International Chemistry Olympiad

IChO 1968

Prague, Czechoslovakia · 4 theory problems with complete solutions

  1. Problem 1: Composition of an irradiated hydrogen-chlorine mixture

    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?

    Official English text of the problem.

  2. Problem 2: Equations of three redox reactions

    Write down equations for the following reactions:

    2.1 Oxidation of chromium(III) chloride with bromine in alkaline solution (\(\ce{KOH}\)).

    2.2 Oxidation of potassium nitrite with potassium permanganate in acid solution (\(\ce{H2SO4}\)).

    2.3 Action of chlorine on lime water (\(\ce{Ca(OH)2}\)) in a cold reaction mixture.

    Official English text of the problem.

  3. Problem 3: Combustion of blast-furnace gas

    The gas escaping from a blast furnace has the following composition:

    12.0 volume % of \(\ce{CO2}\) 28.0 volume % of \(\ce{CO}\)
    3.0 volume % of \(\ce{H2}\) 0.6 volume % of \(\ce{CH4}\)
    0.2 volume % of \(\ce{C2H4}\) 56.2 volume % of \(\ce{N2}\)

    Problems:

    3.1 Calculate the theoretical consumption of air (in \(\mathrm{m^3}\)) which is necessary for a total combustion of \(200\ \mathrm{m^3}\) 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.

    Official English text of the problem.

  4. Problem 4: Identification of an organic acid from titration and vapour density

    A volume of \(31.7\ \mathrm{cm^3}\) of a 0.1-normal \(\ce{NaOH}\) is required for the neutralization of \(0.19\ \mathrm{g}\) 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.)

    Official English text of the problem.