19th – 29th July 2018
Bratislava, SLOVAKIA
Prague, CZECH REPUBLIC
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PREPARATORY PROBLEMS: PRACTICAL

50th IChO 2018
International Chemistry Olympiad
SLOVAKIA & CZECH REPUBLICBACK TO WHERE IT ALL BEGANUPDATED 1st JUNE 2018

INTERNATIONAL CHEMISTRY OLYMPIAD / SLOVAKIA & CZECH REPUBLIC, 2018

Table of Contents
Contributing Authors................................................................................................................... 2
Fields of Advanced Difficulty ...................................................................................................... 2
Safety ......................................................................................................................................... 3
Problem P1. Determination of a metallic ore composition ........................................................... 4
Problem P2. Determination of a carbonate rock composition ..................................................... 8
Problem P3. Determination and identification of organic acids ................................................. 11
Problem P4. A chemical oscillator and its activation energies................................................... 15
Problem P5. Kinetics of a chemical wave front propagation ..................................................... 19
Problem P6. Separation of acidic, basic and neutral organic compounds ................................. 22
Problem P7. Meerwein–Ponndorf–Verley reduction ................................................................. 26
Problem P8. Transformation of a drug to a sweetener .............................................................. 29

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Contributing Authors
Ambroz Almássy

Comenius University in Bratislava

Iveta Kmentová

Comenius University in Bratislava

Elena Kulichová

Secondary Chemical School in Nováky

Pavel Májek

Slovak Technical University in Bratislava

Erik Szabó

Comenius University in Bratislava

Pavol Tarapčík

Slovak Technical University in Bratislava

Matej Žabka

Comenius University in Bratislava

Edited by
Petra Ménová

University of Chemistry and Technology, Prague

Martin Putala

Comenius University in Bratislava

Fields of Advanced Difficulty1.

Techniques in organic synthesis: thin layer chromatography, filtration and drying of
precipitates

2.

Extraction using immiscible solvents

Notes
During the practical exam, students WILL NOT be expected to: Determine melting points
 Use a rotary evaporator
 Use a spectrophotometer Handle and work up moisture sensitive compounds (using syringes and balloons) Perform column chromatography
Dedication of Problems P4 and P5 to the Belousov–Zhabotinsky (BZ) oscillating reaction isentirely commemorative. Students will not be expected to have received training specificallyaddressing this particular reaction or other chemical oscillators.

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SafetyParticipants in the Olympiad must be prepared to work in a chemical laboratory and be aware of
all relevant rules and safety procedures. The organizers will strictly enforce the safety rules given
in Appendix A of the IChO Regulations during the Olympiad.
The Preparatory Problems are designed to be carried out in properly equipped chemicallaboratories under competent supervision only. We did not include specific and detailed safetyand disposal instructions as regulations are different in each country. Mentors must carefully
adapt the problems accordingly.
The GHS hazard statements (H-phrases) associated with the materials used are indicated in the
problems. Their meanings are as follows.
Definition of GHS hazard statements
Physical hazards
H225 Highly flammable liquid and vapour.
H226 Flammable liquid and vapour.
H228 Flammable solid.
H271 May cause fire or explosion; strong oxidizer.
H272 May intensify fire; oxidizer.
H290 May be corrosive to metals.
Health hazards
H301 Toxic if swallowed.
H302 Harmful if swallowed.
H304 May be fatal if swallowed and enters airways.
H311 Toxic in contact with skin.
H312 Harmful in contact with skin.
H314 Causes severe skin burns and eye damage.
H315 Causes skin irritation.
H317 May cause an allergic skin reaction.
H318 Causes serious eye damage.
H319 Causes serious eye irritation.
H331 Toxic if inhaled.
H332 Harmful if inhaled.
H333 May be harmful if inhaled.
H334 May cause allergy or asthma symptoms or breathing difficulties if inhaled.
H335 May cause respiratory irritation.
H336 May cause drowsiness or dizziness.
H351 Suspected of causing cancer.
H361 Suspected of damaging fertility or the unborn child.
H371 May cause damage to organs.
H372 Causes damage to organs through prolonged or repeated exposure.
H373 May cause damage to organs through prolonged or repeated exposure.
Environmental hazards
H400 Very toxic to aquatic life.
H402 Harmful to aquatic life.
H410 Very toxic to aquatic life with long lasting effects.
H411 Toxic to aquatic life with long lasting effects.
H412 Harmful to aquatic life with long lasting effects.

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Problem P1. Determination of a metallic ore composition
Slovakia has a rich history in mining. Since
the Middle Ages, gold, silver and copper ores
have been mined in Kremnica, Banská
Bystrica and especially in Banská Štiavnica,
where the remnant of the extinct
stratovolcano is rich in mineral raw materials.
Mining in Slovakia has provided notable
technological advancements. In 1763, theAcademy of Mining and Forestry was
founded in Banská Štiavnica. It is one of theoldesttechnically-oriented
educational
institutions in all of Europe. One particularly
extraordinary division at the Academy was
the Department of Chemistry, which allowed
students to experiment in real laboratories.
Figure P1. Academy of Mining and Forestry inBanská Štiavnica.

In this task, you will determine theconcentration of copper and zinc ions ina solution obtained by the decompositionand proper modification of polymetallic ore.

Chemicals and Reagents
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Processed aqueous sample of the ore containing Zn2+ and Cu2+, 50 cm3
Strongly acidic cation exchange resin in hydrogen cycle, equivalent to Dowex 50, 15 cm3
0.1 M standard sodium hydroxide solution, 200 cm3
0.05 M standard Cu2+ solution, 50 cm3
2 M hydrochloric acid solution, 200 cm3
0.15 M standard EDTA disodium salt solution, 200 cm3
25% aqueous ammonia solution (w/w), 50 cm3
6% hydrogen peroxide solution (w/w), 1 cm3
0.25 M ammonium oxalate solution, 100 cm3
Buffer solution (35 cm3 of 25% ammonia (w/w) and 5.4 g of ammonium chloride diluted to 100 cm3)
Indicators: methyl red solution, universal pH indicator paper, murexide (solid indicator mixture),
Eriochrome black T (solid indicator mixture)

Substance

Name

State

GHS Hazard Statement

NaOH

Sodium hydroxide

Aqueous solution

H314

HCl

Hydrochloric acid

Aqueous solution

H314, H318

CuSO4 . 5H2O

Copper sulfate
pentahydrate

Aqueous solution

H302, H315, H410

NH3

Ammonia

Aqueous solution

H314, H400

C10H14N2O8Na2. 2H2O

Disodium ethylenediamine
tetraacetate dihydrate

Aqueous solution

H302, H315, H319, H335

(NH4)2C2O4

Ammonium oxalate

Aqueous solution

H302, H312

NH4Cl

Ammonium chloride

Solid

H302, H319

H2O2

Hydrogen peroxide

Aqueous solution

H271, H302, H314, H333, H402

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C20H12N3O7SNa

Eriochrome black T

Solid

H319

C8H8N6O6

Murexide

Solid

Not classified

C15H15N3O2

Methyl red

Solution

H225, H319, H371

Equipment and Glassware
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Laboratory stand with burette clamp
Volumetric flasks, 250 cm3 (1) and 100 cm3 (4)Titration flasks, 250 cm3 (3)Burette, 25 cm3
Pipettes, 5, 10, 25 and 50 cm3 with pipette filler
Spectrophotometer with cuvettes (2, l = 1 cm)
Ion exchange chromatography column (recommended diameter ca 1.5 cm)
Hotplate

Procedure
I. Determination of the metal ion concentration by alkalimetry and photometry
When a solution of copper and zinc ions is passed through a column packed with a cationexchange resin, the ions are trapped on the resin, releasing an equivalent amount of H+ ions into
the eluate. One of these ions forms a coloured species that enables its determination in the
mixture by spectrophotometry.
1. Fill the column with the strongly acidic cation exchange resin. A suitable height for the resin in
the column is 12–15 cm (recommended volume of the resin is 10–15 cm3).
2. Add 50 cm3 of 2 M hydrochloric acid solution to the column and let the solution pass throughthe column with a flow rate of 2 drops per second. Allow the level of the solution to fall justabove the level of the resin. Discard the eluate. Wash the column at the same flow rate with
deionised water until a neutral pH of the eluate is obtained. Check the pH of the dropping
eluate using the pH indicator paper. Allow the level of water to fall just above the level of theresin. The column is now ready for use in the H+ cycle.
3. Add 10.00 cm3 (V) of a sample stock solution to the column and let the level of the solution
drop just above the level of the resin. Then wash the column with deionised water at a flowrate of 2 drops per second and collect the eluate into a 250 cm3 (Vel) volumetric flask. After
filling half of the flask, check the pH of the dropping eluate. If the pH = 7, the ion exchange isfinished; if the pH < 7, continue washing the column. After a neutral pH has been reached, fill
the flask up to the mark with deionised water.
4. Alkalimetric titration: Pipette 50.00 cm3 (V1at) of the eluate stock solution into the titration flask
and add methyl red indicator. Titrate with the standard sodium hydroxide solution until the firstvisible colour change of the indicator (V2at). Repeat the titration as necessary.
5. Prepare two diluted standard Cu2+ solutions containing ammonia solution: pipette 5.00 cm3 ofthe standard Cu2+ solution into one 100 cm3 volumetric flask and 10.00 cm3 of standard Cu2+
solution into the second 100 cm3 volumetric flask. Add 10 cm3 of the ammonia solution into
each flask and then fill each flask to the mark with deionised water. Label the flasks with theconcentrations of the prepared solutions as cmin and cmax.
6. Pipette 25.00 cm3 (Vorig) of the sample stock solution into a 100 cm3 (Vdil) volumetric flask andadd deionised water to the mark. From this solution, pipette 5.00 cm3 (Vpip) into another100 cm3 (Vx) volumetric flask. Add 10 cm3 of the ammonia solution and add water to the mark.
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7. Measure the absorbance of the diluted standard solutions (Amin and Amax) and the sample
solution (Ax) at proper wavelength, following the instructions given by the spectrophotometer
manufacturer. Use deionized water as a blank solution.
Note: The Cu2+ cation forms a coordinate covalent complex with ammonia, [Cu(NH3)4]2+. This
complex species absorbs light strongly in the visible region 550–650 nm. The wavelength of
maximum absorption lies between 600–620 nm, nominally at 610 nm.
II. Ion exchange separation and complexometric titration
Copper and zinc ions can be trapped from the solution by the ion exchange resin as describedabove in Part I. When ammonium oxalate is passed through the resin, an oxalate copper complex
is released. The zinc ions remain fixed to the resin under these conditions. When a strong acidsolution is passed through the column, the zinc cations are released. Both cations can then be
determined separately by titration using EDTA.
1. Follow steps 1, 2, and 3 from Part I.
2. Releasing the Cu2+ ions: wash the column with 60 cm3 of ammonium oxalate solution (eluate
No. 1).
3. Releasing the Zn2+ ions: wash the column with 50 cm3 of hydrochloric acid solution (eluate No. 2).
4. Determination of copper by EDTA complexometric titration: add 6–7 drops of hydrogen
peroxide solution to eluate No. 1 and boil the solution for 10 minutes. After cooling, add
murexide indicator, neutralize with ammonia solution and titrate with standard EDTA fromyellow to purple. The indicator colour depends on the amount of murexide, copper ion
concentration and pH. The neutralization must proceed carefully to keep the solution yellow. If
the solution is greenish-yellow, dilute it and wait 1–2 minutes, until it turns yellow. If the solution
is not clear yellow (rusty or grey) before the endpoint has been reached, add a few drops ofammonia solution and titrate from yellow to purple. The colour change at the endpoint of thetitration is sharp if the titration is performed correctly.
5. Determination of zinc by EDTA complexometric titration: neutralize acidic eluate No. 2 withammonia solution. Titrate with standard EDTA solution using Eriochrome black T indicator fromwine red to blue. If the colour turns violet before the endpoint is reached, heat it to40–50 °C. If the colour turns to blue, the titration is finished (i.e. the endpoint has beenreached), if not, continue to titrate until a blue colour is observed.

Data Analysis and Questions
I. Determination of the metal ion concentration by alkalimetry and photometryP1.1 Write down the balanced chemical equations of the reactions which occur:a) In the cation exchange between the sample solution and the resin in the H+ cycle(indicated by the symbol {R-H}(s), where (s) denotes the solid phase of the resin),b) At the endpoint of the titration (use HInd and Ind− notation).
P1.2 Explain why the resin must be washed with deionised water before the ion exchange.
P1.3 Explain the role of ammonia in the spectrophotometric determination of copper.
P1.4 Explain why the selected standard concentrations of Cu2+ were used in the
spectrophotometric experiment.
P1.5 Calculate the concentrations of both cations in the sample (in mol dm−3).
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II. Ion exchange separation and complexometric titration
P1.6 Write down the balanced chemical equations describing the release of the Cu2+ and Zn2+
ions from the ion exchange resin.
P1.7 Explain the role of hydrogen peroxide in step II.4.
P1.8 Calculate the number of moles of both cations in 10.00 cm3 of the sample.

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Problem P2. Determination of a carbonate rock composition
Slovakia is a landlocked Central European
country with mountainous regions in thenorth and flat terrain in the south. The
mountains are part of the Carpathian archwith a varied geological structure: ancient
volcanic rock, granite in the alpine mountains
and sedimentary rocks, mainly composed ofcalcite (CaCO3), dolomite (CaMg(CO3)2) andan admixture of ankerite (CaFe(CO3)2).
These carbonate minerals have a common
formula of Ca(Fe,Mg)(CO3)2. Your sample
comes from such a dolomite rock withdolomite as the main component, but
containing also some calcite, ankerite andother inert components.
Figure P2. Krásnohorská Cave in the dolomite
region of Slovak Karst is currently listed by the
Guinness Book of Records as the cavecontaining the largest stalagmite in existence,
generally accepted as being about 12 m indiameter and 32.7 m in height. There are morethan 2 400 caves in Slovakia, of which to datemore than 400 have been explored and 18 canbe visited by tourists.

Chemicals and Reagents
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Powdered sample, ca 1 g (precise weight)
3 M hydrochloric acid solution, 10 cm32 M sodium hydroxide solution, 50 cm3
25% aqueous ammonia solution (w/w), 50 cm34 M ammonium chloride solution, 50 cm3
30% hydrogen peroxide solution (w/w), 5 cm3
5 mM standard EDTA disodium salt solution, 200 cm3
Indicators: methyl red solution, sulfosalicylic acid solution (5%, w/w), Eriochrome black T (solid
indicator mixture), murexide (solid indicator mixture), universal pH indicator paper

Substance
HCl
NaOH
NH3
NH4Cl
H2O2
C10H14N2O8Na2. 2H2OC20H12N3O7SNa
C8H8N6O6

Name
Hydrochloric acid
Sodium hydroxide
Ammonia
Ammonium chloride
Hydrogen peroxide
Disodium ethylenediamine
tetraacetate dihydrate
Eriochrome black T
Murexide

PREPARATORY PROBLEMS: PRACTICAL

State
Aqueous solution
Aqueous solution
Aqueous solution
Aqueous solution
Aqueous solution

GHS Hazard Statement
H314, H318
H314
H314, H400
H302, H319
H271, H302, H314, H333, H402

Aqueous solution

H302, H315, H319, H335

Solid
Solid

H319
Not classified
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C7H6O6S
C7H6O3
C15H15N3O2

Sulfosalicylic acid
Salicylic acid
Methyl red

Aqueous solution
Aqueous solution
Solution

H315, H319, H335
H302, H318
H225, H319, H371

Equipment and Glassware
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Laboratory stand with burette clamp
Volumetric flasks, 250 cm3 (2)Burette, 25 cm3
Pipettes, 50 cm3 and 2 cm3, with pipette filler
Graduated pipette, 1 cm3
Graduated cylinders, 25 cm3 and 5 cm3
Titration flasks, 250 cm3 (3)Beakers, 100 cm3 (2), 150 cm3 (1) and 250 cm3 (1)Watch glass
Plastic Pasteur pipettes
Filtration funnel
Filter paper
Hotplate

Procedure
1. Calculate the volume of 3 M HCl needed to decompose the rock sample. Assume the sample
is pure mineral dolomite and you need 10% excess of the acid.
2. Decompose the powdered rock sample (m0) in a 10% excess of HCl solution. Boil the solution
for two minutes. After cooling, transfer the solution quantitatively to a 250 cm3 volumetric flask
and add deionized water to the mark (V0).
3. Pipette 50.00 cm3 of the sample solution (V1), add 1 cm3 of the H2O2 solution and boil the
resulting solution for two minutes. If necessary, adjust the pH with aqueous ammonia solution
to ca 4 (indicator methyl red, red colour, pH = 4.4). Add a few drops (ca 0.5 cm3) of sulfosalicylic
acid indicator and titrate with the standard EDTA solution from purple to yellowish (V2). Repeat
the titration as necessary.
4. Pipette 50.00 cm3 of the sample solution (V3), add 1 cm3 of the H2O2 solution, adjust the pH to
the range of 6 to 7 and boil the resulting solution for two minutes. After cooling, filter the
precipitate, wash it with deionized water and collect the filtrate into a 250 cm3 volumetric flask(V4). Then add deionized water to the mark.
5. Pipette a 20.00 cm3 aliquot of the sample solution obtained in step 4 (V5) into the titration flask,
dilute with deionized water and adjust the pH to ca 9. Titrate with the standard EDTA solution
using Eriochrome black T indicator. The endpoint of the titration (V6) is indicated by a sharp
colour change from wine red to blue.
6. Pipette 20.00 cm3 of the sample solution obtained in step 4 (V7) into the titration flask, dilutewith water and adjust the pH to ca 12. Titrate with the standard EDTA solution using themurexide indicator until the colour changes from pink (red) to violet (V8).

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Data Analysis and Questions
P2.1 Report the calculated volume of HCl needed to decompose the rock sample.
P2.2 Estimate the pH of the solution prepared in step 2.
P2.3 Explain why it is necessary to boil the mixture in step 2.
P2.4 Explain why it is necessary to boil the mixture after the addition of the hydrogen peroxide
solution in step 3.
P2.5 Explain the role of the added hydrogen peroxide solution, the pH adjustment and boiling instep 4.
P2.6 Calculate the content (%, w/w) of dolomite, ankerite and calcite minerals and inert impurities
in the sample.

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Problem P3. Determination and identification of organic acids
Acid concentrations can be determined by iodometry by reaction with a mixture of iodate/iodide(IO3−/I−). The reaction yields a proportional amount of iodine that can be determined by titration
with thiosulfate. The rate of the reaction depends on the H+ concentration, and is decreased as
the reaction proceeds. Reliable results are obtained with strong acids when the reaction mixture
is left to stand for about 15 minutes. For weak acids, the completeness of the reaction can bereached in hours (or, possibly, more quickly at elevated temperatures) but risks inaccuracies dueto the volatility of the produced iodine. In special cases, the strength of an acid can be modified.
For example, weak oxalic acid can be converted by CaCl2 to an equivalent amount of the strong
acid, HCl, and calcium oxalate which precipitates out, thus driving this reaction in the forward
direction. Similarly, an increased acidity is observed for hydroxy substituted carboxylic acids dueto the formation of calcium complexes.

Chemicals and Reagents
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Sample solutions of unknown acids labelled A and B, 150 cm3. Each solution contains just one
acid from the following:o 0.1 M acetic acid solution
o 0.1 M hydrochloric acid solutiono Hydroxy carboxylic acid (R(OH)x(COOH)y) solution, i.e.:- 0.1 M lactic acid solution- 0.05 M tartaric acid solution or 0.05 M malic acid solution- 0.0333 M citric acid solution
0.05 M standard iodine solution in ca 0.1 M potassium iodide solution, 200 cm3
0.1 M standard sodium hydroxide solution, 25 cm3
0.1 M sodium thiosulfate solution, 500 cm3
1 M potassium iodide solution, 50 cm3
3% potassium iodate solution (w/w), 50 cm3
Calcium chloride, 20 g
Starch indicator solution

Substance

Name

State

GHS Hazard Statement

HCl

Hydrochloric acid

Aqueous solution

H314, H318

CH3COOH

Acetic acid

Aqueous solution

H226, H314

NaOH

Sodium hydroxide

Aqueous solution

H314

Na2S2O3

Sodium thiosulfate

Aqueous solution

H315, H319, H335

I2

IodineAqueous solution

H312, H332, H400

KI

Potassium iodide

Aqueous solution

H302, H315, H317, H319, H334, H335

KIO3

Potassium iodate

Aqueous solution

H272, H302, H315, H317, H319, H335

CaCl2

Calcium chloride

Solid

H312, H319

C6H8O7

Citric acid

Aqueous solution

H315, H319, H335

C3H6O3

Lactic acid

Aqueous solution

H315, H318

C4H6O5

Malic acid

Aqueous solution

H302, H315, H318, H319, H335

C4H6O6

Tartaric acid

Aqueous solution

H315, H318, H319, H335

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Equipment and Glassware
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Laboratory stand equipped with a burette clamp
Burette, 25 cm3
Volumetric pipettes, 20 and 25 cm 3, with pipette filler
Iodine flasks (Erlenmeyer flask with stopper), 250 cm 3 (2)Beakers, 100 cm3 (2) and 250 cm3 (1)Graduated cylinder, 25 cm3
Plastic transfer pipettes, 3 cm3 (2) and 5 cm3 (2)pH-Meter, accuracy ±0.01

Procedure
I. Determination of sodium thiosulfate concentration in solution
Pipette 20.00 cm3 of the standard iodine solution (V1) into an Erlenmeyer flask, add 25 cm3 of
distilled water and titrate with the thiosulfate solution until a colour change to a pale yellow colour
is observed. Add 3 cm3 of the starch indicator and titrate the obtained blue coloured solution until
the colour disappears (V2). Repeat the titration as necessary.
II. Identification of an unknown acid in sample solutions A and B and determination of its
concentration
For the analysis of the unknown acid samples, use the following procedures a–c. You can conduct
these titration experiments in any order. Repeat the titrations as necessary.
Procedure a: Pipette 20.00 cm3 (V11) of an unknown acid solution (sample A or B) into the iodine
flask, add 5 cm3 of the KI solution and 5 cm3 of the KIO3 solution using the plastic transfer pipettes.
Stopper the flask, let it stand in the dark for 15 minutes and then titrate the produced iodine using
the thiosulfate solution (V3, V4, respectively).
Procedure b: Pipette 20.00 cm3 (V12) of an unknown acid solution (sample A or B) into the iodine
flask, add 5 cm3 of the KI solution and 5 cm3 of the KIO3 solution. Add 4 g of CaCl2. Stopper theflask, let it stand in the dark for 15 minutes and then titrate the produced iodine using thethiosulfate solution (V5, V6, respectively).
Procedure c: Pipette 20.00 cm3 (V13) of an unknown acid solution (sample A or B) into the iodine
flask, add 5 cm3 of the KI solution and 5 cm3 of the KIO3 solution, then 25.00 cm3 (V23) of thethiosulfate solution. Stopper the flask and let it stand in the dark for 15 minutes. Add 20.00 cm3(V33) of the standard iodine solution and titrate the excess iodine in the flask using the thiosulfate
solution (V5, V7, respectively).
III. Identification of an unknown hydroxy carboxylic acid in the sample
There is a possibility that the sample contains an unknown hydroxy carboxylic acid that can be
determined using iodometry as described above. Differentiate the hydroxy carboxylic acids
according to their acid-base properties (Table P3).
Table P3. pKa values of selected hydroxy carboxylic acids.
Acid

pKa1

pKa2

pKa3

Lactic

3.86

-

-

Malic

3.46

5.10

-

Tartaric

3.04

4.37

-

Citric

3.13

4.76

6.40

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The acids can be identified by measuring the pH of the buffer prepared from the unknown acidand sodium hydroxide. The precise concentration of the hydroxy carboxylic acid is known fromPart II. Calculate the volume of the NaOH standard solution needed to prepare the buffer, forexample in the molar ratio 1 : 1. The pH of such solution can be determined using the available
software (e.g., http://www.iq.usp.br/gutz/Curtipot_.html).
Prepare such buffers from sample A or B identified as hydroxy carboxylic acid and measure thepH.

Data Analysis and Questions
I. Determination of sodium thiosulfate concentration in solution
P3.1 Provide a balanced chemical equation for the standardization of the thiosulfate solution.
P3.2 Derive the formulae for calculating the molar concentration of the sodium thiosulfate in thesolution.
P3.3 Calculate the molar concentration of the sodium thiosulfate in the solution.
II. Identification of an unknown acid in sample solutions A and B and determination of its
concentration
P3.4 Based on the results obtained in Part II, fill in the table and identify the acids in the samples.
Volume of sample solution A or B added to the titration flask
V11 =Procedure a

Volumes read from the burette (perform only the necessary analyses)
Sample A

V3a =

V3b =

Note/observation:
Sample B

V4a =

V4b =

Note/observation:
Accepted
volumes

V3 =

V4 =

Volume of sample solution A or B added to the titration flask

Procedure b

V12 =Volumes read from burette (perform only the necessary analyses)
Sample A

V5a =

V5b =

Note/observation:
Sample B

V6a =

V6b =

Note/observation:

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Accepted
volumes

V5 =

V6 =

Volume of sample solution A or B added to the titration flask
V13 =Procedure cVolumes read from burette (perform only the necessary analyses)
Sample A

V7a =

V7b =

V8a =

V8b =

Note/Observation:
Sample B

Note/Observation:
Accepted
volumes

V7 =

V8 =

Indicate with a  the identified component in sample A
HCl

CH3COOH(R(OH)x(COOH)y)

Indicate with a  the identified component in sample B
HCl

CH3COOH(R(OH)x(COOH)y)P3.5

Provide reasons for your conclusions about the acids identified in the samples.

P3.6

Write down the balanced chemical equations of the reactions necessary to calculate theresult.

P3.7

Derive the formulae for calculating the concentration of the strong acid when Procedure a
was used.

P3.8

Derive the formulae for calculating the concentration of the hydroxy acid when
Procedure b was used.

P3.9

Explain the role of the excess thiosulfate in Procedure c.

P3.10 In an acid solution, thiosulfate undergoes an undesired side reaction. Write down thebalanced chemical equation of this unwanted side reaction. Explain why it is possible to
add an excess of thiosulfate to the acid sample in Procedure c.
P3.11 Derive the formulae for calculating the concentration of the weak acid when Procedure c
was used.
P3.12 Calculate the molar concentration of the acid in each sample.
III. Identification of an unknown hydroxy carboxylic acid in the sample
P3.13 Identify the unknown hydroxy carboxylic acid (if present) by comparing the measured andtheoretical pH values of the buffer solution.

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Problem P4. A chemical oscillator and its activation energies
In 2018, we celebrate the 50th anniversary of the International Chemistry Olympiad, which was
first organized in 1968 in Czechoslovakia. By coincidence, it is also the 50th anniversary of animportant breakthrough that began a new era in chemical kinetics.
In July 1968, Prague hosted an international conference called "Biological and Biochemical
Oscillators", one of a few rare occasions that brought together Western scientists with thescientists from the Eastern Bloc. At this conference, a young Russian chemist Anatol Zhabotinsky
introduced to the crowd a new, remarkable system, an oscillator based on nothing else but
chemical reactions.
The oscillations were originally discovered in the early 1950s by Boris Belousov, who was looking
for an inorganic analogue of the Krebs cycle. Unfortunately, at that time, his colleagues did not
accept that a homogeneous chemical oscillator could exist. For many years, Belousov’s recipe
survived only as a bizarre chemical curiosity, passed on among a few Chemistry departments in
Moscow.
It was the 1968 conference in Prague that marked the real turning point. Zhabotinsky’s careful
verifications and extensions of Belousov’s work finally attracted the attention they deserved, andresearch groups studying oscillatory kinetics formed all throughout the Eastern Bloc, including
Czechoslovakia, as well as in the West. The field of nonlinear chemical kinetics was born.
This famous oscillator became known as the Belousov-Zhabotinsky or, for short, the BZ reaction.
In this task, your own observations of the oscillations will enable you to elucidate their coremechanism. Furthermore, you will explore a remarkable island of simplicity in the rather complex
phenomenon. You will verify that the periods of the BZ oscillations still obey the Arrhenius law.

Chemicals and Reagents







1.50 M sulfuric acid solution, 150 cm 3
Malonic acid, 5.203 g
Cerium(III) sulfate tetrahydrate, 0.801 g
7.5 mM ferroin sulfate solution, 20 cm3
Sodium bromate(V), 7.545 g
0.05 M potassium bromide solution, 50 cm 3
Substance

a

b
c

Name

State

GHS Hazard Statements

H2SO4

Sulfuric acid

Aqueous solution

H290, H314

C3H4O4

Malonic acid

SolidaH319

Ce2(SO4)3 . 4 H2O

Cerium(III) sulfate
tetrahydrateb

SolidaH315, H319, H335

[Fe(C12H8N2)3]SO4

Ferroin sulfatec

Aqueous solution

Not hazardous

NaBrO3

Sodium bromate(V)SolidaH272, H315, H319, H335

KBr

Potassium bromide

Aqueous solution

Not hazardous

It is recommended to start from solids if reproducible results are to be obtained. Stock solutions ofthese substances age quickly and results will drift as the solutions are stored, especially in the caseof Ce2(SO4)3.
Other hydrates of Ce2(SO4)3 may be used. Anhydrous Ce2(SO4)3 can be very difficult to dissolve.
The stock solution may also be prepared from FeSO 4 and o-phenanthroline, but the results mayvary. Commercial ferroin sulfate indicator solution is preferred as starting material.

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Equipment and Glassware












Digital stop-watch capable of split timing
Laboratory stand with clamps
Jacketed beaker, 50 cm 3
Circulating thermostat bath
Thermometer
Magnetic stirrer and a PTFE-coated stir bar
Graduated pipettes, 10 cm 3, 5 cm3 and 1 cm3
Volumetric flask, 50 cm 3
Bottles for stock solutions, 50 cm 3 (3)Wash-bottle with deionized water
Ultrasonic bath (if needed)

Procedure
I. Preparation of stock solutions
Note: This part may be omitted if reagents are supplied as solutions. It must be noted, however,that results will depend on storage time and conditions.
Mix solid cerium(III) sulfate with some water and transfer the suspension quantitatively intoa volumetric flask charged with 1.5 cm3 of 1.50 M sulfuric acid solution. Add enough water todissolve and, if needed, treat with ultrasound. Then, add water to the mark, transfer the solution
into the stock bottle and wash the flask well. Repeat the procedure with bromate(V) and malonicacid, except adding any sulfuric acid.
II. Setting up and getting familiar with the BZ oscillator
1. Select pipettes of appropriate volumes, one for each stock solution plus one for water.
2. To assemble the apparatus, connect the jacketed beaker to the circulating thermostat and fix
it on the magnetic stirrer with a clamp. Turn on the thermostat and set the temperature to25.0 °C.
3. Charge the jacketed beaker with 10.0 cm3 water, 10.0 cm3 sulfuric acid solution, 3.0 cm3malonic acid solution, 3.0 cm3 cerium(III) solution, and 1.0 cm3 ferroin solution.
4. If the stirring intensity is not set for you, you will need to find it. It should be as high as possible,
but the vortex must not be so deep that bubbles of air get stirred into the solution. Once you
set the right stirring intensity, maintain this setting during all your work.
Note: The results can vary significantly with stirring intensity, just as they depend on the overall
geometry of the reactor vessel, of the stir bar etc. If the results are to be compared against
benchmark values, all these parameters must be preset and fixed carefully.
5. Start the reaction by adding 3.0 cm3 of the bromate(V) solution. Initially, the solution will
maintain one colour and then it will start changing gradually. At some point, there will bea sudden colour change that will restore the first colour. This colour cycle will be repeated.
Note down the colour changes.
III. Determining the building blocks of the BZ chemistry
1. Prepare a BZ oscillator mixture with the same concentrations of sulfuric acid, malonic acid andbromate(V) as in Part II, but omit the metal catalysts – cerium(III) and ferroin. Instead, add
3.0 cm3 of the bromide stock solution and increase the volume of water accordingly to keep
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the total volume at 30 cm3. Note the colour changes after you start the reaction by adding thebromate(V) solution.
2. Prepare a BZ oscillator mixture with the same concentrations of sulfuric acid, cerium(III), ferroin
and bromate(V) as in Part II, but omit the malonic acid. Instead, add the same volume of thebromide stock solution. As indicated by a thermometer, wait until the solution temperature hasstabilized, and record the reading. Finally, once you begin adding 3.0 cm3 of the bromate(V)solution, immediately start the stop-watch. Note how the colour of the reaction mixture
develops, and record the time when the colour changes abruptly.
IV. Timing the oscillations for various amounts of cerium(III)
1. Prepare a BZ oscillator mixture with the same concentrations of sulfuric acid, malonic acid,ferroin and bromate(V) as in Part II, but only half of the volume of cerium(III) solution. Do not
add any bromide solution, but increase the volume of water accordingly to keep the total
volume of the mixture at 30 cm3. Wait until the solution temperature has stabilized and record
the reading.
2. Finally, once you begin adding 3.0 cm3 of the bromate(V) solution, immediately start thestop-watch. Every time a sudden colour transition occurs, hence indicating a new colour cycle
has begun, press the SPLIT button to read the exact time while continuing to time. In this way,
record the times of the first four sudden colour transitions.
3. Repeat the same timing procedure with the original volume of cerium(III) solution, 3.0 cm 3.
V. Temperature dependence
Repeat the same timing procedure with the same BZ oscillator that you observed in Part IV.3 atapproximately 25 °C, with 3.0 cm3 of the cerium(III) solution, but increase the temperature setting
on the thermostat to 27.0 °C, 29.0 °C, 31.0 °C and 33.0 °C. For each temperature, record thetimes of the first four sudden colour changes.

Data Analysis and Questions
P4.1 Write a balanced ionic equation for the chemical reaction responsible for the colour
observed when bromate(V) and bromide are mixed in an acidic solution. Write a balanced
equation for the chemical reaction responsible for the disappearance of this colour in thepresence of malonic acid. Sum the two equations appropriately to provide the overall
reaction that has taken place in the mixture when the colour has disappeared.
P4.2 Consider your observation in the reaction in which malonic acid (MA) was replaced with Br−.
Provided that the recorded reaction time is proportional to [Br−], calculate the rate at which[Br−] is consumed. Using the average period of oscillation recorded in the BZ oscillator at
25 °C, calculate the concentration [Br−] consumed in each cycle of the BZ oscillator. How
much [MA] does this consume? Where does the Br− for each cycle come from?
P4.3 The most concise version of the BZ oscillations mechanism consist of steps that are all in
the form of redox reactions with a simple 1:1:n stoichiometry:oxidizing-agent species + reducing-agent species + n H+ = products (n can be 0, 1, 2, …)
Usually, only a single organic step (bromomalonic acid cleavage with Ce4+) is included, andthe stoichiometry of its products is traditionally formulated as adjustable. In the inorganic
subset, however, all steps are perfectly balanced, and stoichiometric coefficients are always

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integers, even for all the products. Only the following bromine-containing species are
considered: Br−, Br2, HBrO, HBrO2, BrO2, BrO3−.
How many balanced equations that satisfy these criteria can you write for the step of Ce3+oxidation to Ce4+? Which of your experimental observations can you combine with theseequations to conclude that Ce3+ is oxidized by BrO2? Write down the step producing BrO2.
Which species can be eliminated in the combined equation for Ce3+ oxidation and BrO2
production to show that this pair of reactions forms an autocatalytic cycle? Write down thestep responsible for the inhibition of this autocatalytic cycle with Br−.
P4.4 Compare the BZ oscillations at the two different concentrations of cerium(III) catalyst. How
is increased catalyst concentration reflected in the lengths of the induction periods, i.e. inthe times taken until the first sudden colour changes, and how is it reflected in the average
lengths of the first three periods of oscillation? What role does this suggest for cerium(III) in
the oscillations?
P4.5 Assuming that the induction periods and the average periods of oscillation directly reflect
the rates of the rate-determining steps in the system, use your experimental data measured
at various temperatures to plot their natural logarithms against 1/T, and find thecorresponding activation energies. Compare the results to the reference data, around
60 kJ mol−1 for cerium-catalyzed oscillations and around 75 kJ mol−1 for ferroin-catalyzed
oscillations.

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Problem P5. Kinetics of a chemical wave front propagation
We usually tend to think of synthesis as of making substances. In this task, however, you will use
chemical reagents to synthesize patterns.
When a BZ oscillating reaction solution is poured onto a Petri dish, the interaction between an
autocatalytic reaction and diffusion has the ability to transform the solution, initially homogeneous,
into a beautifully self-ordered sea of chemical waves. This phenomenon is not only pretty, but the
movement of the structures can also be used to study the kinetics of the underlying reactions.
If we have an autocatalytic reaction producing autocatalytic species X, the simplest form of
autocatalysis is described by a simple reaction rate equation:d[X]= k' [X]dt(1)

An interesting thing happens when we have a medium capable of undergoing such an
autocatalytic reaction, but X is initially present only in a selected region. As expected from an
autocatalytic reaction, wherever X is available, a burst of production of even more X occurs. In
addition, if diffusion can take place, the diffused X can trigger the autocatalytic production of X in
the adjacent regions, too. This spreads like fire and we observe a chemical trigger wave. If D isthe diffusion coefficient of X, the velocity v of the trigger wave is:v = 2√k' D(2)In the BZ oscillator, the examination of how the rate of the autocatalytic step depends on acidity
and on the concentration of bromate(V) yielded the following result:k' = 20 M-2 s-1 [H+ ][BrO–3 ](3)

Your task is to validate this relationship experimentally, by measuring the velocity of the wave
fronts at various concentrations.

Chemicals and Reagents






1.50 M sulfuric acid solution, 150 cm 3
Malonic acid, 5.203 g
Cerium(III) sulfate tetrahydrate, 0.801 g
25 mM ferroin sulfate solution, 25 cm 3
Sodium bromate(V), 7.545 g

Note: The chemicals and reagents are the same as in Problem P4, except that the ferroin sulfate solution
is now more concentrated, 25 mM. All safety information and all notes regarding handling and storage apply
as in Problem P4.

Equipment and Glassware







Digital stop-watch
Petri dish, 14 cm diameter, with lid
Millimeter graph paper
Beaker, 100 cm3
Graduated pipettes, 10 cm 3 and 5 cm3
Wash-bottle with deionized water

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Procedure
I. Preparation of stock solutions and equipment
1. The procedure for the preparation of the stock solutions is the same as in Problem P4.
2. Select pipettes of appropriate volumes, one for each stock solution plus one for water. Placethe Petri dish on a sheet of millimeter graph paper.
Note: The benchtop for this experiment must be perfectly level. Leaning against the table whilea measurement is in progress must be avoided. Since the temperature of the Petri dish is notcontrolled, the experiment must not be performed near a source of heat or a draught.
II. General procedure for finding the chemical wave front velocity
1. Prepare a BZ oscillator by charging the beaker with water and solutions of sulfuric acid, malonicacid, cerium(III) sulfate, and ferroin sulfate, using the volumes specified in Part III. Finally, start
the reaction by adding the solution of bromate(V) and swirling the beaker with your hand.
2. Pour the oscillator solution from the beaker onto the Petri dish. Swirl the dish a few times to
distribute the solution evenly over its entire surface, and cover the dish with its lid. Initially, thesolution will change colour uniformly, but eventually, spots of a different colour will appear. The
spots will grow into rings, and when a ring becomes large enough, a new spot will appear in
its center. This leads to the formation of target patterns (Fig. P5).

Figure P5. The patterns to be formed in a Petri dish.

3. To find the wave front velocity, measure the time that it takes for a front, preferably inside
a target pattern, to advance by 5 mm. This will not be possible immediately, as the outmost
rings in each target pattern will be regularly annihilated. At some point, however, the patterns
will become large enough to allow the fronts to be followed across a 5 mm long path, at leastin one direction.
Note: Tracking the fronts along the left–right axis is preferred. To read the position of a front
that is moving towards or away from the observer, it may be neccessary to close one eye, or
watch the pattern from another angle. Be careful not to perturb the dish!
4. To find the mean wave front velocity in the dish, repeat the reading of the time required tocover a 5 mm distance for three different fronts, preferably in three different places on the Petri
dish.
III. Dependence of the chemical wave front velocity on concentrations
Using the procedure described above, find the average wave front velocities at four different
concentration sets (Table P5). All contain 3.0 cm3 malonic acid solution, 3.0 cm3 cerium(III) sulfate
solution and 2.0 cm3 ferroin sulfate solution. The first two sets will differ in the volumes of sulfuric
acid and the other two sets will differ in the volumes of bromate(V) solution. To make sure that
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your data is correct, replicate each concentration set twice. If the data disagree, add more
replicates for verification.
Table P5. Concentration sets for finding the dependence of the chemical wave front velocity.
Set

Water

Sulfuric acid solution

Bromate(V) solution#1

9.0 cm3

10.0 cm3

3.0 cm3#2

12.0 cm3

7.0 cm3

3.0 cm3#3

8.1 cm3

10.0 cm3

3.9 cm3#4

9.9 cm3

10.0 cm3

2.1 cm3

Data Analysis and Questions
P5.1 Assume that the total volumes of the reaction mixtures always add up to 30 cm 3. Calculate
the concentrations of sulfuric acid and bromate(V) in the four concentration sets
examined. Using all time readings taken in accepted replicates, calculate one mean wave
front velocity, expressed in mm min −1, for each concentration set.
M(NaBrO3) = 150.89 g mol–1
P5.2 Assume that instead of equation (3), the dependence of v2 on [BrO3−] is described asv2 = p [BrO3−] + q. What would it suggest about the kinetics of the autocatalysis, if q > 0,
and what would it suggest if q < 0? Use the results from Sets #3 and #4 to evaluate p andq. Calculate the percentage of the overall reaction rate that is contributed by q. Is thissignificant?
P5.3 Assume that the wave front propagation velocity v is a power function of both, [H2SO4] and[BrO3−], i.e. v = k [H2SO4]a [BrO3−]b. Use the results from Sets #1 and #2 to calculate theexponent a, and the results from Sets #3 and #4 to calculate the exponent b. Whatassumption would allow us to deduce the reaction order with respect to [H+] from a?
Compare the results to the values that are expected based on equation (3). Are a and b
roughly as expected or does any value suggest that, for the conditions studied, the rateequation (3) should be revised?
P5.4 Assume that equation (3) applies, and that [H+] ≈ [H2SO4]. Using the reference value of the
autocatalytic species diffusion coefficient D = 2.0  10−5 cm2 s−1, calculate what values aresuggested for the autocatalytic reaction rate constant from your experimental data. Does
any of the concentration sets come close to the reference value 20 M−2 s−1?

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Problem P6. Separation of acidic, basic and neutral organic
compounds
This task is designed to help you understand the chemical basis of separation of up toa four-component mixture using extraction techniques and visualizing the separation by checking
the composition of the organic layer after each extraction. Extraction in an organic chemistrylaboratory is most often used to isolate organic compounds from reaction mixtures after anaqueous work-up. Extraction is a particularly useful method for separating organic compounds if
one compound in the mixture can be chemically converted to an ionic form. The ionic form is often
more soluble in an aqueous layer and can be extracted into it. Non-ionic organic compounds inthe mixture will remain dissolved in the organic layer. The separation of the two layers results inthe separation of the compounds. The pKa values of the acids provide a measure of the acidity ofeach compound. The extent to which an acidbase reaction proceeds to completion depends on
the relative acidity of the reactants and products.

Chemicals and Reagents









Unknown solid sample containing 3–4 of these compounds: benzoic acid, 4-nitroaniline,
2-naphthol, naphthalene; 750 mg
Chloroform, 20 cm3
20% hydrochloric acid aqueous solution (w/w), 42 cm3
10% sodium bicarbonate aqueous solution (w/w), 24 cm3
10% sodium hydroxide aqueous solution (w/w), 24 cm3
20% potassium hydroxide aqueous solution (w/w), 30 cm3
Anhydrous sodium sulfate, 2 tea spoons
Hexanes/ethyl acetate 3:1 mixture (TLC eluent), 5 cm 3

Substance

Name

State

GHS Hazard Statements

C7H6O2

Benzoic acidSolid

H315, H318, H372

C6H6N2O2

4-Nitroaniline

Solid

H301, H311, H331, H373, H412

C10H8O

2-NaphtholSolidH302, H332, H400

C10H8

NaphthaleneSolid

H228, H302, H351, H410

CHCl3

Chloroform

LiquidH302, H315, H319, H331,
H336, H351, H361d, H372

HCl

Hydrochloric acid

Aqueous solution

H290, H314, H335

NaHCO3

Sodium bicarbonate

Aqueous solution

H319

NaOH

Sodium hydroxide

Aqueous solution

H290, H314

KOH

Potassium hydroxide

Aqueous solution

H290, H302, H314, H315, H319

C4H8O2Ethyl acetate

LiquidH225, H319, H336

C6H14Hexanes (mixture of isomers)

LiquidH225, H304, H315, H336, H411

Na2SO4

Sodium sulfate

Solid

Not hazardous

Equipment and GlasswareLaboratory stand with clamps and metal ring
Magnetic hotplate stirrer and a PTFE-coated stir bar
Rotary evaporator
Water aspirator (or other vacuum source for suction filtration and vacuum rotary evaporator)

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
















Measuring cylinders, 10 cm3 and 20 cm3
Erlenmeyer flasks, 50 cm3 (2)Glass rod
TLC chamber or a Petri dish covered small beaker
TLC plates, silica gel 60 F254 (4), and capillaries
UV lamp (254 nm)
Beakers, 50 cm3 (1) and 100 cm3 (3)Separatory funnel, 100 cm3
pH indicator paper
Büchner filter funnel
Filter paper
Suction flask, 100 cm3, with rubber adapter for filter funnel
Round bottom flask, 50 cm3
SpatulaTweezers
Marker for glass

Procedure
Warning: Chloroform and naphthalene should be handled only in a well-ventilated fumehood.
I. Sample preparation
The sample weighing 750 mg contains three to four of these compounds: benzoic acid,
4-nitroaniline, naphthalene-2-ol and naphthalene. Dissolve this sample in 20 cm3 of chloroform in
a 50 cm3 Erlenmeyer flask.
II. TLC analysis
Check the composition of the solution before extractions (Plate 1). Spot the chloroform solution
on the TLC plate using a glass capillary spotter (mark the start line at a height of 1 cm, FigureP6). Take a 50 cm3 beaker, load it with 2 cm3 of the TLC eluent using a measuring cylinder. Insert
the TLC plate upright into the TLC developing chamber. Ensure that the eluent level is below thestart line. Cover the beaker with one of the Petri dishes. Wait until the solvent system reaches thepre-drawn eluent front line. Remove the TLC plate using tweezers and let the eluent dry in air.
Place the TLC plate under a UV lamp. Mark the spots of the compounds with a pencil andcalculate the Rf values.

Figure P6. Developing a TLC plate (left), evaluation of Rf value (right).

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III. Separation of the basic compound A
1. Place a separatory funnel with a closed stopcock into a metal ring and place a 50 cm3
Erlenmeyer flask under it. Using a glass filter funnel, pour the chloroform solution into theseparatory funnel. Measure 6 cm3 of 20% solution of HCl using a measuring cylinder. Add it
into the separatory funnel using a conic filter funnel. Hold the funnel around the top, lift it outof the supporting ring and swirl it gently (chloroform vapours may cause pressure build-up in
the funnel). Return the separatory funnel to the ring and insert the stopper.
2. To perform the extraction, use both hands; hold the body of the funnel around stopcock with
one and the stopper with the other. Take out the funnel from the support ring and invert it andvent it by opening the stopcock. Repeat the swirling-venting process until the pressurebuild-up diminishes. Then shake the funnel for 5 × 10 s. Make sure that the stopcock is closed
and return the separatory funnel to the metal ring over the 50 cm3 Erlenmeyer flask and remove
the stopper.
3. Allow the layers to separate and collect the organic layer by opening the stopcock andcollecting the bottom layer into the 50 cm3 Erlenmeyer flask. Close the stopcock and pour theaqueous layer through the top neck and into the 100 cm3 beaker, using a glass filter funnel.
Keep both phases.
4. Pour the organic phase back into separatory funnel and repeat the extraction with another6 cm3 of the 20% solution of HCl. Combine the aqueous layers after both extractions, label the
beaker as A and keep aside for subsequent isolation.
5. Check the composition of the organic solution after the extraction with the diluted HCl solution
using TLC analysis (Plate 2).
IV. Separation of the acidic compounds B and C
1. Extract the organic layer twice with 12 cm3 of 10% solution of NaHCO3 and combine theaqueous layers after both extractions in a 100 cm3 beaker. Label the beaker as B and keep
aside for subsequent isolation.
2. Check the composition of your organic layer (Plate 3).
3. Then extract the organic layer twice with 12 cm3 of 10% solution of NaOH and combine theaqueous layers after both extractions in a 100 cm3 beaker. Label the beaker as C and keep
aside for subsequent isolation.
4. Collect the organic phase into a 50 cm3 Erlenmeyer flask. Check the composition of the organic
layer (Plate 4).
V. Isolation of organic compounds A, B and C from the aqueous layers
1. Basify the acidic aqueous layer in the beaker labelled A with a 20% solution of KOH (adjust
the pH to 11, ca 12 cm3). Yellow precipitate A is formed.
2. Acidify the basic aqueous extracts in beakers labelled B and C with a 20% solution of HCl(to pH 1, ca 12 cm3). Watch out for the CO2 evolution during the neutralization of thebicarbonate extract. White precipitate B and pink precipitate C are formed, respectively.
3. Isolate each of the precipitated compounds (A, B, C) by suction filtration using a Büchner
funnel and filter paper. Dry all the products in air and then record the yields.
VI. Isolation of neutral organic compound D from organic layer
Dry the organic layer over anhydrous Na2SO4 for 10 min. Filter off the used drying agent throughfilter paper and collect the filtrate in a pre-weighed round bottom flask. Compound D can berecovered from the filtrate by evaporating the solvent on a rotary evaporator. Record the yield.
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Data Analysis and Questions
P6.1 Fill in the structures of all the missing compounds and the colour of the precipitates into theflow chart:

P6.2

Compare all four TLC plates from the task and explain your observation.

P6.3 Write the equations of the acidbase reactions for the separations and isolations.
P6.4 Explain why it is important to perform the second extraction (the first extraction using thebasic aqueous solution) with NaHCO3 and not with the NaOH solution.
P6.5 Fill in the following table and identify compounds A–D.
Compound

Rf

m (g)

Compound name

A
B
C
D

P6.6 Determine the ratio of the compounds in your sample and discuss the quantitative differenceof the initial sample mass and the sum of the masses of the pure isolated compounds.
Explain the difference.

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Problem P7. Meerwein–Ponndorf–Verley reduction
The Meerwein–Pondorf–Verley reduction is an aluminium(III)-catalyzed hydride transfer from the
α-carbon of isopropyl alcohol to the carbonyl carbon of an aldehyde or ketone. The product of thisreaction is the corresponding primary or secondary alcohol, respectively, while an equimolar
amount of isopropyl alcohol (which is used as a solvent and is present in large excess) is oxidized
to acetone. The advantages of this reduction lie in the high degree of chemoselectivity and use ofa cheap, environmentally friendly metal catalyst.
In this task, you will perform the Meerwein–Pondorf–Verley reduction on (2-naphthyl)ethanone(2-acetonaphthone).

Chemicals and Reagents
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2-Acetonaphthone, 200 mg
Aluminum isopropoxide, 300 mg
Isopropyl alcohol, 4 cm 3
Ethyl acetate, 20 cm 3
Hexanes, 15 cm3
Saturated ammonium chloride aqueous solution, 8 cm 3
Anhydrous sodium sulfate
Inert gas (nitrogen or argon)

Substance

Name

State

GHS Hazard Statements

C12H10O

2-Acetonaphthone

Solid

H302, H315, H319, H335, H411

Al[OCH(CH3)2]3

Aluminum isopropoxide

Solid

H228

(CH3)2CHOH

Isopropyl alcohol

LiquidH225, H319, H336

CH3COOC2H5Ethyl acetate

LiquidH225, H319, H336

C6H14Hexanes (mixture of isomers)

LiquidH225, H304, H315, H336, H411

NH4Cl

Ammonium chloride

Aqueous solution

H302, H319

Na2SO4

Anhydrous sodium sulfate

Solid

Not hazardous

Equipment and Glassware
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Laboratory stand with clamps
Magnetic hotplate stirrer and a PTFE-coated stir bar
Round-bottom flask, 25 cm3
Reflux condenser
Inert gas joint
Inflatable balloon
Water bath with paper clip
Graduated cylinder, 10 cm 3
Separatory funnel, 50 cm 3
Erlenmeyer flask, 25 cm 3
Filtration funnel
Paper filter

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Round bottom flask, 50 cm 3
TLC plates, silica gel 60 F254 (2)TLC chamber or a Petri dish covered small beaker
UV lamp (254 nm)
Petri dishSpatulaCapillary
Vial
Ice bath
Teflon sleeves for tapered joints or vacuum grease
Vacuum rotary evaporator with vacuum source
Melting point apparatus

Procedure
I. Drying of isopropyl alcohol
Place 300 mg of aluminium isopropoxide into a 25 cm3 round-bottom flask equipped witha magnetic stir bar. Add 4 cm3 of isopropyl alcohol and fit the reflux condenser. Fix the apparatus
at the laboratory stand over the magnetic stirrer (Figure P7). Attach an inflatable balloon filledwith an inert gas (N2 or Ar). Heat the water bath with a paper clip to 90 °C. Place the flask in thewater bath and stir the reaction mixture under an inert atmosphere for 1 hour. At this stage, theexcess aluminium isopropoxide is used to remove the moisture present in isopropyl alcohol(w(H2O) ≤ 0.002). Remove the flask from the water bath and let the reaction mixture cool under
the inert atmosphere.
II. Meerwein–Ponndorf–Verley reduction of 2-acetonaphthone and isolation of the product1. Add 2-acetonaphthone to the reaction mixture, leaving a small amount (on the tip of a spatula)in the vial as a standard for TLC analysis. Then, reattach the reflux condenser with an inflatableballoon and place the flask in the water bath heated to 90 °C. Stir the reaction mixture under
an inert atmosphere for 2 hours. Remove the flask from the water bath and let the reaction
mixture cool down. Add 8 cm3 of NH4Cl saturated aqueous solution and stir the mixture at room
temperature for 10 min.
2. Transfer the white suspension into the separatory funnel. Extract the aqueous phase 3 times
with 5 cm3 of ethyl acetate. Collect the organic extracts in a 25 cm3 Erlenmeyer flask. Add one
teaspoon of anhydrous Na2SO4, and let the organic phase stand over the drying agent for
20 min.
3. Prepare the standard solution of the starting material in a vial by dissolving a small amountof 2-acetonaphthone (set aside in step 1) in 0.5 cm3 of ethyl acetate. Prepare the eluent mixture
hexanes/ethyl acetate 6:1 and pour it into the developing chamber and cover it with a Petridish. Spot a sample of the starting material and a sample of the extract with a capillary tube
on a TLC plate. Place the TLC plate into the developing chamber, close the lid and let theeluent evolve. Mark the solvent front and the position of the starting material and the productspots under a UV light. Calculate the retention factors of the starting material and the product.
4. After 20 minutes of drying have elapsed (step 2), filter the extract through filter paper into
a 50 cm3 round-bottom flask. Remove the solvents using a vacuum rotary evaporator.

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Figure P7. Apparatus for drying of isopropyl alcohol.

III. Crystallization of the product
Dilute the residue after the evaporation with 10 cm3 of hexanes. If the crude product precipitates,
attach a reflux condenser and heat the solvent to the boiling point in the water bath heated to
90 °C until the solid material dissolves. Place the flask in the ice bath and let the product crystalize.
Separate the crystals by filtration on filter paper and wash them with 5 cm3 of hexanes. Let theisolated product dry in air. Weigh the product and calculate the yield. Determine the melting pointof the product. Compare the value with the reference data and draw a conclusion about the
product purity.

Data Analysis and Questions
P7.1 Calculate the theoretical yield of the product in mg.
P7.2 Calculate the experimental yield of the product in %.
P7.3 Provide the melting point of the product.
P7.4 Provide the Rf values of the starting material and the product.
P7.5 Calculate the number of moles of water present in 4 cm3 of isopropyl alcohol(w(H2O) = 0.002; d(iPrOH) = 0.786 g.cm−3).
P7.6 What is the final product of the aluminium isopropoxide hydrolysis in the final step of thesynthesis?
P7.7 Explain the difference in the retention factors of the starting 2-acetonaphthone and theobtained 1-(2-naphthyl)ethanol.
P7.8 Propose an alternative synthetic method for the transformation of 2-acetonaphthone to1-(2-naphthyl)ethanol.
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INTERNATIONAL CHEMISTRY OLYMPIAD / SLOVAKIA & CZECH REPUBLIC, 2018

Problem P8. Transformation of a drug to a sweetenerIn this task, you will conduct a multistep synthesis of the artificial sweetener dulcin. You will startwith paracetamol (acetaminophen) tablets, which can be bought, for example, in local drug storesas the well-known drug Paralen®.

Chemicals and Reagents
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Paracetamol tablets with paracetamol content 1.00 g (or pure paracetamol)
1.0 M sodium hydroxide solution in 95% ethanol, 8 cm3
Iodoethane, 1 cm3
6.0 M hydrochloric acid solution (20% w/w), 5 cm3
Sodium bicarbonate, 3.00 g
Acetic acid, 2 drops
Urea, 1.37 g
Hexanes, 5 cm3
95% ethanol (w/w), 5 cm3Ethyl acetate, 5 cm3

Substance

Name

State

GHS Hazard Statements

C8H9NO2

Paracetamol

Tablets or pure solid

H302, H315, H317, H319

NaOH

Sodium hydroxide

Solution in 95% ethanol

H314

CH3CH2I

Iodoethane

Liquid (in a syringe)

H302, H315, H317, H319,
H334, H335

HCl

Hydrochloric acid

Aqueous solution

H315

NaHCO3

Sodium bicarbonate

Solid

Not hazardous

NH2CONH2

Urea

Solid

Not hazardous

CH3COOH

Acetic acid

LiquidH226, H314

C6H14Hexanes (mixture ofisomers)

LiquidH225, H304, H315, H336,
H411

CH3COOCH2CH3

Ethyl acetate

LiquidH225, H319, H336

CH3CH2OH

EthanolLiquid azeotropic mixture

H225, H319

CH3COCH3

AcetoneLiquid (in a wash-bottle)

H225, H319, H336

Equipment and Glassware
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Laboratory stand with clamps
Magnetic hotplate stirrer and a PTFE-coated stir bar
Water aspirator (or other vacuum source for suction filtration)
Two-neck round bottom flask, 50 cm 3
Round-bottom flask, 50 cm3 (2)PREPARATORY PROBLEMS: PRACTICAL

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Round-bottom flask, 25 cm3
Reflux condenser with water hoses
Suction flask, 100 cm 3 (2), with rubber adapter
Sintered glass filter funnel, porosity S2 (2)Graduated cylinder, 10 cm3 (2)TLC plates, silica gel 60 F254 (2), and capillaries
TLC chamber or a Petri dish covered small beaker
UV lamp (254 nm)
Erlenmeyer flask, 50 or 100 cm 3 (2)Filtration funnel and filter paper
Pasteur pipettes with rubber bulb
Syringe, 1 cm3, with needle
Rubber septum
pH indicator paper
SpatulaVials (3), labelled P, A and C
Mortar with pestle
Glass rod
Wash-bottle
Oil bath
Ice bath
Melting point apparatus

Procedure
I. Synthesis of phenacetine (A)1. Grind the paracetamol tablets with the total paracetamol content of 1.0 g using a mortar andpestle. Transfer a small amount of the material (on the tip of a spatula) in vial P for TLC
analysis. Transfer the remaining powder into a 50 cm3 two-neck round-bottom flask, equippedwith a magnetic stir bar, via plastic funnel or by using a folded weighing paper.
2. Add 8 cm3 of 1 M NaOH solution in 95% ethanol into the flask using a Pasteur pipette. Stopper
the side neck with a rubber septum and fold it over the neck. Equip the flask top neck witha reflux condenser, start running the cooling water in the condenser and immerse the flask inan oil bath. Turn the stirring on. Heat the mixture at reflux for 15 min after it has reached boilingpoint (the boiling point of ethanol is 78 °C).
3. Take the flask out of the oil bath (Caution! Hot.). Take 1.0 cm3 of iodoethane using a 1 cm3syringe with a needle, pierce the septum with the needle and add the iodoethane dropwise to
the hot solution (Figure P8). Remove the syringe, immerse the flask again to the oil bath andcontinue heating the mixture. Reflux for a further 15 min.
4. Prepare a suction filtration apparatus with a sintered glass funnel. The collector flask should
contain approximately 25 cm3 of a mixture of water and ice. Lift the flask from the oil bath,
disconnect the condenser and filter the hot mixture under vacuum. You will thus filter off theinsoluble starch (used as a tablet filler). Let the collector flask stand for about 2 min.
A precipitate will form. Prepare another suction filtration apparatus with a sintered glass funnel
and filter the contents of the collector flask under vacuum. Rinse the flask with a small amountof ice-cold water (2 × 5 cm3). Leave a small amount of solid A (on the tip of a spatula) for TLC
analysis in a vial labelled A.

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INTERNATIONAL CHEMISTRY OLYMPIAD / SLOVAKIA & CZECH REPUBLIC, 2018

Figure P8. Adding iodoethane by syringe.

II. Synthesis of dulcin (C)1. Transfer the filtered solid (product A) to a clean 50 cm3 round-bottom flask, equipped witha magnetic stir bar. Add 5 cm3 of 6 M HCl (aq.) by a Pasteur pipette. Equip the flask witha reflux condenser and turn on the stirring. Heat the mixture at reflux for 15 min.
2. Remove the flask from the oil bath and add solid NaHCO3 to the hot mixture (3 g in 3–5
portions) for neutralization. Be careful, as CO2 gas evolves. At the same time, stir the mixture
vigorously and do not let it solidify. Check the pH of the mixture using glass rod and pH indicator
paper. The final pH should be 6.0–6.5. If not, add more solid NaHCO3. If the pH is higher, add
diluted aq. HCl to adjust the final pH.
3. After neutralization, add 1.37 g of urea and two drops of acetic acid to the mixture usinga Pasteur pipette. Immerse the flask fitted with the condenser in the oil bath. Heat the mixture
under reflux for 60 min.
4. Remove the flask from the oil bath and let it cool down for 10 min. Then, immerse the flask in
an ice bath. A solid will precipitate. Prepare a suction filtration apparatus with a sintered glass
funnel. Filter product C under vacuum and wash it with ice-cold water (2 × 5 cm3).
III. Recrystallization of dulcin (C)1. Transfer product C to a clean 50 cm3 round-bottom flask, equipped with a magnetic stir bar.
Add 15 cm3 of water, attach a reflux condenser and immerse the flask in an oil bath. Heat the
mixture under reflux until all the solid dissolves. If necessary, add more water (but not morethan additional 15 cm3).
2. Remove the flask from the oil bath, filter the hot solution through filter paper into an Erlenmeyer
flask and let it cool to room temperature. Then, cool the flask in an ice bath for 10 min. Crystals
will start to form. Prepare a suction filtration apparatus with a sintered glass funnel. Filter the
crystals of product C under vacuum and wash them with ice-cold water(2 × 5 cm3). Let them air dry on the funnel.
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3. If the product is not pure enough (brown colour persists), repeat the crystallization usingorganic solvents: Transfer the product into a 25 cm3 round-bottom flask equipped witha magnetic stir bar and add 5 cm3 of hexanes. Attach the reflux condenser and heat to reflux.
At this point, add a few drops of ethanol by a Pasteur pipette, until all the solid dissolves.
Remove the flask from the oil bath and filter the hot solution through filter paper into an
Erlenmeyer flask. Let it cool for 5 min, then immerse the flask in an ice bath for 10 min. Collectthe formed crystalline material using the suction filtration apparatus, as described before.
4. Transfer the product to a pre-weighed Petri dish.
5. Leave a small amount of the solid (C) for TLC analysis in a small vial labelled C.
6. Weigh the product and determine the melting point of product C.
7. Perform TLC analysis of the paracetamol standard (P) and your samples A and C (silica gelplate, eluent ethyl acetate).

Data Analysis and Questions
P8.1 Draw the structures of compounds A, B, and C.
P8.2 Calculate the theoretical yield of product C in mg, based on the amount of the starting
material P.
P8.3 Calculate the experimental yield of product C in %.
P8.4 Provide the melting point of product C.
P8.5 Provide the Rf values of compounds P, A, and C.
P8.6 Select the correct statements, based on the observations and expected reactivity:a) NaOH deprotonates the OH group of paracetamol to give a coloured phenolate.
b) NaOH deprotonates the methyl protons of the acetamide.
c) NaOH does not react with paracetamol; it only reacts with H+, which is released after the
addition of iodoethane.
d) The deprotonated, anionic substrate is much more reactive than the neutral paracetamol.
e) Nucleophilic substitutions with iododethane are usually SN1 reactions (i.e., the rate isindependent of the nucleophile concentration and reactivity).
f) Acetamide functional group is stable towards an aqueous acid (aq. HCl).
g) Acetamide functional group is stable towards a base (NaOH in 95% EtOH).
h) Aryl ethyl ether functional group is stable towards an aqueous acid (aq. HCl).
i) Product B is a salt (it contains a cation and an anion).
j) Product C is a salt.
P8.7 In the last step of the process, urea and acetic acid react to form ammonium acetate anda reactive species:a) Hydrogen cyanide, H–C≡N,b) Fulminic acid, (−)O–N(+)≡C–H,c) Hydrogen isocyanide, H–N(+)≡C(−),d) Isocyanic acid, H–N=C=O.

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