Съдържание

Recommendations Условие Constants Решение

IOM 2018, Теория — Задача 1. Inorganic puzzle

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Всички материали от IOM 2018

3rd Olympiad of Metropolises — Chemistry, Theoretical Problems, Official English version · 5 септември 2018 г.

Original cover

Country ______

Participant code ______

3rd Olympiad of Metropolises

Chemistry

Theoretical Problems

September 5, 2018

Moscow, Russia

Chemistry. Theoretical problems. Official English version

Указания

Begin only when the START command is given. You have 4 hours to work on the problems.
Use only the pen and calculator provided.
All results must be written in the appropriate boxes within the text. Anything written elsewhere will not be graded. Use the reverse of the problem pages if you need scratch paper.
Write relevant calculations in the appropriate boxes when necessary. If you provide only correct end results for complicated questions, you will receive no score.
Raise your hand if you have any questions concerning the text of the problems.
Raise your hand if you need a restroom break.
The official English version of this examination is available on request only for clarification.

Recommendations

Read the text carefully. Try to understand properly: a) what is given to you, b) what is required from you.
All the problems contain questions of various complexity including very simple ones. Try to answer as many questions as you can. Try to leave as few empty spaces in the answer sheets as you can.
In the calculations, use the atomic masses from the Periodic table given to you.

Good luck!

Original key cover

3rd Olympiad of Metropolises

Chemistry

Theoretical Problems

Answers, solutions, and grading scheme

September5,2018

Moscow,Russia

Chemistry. Theoretical problems. Official English version

Условие

Constants

Constants	Value
Avogadro constant:	$N_\mathrm A=6.022\cdot10^{23}\ \mathrm{mol^{-1}}$
Gas constant:	$R=8.314\ \mathrm{J\ K^{-1}\ mol^{-1}}$
Zero of the Celsius scale:	$273.15\ \mathrm K$

Consider all gases ideal.

Periodic table with relative atomic masses

Complete native periodic table with all relative atomic masses, group numbers, lanthanides and actinides.

Problem 1. Inorganic puzzle (12 marks)

Question	1	2	3	4	5	6	7	Total
Points	20	10	10	5	5	5	10	65
Result

Mineral X₁ is a binary compound formed by two elements X and Y with mass ratio $\mathrm{X/Y}\approx2/1$ . Upon heating on air X₁ turns into a black powder X₂ and a colorless gas Y₂, which is able to decolor a solution of potassium permanganate. The crystal structure of X₁ contains two different anions in equal amounts and two cations with different coordination numbers.

1 Write the chemical formula of X₁, explain its ionic composition by writing the formulas of all ions, and write down the balanced equations of the reactions described.

X₁ – ______

Ionic composition of X₁ – ______

Reactions: ______ [20 т.]

In the lab, the compound X₁ can be prepared by passing the gas Y₃ through the solution of the salt X₃ formed by the element X. This salt gives a white precipitate with an acidified solution of barium chloride.

2 Write a balanced equation and specify the oxidizer and the reducing agent.

Reaction: ______

Oxidizer: ______

Reducing agent: ______ [10 т.]

3 The simultaneous passing of gases Y₂ and Y₃ through the sodium hydroxide solution gives only one main product Y₄, containing element Y. Write a balanced equation of this reaction.

Reaction: ______ [10 т.]

4 Under cooling of the solution of Y₄ the precipitate Y₅ (25.8 wt.% of element Y) is formed. Determine the formula of Y₅.

Calculation

Y₅ – ______ [5 т.]

The simultaneous passing of gases Y₂ and Y₃ through water leads to a colloidal solution of element Y. In addition to Y, this solution contains various types of anions.

5 Draw the structure of one of the anions, Y₆, from this solution taking into account that Y₆ can be produced by the reaction between a solution of Y₄ and elemental iodine.

Structure of anion Y₆: ______ [5 т.]

6 The addition of a large amount of aqueous solution of Y₄ to an aqueous solution of X₃ results in the gradual discoloration of a solution and precipitation of X₁. Write the balanced equation of this reaction.

Reaction: ______ [5 т.]

7 From the solution prepared after dissolving of X₁ in 10 M nitric acid the blue crystals of X₇ (25.5 wt.% of element X) are formed. Determine the formula of X₇ and write the reaction equation.

Calculation

X₇ – ______

Reaction: ______ [10 т.]

Решение

Official answers and grading scheme

1 $\mathrm{X_1}$ – $\mathrm{CuS}$ : 5 pts.

Ionic composition of $\mathrm{X_1}$ – $\mathrm{(Cu^+)_2Cu^{2+}S^{2-}(S_2)^{2-}}$ : 5 pts.

Reactions:

\mathrm{2CuS+3O_2=2CuO+2SO_2}

5 pts.

\mathrm{5SO_2+2KMnO_4+2H_2O=K_2SO_4+2MnSO_4+2H_2SO_4}

5 pts.

( $\mathrm{X_2}$ – CuO, $\mathrm{Y_2}$ – $\mathrm{SO_2}$ ) [20 т.]

2 Reaction:

\mathrm{CuSO_4+H_2S=CuS+Na_2SO_4}

( $\mathrm{Y_3}$ – $\mathrm{H_2S}$ , $\mathrm{X_3}$ – $\mathrm{CuSO_4}$ ): 5 pts.

Oxidizer: $\mathrm{Cu^{2+}}$ ( $\mathrm{Cu^{2+}+e\to Cu^+}$ ): 2.5 pts.

Reducing agent: $\mathrm{S^{2-}}$ ( $\mathrm{2S^{2-}-2e\to S_2^{2-}}$ ): 2.5 pts. [10 т.]

3 Reaction:

\mathrm{6NaOH+4SO_2+2H_2S=3Na_2S_2O_3+5H_2O}

5 pts.

( $\mathrm{Y_4}$ – $\mathrm{Na_2S_2O_3}$ ) [5 т.]

4 Calculation. $\mathrm{Y_5}$ – $\mathrm{Na_2S_2O_3\mathord\cdot nH_2O}$ .

\omega(\mathrm S)=\frac{2\cdot32.06}{2\cdot22.99+2\cdot32.06+3\cdot16+n\cdot18.02}=0.258

$n=5$ .

$\mathrm{Y_5}$ – $\mathrm{Na_2S_2O_3\mathord\cdot5H_2O}$ : 5 pts.

(0 pts if the answer is given without any calculations) [5 т.]

5 Structure of anion $\mathrm{Y_6}$ :

Native Y6 sulfur-chain dianion, complete oxygen double bonds, sulfur chain and terminal negative charges

5 pts. [5 т.]

6 Reaction:

\mathrm{CuSO_4+Na_2S_2O_3+H_2O=CuS}\downarrow\mathrm{+Na_2SO_4+H_2SO_4}

5 pts. [5 т.]

7 Calculation. $M(\mathrm{X_7})=63.55/0.255=249.2\ \mathrm{g/mol}$ .

$\mathrm{X_7}$ – $\mathrm{CuSO_4\mathord\cdot5H_2O}$ : 5 pts.

Reaction:

\mathrm{CuS+8HNO_3=CuSO_4+8NO_2+4H_2O}

5 pts. [10 т.]

Бележка от източника

Each native problem heading says 12 marks, while its printed score grid totals 65, 30, 18, 50 or 30. Problem1 request3 is 10 points in the grid but5 in the key; its printed permanganate equation and sodium-containing answer to request2 remain literal. Problem3 first Claus-stage equation prints2H2O. Problem4 requests Fischer projections A–C and Haworth D–G, while its key shows the opposite projection types; request2 awards2points for each of three structures despite its4-point grid. Problem5 methane price is0.75 $/kg in the question and0.70$ /kg in the repeated key request and calculations. These original inconsistencies are retained. Molecular drawings, reaction schemes, reference tables and answer grids reproduce the native originals. Empty calculation spaces retain their printed labels and blank response fields.

Оригинал в Архива: Problems.pdf · официални решения: Solutions.pdf