36th IChO Practical Problems- safety rules

follow them as in the preparatory problems
described, in particular you have to wear safety
goggles all the time, no eating or drinking is allowedin the lab.

- violating safety rules

you get one warning, offend again: you are out.

- problem booklet

12 pages with 2 problems. Start with problem 1 andcontinue until a hint is given to start problem 2.

- time5 hours, 30 minutes warning before the end.

- answer sheets:

3 pages- your name and student code

write it on every answer sheet.

- answers

only in the appropriate boxes of the answer sheets,nothing else will be marked. Relevant calculations
have to be shown.

- use only the pen and calculator provided- results

the number of significant figures in numericalanswers must conform to the rules of evaluation ofexperimental error. Mistakes will result in penalty
points even if your experimental technique isflawless.

- burette

read it as accurately as possible.

- more chemicalsof Na2EDTA, Na2S2O3, superconductor solution,
superconductor solid, polycarbonate or bisphenol A
needed? Ask the instructor. You get a penalty of -5
points only for each of these extra chemicals.

- questions

concerning safety, apparatus, chemicals,organisation, toilet break: ask your instructor.

- chemical waste

only in the designated containers.

- official English-language version

available on request for clarification only. Ask the
instructor.

- after the stop signal

put your answer sheets in the envelope (don’t seal),deliver them at the appropriate instructor room.
Keep the problem booklet together with the pen andcalculator.

You must stop your work immediately after the stop signal has been given. A delay of
5 minutes will result in zero points for the current task.

final

1

Periodic table of elements

1

H

2

He

with atomic masses / u

1.01
3

4

5

6

7

8

9

4.00
10

Li

Be

B

C

N

O

F

Ne

6.94
11

9.01
12

10.81
13

12.01
14

14.01
15

16.00
16

19.00
17

20.18
18

Na

Mg

Al

Si

P

S

Cl

Ar

22.99
19

24.31
20
21

22

23

24

25

26

27

28

29

30

26.98
31

28.09
32

30.97
33

32.07
34

35.45
35

39.95
36

K

Ca

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

Ga

Ge

As

Se

Br

Kr

39.10
37

40.08 44.96 47.88
38
39
40

50.94
41

52.00
42

54.94
43

55.85
44

58.93
45

58.69
46

63.55
47

65.39
48

69.72
49

72.61
50

74.92
51

78.96
52

79.90
53

83.80
54

Rb

Sr

Nb

Mo

Tc

Ru

Rh

Pd

Ag

Cd

In

Sn

Sb

Te

I

Xe

85.47
55

87.62 88.91 91.22
56
57-71 72

92.91
73

95.94
74

98.91
75

101.07 102.91 106.42 107.87 112.41 114.82 118.71 121.76 127.60 126.90 131.29
76
77
78
79
80
81
82
83
84
85
86

Cs

Ba

Ta

W

Re

Os

Sc
Y

Zr
Hf

132.91 137.3
178.49 180.95
87
88
89104
105
103 Rf
Fr
Ra
Db
223
226
261
262
58
57

La

Ce

Ir

Pt

Au

Hg

Tl

Pb

Bi

Po

At

Rn

183.84 186.21 190.23 192.22 195.08 196.97 200.59 204.38 207.19 208.98 208.98 209.99 222.02
106
107
108
109

Sg

Bh

Hs

Mt

263
59

264
60

265
61

268
62

63

64

65

66

67

68

69

70

71

Pr

Nd

Pm

Sm

Eu

Gd

Tb

Dy

Ho

Er

Tm

Yb

Lu

138.91 140.12 140.91 144.24 144.92 150.36 151.96 157.25 158.93 162.50 164.93 167.26 168.93 173.04 174.97
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103

final

Ac

Th

Pa

U

Np

Pu

Am

Cm

Bk

Cf

Es

Fm

Md

No

Lr

227

232

231

238

237

244

243

247

247

251

252

257

258

259

262

Apparatus
During the practical examination some of your glassware will have to be used more thanonce. Clean it carefully.
The hoods and the equipment within will also be used by several students. The numbers ofyour hood and of your instructor room is written on your bench.
apparatus
2 beakers (100 mL)
1 beaker (weighed, labelled “beaker A”)
1 beaker (weighed, labelled “beaker B”)
1 beaker (400 mL)
1 pair of “rubber fingers” for handling hot
beakers
1 bottle with dem. water (500 mL)
2 brackets for condenser and flask
1 bracket for the burette with sleeve
1 burette (25 mL)
1 suction filter (90 mm)
1 condenser (NS 29)
1 Erlenmeyer flask (100 mL, NS 29)
4 Erlenmeyer flask (300 mL)
1 g fibreglass
6 filter papers for problem 1
6 filter papers for problem 2
1 filter rack
2 folded filter papers for problem 1
1 funnel for analysis ∅ = 80 mm
1 funnel for liquids∅ = 100 mm
1 funnel for powder ∅ = 80 mm
1 funnel for the burette
2 glass rods 15 cm
1 glass rod 21 cm
1 graduated cylinder (10 mL)
1 graduated cylinder (100 mL)

apparatus
1 heating plate with magnetic stirrer
1 magnetic stirring bar
3 melting-point tubes in a test tube
(labelled “tube B”)
1 measure for melting point tubes
1 Pasteur pipette (2 mL, grad.) with ball
1 Peleus ball
1 pipette (25 mL)
1 plastic plug (NS 29)
1 glass-ceramics (Ceran™) plate
1 pair of protective glasses
1 role of pH paper
2 shards (2.5 cm x 2.5 cm)
2 sleeves for the brackets
1 spatula
1 micro spatula
2 stands
1 suction bottle (500 mL) with ring
1 Teflon coupling (NS 29)
4 test tubes
1 test-tube rack
1 volumetric flask (100 mL)
1 volumetric flask (250 mL)
75 cm glass tube
1 pair of tweesers
1 wiper
1 test-tube brushChemicals for each student
No

chemicals

formulaconc.

amount R phrases S phrases

-

solid

2.54 gC2H5OH

96 %

HCl

25 %

ClCH2COONa--

150 mL

11

7-16

60 mL

36/37/38

26

solid

5g

25-38-50

22-37-45-61

NaOH

solid

4g

35

26-37/39-45

sodium-hydroxide solution

NaOH

10%

100 mL35

disodium-EDTA solution

Na2-EDTA

0.1000mol L-1

100 mL8

sodium acetate

CH3COONa

solid

10 g

-

-

9

sodium-iodide solution

NaI

80 mL

-

22-24/25 *10 sodium-thiosulfate solution

Na2S2O3

10 %0.01000
mol L-1

100 mL--1

polycarbonate (Makrolon)

2ethanol

3hydrochloric acid4

sodium chloro acetate

5sodium hydroxide

6
7

final

26-36/37/39-45
22-36/37/38
26-36

3

11 starch solution
12 sulfuric acid

H2SO4

2 mol L

-1

20 mL

-

-

50 mL

35

26-30-45

1)

22-24/25 1)

13 superconductor solution

LaxM(2-x)CuO4

-

-

22

14 superconductor solidLaxM(2-x)CuO4

solid

250 mg22

22-24/25

15 xylenol orange indicator

-

solid

500 mg8

16-41

27 bisphenol A

2)

C15H16O2

solid

36/37/38-43

24-26-37

28 bisphenol A

3)

C15H16O2

solid

36/37/38-43

24-26-37

1)

for the solid compound
will be handed out by the instructor on request during problem 1
3)will be handed out after the first step of problem 1 in the appropriate instructor room
2)

Chemicals that have to be used in common (to be found in the hoods)
NochemicalsRphrasesSphrasesformulaconc.

16 acetic acid

CH3COOH

10-35

23.2-26-45

17 ammonia solution

NH3 (aq)

2 mol L-1
25 %

34-50

18 ammonium-carbonate solution
19 ammonium-oxalate solution(NH4)2CO3

2 mol L-1

26-36/37/3945-61

36/37/38 *26-37/39 *(NH4)2C2O4

0.25
mol L-1

21/22 *

24/25 *

20 ammonium-sulfate solution(NH4)2SO4

1 mol L-1--

21 calcium-sulfate solution

CaSO4

satur.

--

22 perchloric acid

HClO4

10 %

34

23-26-36-45

23 potassium-dichromate solution

K2Cr2O7

0.05
mol L-1

43

24-37-45-60* for the solid compound

Chemicals to perform a blank test which can be obtained from the instructor:
formulaconc.

RphrasesSphrases

24 barium-chloride dihydrate

BaCl2 ⋅ 2 H2O

solid

20-25

45

25 calcium-chloride hexahydrate

CaCl2 ⋅ 6 H2O

solid

36

22-24

26 strontium-chloride hexahydrate

SrCl2 ⋅ 6 H2O

solid

-

22-24/25

No

final

chemicals

4

Risk phrases (R)
R 8
R 10
R 11
R 20
R 22
R 25
R 34
R 35
R 36
R 37
R 38
R 43
R 50

Contact with combustible material may cause fire.
Flammable.
Highly flammable.
Harmful by inhalation.
Harmful if swallowed.
Toxic if swallowed.
Causes burns.
Causes severe burns.
Irritating to eyes.
Irritating to respiratory system.
Irritating to skin.
May cause sensitization by skin contact.
Very toxic to aquatic organisms.

Combination of risk phrases
R 21/22
R 36/37/38

Harmful in contact with skin and if swallowed.
Irritating to eyes, respiratory system and skin.

Safety phrases (S)
S7
S 16
S 22
S 23
S 23.2
S 24
S 26
S 30
S 36
S 37
S 41
S 45
S 60
S 61

Keep container tightly closed.
Keep away from sources of ignition - No smoking.
Do not breathe dust.
Do not breathe gas/fumes/vapour/spray (appropriate wording to be specified
by the manufacturer).
Do not breathe vapour.
Avoid contact with skin.
In case of contact with eyes, rinse immediately with plenty of water and seek
medical advice.
Never add water to this product.
Wear suitable protective clothing.
Wear suitable gloves.
In case of fire and/or explosion do not breathe fumes.
In case of accident or if you feel unwell, seek medical advice immediately(show the label where possible).
This material and its container must be disposed of as hazardous waste.
Avoid release to the environment. Refer to special instructions / Safety data
sheets.

Combination of safety phrases (S)S 24/25
S 36/37/39
S 37/39

final

Avoid contact with skin and eyes.
Wear suitable protective clothing, gloves and eye/face protection.
Wear suitable gloves and eye/face protection.

5

1.

Two-Step Organic Synthesis of 2,2-Bis(p-phenyleneoxyaceticacid)propane (Bisphenol A bis(carboxymethyl)ether)(100 points)

Introduction
In the first step the sodium salt of bisphenol A results as an intermediate from the alkalinehydrolysis of a polycarbonate. By adding an acid this salt is converted into the free 2,2-bis(4hydroxyphenyl)propane (bisphenol A).
O
CH3

O

C

O

O

CH3

n

+

H3O , H2O

NaOH, H2O

n HO

CH3
C

OH

CH3

In the second step bisphenol A reacts with sodium chloroacetate to form the phenolic ether,bisphenol A bis(carboxymethyl)ether.
CH3
HO

C

OH

ClCH2COONa, NaOH, H2O+

H3O , H2O

CH3
O
C
HO

CH2

CH3

O

C
CH3

O

O
H2C

C
OH

•

In each step the product has to be isolated.
(Drying and weighing will be done by the organizer.)•

For the product of step 2 three melting point tubes have to be filled.
(Filling of the melting point tubes in step 1 will be done by the organizer.)(The melting points will be determined by the organizer.)•

When the organizer receives your labelled beaker A of step 1 you will get 2.00 g ofbisphenol A as starting material for the second step.

•

Answer the additional questions on the answer sheet P1.

•

Do not remove the Ceran plate from the magnetic stirrer.

final

6

Procedures
Step 1

Preparation of bisphenol A by alkaline hydrolysis of a polycarbonate

Preparation:•

Put the pre-weighed 2.54 g of polycarbonate (No. 1), 4.0 g of sodium hydroxide (No. 5)
and 3 mL of demineralized water into a 100 mL Erlenmeyer flask with ground-glass joint.

•

Close the flask with a plastic plug and swirl it gently so that the solution does not contact
the ground-glass joint. For aeration open the plastic plug occasionally. Strong heating
can be observed, as the sodium hydroxide partially dissolves.

•

Remove the plastic plug after swirling for about 4 minutes, add a magnetic stirring bar
and put the flask onto a heating plate. Put a reflux condenser above the neck of the flask.
Use a Teflon coupling as a connection between flask and condenser. Fix the apparatus
tightly to a stand.

•

Finally, add 20 mL of ethanol (No. 2) through the condenser while stirring the reaction
mixture.

•Heat the reaction mixture under reflux for 60 minutes. In the beginning adjust thethermostat of the heating plate to maximum. When the mixture starts boiling reduce theheat carefully, so that the mixture is kept under gentle reflux.

•

A white precipitate is formed on heating.

During this waiting period you are highly advised to start working on theanalytical chemistry experiment.
Isolation:•

Stop heating after one hour, allow the reaction mixture to cool down to ambient
temperature, remove the condenser, add 25 mL of demineralized water and transfer thereaction mixture into a 400 mL beaker. Rinse the Erlenmeyer flask with 25 mL ofdemineralized water and add this to the contents of the beaker.

•

Finally, fill up to 150 mL with demineralized water.

•

If the reaction mixture is not clear, the mixture has to be filtered over fibre glass into an
Erlenmeyer flask.

•

Add slowly 15 mL of hydrochloric acid (No. 3) stirring the mixture simultaneously with aglass rod. A rather oily or sometimes crystalline precipitate is formed.

•

Ask your instructor for some seed crystals of bisphenol A (No. 27) in order to accelerate
the crystallization.

•

Stir the reaction mixture thoroughly with the glass rod. For a quantitative crystallisation
continue stirring from time to time till the supernatant aqueous solution is nearly clear.

•

Collect the crude product by vacuum filtration, wash it twice with 10 mL portions ofdemineralized water and transfer it quantitatively into the tared and labelled beaker A.

•

For drying and weighing deliver your labelled beaker A into the instructor room.

•

Afterwards you will get a small jar filled with 2.00 g of bisphenol A (No. 28), your starting
material of the second step.

final

7

•

On delivery of your product and on receipt of the starting material you have to sign. Even
if you do not have any bisphenol A, please bring the empty beaker A to the instructors’room in order to get the starting material for step 2.

Step 2

Reaction of Bisphenol A with Chloroacetic Acid forming 2,2-Bis(p-phenyleneoxyacetic acid)propane (Bisphenol A bis(carboxymethyl)ether)

Preparation:•

Pour all the bisphenol A (No. 28) you have received from the organizer when you had
finished step 1 into a 100 mL Erlenmeyer flask with ground-glass joint.

•

Add 10 mL of an aqueous sodium-hydroxide solution (No. 6), 1 mL of demineralized
water and a magnetic stirring bar.

•

Put the flask onto a heating plate. Put a reflux condenser above the neck of the flask.
Use a Teflon coupling as a connection between flask and condenser. Fix the apparatus
tightly to a stand.

•Heat the reaction mixture with gentle stirring until a clear solution is formed.

•

Remove the heating plate and the condenser and add 5.0 g of the sodium salt ofchloroacetic acid (No. 4) to the reaction mixture.

•

After reconnecting the flask with the reflux condenser, heat the mixture to reflux withvigorous stirring for 30 min.

•Initially a clear solution is formed on heating. In some cases a colorless solid precipitates.
If the complete mixture becomes solid in the course of the reaction, heating must be
stopped.

•After that, 50 mL of ethanol (No. 2) are added carefully through the condenser (beware ofsudden boiling!). The mixture is stirred and heated under reflux for 5 minutes. A
colourless solid precipitates, or the crystallisation which has already started is completed.

Isolation:•

After leaving it to cool down for 5 minutes, transfer the reaction mixture with another
50 mL of ethanol (No. 2) quantitatively to a beaker. The reaction mixture should be stirred
vigorously.

•

The magnetic stirring bar is removed and the reaction mixture is filtered through a suction
filter. Solids which separate in the filtrate are rejected. Rinse the beaker with 10 mL ofethanol (No. 2). The precipitate is washed twice with 10 mL portions of ethanol (No. 2).
(The filtrate must be disposed of in the organic solvent waste!)•Transfer the precipitate quantitatively into a beaker, add a stirring bar and dissolve it in
150 mL of demineralized water. The mixture must be stirred vigorously. Larger lumps ofthe solid must be crushed with the spatula.

•

If the solution is not clear, it has to be filtered over a folded filter paper into an Erlenmeyer
flask.

final

8

•

The slow addition of 5 mL of hydrochloric acid (No. 3) to the stirred reaction mixture
results in the formation of a white precipitate.

•

Collect the crude product by vacuum filtration, wash it twice with 10 mL portions ofdemineralized water and transfer it quantitatively into the tared and labelled beaker B.

•

Take a small sample of the product with a micro spatula, crush it and dry it on a shard.
Fill three melting point tubes with the homogenized, dried sample. For a close-packed
and 5 mm high filling use the 75 cm glass tube and the measure.

•Put all three melting point tubes into the test tube B, which is labelled with yourstudent code, and give it together with your labelled beaker B with the product tothe instructor. On delivery you have to sign.

final

9

2.

Qualitative and Quantitative Analysis of a Superconductor(113 points)

Introduction
Superconductors based on lanthanum cuprate (La2CuO4) have the general composition ofLaxM(2-x)CuO4 (M = Ca, Sr, Ba).
This problem consists of two parts:
the qualitative determination of the alkaline earth metal(s)the quantitative determination of lanthanum and copper.
Read the burette as accurately as possible.
Report your results on the answer sheets.
Answer the additional questions and write the results with adequate accuracy.
The qualitative and quantitative parts of this experiment may be done in any order.

Procedures
2.1 Qualitative determination of the alkaline earth metal(s) (If the hood is occupied startwith the titration 2.2)
In this experiment you have to use the superconductor as a solid (LaxM(2-x)CuO4; No. 14).
At the beginning, lanthanum has to be separated as an insoluble residue.
All steps must be carried out in the hood!
Dissolve the complete sample in a beaker in about 5 mL of perchloric acid (No. 22) byheating the mixture. Add 5 mL of demineralized water afterwards.
Cool down the solution until it is lukewarm.
Add about 5 mL of demineralized water and then ammonia solution (No. 17), until thereaction mixture shows a basic reaction. Lanthanum precipitates as hydroxide and copper
forms an intense blue-coloured tetraammine complex. The precipitate is filtered off andwashed with a small amount of demineralized water.
An excess of ammonium-carbonate solution (No. 18) is added to the filtrate and the mixture
is being boiled for some minutes. The alkaline earth metal(s) will precipitate as carbonate(s).
The precipitate is filtered off and washed a few times with a small amount of demineralized
water.
Then, the precipitate is dissolved in acetic acid (No. 16). Add sodium acetate (No. 9) and an
excess of potassium-dichromate solution (No. 23). In the presence of barium, yellow BaCrO4
precipitates. After boiling the mixture for one minute barium chromate is filtered off andwashed with demineralized water.
(If there is no barium chromate precipitation, proceed in a way as if there were precipitation.)
Ammonia solution (No. 17) is added to the clear filtrate until it is basic. Add an excess ofammonium-carbonate solution (No. 18) and boil the mixture for some minutes. In thepresence of strontium and/or calcium, white carbonate(s) precipitate(s).
final

10

The precipitate is filtered off and washed a few times with demineralized water.
Then it is dissolved in a mixture of about 2 mL of demineralized water and a few drops ofhydrochloric acid (No. 3). This solution is devided between two test tubes:•

Saturated calcium-sulfate solution (No. 21) is added to one of the test tubes. In thepresence of strontium a small amount of white strontium sulfate precipitates. To
accelerate the precipitation, you can grind the inner surface of the test tube with a glassrod for a few minutes.

•

Ammonium-sulfate solution (No. 20) is added to the second test tube. In the presence ofstrontium and/or calcium, white sulfate(s) precipitate(s). The precipitate is filtered off andwashed with a very small amount of demineralized water.
1 mL of ammonium-oxalate solution (No. 19) is added to the filtrate. In the presence of
calcium, white calcium oxalate precipitates after a few minutes.

Preparation of the superconductor parent solution
There is a superconductor solution (LaxM(2-x)CuO4 in perchloric acid; No. 13) in a volumetricflask.
Fill it up with demineralized water to a volume of 250.0 mL. From now on this solution iscalled “parent solution”.

2.2 Quantitative determination of the total content of lanthanum and copper
Transfer 25.00 mL of the parent solution into an Erlenmeyer flask.
Add about 5-6 piled spatula of sodium acetate (CH3COONa; No. 8) and 2 micro spatula ofxylenol orange indicator (No. 15) to this solution and make up with demineralized water to a
volume of about 75 mL.
The pH-value has to be about pH 6 before the determination, otherwise add more sodium
acetate.
Titrate the solution with Na2-EDTA solution (No. 7). The color of the solution changes fromlight violet to intensely light-green. (In between, the color changes a few times.)
Repeat this procedure as many times as necessary.

2.3 Quantitative determination of the copper content
Transfer 25.00 mL of your parent solution (No. 13) into the 100 mL volumetric flask and fill up
with demineralized water to a volume of 100.0 mL.
For each titration, transfer 25.00 mL of this solution into an Erlenmeyer flask and add sodiumhydroxide solution (No. 6), until the solution shows an alkaline reaction. During thisprocedure, a blue precipitate forms. Add sulfuric acid (No. 12) until the blue precipitate
dissolves. The solution has to be acidic (pH 1-2) and will contain a small amount of a white
precipitate.
Add 10 mL of sodium-iodide solution (No. 9), and swirl the Erlenmeyer flask for about 1
minute. Titrate the solution with sodium-thiosulfate solution (No. 10). Add some starch
final

11

solution (No. 11) as an indicator just before the end of the titration. At the end, the solution
has to be colourless for at least 60 seconds.
Repeat this procedure as many times as necessary.

final

12