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2002 HKCEE Chemistry Paper I Marking Scheme
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Transcript of 2002 HKCEE Chemistry Paper I Marking Scheme
2002 - CE-CHEM p.1
2002 HKCEE Chemistry paper I marking scheme Marks
(1)
(a) Nitrogen is required for the formation of amino acids / proteins / chlorophyll /
chloroplast.
1
(b) Nitrogen, hydrogen, phosphorus and oxygen
or
N, H, P and O
1 / 0
(c)(i) Formula mass of (NH4)2SO4 = (14+4) × 2 + 32 + 16×4 = 132
% by mass of N = %100132
214×
× = 21.2 % (Accept 21, 21.2 and 21.21 )
1
1
(ii) Calcium hydroxide / calcium oxide / calcium carbonate
( slaked lime / lime water / quick lime / limestone / marble / calcite )
1
Calcium hydroxide / calcium oxide / calcium carbonate reacts with H+ in soil
( neutralizes acid in soil )
or
Ca(OH)2 / CaO / CaCO3 is not very soluble in water. It will not make the soil too
alkaline.
or
Ammonia solution / NH3(aq)
Ammonia reacts with H+ in soil ( neutralizes acid in soil )
or
Ammonia is a weak alkali. It will not increase the soil pH to a great extent .
1
(1)
(1)
6 marks
(2) (a) Magnesium burns with a brilliant flame / white or bright light.
A white solid (MgO) or a yellow solid (Mg 3N 2) is formed.
2 Mg + O2 à 2 MgO ( white )
or 3 Mg + N2 à Mg3N2 ( yellow )
1
(1)
1
(1)
(b) The colour of the potassium permanganate solution changes from purple to yellow
5 Fe2+ + MnO4− + 8 H+ à 5 Fe3+ + Mn2+ + 4 H2O
10 FeSO4 + 2 KMnO4 + 8 H2SO4 à 5 Fe2(SO4)3 + 2 MnSO4 + K2SO4 + 8 H2O
1
1
(1)
2002 - CE-CHEM p.2
(c) The solution changes from colourless to brown / orange / yellow ( NOT GAS )
Cl2 + 2 Br− à 2 Cl− + Br2
or Cl2 + 2 NaBr à 2 NaCl + Br2
or 2 H+ + OCl− + 2 Br− à H2O + Cl− + Br2
1
1
(1)
(1)
6 marks
(3)
(a) Sodium nitrite
It is toxic to micro-organisms / bacteria
1
1
(b) Manganese(IV) oxide
It acts as an oxidizing agent / It reacts with ( removes ) H 2(g) produced at the cathode.
1
1
(c) Sodium dichromate
It changes from orange to green
1
1
6 marks
Chemical Knowledge ( 6 marks ) + Effective Communication ( 3 marks )
4. • Position of ion in the electrochemical series
( 1 mark for stating the factor and 1 mark for explanation in terms of comparison of two
discharging processes. )
− If carbon / platinum / copper ( any appropriate material ) is used as the cathode, Cu2+ ions
instead of H+ ions will be discharged because Cu2+ ion occupies a lower position on the
e.c.s. ( Cu2+ ion is more easily to be reduced / has a stronger oxidizing power than H+ )
OR
− In the electrolysis of dilute CuCl2(aq) using carbon / platinum as anode ( any appropriate
material ), OH− ions instead of Cl− ions will be discharged because OH− occupies a higher
position in the e.c.s.
( OH− ion is more easily to be oxidized / has a stronger reducing power than Cl− )
• Concentration of ion
( 1 mark for stating the factor and 1 mark for explanation in terms of comparison of two
discharging processes. )
− In the electrolysis of very dilute / dilute CuCl2(aq) using carbon / platinum as anode, OH−
ions will be discharged / O2 is liberated at the anode.
1
1
(1)
1
2002 - CE-CHEM p.3
ions will be discharged / O2 is liberated at the anode.
− If concentrated CuCl2(aq) is used, Cl− ions will be discharged / chlorine gas will be
liberated instead.
• Nature of electrode
( 1 mark for stating the factor and 1 mark for explanation in terms of comparison of two
discharging processes. )
− If carbon / platinum is used as the anode, Cl2 / O2 ( conc. / dilute ) will be liberated at the
anode.
− If copper is used as the anode, the anode will dissolve / oxidize.
1
1
1
6 marks
Chemical Knowledge ( 6 marks ) + Effective Communication ( 3 marks )
5. ( Award 2 marks for characteristic related to structure / formula ; 2 marks for physical
property ; 2 marks for chemical property )
2 marks for characteristic related to structure / formula
− Members of a homologous series can be represented by the same general formula
− General formula of alkenes : CnH2n or (CH2)n
OR
− Successive members of a homologous series differ in their structure by one CH2 unit
− Molecular Formulae : ethene ( C2H4 ) , propene ( C3H6 ) etc.
OR
− Members of a homologous series have the same functional group
− Functional group of alkenes : C=C
OR
− Alkenes possess the C=C functionality.
− Structures ( structural formula ) of alkenes : ethene ( CH2=CH2 ) ; propene ( CH3CH=CH2 )
2 marks for physical property
− Their physical properties change gradually from one member to the next.
− The melting point / boiling point of alkene increases with increase in relative molecular mass
OR
− The volatility / flammability of alkenes decreases with increase in relative molecular mass.
2 marks for chemical property
− Members of a homologous series have similar ( BUT NOT SAME ) chemical properties.
− ONE example of the reaction of alkenes which is characteristic of unsaturated
hydrocarbons
1
1
(1)
(1)
(1)
(1)
(1)
(1)
1
1
(1)
1
1
2002 - CE-CHEM p.4
( accept a description of the reaction or a chemical equation. )
e.g.
( Accept other reactions : e.g. addition polymerization )
(1)
(1)
6 marks
6(a)(i) Calcium hydroxide / Ca(OH)2 1
(ii) Mg(OH)2 (s) + 2 HCl (g) à MgCl2 (s) + 2 H2O (g/ l )
( 1 mark for a balanced equation ; 1 mark for state symbols if the formulae are correct )
1 + 1
(iii) molten magnesium chlorides contains mobile ions / ( movable ions ) / ( freely moving ions )
BUT NOT ACCEPT free ions )
1
(iv) duralumin 1
5 marks
6(b)(i) Isotopes are atoms with the same atomic number but different mass number /
the same number of protons but different number of neutrons .
1
(ii) relative atomic mass = 24 × 0.786 + 25 × 0.101 + 26 × 0.113
= 24.3 ( or 24.33 or 24.327 ) ( NO g unit !)
1
1
(iii) No, because isotopes of an element have the same chemical properties ( NOT similar )
1
4 marks
6(c)
(i) concentrated sulphuric acid / conc. H2SO4 / H2SO4 (l)
1
(ii) Diagram :
2
CH2 CH2CH2 CH2
Cl Cl
CH2 CH2CH2 CH2
OH OH
+ Cl2
+ H2O
+ ( O )
KMnO4 / H+
2002 - CE-CHEM p.5
( 1 mark for safe and appropriate set-up diagram , e.g. open but not close system )
( 1 mark for direction of water flow in the condenser )
( 0 mark for wrong set−up : e.g. closed system or distillation )
(iii) • Iodine has a simple molecular structure / Attraction between I 2 molecule is weak van der
Waals’ forces.
• Sodium iodide has an ionic structure / Attraction between Na+ and I− ions is strong ionic
bonds.
• Strength of inter-particle attraction in ethyl ethanoate is comparable to that in iodine.
( Indication of an understanding of the idea of ‘like dissolve like’ in terms of the strength of
attraction between particles. )
1
1
1
(iv) Flammable / inflammable / C 1
7(a)(i) CaCO3 + 2 HNO3 à Ca(NO3)2 + H2O + CO2
OR
CaCO3 + 2 H+ à Ca2+ + H2O + CO2
Evolution of CO2 stops ;
Test the pH of the solution using pH paper, the pH should be less than 7.
1
(1)
1
(1)
(ii) Diagram :
2
water out
water in
mixture of ethanol, ethanoic acid and conc. H2SO4
heat
open
2002 - CE-CHEM p.6
( 1 mark for the diagram ; 1 mark for labeling the funnel and filter paper )
(iii) Ca2+ + SO42− à CaSO4
1
(iv) To remove any soluble impurities ( or appropriate example : Na 2SO4 ; NaNO3 ; HNO3 ) 1
(v) (1) no. of mole of CaSO4 = 10.52 / ( 40 + 32 + 16× 4 )
= 0.0774
mass of CaCO3 in the sample of calcite = 0.077 × ( 40 + 12 + 16 × 3 )
= 7.74 g
% by mass of CaCO3 = ( 7.74 / 7.98 ) × 100
= 97.0 %
( Also accept answers from 96.5 to 97.0 )
1
(1)
1*
1
(2) The sample does not contain ions which form insoluble sulphate, e.g. Ba2+ , Sr2+, Pb2+
OR There is no loss of Ca2+ ions during the experiment
OR CaCO3 is the only calcium−containing compound present in the sample.
1
(1)
(1)
10 marks
7(b)(i) Cl2 + 2 OH− à OCl− + Cl− + H2O
OR
Cl2 + 2 NaOH à NaOCl + NaCl + H2O
1
(1)
(ii) both oxidizing agent and reducing agent.
O.N. of Cl decreases from 0 to −1 ( Cl2 acts as an oxidizing agent )
O.N. of Cl increases from 0 to +1 ( Cl2 acts as a reducing agent )
1
1
1
(iii) Sterilizing agent / making solvents ( CHCl=CCl2 ) / production of insecticides /
production of vinyl chloride ( CH2=CHCl ) / used as chemical weapons / making HCl(aq)
1
filter funnel filter paper
2002 - CE-CHEM p.7
7(c)(i) 3 Cl2 + 8 NH3 à 6 NH4Cl + N2
( 1 mark for the correct formulae ; 1 mark for balancing the equation )
1 + 1
(ii) ammonium chloride / NH4Cl 1
8 marks
8(a)(i) no. of moles of SO2 released = no. of mole of S
= ( 1000 × 0.015 ) / 32
= 15 / 32 ( or 0.46875 )
volume of SO2 released = (15 / 32 ) × 24
= 11.25 dm3
( Accept 11 to 11.3 dm3 )
1
1*
1
(ii)
acid rain / high incidence of respiratory illnesses / corrosion of buildings / lower crop yield
( NOT ACCEPT : affect … cause cancer )
1
(iii)
installation of scrubbers / installation of desulphurization system /
use coal of lower sulphur content.
1
(iv)
(1) high incidence of respiration illnesses / causing cancer / darkening of building walls /
reduce visibility / smog.
1
(2) installation of electrostatic precipitator.
1
7 marks
8(b)(i)
1
(ii) Carbon dioxide is denser than air
It can exclude air (oxygen ) from the fuel / can blanket the fire from air.
1
1
O C O
2002 - CE-CHEM p.8
(iii) Silicon dioxide has a covalent network structure / giant covalent structure .
Attraction between CO2 molecules is van der Waals’ forces.
The attraction between CO2 molecules is weak while the attraction between atoms in SiO2 is
strong covalent bond.
( 1 mark for the structure of SiO2 ; 1 mark for the attraction between CO2 molecules ;
1 mark for comparing the strength of inter−particle attractions. )
1
1
1
(iv) (1) SiO2 + 2C à Si + 2 CO
or SiO2 + C à Si + CO2
1
(1)
(2) making computer chips / electronic parts / alloys / semi−conductors / silicone
( accept other uses of silicon : Integrated Circuit )
1
8 marks
(v) Any ONE of the following :
( 1 mark for structure ; 1 mark for name )
1 + 1
9 marks
8 (c)(i) A reaction in which monomer molecules join together to form polymer molecules, with the
elimination of small molecules.
1
(ii)
1 + 1
C
O
C
O
Cl Cl
C
O
C
O
OH OH
C
O
C
O
OO CH3CH3
HOCH2CH2OH
H C
O
OCH2
CH2
CH3H C
O
OCH
CH3
CH3
CH3
CH2C
O
OCH3
propyl methanoate methylethyl methanoate( iso-propyl methanoate )
methyl propanoate
2002 - CE-CHEM p.9
3 marks
9 (a) (i) (1) NH4+ + H2O à NH4
+ + OH−
1
(2) Oils react with alkalis ( undergoes hydrolysis ) to give soaps ( soapy detergent ) /
water soluble substances.
1
(ii) The glass cleaner should be used in a well−ventilated environment because ammonia has a
pungent smell / is toxic.
OR
Wear gloves because alkaline solutions can attack skin / cause skin allergy / it is corrosive .
OR
Wear safety spectacles / safety glasses / goggles because ammonia solution attack eyes / it is
corrosive.
1
1
(1) + (1)
(1) + (1)
9(b)(i) (1) distilled water / deionized water
(2) distilled water / deionized water
1
1
(ii) pipette 1
(iii) NH3 + HCl à NH4+ + Cl−
No. of moles of HCl(aq) used = 0.23 × 28.7 × 10−3
= 6.60 × 10−3 ( 0.00660 )
Concentration of NH3 in glass cleaner = 6.60 × 10−3 / ( 25×10−3 ) × ( 250 / 25 )
= 2.64 mol dm−3
( Also accept 2.6, 2.64, 2.640 and 2.6404 mol dm −3 )
1
1*
1
6 marks
(9)(c)
(i)
(1) violet / purple / blue
2 H+ + 2 e− à H2
∴ OH− concentration increases around carbon rod A /
concentration of OH−(aq) is higher than that of H+(aq).
1
1
1
(1)
(2) oxygen / O2
OH− is discharged at carbon rod B ( anode ) / +ve pole
OR 4 OH− à O2 + 2 H2O + 4 e−
1
1
(1)
(ii) pencils / zinc−carbon cells. 1
2002 - CE-CHEM p.10
(iii) Any TWO of the following :
• save chemicals / reduce the cost of chemicals ( or laboratory equipment ) used
• reduce chance of chemical hazards
• reduce chemical wastes produced / environmental problems
• shorten the time required for conducting an experiment
• require less working space for carrying out an experiment
• easy to set−up / convenient to set up
2
8 marks