Section A (Answer ALL questions.)
1.
Lithium is a Group I element in the Periodic Table. It occurs naturally in two isotopic forms.
The relative abundance of the each of these isotopes is shown in the table below:
6
7
Istope
Li
Li
Relative abundance (%)
7.4
92.6
(a) What is the meaning of the term 'isotope'?
(b) Calculate the relative atomic mass of lithium.
(c) A piece of freshly cut lithium metal is placed in air.
(i) What would be observed on the surface of the metal after some time? Write the
relevent chemical equation.
(ii) Draw the electronic diagram of the product in (i), showing electrons in the
outermost shells only.
(6 marks)
1.
(a)
(b)
(c)
Atoms with the same atomic number but different mass number/atoms with
the same no. of protons but different no. of neutrons
(Accept any correct definition of isotope.)
Relative atomic mass = 6×0.074 + 7×0.926
= 6.93
(Also accept 6.9 and 6.926)
(i) The metal surface will tarnish/turn dull
4Li  O2  2Li 2O
(ii)
1
1
1
1
1
1
2.
For each of the following experiments, state the expected observation and write a relevent
chemical equation.
(a) Ethene is passed into an acidified potassium permanganate solution.
(b) A mixture of butane and bromine vapour is exposed to diffused sunlight.
(c) A sodium sulphite solution is added to an iodine solution (iodine dissolved in
aqueous potassium iodide).
(6 marks)
2.
(a)
(b)
(c)
potassium permanganate solution changes from purple to colourless /
purple colour of potassium permanganate fades.
CH2  CH2  [O]  H 2O  CH2 (OH)CH2 (OH)
or, 5CH2  CH2  2H 2O  2MnO 4   6H   5CH2 (OH)CH2 (OH)  2Mn 2 
(Also accept equations showing further oxidation of ethane-1,2-diol to
ethanedioic acid/carbon dioxide. DO NOT accept half equations.)
Brown / red / orange colour of bromine fades slowly/changes to colourless
slowly.
or, Colourless oily droplets are formed.
CH 3CH 2 CH 2 CH 3  Br2  CH 3CH 2 CHBrCH 3  HBr
or, C4 H10  Br2  C4 H 9 Br  HBr
(Accept any equation showing substitution of butane by Br2 / equation
showing further substitution.)
Brown colour of iodine fades/turns colourless.
2

2

SO3  H 2 O  I 2  2I  SO4  2H
or, Na 2SO3  H 2 O  I 2  2HI  Na 2SO4
3.
Consider the following substances:
sodium benzoate, sodium chloride, sodium hypochlorite,
sodium hydrogencarbonate, sodium hydroxide,
sodium sulphite and monosodium glutamate
1
1
(1)
1
(1)
1
(1)
1
1
(1)
(a)
(b)
(c)
3.
(a)
(b)
(c)
Which substance is commonly used for preserving fish? Briefly explain its action.
Which substance is commonly used as an active ingredient in toilet disinfectants?
Briefly explain its action.
Which substance is commonly used as an active ingredient in oven cleaners? Briefly
explain its action.
(7 marks)
Sodium chloride
It dehydrates / removes water from fish and makes the environment
unfavourable for the growth of bacteria / germs / micro-organisms
Sodium hypochlorite
it can kill germs/bacteria
or, it is toxic to germs/bacteria
Sodium hydroxide
it can hydrolyse / react with oil to give soap (which helps cleaning) /
soluble products
1
1
1
1
(1)
1
1
For questions 4 and 5, candidates are required to give paragraph-length answers. 3 of the
marks for each of these two questions will be awarded for effective communication of
knowledge in Chemistry.
4.
On a hot summer day, the engine of a moving bus suddenly caught fire. When the firemen
arrived, they used foam, instead of water, to put out the fire. After the fire was extinguished,
the firemen sprayed a lot of water onto the hot engine.
Discuss the conditions required for the fire to occur and explain the underlying principles of
the actions taken by the firemen.
(9 marks)
4.
Chemical Knowledge (6 marks)
Conditions for the fire to occur
diesel / lubricating oil / fuel used in the bus
oxygen / air / oxidant
the high temperature / heat of the bus engine
Water cannot be used because it is immiscible with diesel / lubricating oil / fuel
and will spread the fire
or, diesel / lubricating oil / fuel floats on/is less dense than water and the fire will
spread
Foam can keep air away and the fire goes out
A lot of water was sprayed onto the engine to remove heat / to lower the
temperature, so as to eliminate the possibility of the re-ignition of diesel /
lubricating oil / fuel.
3
(1)
(1)
(1)
1
(1)
1
1
5.
Each of five unlabelled bottles contains one of the following chemicals:
2 M hydrochloric acid
2 M nitric acid
2 M sodium chloride solution
2 M sodium hydroxide solution
distilled water
Suggest how you would carry out tests to identify the contents of each bottle, using the
materials and apparatus listed below. Your answer should include the observation of each
test.
copper foil, solid copper(II) carbonate, 2 M copper(II) chloride solution,
test tubes and a Bunsen burner
(You are NOT required to write chemical equations. Answers in the form of flow diagrams
will NOT be marked.)
(8 marks)
5.
Chemical Knowledge (5 marks)
(For this question, candidates may give answers in an order different from that
illustrated below. In such cases, award one mark for each test which can identify /
eliminate a substance in the list.)
Add copper foil to each chemical (and heat).
Only nitric acid can dissolve copper / gives a blue solution / brown fumes
1
Add copper(II) chloride solution to the remaining four chemicals. Only sodium
hydroxide gives (blue) precipitate
Add copper(II) carbonate to the remaining three chemicals. Only hydrochloric
acid gives (colourless) gas bubbles / effervescence
Evaporate the remaining two solution to dryness. Only sodium chloride solution
will leave (white) residue
The remaining one is distilled water
1
1
1
1
Section B (Answer any THREE questions.)
6.
(a)
(i)
A student prepared sodium nitrate solution by reacting 1 M sodium hydroxide
solution with dilute nitric acid. The student carried out a titration to determine
the amount of dilute nitric acid required to react with a known volume of 1 M
sodium hydroxide solution.
(1) Write the chemical equation for the reaction. (An ionic equation will
NOT be accepted for this question.)
(2) Draw a labelled diagram for the set-up of the titration.
(3) Phenolphthalein can be used to determine the end point of the titration.
State the colour change at the end point.
(4) Suggest how the student can prepare a sodium nitrate solution using the
titration results.
(ii) Sodium nitrate is a nitrogenous fertilizer.
(1) Calculate the percentage by mass of nitrogen in sodium nitrate.
(2) Explain why nitrogen is essential for the growth of plants.
(Relative atomic masses: N = 14.0, O = 16.0, Na = 23.0)
(9 marks)
6.
(a)
(i)
(1)
(2)
(3)
(4)
(ii)
(1)
(2)
NaOH  HNO 3  NaNO3  H 2 O
(1 mark for a diagram showing the set-up for the titration
experiment; 2 marks for labelling the apparatus and reagents)
(Criteria for marking the labels: 2 marks for all four labels; 1
mark for three labels / two labels of which one should be a
reagent.)
from pink / purple / red to colourless
Add dilute nitric acid to 1 M sodium hydroxide solution in the
same volume ratio so that in the titration result, without adding
the indicator
or, repeat the titration procedure without adding the indicator
Formula mass of NaNO3 = 23 + 14 + 16×3
= 85
14
% by mass of N   100%
85
= 16.5% (or 16.47%)
Nitrogen is used in plants to produce amino acids / proteins /
cytoplasm / chlorophyll / nucleotide
1
1+2
1
1
(1)
1
(1)
1
1
(b)
The table below includes some information about three types of dry cells. The
voltahge of each type of cell is 1.5 V.
Type
Voltage over
Price per
Shelf
Life/minutes
discharge
cell/$
life/years
Zinc-carbon cell falls quite
2.5
1.5
70
(AA size)
rapidly
Alkaline
remains steady
5.0
3
90
manganese cell
(AA size)
Silver oxide cell remains steady
8.0
2
30
(button type)
(The life of a cell has been determined from its use in a test with a motorized toy.)
(i) Decide and explain which type of cell should be used in a small CD-player
(Discman).
(ii) A package of 24 zinc-carbon cells is now being offered at a special price of
$49.90. Assuming that your radio consumes one zinc-carbon cell per month,
would you buy a package of these specially-priced cells for the use of your
radio? Explain your answer.
(iii) The half-equations below show the changes at the two electrodes, A and B, of a
silver oxide cell during discharge:
Zn( s)  2OH  ( aq )  ZnO( s)  H2O( l )  2e
A:
Ag2O( s)  H2O( l )  2e  2Ag( s)  2OH  ( l )
B:
(1) Decide and explain which electrode, A or B, is the anode.
(2) Write the overall equation for the reaction that would occur in the cell during
discharge.
(iv) The following information was found on the packaging of a brand of zinc-carbon
cells:
Caution: 1.
Do not dispose of used cells in fire.
2.
Remove cells when not in use for prolonged periods.
(1) Explain why used cells should not be disposed of in fire.
(2) Explain why the cells should be removed when not in use for prolonged periods.
(9 marks)
6.
7.
(b)
(a)
(i)
Alkaline-manganese cell.
Silver oxide cell is not used because it is not of the right size.
Zinc-carbon cell is not used because its voltage drops quite rapidly.
(Award 1 mark only for the explanation:
alkaline-manganese cell is of the right size and has a steady voltage
over discharge.)
(ii) No.
The shelf life of zinc-carbon cell is 1.5 y and only 18 pieces can be
consumed/6 pieces will be wasted.
The average price per cell used = $49.9/18
= $2.77
which is more expensive than the normal price of a zinc-carbon dry
cell.
or, the price for 18 zinc-carbon cells = $2.5×18 = $45
which is cheaper than the price of the package
(iii) (1) Electrode A/zinc metal because an oxidation occurs
(2) Zn  Ag 2O  ZnO  2Ag
(iv) (1) An explosion may occur
or, Liberation of mercury/toxic substances
(2) The zinc-carbon cell may leak and damage the electrical item.
1
1
1
1
1
(1)
1
1
1
(1)
1
Both carbon and silicon are Group IV elements in the Periodic Table. The diagram
below show the structures of dry ice (solid carbon dioxide) and quartz (a form of
silicon dioxide).
dry ice
quartz
With reference to the structures of the two substances, explain why quartz is a
solid which melts at a high temperature, while carbon dioxide is a gas at room
temperature.
(ii) With the help of a labelled diagram, suggest how to show experimentally that
dry ice sublimes to give gaseous carbon dioxide.
(iii) Sand (an impure form of quartz) and limestone are raw materials used for
making glass.
(1) Name the main chemical constituent of limestone.
(2) Suggest ONE reason why glass had been used by mankind for a long
time.
(3) Suggest ONE reason why glass bottles are preferred to plastic bottles for
the storage of champagne.
(9 marks)
(i)
7.
(a)
(i)
(ii)
Quartz is a giant covalent network / covalent crystal.
or, The attraction between (Si and O) atoms in quartz is covalent
bond.
Carbon dioxide has a simple molecular structure and the attraction
between molecules is van der Waals’ forces
Covalent bond is stronger than van der Waals’ forces / intermolecular
force
∴Quartz is solid and CO2 is gas
diagram of a workable set-up
observation: lime water turns milky, no liquid residue remains (in the
test tube)
(iii) (1) †calcium carbonate
(2) the materials for making glass are easily available / abundant in
the earth crust.
or, Glass can easily be manufactured by heating sand, limestone
and sodium hydroxide.
(3) champagne contains a pressurized carbon dioxide solution.
Glass can withstand the pressure.
or, the ethanol solution (champagne) can dissolve
unpolymerized monomers in plastic
(b)
1
(1)
1
1
1
1+1
1
1
(1)
1
(1)
Polyvinyl chloride (PVC) is a plastic which has a wide range of uses.
(i) Write the chemical equation for the formation of PVC from its monomers.
(ii) Plastic products made of PVC may vary greatly in rigidity.
(1) Give ONE flexible product made of PVC.
(2) Give ONE rigid product made of PVC.
(3) Explain whether PVC is suitable for making electric sockets or not.
(iii) Incineration of PVC wastes produces hydrogen chloride which causes air
pollution.
(1) State ONE harmful effect of the discharge of hydrogen chloride into the
atmosphere.
(2)
(3)
Suggest how hydrogen chloride can be removed from incinerator flue gas
prior to its discharge to the atmosphere.
Suppose that all the chlorine in PVC is converted to hydrogen chloride
upon incineration. Calculate the volume of hydrogen chloride produced,
measured at room temperature and pressure, when a plastic waste
containing 1000 kg of PVC is incinerated.
(You may assume that no other chlorine-containing compounds are
preseent in the waste.)
(Relative atomic masses: H = 1.0, C = 12.0, Cl = 35.5;
3
molar volume of gas at room temperature and pressure = 24.0 dm )
(9 marks)
7.
8.
(b)
(a)
nCH 2  CHCl  [CH2CHCl]n
(For (1) and (2), accept other correct uses of PVC)
(1) garment / surface of sofa / hose / cable sheathing / foot wear /
tiles / curtains / rain coats / bottles
(2) pipes / bottles / record
(3) No. PVC is a thermoplastic / melts upon heating
(iii) (1) acid rain / damage to the respiratory system
(2) washing the flue gas with alkali / water
or, passing flue gas through scrubber
(3) No. of moles of HCl produced = no. of moles of PVC repeating
units
= 1000000/(12×2 + 1×3 + 35.5)
= 16000
Volume of HCl produced = 16000×24
= 384000 dm 3
(i)
(ii)
1
1
1
1
1
1
(1)
1
(1)
(1)
1
1
A student added concentrated sulphuric acid dropwise to some sugar cubes as
illustrated in the diagram below:
State the observable changes in the above experiment and write the
chemical equation for the reaction involved.
(2) What property of concentrated sulphuric acid is responsible for the
reaction?
(ii) When there was no further change, the student added excess concentrated
sulphuric acid to the reaction mixture. Upon heating, carbon dioxide, sulphur
dioxide and water were produced.
(1) Write the chemical equation for the reaction that occurred during heating.
(2) What property of concentrated sulphuric acid is responsible for this
reaction?
(3) State ONE safety precaution that should be taken. Explain your answer.
(iii) Draw ONE hazard warning label which should be displayed on a bottle of
concentrated sulphuric acid.
(9 marks)
8.
(a)
(i)
(1)
(i)
(1)
(ii)
(2)
(1)
(2)
sugar chars / turns black / brown
misty fumes (steam) / heat is evolved
C12 H 22O11  12C  11H 2O
dehydration / dehydrating
C  2H 2SO4  CO2  2SO2  2H 2O
oxidation / oxidizing
1
1
1
1
1
1
(3)
The experiment should be carried out in a fume cupboard
because the experiment produces sulphur dioxide which is a
toxic gas
or, wearing safety spectacles / safety goggles / face shield
because concentrated sulphuric acid is corrosive
(Award 1 mark only for wearing gloves because concentrated
sulphuric acid is corrosive)
(iii) hazard warning label:
corrosive:
1
1
(1)
(1)
1
(1)
CORROSIVE
(The label should show the corrosive property of H 2SO4 on skin
and / or on materials such as metal or wooden surface.)
or, oxidizing
(1)
OXIDISING
(b)
The photograph below shows a can of fruit juice. The body of the can is made of iron
coated with another metal. The top of the can and the ring-pull are made of
aluminium.
(i)
(1) Suggest ONE reason why the iron body is coated with another metal.
(2) Name ONE metal commonly used for coating the iron body.
(ii) Suggest ONE reason why aluminium, rather than iron, is used for making the
top of the can and the ring-pull.
(iii) Explain why it is not advisable to buy cans of fruit juice
(1) if the cans have scratches on the iron body;
(2) if the cans are swollen.
(iv) There is an increasing tendency for manufacturers to use cans made entirely of
aluminium for the storage of fruit juice. Suggest ONE advantage and ONE
disadvantage of using aluminium cans for the storage of fruit juice.
(9 marks)
8.
(b)
(i)
(1) To prevent iron from rusting / corrosion
(2) †Tin
(ii) Al is softer than iron. The ring pull can be pulled off more easily.
(iii) (1) Tin is less reactive / weaker reducing agent / occupies a lower
position in the electrochemical series than iron. Iron exposed to
air will corrode faster / rust faster.
(2) Fruit juice in swollen cans has already deteriorated. Gas
generated by (anaerobic) respiration of bacteria causes the can
to swell.
(iv) Adantage: Al is lighter / is more resistant to corrosion than Fe / can
1
1
1
1
1
1
1
be recycled more easily / can be dyed more easily
Disadvantage: Al is more expensive / is not so strong as Fe
9.
(a)
1
1
A student used the following set-up to prepare propanoic acid:
water out
X
water in
pumice stones
a mixture of propan-1-ol and
acidified potassium dichromate solution
heat
(i) Name apparatus X.
(ii) Explain why some pumice stones were added to the reaction mixture before
heating.
(iii) Write the chemical equation for the reaction involved.
(iv) Suggest a method to obtain propanoic acid from the reaction mixture.
The student used the propanoic acid obtained to carry out the following experiment:
(v)
Why is a water bath, instead of a naked flame, used for heating the test tube and
its contents?
(vi) (1) State TWO observable changes when the contents of the test tube were
added to the sodium carbonate solution.
(2) Give the systematic name of the carbon compound formed in the
experiment.
(8 marks)
9.
(a)
(b)
(i) †condenser
(ii) to prevent bumping / to ensure uniform heating / to smooth boiling
(iii) CH 3CH 2 CH 2 OH  2[O]  CH 3CH 2 CO2 H  H 2 O
or, 3CH3CH 2CH 2OH  2Cr2O7 2   16H   3CH3CH 2CO2 H  4Cr 3  11H 2O
[O ]
 CH 3CH 2 CO2 H  H 2 O
or, CH 3CH 2 CH 2 OH 
(iv) (fractional) distillation
(v) The methanol in the reaction mixture is flammable
(vi) Any TWO of the following:
(1) effervescence / gas bubbles
two layers of liquids resulted
pleasant / sweet smell is detected
(2) †methyl propanoate
Each of the following experiment produces a sodium hydroxide solution.
1
1
1
(1)
(1)
1
1
2
(1)
(1)
(1)
1
Action of sodium on water
experiment I
Sodium hydroxide solution
Electrolysis of brine
experiment II
(i)
(ii)
What would be observed when a small piece of sodium is added to water?
Explain whether experiment I or experiment II is preferred for preparing a
sodium hydroxide solution.
(iii) During the electrolysis of brine, chlorine and hydrogen are liberated at the
anode and cathode respectively. A sodium hydroxide solution remains in the
electrolytic cell after some time.
(1) Explain why hydrogen, instead of sodium, is liberated at the cathode.
3
(2) Suppose that 50.0 cm of hydrogen is liberated at the cathode at room
temperature and pressure. Deduce the theoretical volume of chlorine
liberated at the anode under the same conditions.
(3) Explain why a sodium hydroxide solution remains in the electrolytic cell.
(iv) Draw a labelled diagram to show the laboratory set-up for the electrolysis of
brine and the collection of the gaseous products.
(10 marks)
9.
(b)
(i)
Any TWO of the following
sodium melts into a silvery ball / dashes around on the surface of
water / floats on surface of water
sodium burns with a yellow flame
colourless gas evolved
(ii) Open-ended question
Experiment II because sodium metal is highly reactive / it is
dangerous to handle sodium metal / the reaction in experiment I is too
violent and difficult to control
or, Experiment I because a sodium hydroxide solution with high
purity can be obtained
(DO NOT accept explanation in terms of cost.)
(iii) (1) Na occupies a higher position than H in the e.c.s. / H  is more
readily reduced than Na 
(2)
(1)
(1)
(1)
1
(1)
1
At anode: 2Cl   Cl 2  2e 
At cathode: 2H   2e   H 2
Equal number of moles of Cl 2 and H 2 will be liberated
during electrolysis
Under the same temperature and pressure, equal no. of moles of
gases occupy the same volume.
∴Theoretical volume of chlorine liberated = 50.0 cm 3
(3)
2
After the removal of Cl  and H  , only Na  (aq) and
OH  (aq) ions remain in the solution.
(iv) Labelled diagram of laboratory set-up
(Marks will only be awarded to set-ups which are workable.)
(1 mark for labelling the two electrodes; 1 mark for showing the
1
(1)
1
1
1
3
collection of gaseous products at the electrodes; 1 mark for
labelling the correct products.)
END OF PAPER