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43rd International Chemistry Olympiad

Practical Tasks Answer Sheets Grading
12 July 2011 Ankara, Turkey

43rd IChO Practical Tasks Answer Sheets, Official English version


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Task 1
A 16 B 16 1 2

12% of the total

Analysis of Chloride Mixtures
2 2 3 6 Task 1 42 x% 12

A. Determination of total chloride by Fajans Method

Exact concentration of AgNO3 in standard solution = 0.09968 mol/L

Volume of standard AgNO3 solution used V= mL, Volume of AgNO
3

15 points Unk Unk Unk Unk no no no no w w w w n n n n 1 2 3 4

pnts = -27.27 (|V-V

true|

) + 19.09

Vtrue 18.0 20.0 22.0 24.0

(mL) 0 0 0 0

0 pnts -0.7 mL -0.15 mL 0 +0.15 mL
ue

0 pnts +0.7 mL

V-Vtr

1 point is for correct number of significant figures from reading volumes.

(15 +1 points)

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B. Determination of Mg
2+

Code:
by direct titration with EDTA
mol/L

Exact concentration of EDTA in standard solution = 0.01019

Volume of standard EDTA solution used V= mL 15 points

Volume of EDTA

pnts = -15 (|V-V

true|)

+ 18.75

Unkno Unkno Unkno Unkno

wn wn wn wn

1 2 3 4

Vtrue (mL) 24.00 22.00 20.00 18.00

0 pnts -2.25 mL
-0.25 mL 0 +0.25 mL
ue

0 pnts +1.25 mL

V-Vtr

1 point is for correct number of significant figures from reading volumes.

(15+1 points)

Treatment of Data 1.
Total amount of Cl- ion in 100.0 mL unknown solution = Unk Unk Unk Unk nown nown nown nown 1 2 3 4 17. 19. 21. 23. 94 94 93 92 mmol (2 pt, within ±10%)

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2.
Total amount of Mg
2+

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ion in 100.0 mL unknown solution = Unk Unk Unk Unk nown nown nown nown 1 2 3 4

mmol (2 pt, within ±10%) 0.9782 0.8967 0.8152 0.7337

3. For MgCl2 =
Unk Unk Unk Unk nown nown nown nown 1 2 3 4 0. 0. 0. 0.

g/100 mL
09313 08537 07762 06986

(2 pt, within ±10%)

For NaCl =
Unk Unk Unk Unk nown nown nown nown 1 2 3 4

g/100 mL
0.9341 1.061 1.186 1.312

(4 pt, within ±10%)

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Task 2
A 1 3 2 1 1 12 2 2

12% of the total
B 3 i 2 ii 2 4 2 24 12 Task 2 x%

Hydrogen generation from ammonia borane
Part A. Reaction of ammonia borane in the absence of catalyst
1. The gas volume versus time data and the graph for the reaction of ammonia borane in the absence of catalyst Time (min) 0 1 2 3 4 5 6 7 8 9 10 Vgas (mL)

Part A. 4 in the absence of catalyst (mL)

(3 points) 1 point for the graph If the volume of gas produced stays within the range of 0-2 mL 2 points >2 mL 1 points >3 mL 0 points 43rd IChO Practical Tasks Answer Sheets, Official English version 4


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2. Report the volume of gas evolved, V
uncatalyzed.

Code:

V

uncatalyzed

=

0

mL

(1 point)

Part B. Reaction of ammonia borane in the presence of catalyst
1. The gas volume versus time data and the graph for the reaction of ammonia borane in the presence of catalyst Time (min) Vgas (mL) Part B. Gas volume versus time graph in the presence of catalyst

0 1 2 3 4 5 6 7 8 9 10

0 17 31 45 57 68 73 73 73 73

(12 points)

6 points for Vm 6 points for rate
measured

easured

> 0.92 Vmax, Points for volume = 30 (Vm
max

easured

- 0.8Vmax)/V

max ax

> 0.92 rate

, Points for rate = 30 (rate

measured

- 0.8ratemax)/ratem

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°C. The atmospheric pressure is 690 torr.

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2. Calculate the maximum number of moles and the maximum volume (mL) of hydrogen gas which will be evolved theoretically from the hydrolysis of 29.5 mg ammonia borane with a purity of 97% w/w at 25

V(H2)

max

=

mL

(2 points)

3. Calculate the rate of hydrogen generation in your experiment. i) in mL H2/ min

Rate =

mL H2·min

-1

(2 points)

ii) in mmol H2/ min by assuming that the temperature is 25 °C. The atmospheric pressure is 690 torr.

Rate =

mmol H2·min

-1

(2 points)

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4. purity of potassium tetrachloropalladate(II) is 98% w/w.

Code:

Calculate the rate of hydrogen production per mole of palladium in (mol H2)·(mol Pd)-1·(min)-1. The

The rate of hydrogen production per mole of palladium =

mol H2·(mol Pd)-1·min

-1

(2 points)

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Task 3
1 5 2 6

16% of the total
3 3 4 i 12 ii 12 38 16 Task 3 X%

Synthesis, purification and separation of a diastereomeric mixture
1. Copy (sketch) the TLC1 plate in bag "TLC1" on your answer sheet.

TLC1 1) For the appearance of three spots loaded on the base line, 1 point. 2) For the well developed and separated spots on the TLC. 2 points 3) For the solvent front line and the base line 1 point 4) For the accurate representation of the sketch of the TLC plate. 1 point

5 points

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2. Copy (sketch) the TLC2 plate in bag "TLC2" on your answer sheet.

Code:

TLC2 1) For the appearance of three spots loaded on the base line. 1 point. 2) For the well developed and separated spots on the TLC. 2 points 3) For the solvent front line and the base line 1 point 4) For the accurate representation of the sketch of the TLC plate. 1 point 5) For the absence of fraction B in fraction A and vice versa. 1 point

6 points
3. Determine and record the Rf values of the spots on the TLC2 plate in bag " TLC2."

Spots Fraction A Fraction B Starting material (SM)

Rf value

0.40-0.50 0.20-0.30 0.65-0.75

3 points

4. Measure and record the volume and absorbance values for fraction A and fraction B.

Sample Fraction A
Fraction B

Volume mL 3 points
mL 3 points

Absorbance
3 points 3 points

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If If If If If

20.0 20.0 30.0 45.0 55.0

mL volume 0.0 point mL volume < 30.0 mL, 0.0-3.0 points mL volume < 45.0 mL, 3.0 points volume < 55.0 mL, 3.0-0.0 points volume 0.0 points

If If If If If

80.0 mL volume 0.0 points 80.0 mL < volume 100.0 mL, 0.0-3.0 points 100.0 volume < 140.0 mL, 3.0 points 140.0 volume < 150.0 mL, 3.0-0.0 points volume 150.0 mL, 0.0 points

If If If If If

absorbance < 0.30, 0 points 0,30 absorbance < 0.40, 0-3 point 0,40 absorbance < 0.60, 3.0 points 0,60 absorbance < 0.70, 3-0 points absorbance 0.75, 0 points

If If If If If

absorbance < 0.45, 0 points 0.45 absorbance < 0.55, 0-3 point 0.55 absorbance < 0.70, 3.0 points 0,70 absorbance < 0.80, 3.0-0.0 points absorbance 0.8, 0.0 points

If If If If If

%yie 35.0 45.0 53.0 %yie

ld ld

< % % %

35, 0.0 points yield < 45.0, 0-6 points yield < 53.0, 6 points yield < 56.0, 6-0 points 56, 0 points

If If If If If

%yie 23.0 33.0 41.0 %yie

ld ld

< % % %

23, 0.0 points yield < 33.0, 0-6 points yield < 41.0, 6 points yield < 44, 6-0 points 45, 0 point

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