Bowen 2005 Ans Key

Bowen Sec Sch 2005 Preliminary Examinations Chemistry (5068) P1 Answers 1. B 2. C 3. D 4. A 5. A 6. B 7. C 8. D 9. A 10. C 11. C 12. A 13. B 14. B 15. C 16. D 17. A 18. C 19. D 20. D 21. C 22. B 23. A 24. D 25. B 26. C 27. A 28. D 29. C 30. C 31. B 32. B 33. B 34. B 35. D 36. A 37. C 38. D 39. B 40. C

PRELIM EXAM 2005 Paper 2 CHEMISTRY 5068/2 ANSWER KEY SECTION A Qn No

Part

A1

a

lithium oxide

1

b

carbon monoxide

1

c

sulphur trioxide

1

d

aluminium oxide

1

e

vanadium (V) oxide

1

f

Sulphur dioxide, carbon dioxide or sulphur trioxide

1

a

Ionic bonding with cation and anion correctly shown Stable octet clearly indicated (Do not read further if ionic bonding is not indicated.)

1

b

Covalent bonding clearly shown Electrons correctly shared between Cl and O (Do not read further if covalent bonding is not indicated.)

1 1

c

SiO2 - giant molecular structure P4O6 – simple molecular structure More energy needed to break the network of bonds in SiO2 than the bonds in P4O6

1 1 1

a

Burette or pipette

1

b

It is a catalyst.

1

c

A colourless solution of sodium chloride and a black precipitate of manganese (IV) oxide

1

A2

A3

Su bp art

Answer

Marks

1

d

i

ii A4

1 1

O2 is soluble in water.

1

a

Fractional distillation of liquid air

1

b

Catalytic cracking of petroleum

1

c

There would be more collisions between the particles. This would increase the speed of the reaction

1

d

e

A5

No of moles of NaClO3 used = (20*0.1)/1000 = 0.002 Number of moles of O2 expected = (0.002*3)/2 = 0.003 Volume of O2 = 0.003*24 = 0.0 72 dm3

NH4NO3 : (28/80)*100 (NH4)2SO4 : (28/132)*100 (NH2)2CO : (28/60)*100 Urea has the most nitrogen per kilogram

1

1 1

i

Addition polymerisation There is a carbon to carbon double bond in the monomer or it is unsaturated.

1 1

ii

Polyacrylonitrile

1

iii

Structural formula of polyacrylonitrile with C-C bonds

1

a

H – F bond Its bond energy is the highest.

1 1

b

H2 + F2  2HF

1

Enthalpy change = 436 + 158 – 2(565) = - 536 kJmol-1 (No marks if sign is not shown)

1

c

Exothermic

1

The breaking of the H2 and F2 bonds is endothermic. The forming of the HF bonds is exothermic. However, as the bond energy for 2 mols of HF bonds is greater than the total bond energy for 1 mol of H2 and 1 mol F2 bonds, the overall reaction is exothermic. A6

A7

1

1

a

Copper, nickel, iron, zinc, scandium

1

b

Pink deposit of copper Blue solution changes to colourless

1 1

c

Zn + Cu2+  Zn2+ + Cu

1

d

2Sc + 3PbO  Sc2O3 + 3Pb

1

e

Nickel is extracted by roasting with a reducing agent Scandium is extracted by electrolysis

1

a

CH3COOH

1

b

C2H5OH or CH3COOH

1

c

C3H6 and C7H14

1

d

CH3COOH and C2H5OH

1

e

C3H6 or C7H14

1

f

C2H5OH

1

1

Total = 50 marks

SECTION B Qn No

Part

Sub Part

Answer

Marks

B1

a

b

c

d e

B2

a

% of O2 in air = 20 % Volume of O2 in 10 dm3 of air = 2 dm3 Volume of O2 in exhaust gases = (9/100) * 10 = 0.9 dm3 Volume of O2 reacted with gasoline = 2 – 0.9 = 1.1 dm3

1 1

Nitrogen is unreactive and passes through the car engine unchanged. Carbon dioxide and water are products of the combustion of gasoline.

1

Carbon dioxide Global warming could result in the melting of the polar ice caps, rising sea levels and increased flooding. The temperature in the car engine is high. The surface area of the converter is large.

1

Carbon monoxide is converted into carbon dioxide Hence, a reduction in CO but an increase in CO2 Nitrogen oxides are converted into nitrogen and oxygen Hence, a reduction in oxides of nitrogen but an increase in N2 Unburnt hydrocarbons react with the oxygen above to produce carbon dioxide and water Hence, a reduction in unburnt hydrocarbons but an increase in H2O while O2 remains constant. (Full mark of 1 only if all the data is referred to) 2CO + O2  2CO2 2NO  N2 + O2 2C8H18 + 25O2  16CO2 + 18H2O (Full mark of 1 for any 2 equations) The hot oxygen evolved burns away the carbon anodes C + O2  CO2

`

1

1 1 1

1

1

1 1

b

The melting point of bauxite is over 2000oC. The addition of cryolite reduces its melting point to well below 1000oC.

1 1

c

Labelled diagram of electrolytic cell with complete circuit

1 1

Cathode is nickel and anode is silver

d

B3

At the anode: Ag (s)  Ag+(aq) + e-

1

At the cathode: Ag+(aq) + e-  Ag (s)

1

e

A is sodium sulphate B is sodium chloride

1 1

a

The 2 monomers are H2N - COOH

-NH2 and HOOC -

1,1 1

The 2 monomers join and eliminate a water molecule. Both nylon and protein are polyamides. They both contain amide linkages. However, proteins are made up of amino acid units with -COOH and -NH2 in their molecules while nylons are made up of diamine H2N-NH2 and dicarboxylic HOOC- _- - -COOH molecules.

b

c

i

Heat with dilute hydrochloric acid.

ii

A chromatogram is spotted with proline and lysine. The paper is left for some time to dry and then sprayed with ninhydrin to make the amino acids visible.

1 1

1,1 1 1 1

Scientific diagram should include appropriate apparatus and labels. B4

a

b

c

C4H9COOH

1

Mr = 102

1

The data provided does not show a consistent decrease in the melting points while they do show a consistent increase with the boiling points. Accept any correctly drawn isomer of propanoic acid

1

1

d Element Mass/Ar C 0.060/12 H 0.010/1 O 0.160/16 Empirical formula is CH2O2 e

Molar Ratio 0.005 0.010 0.010

Magnesium ethanoate and water 2CH3COOH + MgO  (CH3COO)2Mg + H2O

f

Preparation - Equal volumes of ethanol and ethanoic acid are placed in a boiling tube. The boiling tube is swirled to ensure that the liquids are thoroughly mixed. A few drops of concentrated sulphuric acid are added to act as a catalyst. The mixture is heated in a water bath. Collection - The mixture is poured into a beaker containing 5% sodium hydrogencarbonate solution. The ester ethyl ethanoate floats while the unreacted acid dissolves in the solution.

1

1 1 1

1

1

(Award no marks if any step is missing in the preparation or collection respectively) T otal = 30 marks

BOWEN SECONDARY SCHOOL

MARK SCHEME Paper 3 Preliminary Examination 2005 5152/03 SCIENCE (CHEMISTRY) Level: O-level

Setter: Ng Wah Kian

Question

Answer

1 (a)(i) Isotopes are atoms of the same element with different numbers of neutrons.

Marks

1

(ii) 17 electrons 17 protons 20 neutrons

1 1 1

(b) Correct number of valence electrons in each ion. Correct charge for each ion.

1 1

(c) In solid state, ions cannot move freely as they are held together in giant crystal lattice. In liquid state, ions can move freely to carry electricity.

1 1

(d) The colourless solution turns reddish brown.

1

(e) Added to swimming pool for killing bacteria.

1

2 (a)(i) Hydrogen

1

(ii) Calcium sulphate

1

(b) H2 CaSO4

1 1

(c) 70 cm3

1

(d)(i) Data correctly plotted and smooth curve.

1

(ii) 50 cm3 (acceptable range: 49 – 51 cm3)

1

3 (a)(i) 25.2 g

1

(ii)

(iii)

(b)(i)

25.2 18 = 1.4 mol

1 1

24 24 + 32 + 16 × 4 = 0.2 mol

1 1

1.4 0.2 = 7 mol

1 1

(ii) 7

1

4 (a) Ethanol Correct structural formulae showing all the bonds

1 3

(b)(i) C9H8O4

1

(ii) Circle —COOH

1

(iii) Carboxylic acid

1

5 (a) A: hydrogen gas B: water C: anhydrous copper(II) sulphate E: iron(II) sulphate F: copper

1 1 1 1 1

(b) The blue precipitate dissolves to form deep blue solution.

1

(c) Displacement reaction

1

6 (a) R, P, Q, S. (one letter correct – 1 mark; two letters correct – 2 marks)

3

(b)(i) Coke (or carbon) Limestone (or calcium carbonate) (ii) Air 7 (a)(i) Bromine water decolourise.

1 1 1

1

(ii) Colour of mixture changes from orange to green.

1

(iii) Amide link or peptide link Natural polymer: proteins Synthetic polymer: nylon

1 1 1

(iv) Eat some vinegar, milk or oil. (Accept any edible organic solvent)

1

(b)(i) Polytetrafluoroethene (or teflon or PTFE) Correct full structural formula of tetrafluoroethene showing all bonds Correct full structural formula of PTFE showing all bonds

1 1 1

(ii) Non-stick saucepans or bridge bearings

1

8 (a) A reaction where energy is given out to the surroundings.

1

(i) 2Mg + O2 → 2MgO Correct reactants and products Correctly balanced

1 1

(ii) 2H2 + O2 → 2H2O Correct reactants and products Correctly balanced

1 1

(b) Any two of the followings: Increase concentration of reactants Increase pressure of gaseous reactants Decrease the particle size of the reactants Increase the temperature of the reactants Use of catalysts

2

Correct explanation for the two methods listed.

2

(c) Cl2

1

9 (a) Any two of the followings: sulphur dioxide, carbon monoxide, oxides of nitrogen, ozone or hydrocarbon.

2

(i) Correct sources of the two pollutant gases.

2

(ii) Correct effects of the two pollutant gases.

2

(b)(i) Fractional distillation

1

(ii) Correct drawing Correct labels

1 1

(iii) Test if the boiling or melting point is exact.

1