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: anton.sirota@stuba.sk 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 [...]... decreased to 65 3 cm This mixture then reacted with a potassium hydroxide solution and the volume of 3 gases decreased to 45 cm Problem: What is the molecular formula of the unknown hydrocarbon if volumes of gases were measured at standard temperature and pressure (STP) conditions? SOLUTION The unknown gaseous hydrocarbon has the general formula: CxHy 0 .010 dm 3 0 .010 n(C x H y ) = = mol... O2 22.4 According to the equation: CxHy + (x + Hence, y y ) O2 = x CO2 + H2O 4 2 0.020 0.020 mol of O2 reacted with carbon and mol of CO2 was formed 22.4 22.4 (C + O2 = CO2), 0. 005 mol O2 combined with hydrogen and 22.4 0 .010 mol of water was obtained 22.4 (2 H2 + O2 = 2 H2O) THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1 Edited by Anton Sirota, ICHO International Information... Slovakia 20 rd 3 6 theoretical problems 2 practical problems THE 3 RD INTERNATIONAL CHEMISTRY OLYMPIAD, 1970 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 at STP) when burned, gives 44 g of -3 carbon dioxide and 27 g of water Problem: What is the structural... Information Centre, Bratislava, Slovakia 24 THE 3 RD INTERNATIONAL CHEMISTRY OLYMPIAD, 1970 2.2 Sample B: Na2CO3 x H2O m(B) = 0.715 g H2SO4 + 2 NaOH = Na2SO4 + 2 H2O n(NaOH) = c V = 0.1 mol dm × 0 .05 dm = 0. 005 mol -3 3 Excess of H2SO4: n(H2SO4) = 0.0025 mol Amount of substance combined with sample B: n(H2SO4) = 0.0025 mol = n(B) M (B) = 0.715 g = 286 g mol-1 -1 0.0025 g mol Sample B: Na2CO3 10 H2O THE... Reaction: 2 M + 2 H2O → 2 MOH + H2 n(H2) = 0.1 mol n(M) = 0.2 mol Mean molar mass: M = 4.6 g = 23 g mol-1 0.2 mol 4.2 Concerning the molar masses of alkali metals, only lithium can come into consideration, i.e the alloy consists of rubidium and lithium n(Rb) + n(Li) = 0.2 mol m(Rb) + m(Li) = 4.6 g n(Rb) M(Rb) + n(Li) M(Li) = 4.6 g n(Rb) M(Rb) + (0.2 – n(Rb)) M(Li) = 4.6 n(Rb) 85.5 + (0.2 – n(Rb)) × 7 = 4.6... Edited by Anton Sirota, ICHO International Information Centre, Bratislava, Slovakia 12 THE 2 V (H2 ) = ND INTERNATIONAL CHEMISTRY OLYMPIAD, 1969 n(H2 ) RT 2.04 mol × 8.314 J mol-1 K -1 × 293.15 K = p 1013 25 Pa ≈ 0.049 m , resp 49 dm 3 3 V(O2) = ½ V(H2) ≈ 0.0245 m ≈ 24.5 dm 3 3 THE COMPETITION PROBLEMS FROM THE INTERNATIONAL CHEMISTRY OLYMPIADS, Volume 1 Edited by Anton Sirota, ICHO International Information... Bratislava, Slovakia 8 THE 1 ST INTERNATIONAL CHEMISTRY OLYMPIAD, 1968 PROBLEM 4 3 A volume of 31.7 cm 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.) SOLUTION 4.1 a) The supposed acid may be:... 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 ° and a C pressure of 101 325 Pa? SOLUTION 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 . 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, 19 69 THE. Slovakia 13 -1 -1 2 2 (H ) 2.04 mol 8. 314 J mol K 293 . 15 K (H ) 10 13 25 Pa n RT V p × × = = ≈ 0.049 m 3 , resp. 49 dm 3 V(O 2 ) = ½ V(H 2 ) ≈ 0.02 45 m 3 ≈ 24 .5 dm 3 THE 2 ND INTERNATIONAL. ___________________________________________ 41. 00 4.60 13 9.24 3.46 Total: 41. 00 + 4.60 + 13 9.24 + 3.46 = 18 8.30 of volume parts of the gaseous components. 2 4.60 % H O 10 0 2.44 18 8.30 = × = 2 13 9.24 % N 10 0 73. 95 18 8.30 =