International Chemistry Olympiad

IChO 1979

Leningrad, Soviet Union · 6 theory problems with complete solutions

  1. Problem 1: Programmed assignment: 20 multiple-choice questions

    When carrying out this programmed assignment, encircle those letters which in your opinion correspond to the correct answers to each of the 20 questions.

    1. Which element is oxidized in the reaction between ethylene and an aqueous solution of potassium permanganate?

    A) carbon, B) hydrogen, C) potassium, D) manganese, E) oxygen.

    1. How many litres of \(\ce{CO2}\) will approximately be evolved in the reaction of 18 g of potassium hydrogen carbonate with 65 g of 10 % sulphuric acid?

    A) 1, B) 2, C) 3, D) 4, E) 5.

    1. Which of the following hydrocarbons gives the maximum heat yield on complete combustion of 1 litre of the gas:

    A) propane, B) methane, C) acetylene, D) ethylene, E) all give the same yield.

    1. How many isomers can have a compound if its formula is \(\ce{C3H5Br}\)?

    A) 1, B) 2, C) 3, D) 4, E) 5.

    1. Which of the following hydrocarbons will be the best engine fuel?

    A) cyclooctane, B) 2,2-dimethylhexane, C) normal octane, D) 3-ethylhexane, E) 2,2,4-trimethylpentane.

    1. With which of the following compounds will an aqueous solution of a higher oxide of element No 33 react?

    A) \(\ce{CO2}\), B) \(\ce{K2SO4}\), C) \(\ce{HCl}\), D) \(\ce{NaOH}\), E) magnesium.

    1. What must be the minimum concentration (% by mass) of 1 kg of a potassium hydroxide solution for a complete neutralisation of 3.57 moles of nitric acid?

    A) 5 %, B) 10 %, C) 15 %, D) 20 %, E) 25 %.

    1. How many compounds with the formula \(\ce{C3H9N}\) can exist?

    A) 1, B) 2, C) 3, D) 4, E) 5.

    1. In which of the following compounds has the nitrogen content (in mass %) a maximum value?

    A) potassium nitrate, B) barium nitrate, C) aluminium nitrate, D) lithium nitrate, E) sodium nitrate.

    1. To which carbon atom (indicate the serial number) will chlorine mainly add in the reaction of \(\ce{HCl}\) with penten-2-oic acid?

      A) 1, B) 2, C) 3, D) 4, E) 5.

    2. How many moles of water are there per mole of calcium nitrate in a crystallohydrate if the water content is 30.5 % by mass?

      A) 1, B) 2, C) 3, D) 4, E) 5.

    3. Which of these organic acids is the strongest?

      A) benzoic, B) 2-chlorobenzoic, C) 4-methylbenzoic, D) 2-aminobenzoic, E) 4-bromobenzoic.

    4. Which of these acids has the highest degree of dissociation?

      A) \(\ce{HClO}\), B) \(\ce{HClO2}\), C) \(\ce{HClO3}\), D) \(\ce{HClO4}\), E) all have the same degree.

    5. Which of the salts given below do not undergo hydrolysis?

      A) potassium bromide, B) aluminium sulphate, C) sodium carbonate, D) iron(III) nitrate, E) barium sulphate.

    6. How many litres of air are approximately required for complete combustion of 1 litre of ammonia?

      A) 1, B) 2, C) 3, D) 4, E) 5.

    7. Which element is oxidised in the thermal decomposition of sodium hydrogen carbonate?

      A) sodium, B) hydrogen, C) oxygen, D) carbon, E) none.

    8. Which of the following changes have no effect on the chemical equilibrium in the thermal decomposition of \(\ce{CaCO3}\)?

      A) temperature elevation, B) pressure decrease, C) addition of catalyst, D) a change in the \(\ce{CO2}\) concentration, E) an increase in the amount of the initial substance.

    9. Which of the substances given bellow will be formed at the Pt-anode in the electrolysis of an aqueous solution of aluminium chloride?

      A) aluminium, B) oxygen, C) hydrogen, D) aluminium hydroxide, E) chlorine.

    10. The apparatus shown in the figures is intended for preparing ammonia under laboratory conditions. The test tube being heated contains a mixture of \(\ce{NH4Cl}\) and \(\ce{Ca(OH)2}\). Which of the figures is correct?

    Figure 1
    1. Which of the apparatuses shown in the figures is the best one for the synthesis of bromethane from potassium bromide, concentrated sulphuric acid and ethanol?
    Figure 2
    Figure 3

    Official English text of the problem.

  2. Problem 2: Gravimetric and titrimetric analysis of a Cd-Sn-Bi-Pb alloy

    An alloy comprises the following metals: cadmium, tin, bismuth, and lead. A sample of this alloy weighing 1.2860 g, was treated with a solution of concentrated nitric acid. The individual compound of metal A obtained as a precipitate, was separated, thoroughly washed, dried and calcinated. The mass of the precipitate after the calcination to constant mass, was 0.3265 g.

    An aqueous ammonia solution was added in excess to the solution obtained after separation of the precipitate. A compound of metal B remained in the solution while all the other metals precipitated in the form of sparingly soluble compounds. The solution was first quantitatively separated from the precipitate, and then hydrogen sulphide was passed through the separated solution to saturation. The resulting precipitate containing metal B was separated, washed and dried. The mass of the precipitate was 0.6613 g.

    The precipitate containing the compounds of metals C and D was treated with an excess of a \(\ce{NaOH}\) solution. The solution and the precipitate were then quantitatively separated. A solution of \(\ce{HNO3}\) was added to the alkaline solution to reach pH 5 – 6, and an excess of \(\ce{K2CrO4}\) solution was added to the resulting transparent solution. The yellow precipitate was separated, washed and quantitatively transferred to a beaker. Finally a dilute \(\ce{H2SO4}\) solution and crystalline \(\ce{KI}\) were added. Iodine produced as a result of the reaction was titrated with sodium thiosulphate solution in the presence of starch as an indicator. 18.46 \(\mathrm{cm^3}\) of 0.1512 normal \(\ce{Na2S2O3}\) solution were required.

    The last metal contained in the precipitate as a sparingly soluble compound was transformed to an even less soluble phosphate and its mass was found to be 0.4675 g.

    2.1 Write all equations of the chemical reactions on which the quantitative analysis of the alloy sample is based. Name metals A, B, C, and D. Calculate the mass percentage of the metals in the alloy.

    Official English text of the problem.

  3. Problem 3: Chemical processes in five mixtures of reagents (ionic and organic equations)

    Which chemical processes can take place in the interaction of:

    a) aluminium ammonium sulphate with baryta water,

    b) potassium chromate, ferrous chloride and sulphuric acid,

    c) calcinated soda and sodium hydrogen sulphate,

    d) 4-bromoethyl benzene and chlorine,

    e) n-propyl alcohol, phenol and concentrated sulphuric acid?

    Write ionic equations for the reactions that proceed in aqueous solutions. For the other chemical reactions write complete equations and indicate the type of the reaction. Indicate the differences in the reaction conditions for those reactions that may lead to the formation of various substances.

    Official English text of the problem.

  4. Problem 4: Formula of a nitrogen-hydrogen compound X from its thermal decomposition

    Compound X contains nitrogen and hydrogen. Strong heating of 3.2 g of X leads to its decomposition without the formation of a solid residue. The resulting mixture of gases is partially absorbed by sulphuric acid (the volume of the gaseous mixture decreased by a factor of 2.8). The non-absorbed gas, that is a mixture of hydrogen and nitrogen, occupies under normal conditions a volume of 1.4 dm³ and has a density of 0.786 g dm⁻³.

    Determine the formula of compound X.

    Official English text of the problem.

  5. Problem 5: Structure of a benzene derivative C9H12 from its bromination products

    Benzene derivative X has the empirical formula \(\ce{C9H12}\). Its bromination in the light leads to the formation of two monobromo derivatives in approximately identical yield. Bromination in the dark in the presence of iron also gives two monobromo derivatives. If the reaction is carried out to a higher degree, the formation of four dibromo derivatives may occur.

    Suggest the structure for compound X and for the bromination products. Write schemes for the reactions.

    Official English text of the problem.

  6. Problem 6: Identification of a metal M dissolved in dilute nitric acid

    130 g of an unknown metal M were treated with excess of a dilute nitric acid. Excess hot alkaline solution was added to the resulting solution and 1.12 dm³ of a gas evolved (normal conditions).

    What metal M was dissolved in the nitric solution?

    Official English text of the problem.