmonized System of Classification and Labeling ofChemicals (not to be printed for students)
Substance
C6H14
NaOH
HNO3
AgNO3
Al2(SO4)3Ba(NO3)2
Fe(NO3)3
KI
KIO3
MgCl2
Na2CO3
Na2SO3NH3NaF
ZrOCl2 + C14H7NaO7S
NaCl
NH4Fe(SO4)212H2O
NH4SCNK2CrO4
C8H16O
C9H20OC7H14O2
C12H20O2
C10H16
C10H14O
C10H18O
C10H18O
C10H18
C10H18O2
C6H6O3
C12H14O3
C6H6N2OKMnO4Ce(NH4)2(NO3)6

Name
HexaneSodium hydroxide
Nitric acid
Silver nitrate
Aluminium sulfate
Barium nitrate
Iron(III) nitrate
Potassium iodide
Potassium iodate
Manganese chloride
Sodium carbonate
Sodium sulfite
Ammonia
Sodium fluoride
Zirconyl Alizarin indicator
Sodium chloride
Ammonium iron(III)sulfate dodecahydrate
Ammonium thiocyanate
Potassium chromate
1-Octen-3-ol, Matsutake
alcohol
2,6-Dimethyl-2-heptanol,
Dimetol, Freesiol
Isoamyl Acetate
Geranyl acetate
Limonene(+)-Carvone(−)-Menthone
1,8-Cineole
Pinane8-Hydroxy-p-menthan-3one
MaltolRaspberry ketone acetate
2-Acetylpyrazine
Potassium permanganate
Ammonium cerium(IV)nitrate48th IChO Practical Tasks, Official English version

GHS Hazard Statement
225, 304, 315, 336, 361f, 373,
411
290, 314
272, 290, 314
272, 290, 314, 400, 410
290, 318
272, 302+332, 319
314
302, 315, 319
272, 315, 319, 335
221, 280, 314, 331, 400, 410
301, 315, 319
314
315, 319
302, 312, 332, 412
301, 315, 317, 319, 335, 400,
410

302, 315, 319
302, 318226
315, 319, 335
226, 315, 317, 410
315, 317226
226
315, 317
302, 315, 319, 335
315, 319, 335
400, 410
272, 290, 302, 314, 317, 400,410

12

Code: XXX-01
CH3CN
C6H6N4O4Acetonitrile
2,4-Dinitrophenylhydrazine
Iron(III) chloride
Hydroxylaminehydrochloride
Hydrochloric acid

FeCl3
NH2OH∙HCl
HCl

225, 302, 312, 319, 332
228, 302
290, 302, 315, 318
290, 302, 312, 315, 317, 319,
373, 400, 410
290, 315, 319, 335

Appendix B
Hazard Statement Descriptions
Statement
H221
H225
H272
H226
H228
H280
H290
H301
H302
H302+332
H304
H312
H314
H315
H317
H318
H319
H331
H332
H335
H336
H361f
H373
H400
H410
H411
H412

Description
Flammable gases
Highly flammable liquid and vapour
May intensify fire; oxidizer
Flammable liquid and vapour
Flammable solid
Gases under pressure
May be corrosive to metals
Acute toxicity, oral
Acute toxicity, oral
Harmful if swallowed or if inhaled
May be fatal if swallowed and enters airways
Acute toxicity, dermal
Causes severe skin burns and eye damage
Causes skin irritation
Skin sensitisation
Causes serious eye damage
Causes serious eye irritation.
Acute toxicity, inhalation
Acute toxicity, inhalation
May cause respiratory irritation
May cause drowsiness or dizziness
Suspected of damaging fertility
May cause damage to organs through prolonged or repeatedexposure
Acute aquatic toxicity
Chronic aquatic toxicity
Toxic to aquatic life with long lasting effects
Chronic aquatic toxicity

48th IChO Practical Tasks, Official English version

13