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38th INTERNATIONAL CHEMISTRY OLYMPIAD UK Round One - 2006 MARKING SCHEME

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(1)

UK Round One - 2006

MARKING SCHEME

Notes

Chemical equations may be given as sensible multiples of those given here.

State symbols do not need to be included in the chemical equations to obtain the mark(s).

Answers should be given to an appropriate number of significant figures although the marker should only penalise this once.

Total 78 marks.

Question 1

Answer Marks

(a) C12H22O11 + 12O2 12CO2 + 11H2O 1

(b) Allow 110 kJ or 111kJ (rounded to 3 sig fig) 1

(c) 95 sweets [Allow ecf from (b)] 1

(d) Mass of sodium hydrogencarbonate = 0.0210g Mass of tartaric acid = 0.0188g

1 1

(e)

2 marks for all 3 structures shown correctly. 1 further mark for enantiomers correctly identified.

C C

HO2C CO2H

H OH

HO H

---

C C

HO2C CO2H

HO H

H OH

C C

HO2C CO2H

HO OH

H H

enantiomers

3

(f) None 1

9 marks

(2)

Question 2

Answer Marks

(a) C8H18 + 12½O2 8CO2 + 9H2O 1

i) CO + ½O2 CO2

(b)

ii) CO + H2O CO2 + H2

1 for both equations

correct i) NO + CO ½N2 + CO2

(c)

ii) NO + H2 ½N2 + H2O

1 for both equations

correct

(d) Ce2O3 + ½O2 2CeO2 1

(e) C + 2NO2 CO2 + 2NO 1

(f)

1 mark for structure shown correctly. 1 mark for both bond angles correct.

O C

N

N H

H

H

H

120-123o

107-120o

2

(g) CO(NH2)2 + H2O CO2 + 2NH3 1

(h) i) 2NH3 + 3NO 2½ N2 + 3H2O 1

ii) 4NH3 + 3NO2 3½ N2 + 6H2O 1

(i)

Award marks here provided that candidates have a minimum of 5 of the 8 equations correct. Allow 4 marks for all 8 redox changes correct, 3 marks for 7, 2 marks for 6 and 1 mark for 5 redox changes correct.

See underlining (b), (c), (d), (e) and (h) above

4

14 marks

(3)

(a) CH3COCl + H2O CH3COOH + HCl 1

(b) CH3CH2COCl + CH3CH2OH CH3CH2COOCH2CH3 + HCl 1

(c)

1

(d)

1 mark for each structure with correct shape indicated.

1 mark for both oxidation states correct.

Tetrahedral Pyramidal P = +5 S = +4

3

(e) SOCl2 + H2O SO2 + 2HCl

SOCl2 + 2H2O H2SO3 + 2HCl [allow either answer]

1

(f) i)

1

ii)

1

(g)

5H3PO4 + POCl3 3H4P2O7 + 3HCl

2

11 marks S

O

Cl P Cl

O

Cl

Cl Cl

O

P Cl Cl

OCH3

O

P Cl OCH3

OCH3

O

P O HO P

HO

O

OH OH

O C O

Cl

(4)

Question 4

Answer Marks

(a)

A: CuSO4.3H2O B: CuSO4.H2O C: CuSO4

1 1 1

(b) E: CuO

F: Cu2O

2CuO Cu2O + ½O2

1 1 1

(c) D: Cu2SO5 1

7 marks Question 5

Answer Marks

(a) NaClO3 NaCl + 1½O2 1

i) BaO2 + Cl2 BaCl2 + O2 1

(b)

ii) BaO2 + 2HClO BaCl2 + 1½O2 + H2O 1

(c) 15dm3 1

(d) Allow 117g or178g 1

(e) i) ii) iii)

2 marks for all 3 oxidation states correct. 1 mark for 2 correct -2

-1 -

½

2

(f) i) 2KO2 + H2O 2KOH + 1½O2 1

ii) 2KOH + CO2 K2CO3 + H2O [Allow also KOH + CO2

KHCO

3

]

1

9 marks

(5)

Answer Marks (a)

Allow 1 mark for each correct structure. Give credit where the candidate has identified the relevant part of the structure correctly – do not deduct marks for trivial errors in copying the remainder of the molecule.

N N O

O H3C

B

N N O

OH H3C

NO2

D

N N O

Cl H3C

NO2

E

N N O

NH2 H3C

NO2

F

N N O

NH2 H3C

NH2

G

N N H3C

N N

O

H O

I

N N H3C

N N

O

H

S Cl

O O O

J

7

(6)

Question 6 continued

Answer Marks

(b) i) HCl(aq) 1

ii) NH3 1

(c)

N N O

H2N H3C

O NH

H

O

1

(d)

H N

N CH3

1

(e) i)

N N H

H

H

H

allow any diagram showing correct structure

1

ii)

O

O

O

O

1

13 marks

(7)

(a)

C35Cl2F2

+ = 120 C35Cl3 7ClF2

+ = 122 C37Cl2F2

+ = 124 ratio 9 : 6 : 1

1 1

(b)

1 mark for peaks at correct masses , 1 mark for correct relative intensities and 1 mark for the formulae of the ions indicated correctly (allow mark if

‘+’ sign omitted - as here).

3

(c)

ratio 1 : 2 : 3 : 4 : 3 : 2 : 1 1

(d)

Common name Structural formula

Number of different fluorine environments

A CFC-113 Cl

2

FC-CClF

2

2

B CFC-113a Cl

3

C-CF

3

1

C HFC-134a F

3

C-CH

2

F 2

D CFC-11 (Freon-11, R-

11) CCl

3

F 1

E CFC-12 (Freon-12, R-

12) CCl

2

F

2

1

F CFC-13 CClF

3

1

G Halon 1211 CBrClF

2

1

3 marks for all 7 correct, 2 marks for 6 correct, 1 mark for

5 correct

(8)

Question 7 continued Marks

(e)

1 mark for structure showing -CF3 group. 1 mark for mirror images shown correctly.

Br

F3C H Cl

Br

CF3 H

Cl

2

(f)

Common name Structural formula

Expected intensity ratio

A CFC-113 Cl

2

FC-CClF

2

1 : 2

B CFC-113a Cl

3

C-CF

3

C HFC-134a F

3

C-CH

2

F 3 : 1

D CFC-11 (Freon-11, R-

11) CCl

3

F

E CFC-12 (Freon-12, R-

12) CCl

2

F

2

F CFC-13 CClF

3

G Halon 1211 CBrClF

2

2

(g)

F Cl

Cl F

Cl F

X

Y

Allow 1 mark for the correct structure and 1 mark for correct identification of fluorines.

2

15 marks

Riferimenti

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