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