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THE COMPETITION PROBLEMS FROM THE
INTERNATIONAL CHEMISTRY OLYMPIADS








Volume 1



1
st
– 20

th
ICHO
1968 – 1988





Edited by Anton Sirota










IUVENTA, Bratislava, 2008

THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Editor: Anton Sirota
ISBN 978-80-8072-082-7
Copyright © 2008 by IUVENTA – ICHO International Information Centre, Bratislava, Slovakia
You are free to copy, distribute, transmit or adapt this publication or its parts for unlimited teaching purposes,
however, you are obliged to attribute your copies, transmissions or adaptations with a reference to "The
Competition Problems from the International Chemistry Olympiads, Volume 1" as it is required in the
chemical literature. The above conditions can be waived if you get permission from the copyright holder.


Issued by IUVENTA in 2008
with the financial support of the Ministry of Education of the Slovak Republic

Number of copies: 250
Not for sale.


International Chemistry Olympiad

International Information Centre
IUVENTA
Búdková 2
811 04 Bratislava 1, Slovakia
Phone: +421-907-473367
Fax: +421-2-59296123
E-mail:
Web: www.icho.sk






Contents

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

VOLUME 1
The competition problems of the:
1
st
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2
nd
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

3
rd

ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

4
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34

5
th

ICHO

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

6
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62
7
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79
8
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99
9
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116
10
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 144
11
th

ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 172
12
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 191
13
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220
14
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 243
15
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 268
16
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 296
17
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 319
18
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 340
19
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366
20
th
ICHO . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 383

1



Preface

This publication contains the competition problems from the first twenty International
Chemistry Olympiads (ICHO) organized in the years 1968 – 1988. It has been published
by the ICHO International Information Centre in Bratislava (Slovakia) on the occasion of
the 40th anniversary of this international competition.
Not less than 125 theoretical and 50 practical problems were set in the ICHO in the
mentioned twenty years. In the elaboration of this collection the editor had to face certain
difficulties because the aim was not only to make use of past recordings but also to give
them such a form that they may be used in practice and further chemical education.
Consequently, it was necessary to make some corrections in order to unify the form of the
problems. However, they did not concern the contents and language of the problems.
Many of the first problems were published separately in various national journals, in
different languages and they were hard to obtain. Some of them had to be translated into
English. Most of the xerox copies of the problems could not be used directly and many
texts, schemes and pictures had to be re-written and created again. The changes concern
in particular solutions of the problems set in the first years of the ICHO competition that
were often available in a brief form and necessary extent only, just for the needs of
members of the International Jury. Some practical problems, in which experimental results
and relatively simply calculations are required, have not been accompanied with their
solutions. Recalculations of the solutions were made in some special cases ony when the
numeric results in the original solutions showed to be obviously not correct. Although the
numbers of significant figures in the results of several solutions do not obey the criteria
generally accepted, they were left without change.
In this publication SI quantities and units are used and a more modern method of

chemical calculations is introduced. Only some exceptions have been made when, in an
effort to preserve the original text, the quantities and units have been used that are not SI.
Unfortunately, the authors of the particular competition problems are not known and
due to the procedure of the creation of the ICHO competition problems, it is impossible to
assign any author's name to a particular problem. Nevertheless, responsibility for the
scientific content and language of the problems lies exclusively with the organizers of the
particular International Chemistry Olympiads.

2

Nowadays many possibilities for various activities are offered to a gifted pupil. If we
want to gain the gifted and talented pupil for chemistry we have to look for ways how to
evoke his interest. The International Chemistry Olympiad fulfils all preconditions to play
this role excellently.
This review of the competition problems from the first twenty International Chemistry
Olympiads should serve to both competitors and their teachers as a source of further
ideas in their preparation for this difficult competition. For those who have taken part in
some of these International Chemistry Olympiads the collection of the problems could be
of help as archival and documentary material. The edition of the competition problems will
continue with its second part and will contain the problems set in the International
Chemistry Olympiads in the years 1989 – 2008.
The International Chemistry Olympiad has its 40th birthday. In the previous forty
years many known and unknown people - teachers, authors, pupils, and organizers -
proved their abilities and knowledge and contributed to the success of this already well
known and world-wide competition. We wish to all who will organize and attend the future
International Chemistry Olympiads, success and happiness.

Bratislava, July 2008

Anton Sirota, editor

1
11
1
st
stst
st










4 theoretical problems
2 practical problems

THE 1
ST
INTERNATIONAL CHEMISTRY OLYMPIAD, 1968
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia
4


THE FIRST
INTERNATIONAL CHEMISTRY OLYMPIAD
18–21 JULY 1968, PRAGUE, CZECHOSLOVAKIA

_________________________________________________________________________
__________________________________________________________________________________________________________________________________________________
_________________________________________________________________________





THEORETICAL PROBLEMS

PROBLEM 1
A mixture of hydrogen and chlorine kept in a closed flask at a constant temperature
was irradiated by scattered light. After a certain time the chlorine content decreased by 20

% compared with that of the starting mixture and the resulting mixture had the composition
as follows: 60 volume % of chlorine, 10 volume % of hydrogen, and 30 volume % of
hydrogen chloride.
Problems:
1.1 What is the composition of the initial gaseous mixture?
1.2 How chlorine, hydrogen, and hydrogen chloride are produced?
____________________


SOL UTI ON
1.1 H
2
+ Cl
2
→ 2 HCl
30 volume parts of hydrogen chloride could only be formed by the reaction of 15
volume parts of hydrogen and 15 volume parts of chlorine. Hence, the initial
composition of the mixture had to be:
Cl
2
: 60 + 15 = 75 %
H
2
: 10 + 15 = 25 %

1.2 Chlorine and hydrogen are produced by electrolysis of aqueous solutions of
NaCl: NaCl(aq) → Na
+
(aq) + Cl
-

(aq)


anode: 2 Cl
-
– 2 e → Cl
2

cathode: 2 Na
+
+ 2 e → 2 Na
THE 1
ST
INTERNATIONAL CHEMISTRY OLYMPIAD, 1968
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia
5


2 Na + 2 H
2
O → 2 NaOH + H
2
Hydrogen chloride is produced by the reaction of hydrogen with chlorine.


THE 1
ST
INTERNATIONAL CHEMISTRY OLYMPIAD, 1968

THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia
6




PROBLEM 2



Write down equations for the following reactions:
2.1 Oxidation of chromium(III) chloride with bromine in alkaline solution (KOH).
2.2 Oxidation of potassium nitrite with potassium permanganate in acid solution (H
2
SO
4
).
2.3 Action of chlorine on lime water (Ca(OH)
2
) in a cold reaction mixture.
____________________

S OLU T I ON
2.1 2 CrCl
3
+ 3 Br
2
+ 16 KOH → 2 K

2
CrO
4
+ 6 KBr + 6 KCl + 8 H
2
O

2.2 5 KNO
2
+ 2 KMnO
4
+ 3 H
2
SO
4
→ 2 MnSO
4
+ K
2
SO
4
+ 5 KNO
3
+ 3 H
2
O

2.3. Cl
2
+ Ca(OH)

2
→ CaOCl
2
+ H
2
O





THE 1
ST
INTERNATIONAL CHEMISTRY OLYMPIAD, 1968
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia
7


PROBLEM 3



The gas escaping from a blast furnace has the following composition:
12.0 volume % of CO
2
28.0 volume % of CO
3.0 volume % of H
2

0.6 volume % of CH
4

0.2 volume % of C
2
H
4
56.2 volume % of N
2

Problems:
3.1 Calculate the theoretical consumption of air (in m
3
) which is necessary for a total
combustion of 200 m
3
of the above gas if both the gas and air are measured at the
same temperature. (Oxygen content in the air is about 20 % by volume).
3.2 Determine the composition of combustion products if the gas is burned in a 20 %
excess of air.
____________________

SOL UTI ON

O
2
________
3.1 2 CO + O
2
→ 2 CO

2
14
2 H
2
+ O
2
→ 2 H
2
O 1.5
CH
4
+ 2 O
2
→

CO
2
+ 2 H
2
O 1.2
C
2
H
4
+ 3 O
2
→

2 CO
2

+ 2 H
2
O 0.6
_________
17.3 parts
x
5 = 86.5 parts of the air

200 m
3
of the gas 2
x
86.5 = 173.0 m
3
of the air
+ 20 % 34.6 m
3

________________
207.6 m
3
of the air


3.2 207.6 : 5 = 41.52 parts of O
2
: 2 = 20.76 parts of O
2
for 100 m
3

of the gas
20.76
x
4 = 83.04 parts of N
2
for 100 m
3
of the gas





THE 1
ST
INTERNATIONAL CHEMISTRY OLYMPIAD, 1968
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia
8


Balance: CO
2
H
2
O N
2
O
2

(volume parts) 12.00 3.00 56.20 20.76
28.00 1.20 83.04 - 17.30
0.60 0.40
0.40
___________________________________________
41.00 4.60 139.24 3.46

Total: 41.00 + 4.60 + 139.24 + 3.46 = 188.30 of volume parts of the gaseous components.


2
4.60
% H O 100 2.44
188.30
= × =

2
139.24
% N 100 73.95
188.30
= × =

2
3.46
% O 100 1.84
188.30
= × =


THE 1

ST
INTERNATIONAL CHEMISTRY OLYMPIAD, 1968
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia
9




PROBLEM 4




A volume of 31.7 cm
3
of a 0.1-normal NaOH is required for the neutralization of
0.19 g of an organic acid whose vapour is thirty times as dense as gaseous hydrogen.
Problem:
4.1
Give the name and structural formula of the acid.
(The acid concerned is a common organic acid.)
____________________

SOL UTI ON

4.1
a) The supposed acid may be: HA, H
2

A, H
3
A, etc.


n
(NaOH) =
c V
= 0.1 mol dm
-3
x
0.0317 dm
3
= 3.17 × 10
-3
mol

mol
1017.3
(acid)
3
v
n
−
×
=

where
v
= 1, 2, 3,

(acid)
(acid)
(acid)
M
m
n
=

1
3
molg60
mol1017.3
g19.0
(acid)
−
−
×=
×
×= vvM (1)

b) From the ideal gas law we can obtain:

1
1
2 2
M
M
ρ

ρ
=
M(H
2
) = 2 g mol
-1
M(acid) = 30
x
2 = 60 g mol
-1
By comparing with (1): v = 1
The acid concerned is a monoprotic acid and its molar mass is 60 g mol
-1
.
The acid is acetic acid: CH
3
−COOH


THE 1
ST
INTERNATIONAL CHEMISTRY OLYMPIAD, 1968
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia
10


PRACTICAL PROBLEMS

PROBLEM 1
(Practical)






There are ten test tubes in the rack at your disposal (1 – 10) and each test tube
contains one of aqueous solutions of the following salts: Na
2
SO
4
, AgNO
3
, KI, Ba(OH)
2
,
NH
4
Cl, Ag
2
SO
4
, Pb(NO
3
)
2

, NaOH, NH
4
I, KCl.
For identification of the particular test tubes you can use mutual reactions of the
solutions in the test tubes only.
Determine in which order the solutions of the salts in your rack are and write
chemical equations of the reactions you used for identification of the salts.




PROBLEM 2
(Practical)






Each of the six test tubes (A – F) in the rack contains one of the following
substances:
benzoic acid, salicylic acid, citric acid, tartaric acid, oxalic acid and glucose.
Determine the order in which the substances in the test tubes are placed in your rack
and give chemical reactions you used for identification of the substances.
For identification of the substances the following aqueous solutions are at your
disposal: HCl, H
2
SO
4
, NaOH, NH

4
OH, CuSO
4
, KMnO
4
, FeCl
3
, KCl, and distilled water.
















2
22
2
nd
ndnd
nd

4 theoretical problems
2 practical problems





THE 2
ND
INTERNATIONAL CHEMISTRY OLYMPIAD, 1969
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia

12


THE SECOND
INTERNATIONAL CHEMISTRY OLYMPIAD
16–20 JUNE 1969, KATOWICE, POLAND

_______________________________________________________________________


THEORETICAL PROBLEMS



PROBLEM 1

An amount of 20 g of potassium sulphate was dissolved in 150 cm
3
of water. The
solution was then electrolysed. After electrolysis, the content of potassium sulphate in the
solution was 15 % by mass.
Problem:
What volumes of hydrogen and oxygen were obtained at a temperature of 20 °C and a
pressure of 101 325 Pa?
____________________

SOL UTI ON
On electrolysis, only water is decomposed and the total amount of potassium
sulphate in the electrolyte solution is constant. The mass of water in the solution:
1.1
Before electrolysis (on the assumption that
ρ
= 1 g cm
-3
): m(H
2
O) = 150 g

1.2
After electrolysis:
m(H
2
O) = m(solution) – m(K
2
SO
4
) =
20 g
0.15
– 20 g = 113.3 g
The mass of water decomposed on electrolysis:
m(H
2
O) = 150 – 113.3 = 36.7 g, i. e.
n(H
2
O) = 2.04 mol
Since, 2 H
2
O → 2 H
2
+ O
2
thus, n(H
2
) = 2.04 mol
n(O
2

) = 1.02 mol




THE 2
ND
INTERNATIONAL CHEMISTRY OLYMPIAD, 1969
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia

13


-1 -1
2
2
(H ) 2.04 mol 8.314 J mol K 293.15 K
(H )
101325 Pa
n RT
V
p
× ×
= =

≈ 0.049 m
3
, resp. 49 dm

3

V(O
2
) = ½ V(H
2
) ≈ 0.0245 m
3
≈ 24.5 dm
3


THE 2
ND
INTERNATIONAL CHEMISTRY OLYMPIAD, 1969
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia

14


PROBLEM 2
A compound
A
contains 38.67 % of potassium, 13.85 % of nitrogen, and 47.48 % of
oxygen. On heating, it is converted to a compound
B
containing 45.85 % of potassium,
16.47 % of nitrogen, and 37.66 % of oxygen.

Problem:
2.1
What are the stoichiometric formulas of the compounds?
2.2
Write the corresponding chemical equation.
____________________

SOL UTI ON
2.1
Compound
A
:
K
x
N
y
O
z
16
47.48
14
13.85
39.1
38.67
z:y:x ===
= 0.989 : 0.989 : 2.968 = 1 : 1 : 3
A
: KNO
3
Compound

B
:
K
p
N
q
O
r
16
37.66
14
16.47
39.1
45.85
r:q:p ===
= 1.173 : 1.176 : 2.354 = 1 : 1 : 2
B
: KNO
2

2.2
Equation: 2 KNO
3
→ 2 KNO
2
+ O
2

THE 2
ND

INTERNATIONAL CHEMISTRY OLYMPIAD, 1969
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia

15



PROBLEM 3
A 10 cm
3
sample of an unknown gaseous hydrocarbon was mixed with 70 cm
3
of
oxygen and the mixture was set on fire by means of an electric spark. When the reaction
was over and water vapours were liquefied, the final volume of gases decreased to 65
cm
3
. This mixture then reacted with a potassium hydroxide solution and the volume of
gases decreased to 45 cm
3
.
Problem:
What is the molecular formula of the unknown hydrocarbon if volumes of gases were
measured at standard temperature and pressure (STP) conditions?
____________________

SOL UTI ON

The unknown gaseous hydrocarbon has the general formula: C
x
H
y
mol
22.4
0.010
moldm22.4
dm0.010
)H(C
13
3
yx
==
−
n

Balance of oxygen:
- Before the reaction: 70 cm
3
, i. e.
0.070
22.4
mol
- After the reaction: 45 cm
3
, i. e.
0.045
22.4
mol

Consumed in the reaction:
0.025
22.4
mol of O
2

According to the equation:
C
x
H
y
+ (x +
y
4
) O
2
= x CO
2
+
y
2
H
2
O
Hence,
0.020
22.4
mol of O
2

reacted with carbon and
0.020
22.4
mol of CO
2
was formed
(C + O
2
= CO
2
),
0.005
22.4
mol O
2
combined with hydrogen and
0.010
22.4
mol of water was obtained
(2 H
2
+ O
2
= 2 H
2
O).

THE 2
ND
INTERNATIONAL CHEMISTRY OLYMPIAD, 1969

THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia

16


3
n
(C) =
n
(CO
2
) =
0.020
22.4
mol
n
(H
2
) = 2
n
(H
2
O) =
0.020
22.4
mol
x : y =
n

(C) :
n
(H
2
) = 0.020 : 0.020 = 1 : 1
From the possible solutions C
2
H
2
, C
3
H
3
, C
4
H
4
, C
5
H
5
.only C
2
H
2
satisfies to the conditions
given in the task, i. e. the unknown hydrocarbon is acetylene.

THE 2
ND
INTERNATIONAL CHEMISTRY OLYMPIAD, 1969
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia

17


PROBLEM 4



Calcium carbide and water are the basic raw materials in the production of:
a) ethanol
b) acetic acid
c) ethylene and polyethylene
d) vinyl chloride
e) benzene

Problem:
Give basic chemical equations for each reaction by which the above mentioned
compounds can be obtained.


SOL UTI ON

Basic reaction: CaC

2
+ 2 H
2
O = Ca(OH)
2
+ C
2
H
2
From acetylene can be obtained:
a) ethanol


CH
CH
CH
2
CH
3
CH
3
HgSO
4
(catalyst)
diluted H
2
SO
4
+ H
2

O
CH
OH
vinyl alcohol
rearrangement
CH
O
reduction
CH
2
OH
acetaldehyde
ethanol


b) acetic acid


CH
CH
CH
2
CH
3
CH
3
COOH
acetic acid
HgSO
4

(catalyst)
diluted H
2
SO
4
+ H
2
O
CH
OH
vinyl alcohol
rearrangement
CH
O
oxidation
acetaldehyde



THE 2
ND
INTERNATIONAL CHEMISTRY OLYMPIAD, 1969
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia

18


c) ethylene, polyethylene

CH
CH
CH
2
catalyst
+ H
2
O
CH
2
ethylene



CH
2
CH
2
pressure, temperature
catalyst
( - CH
2
- CH
2
- )
n

polyethylene

d) vinyl chloride
CH
CH
CH
2
+ HCl
CH
Cl
vinyl chloride


e) benzene

CH
CH
3
400 -500 °C



THE 2
ND
INTERNATIONAL CHEMISTRY OLYMPIAD, 1969
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia

19

PRACTICAL PROBLEMS




PROBLEM 1
(Practical)


a) Three numbered test-tubes (1-3) contain mixtures of two substances from the
following pairs (4 variants):
1. ZnSO
4
- NaBr NaCl - Ca(NO
3
)
2
MgSO
4
- NH
4
Cl
2. AlCl
3
- KBr CaCl
2
- NaNO
3

ZnCl
2
- (NH
4
)
2
SO
4
3. KNO
3
- Na
2
CO
3
KCl - MgSO
4
NH
4
Cl - Ba(NO
3
)
2
4. MgCl
2
- KNO
3
K
2
CO
3

- ZnSO
4
Al(NO
3
)
3
- NaCl

b) Each of the test-tubes numbered 4 and 5 contains one of the following substances:
glucose, saccharose, urea, sodium acetate, oxalic acid.

Problem:
By means of reagents that are available on the laboratory desk determine the
content of the individual test-tubes. Give reasons for both the tests performed and your
answers and write the chemical equations of the corresponding reactions.

Note:
For the identification of substances given in the above task, the following reagents
were available to competing pupils: 1 N HCl, 3 N HCl, 1 N H
2
SO
4
, concentrated H
2
SO
4
,
FeSO
4
, 2 N NaOH, 20 % NaOH, 2 N NH

4
Cl, 2 N CuSO
4
, 2 N BaCl
2
, 0,1 N AgNO
3
, 0,1 %
KMnO
4
, distilled water, phenolphtalein, methyl orange. In addition, further laboratory
facilities, such as platinum wire, cobalt glass, etc., were available.










THE 2
ND
INTERNATIONAL CHEMISTRY OLYMPIAD, 1969
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia

20

PROBLEM 2
(Practical)


Allow to react 10 cm
3
of a 3 N HCl solution with the metal sample (competing pupils
were given precisely weighed samples of magnesium, zinc or aluminium) and collect the
hydrogen evolved in the reaction in a measuring cylinder above water. Perform the task by
means of available device and procedure.
In order to simplify the problem, calculate the mass of your metal sample from the
volume of hydrogen on the assumption that it was measured at STP conditions.

3
33
3
rd
rdrd
rd










6 theoretical problems
2 practical problems

THE 3
RD
INTERNATIONAL CHEMISTRY OLYMPIAD, 1970
THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1
Edited by Anton Sirota,
ICHO International Information Centre, Bratislava, Slovakia

22


THE THIRD
INTERNATIONAL CHEMISTRY OLYMPIAD
1–5 JULY 1970, BUDAPEST, HUNGARY

_______________________________________________________________________


THEORETICAL PROBLEMS


PROBLEM 1



An amount of 23 g of gas (density
ρ
= 2.05 g dm

-3
at STP) when burned, gives 44 g of
carbon dioxide and 27 g of water.
Problem:
What is the structural formula of the gas (compound)?
____________________


SOL UTI ON


The unknown gas : X

1
(X)
From the ideal gas law : (X) 46 g mol
R T
M
p
ρ
−
= =


1
23 g
(X) 0.5 mol
46 g mol
n
−

= =

mol1
molg44
g44
)(CO
1
2
==
−
n


n
(C) = 1 mol
m
(C) = 12 g

mol1.5
molg18
g27
O)(H
1
2
==
−
n

n
(H) = 3 mol

m
(H) = 3 g