8th CHEMISTRY OLYMPIAD OF THE BALTIC STATES
RIGA, MAY 35, 2000
Compound X is colored and burning. By burning 2,12 g of it arises 0,752 g of green solid compound with
very high melting temperature. Gases arising in this process were led through the excess of limewater.
There was obtained 6,838 g of white precipitate, which dissolves in hydrochloric acid. When H 2O2 is added
to limewater, the mass of the precipitate is 7,551 g, and in the hydrochloric acid dissolves only 19,7% (by
mass) of the precipitate. Relative density of the arised gas against the air is 1,52.
What is compound X.
Write the balanced chemical equations of all reactions described in this problem.
What you mean about the color of the compound X?
To 10,00 mg of metal A was added 10 mL of water. A stream of chlorine was passed through the water,
until A had dissolved completely and an equilibrium had established. The solution thus obtained was
evaporated in vacuum to leave 20,91 mg of yellow crystals of a strong acid B.
Acid B obtained in the first reaction was dissolved in water and neutralized exactly with 22,53 mL of alkali
with concentration 2,253 mM. The essentially colourless solution was diluted to 100 mL, and a reducing
agent was added. The solution turned bright red. Addition of any salts causes the solution gradually turn
blue. On standing, the blue solution very slowly deposits 10,00 mg of metal A and becomes colourless once
a) Draw and explain the spatial structure of the anion of acid B.
b) Write all reaction equations. What kinds of compounds are best suited to reduce B and obtain the red
solution? What would be observed, if the neutralized solution of B would not be diluted prior to
reduction? Explain the role of salts in the colour change of the solution.
Solutions of alkali metal salts of B are slightly acidic. Acidity decreases considerably, if excess chloride is
present. Explain this finding and calculate the relevant equilibrium constant.
n(B) n(NaCl) Vsol. pH
1,00 mmol 1000 mL 3,17
1,00 mmol 10,0 mmol 1000 mL 3,57
Three compounds A, B and C all have the formula C6H10. All three compounds rapidly decolorise bromine
in CCl4. Compound A gives a precipitate when treated with silver nitrate in ammonia, but compounds B
and C do not. Compounds A and B both yield compound C6H14 when they are treated with excess
hydrogen in the presence platinum catalyst. Under these conditions C absorbs only 1 mol of hydrogen per 1
mol of C and gives the product with the formula C6H12. When A is oxidised with hot potassium
permanganate and the resulting solution acidified, the only organic compound that can be isolated is
npentanoic acid. Similar oxidation of B gives only propanoic acid, and similar treatment of C gives only
1) Give the structure of compouns A, B and C.
2) Write balanced equations of reactions.
3) Give the stereochemical formula of compound, which is produced in the reaction of C with bromine.
Write the mechanism of the reaction.
Novocaine is used as a local anaesthetic. It is commonly obtained from the toluene:
(1 singlet and 2 doublets in the 1HKMR spectrum)
(1 singlet and 2 doublets in the 1HKMR spectrum)
(2 doublets, 1 triplet and 1 quartet in the 1HKMR spectrum)
(1 singlet, 2 doublets, 1 triplet and 1 quartet in the 1HKMR spectrum)
Write all reaction equations. Write a mechanism for the last reaction in the presence of a catalytic amount
of an alcoxide. Outline the 1HKMR spectrum of Novocaine. Name the principal bands in its IR spectrum.
A test reaction for Novocaine includes successive treatment of the sample with an acidified solution of
sodium nitrite and 2naphtol. The reaction is positive, if a highly coloured precipitate is formed. Write the
The Voltaic cell is made up of two half-cells consisting of hydrogen electrodes. One of them is immersed in
100 cm3 of 0,1 M HCl aqueous solution, the second one in 100 cm3 CH3COOH aqueous solution. The
hydrogen pressure over solutions is 1 atm, temperature 20 oC, F = 96485 C mol1, R = 8.314 J mol1 K1,
Ka = 1.75·10-5.
a) EMF of Voltaic cell under given conditions,
b) EMF of Voltaic cell when 60 cm3 of 0,1 M NaOH solution was added to both initial solutions,
c) EMF of Voltaic cell when both initial solutions were diluted 10 times,
d) What volume (in cm3) of 0.1 M NaOH solution should be added to the initial CH3COOH solution to
obtain EMF = 0.150 V?
38 Sr is one of the most common nuclear waste produced from nuclear reactors. The spontaneous
radioactive decay of this isotope can be described with following equations:
(1) 38 Sr = 3990Y + -10e
(2) 39 Y = 4090Zr + -10e (t1/2 = 64 hours).
For a sample of 38 Sr containing 2.64.1010 atoms the absolute disintegration rate was measured as 1238
disintegrations per minute. The final Zr isotope is stable.
a) Calculate the amount of energy in kJ, which is released during one year if we started with one mole of
b) What is the ratio of masses of charcoal and 3890Sr giving this amount of energy?
m(3890Sr) = 89,907738 amu; m(3990Y) = 89,907152 amu;
m(4090Zr) = 89,904703 amu; m(-10e) = 5,4857.10-4 amu;
Heat of combustion for charcoal is 23 000 kJ kg1.