Section A (Answer ALL questions in this Section.)
1.
Rubidium (Rb) and potassium belong to the same group in the Periodic Table. The relative
atomic mass of rubidium is larger than that of potassium.
(a) Explain whether rubidium is more reactive than potassium.
(b) Write a chemical equation for the reaction between rubidium and water. (State
symbols should be given.)
(c) Suggest how rubidium can be stored safely in the laboratory.
(d) Suggest ONE safety precaution for handling rubidium in the laboratory.
(5 marks)
1.
(a)
(b)
(c)
(d)
Rb is more reactive than K because Rb can give away/donate/release its
(outermost) electron more easily/readily.
or, Rb can form ion/cation/positive ion more easily/readily.
or, The strength of metallic bond between Rb atoms is weaker than that
between K atoms/Rb can atomize more readily than K.
(DO NOT accept Rb has one more electron shell than K/Rb atom is larger
than K atom/Rb is below K in the Periodic Table.)
2 Rb(s)  2 H 2 O(l)  2 RbOH (aq )  H 2 (g)


or, 2Rb(s)  2H2O(l)  2Rb (aq)  2OH (aq)  H2 (g)
(Formulae of reactants and products must be correct; award 1 mark for a
balanced equation and 1 mark for correct state symbols.)
Store under oil/paraffin oil/kerosene
Wear gloves/do not touch directly/use a pair of forceps/wear safety
spectacles (goggles)/use a safety screen (DO NOT accept fume cupboard)
1
(1)
(1)
1+1
(1+1)
1
1
2.
In each of the following groups of substances, there is ONE substance which is different
from the others in terms of their properties. In each group, identify the substance which is
different from the others and explain your choice.
(a) argon, fluorine, helium, neon
(b) nylon, perspex, polyethene, urea-methanal
(c) milk of magnesia, soap, vinegar, window cleaner
(d) carbon monoxide, hydrogen, methane, nitrogen
(8 marks)
2.
(a)
(b)
(c)
(d)
fluorine
fluorine is reactive/yellow/coloured gas
or, others are inert/unreactive/stable/colourless (gases).
(DO NOT accept noble gas/halogens.group VII (0) element)
Urea-methanal
It is a thermosetting plastic (cannot be softened by heat)/the other
substances are thermoplastics (can be softened by heat)
Vinegar
It is acidic/the others are alkaline
Nitrogen
It cannot burn in air/the others can burn in air
1+1
1+1
1+1
1+1
3.
Some of the ingredients present in a certain brand of cheese sticks are as follows:
benzoic acid, corn meal, cheese, monosodium glutamate (MSG),
sunset yellow (E110), vegetable oil
Which of the above ingredients are food additives? Suggest ONE function for each of the
food additives.
(6 marks)
3.
Monosodium glutanate (MSG): flavour enhancer/to enhance (increase) flavour
(taste)
(DO NOT accept MSG is flavouring)
Benzoic acid: preservative/toxic to (can kill) micro-organism (bacteria)
Sunset yellow (E110): colouring
(3 marks for the correct choice of 3 food additives, if more than 3 substances are
chosen, deduct 1 mark for each wrong answer. 3 marks for the correct function of
the chosen food additives.
1+1
1+1
1+1
For questions 4 and 5, candidates are required to give paragraph-Iength answers. 3 out of
the marks for each of these two questions will be awarded for the effective communication
of knowledge in Chemistry.
4.
"When atoms combine, they tend to attain noble gas electronic structures."
Discuss how atoms can attain the noble gas electronic structures. In your answer, you
should give suitable examples and the electronic structures of the products formed.
(8 marks)
4.
Chemical knowledge (5 marks)
When atoms of non-metals combine, they tend to share their (valence.outermost)
electrons to form molecules.
Electronic structure of a molecule e.g., HCl/ Cl 2 etc.
(Any appropriate example)
H
Cl
Cl
Cl
/
When metal and non-metal combine, atoms of the metal donate electrons (to atoms
of non-metal) to form cations/positive ions/metallic ions, while atoms of the nonmetal accept electrons to form anions/negative ions/non-metallic ions.
(or, award 1 mark for electron transfer, 1 mark for the formation of cation and
anion)
Electronic structure of an ionic compound e.g. NaCl etc.
(Any appropriate example)
+
+
Na
1
1
Cl
Na
1
1
1
Cl
or
Effective communication (3 marks)
General guidelines for marking effective communication:
(i) The mark for effective communication should relate to the candidate's
knowledge in chemistry. A candidates who wrote a paragraph which is
totally unrelated to the question should deserve zero mark both in chemical
knowledge and in effective communication.
(ii) The table below illustrates the relationship between the mark for chemical
knowledge and the maximum mark for effective communication.
mark for chemical knowledge
maximum mark for effective communication
4 or above
3
3 or below
2
In cases where the mark for effective communication is 3, points (A), (B) and (C)
below will be marked. In cases where the mark for effective communication is 2
marks, only points (B) and (C) will be marked.
(iii) The three marks for effective communication are awarded as follows:
(A) the ability to present ideas in a precise manner, including the correct
use of chemical terms (this mark should not be awarded to answers
which contained a lot of incorrect/superfluous materials);
(B) the ability to present ideas in a systematic manner (i.e., the answer is
easy to follow);
(C) the ability to present answer in paragraph form and to express ideas
using full sentence.
1
1
1
5.
Describe how large crystals of ammonium sulphate can be prepared from an aqueous
solution of ammonia in a school laboratory.
(9 marks)
5.
Chemical Knowledge (6 marks)
Titrate ammonia solution with (dilute) sulphuric acid until the end-point is
reached.
1+1
(DO NOT accept concentrated H 2SO 4 )
or, Add (dilute) sulphuric acid to ammonia solution in correct mole ratio (of 1:2)
(1+1)
Evaporate excess water/heat to obtain a saturated (more concentrated) solution.
1+1
Cool slowly/add small crystals of ammonium sulphate to the saturated solution to
obtain large crystals of ammonium sulphate.
1
Filter/decant the saturated solution to obtain the crystals.
1
or, hang a small crystal of ammonium sulphate in the saturated solution as seed to
(1)
obtain large crystals.
(1)
Effective communication (3 marks)
General guidelines for marking effective communication:
(i) The mark for effective communication should relate to the candidate's
knowledge in chemistry. A candidates who wrote a paragraph which is
totally unrelated to the question should deserve zero mark both in chemical
knowledge and in effective communication.
(ii) The table below illustrates the relationship between the mark for chemical
knowledge and the maximum mark for effective communication.
mark for chemical knowledge
maximum mark for effective communication
4 or above
3
3 or below
2
In cases where the mark for effective communication is 3, points (A), (B) and (C)
below will be marked. In cases where the mark for effective communication is 2
marks, only points (B) and (C) will be marked.
(iii) The three marks for effective communication are awarded as follows:
(A) the ability to present ideas in a precise manner, including the correct
use of chemical terms (this mark should not be awarded to answers
which contained a lot of incorrect/superfluous materials);
1
(B) the ability to present ideas in a systematic manner (i.e., the answer is
easy to follow);
1
(C) the ability to present answer in paragraph form and to express ideas
using full sentence.
1
END OF SECTION A
Section B (Answer any THREE questions.)
6.
(a)
The illustration below shows the plastic bottle of a domestic toilet cleaner and its
label.
(i)
Explain, with the help of a chemical equation, why the toilet cleaner should not
be mixed with bleaches.
(ii) (1) Suggest ONE chemical, other than bleaches, that should not be mixed
with the toilet cleaner?
(2) If the chemical suggested in (l) and the toilet cleaner are mixed together,
what change would be observed? Write a chemical equation for the
reaction involved.
(iii) Explain why it is necessary to handle the toilet cleaner with care.
(iv) (1) Explain why plastic is used for making the bottle for the toilet cleaner.
(2) Name ONE plastic material suitable for making the bottle for the toilet
cleaner.
(9 marks)
6.
(a)
(i)

The H ions/acid (in the toilet cleaner) will react with the bleach


( ClO and Cl ) to give chlorine which is poisonous/toxic.
Cl   ClO  2H   Cl2  H2O
or, NaOCl  2 HCl  NaCl  H 2 O  Cl 2

(DO NOT accept OCl  2HCl  H2O  Cl2
2

or, H ions will react with the bleach ( SO3
in SO 2 bleaches)
to give SO2 which is poisonous/toxic.
(ii)
1
1
1
(1)
(1)
(1)
SO32   2H   SO2  H2O
chemical: metals such as Fe/Zn...(do not accept Pb, Cu, etc.)
change: gas evolves/effervescence occurs/metal dissolves

2
equation: Fe  2H  Fe  H2
(1)
or,
(1)
(2)
chemical: (strong) alkalis/NaOH/KOH/caustic
change: heat evolves/spillage of the alkali


equation: H  OH  H2O
(1)
(1)
(1)
or,
(1)
chemical: carbonate/hydrogencarbonate
change: effervescence/ CO 2 gas evolves
(1)
(1)
(1)
(2)
(2)

2
equation: CO3  2H  H2O  CO2


/ HCO3  H  H2O  CO2
(Accept full or ionic equation; equation should match the chemical
suggested.)
(iii) hydrochloric acid is corrosive/irritating/can cause acid burn
DO NOT accept HCl is harmful)
(iv) (1) it is inert/does not react with HCl/the bottle is not easily
broken/flexible/light in weight/can be moulded etc.
(2) †polyethene/polythene/polypropene/polystyrene/polyvinyl
chloride etc.
(DO NOT accept short forms e.g., PE, PP, PS...)
(DO NOT accpet perspex/name of any thermosetting plastics)
†correct spelling is required.
1
1
1
(1)
1
1
1
(b) The table below gives some information about five metals.
Metal Abundance in Price per kg Relative resistance of Relative strength of
the
earth's ($)
corrosion
metal
crust (%)
(1 = least resistant
(1 = lowest
4 = most resistant)
3 = highest)
Al
8.1
170
3
1
Cu
0.0055
140
3
3
Au
0.0000004
1100000
4
2
Fe
5.0
20
1
3
Zn
0.007
160
2
2
(i) Although gold has a very low abundance in the earth's crust, gold was
discovered by man a long time ago. Why?
(ii) Which of the metals in the above table is the most suitable to make pipes for
hot water? Explain your answer.
(iii) (1) Aluminium does not corrode easily. Why?
(2) Aluminium is a principal material for making aircraft but its strength is
relatively low. Suggest how the strength of aluminium can be improved to
make it suitable for making aircraft.
(iv) (1) Based on the information given in the table, suggest ONE factor that
affects the price of a metal.
(2) Suggest ONE other factor (not indicated in the table) that can also affect
the price of a metal.
(9 marks)
6.
(b)
7.
(a)
7.
(a)
(i)
Gold is very unreactive/inert/is stable/does not combine with other
elements easily/can be found free in nature.
(ii) Copper/Cu
because it does not corrode easily and has a high metallic strength/is
relatively cheap
(Award mark for explanation only if Cu is chosen.)
(iii) (1) Al reacts with oxygen in air to form a (thin) layer of oxide
which is impervious (not permeable) to oxygen/water and
prevents the metal from further corrosion.
(2) Alloying (with other metals e.g. Cu/Mn/Mg...)
(DO NOT accept mix with other metal/alloying with Na, K...)
(iv) (1) the price depends on its abundance in the earth's crust.
(2) Cost of extraction/cost in mining/supply/demand of the metal.
1
1
1
1
1
1
1
1
1
The label on a bottle of 'Effervescent Calcium' tablets is shown below.
Effervescent Calcium
Each bottle contains 10 tablets,
Each tablet contains:
Calcium carbonate
625 mg
Vitamin C
1000 mg
Citric acid
1350 mg
Dosage: 1 tablet daily
Administration: Dissolve one tablet in a glass of water.
Warning: (1) Keep out of reach of children.
(2) Keep ...................................
(i) Effervescence occurs when a tablet of 'Effervescent Calcium' is added to water.
Based on the information given on the label, explain why effervescence occurs.
Write the ionic equation for the reaction that occurs.
(ii) Suppose that a student puts a tablet of 'Effervescent Calcium' into an excess
amount of water and collects the gas liberated.
(1) Assuming that the tablet completely dissolves, calculate the theoretical
volume of gas liberated.
(2) It is found that the volume of gas collected in the experiment is less than
the theoretical volume calculated in (1). Give ONE reason to explain the
difference, assuming that there is no leakage of gas in the experiment.
(iii) On the label, some words are missing in the second warning statement.
Complete the second warning statement, beginning with the word 'Keep'.
Explain your answer.
(Relative atomic masses: C = 12.0, O = 16.0, Ca = 40.0;
3
Molar volume of gas at room temperature and pressure = 24.0 dm )
(9 marks)
(i)
Citric acid/vitamin C (ascorbic acid) when dissolves in water gives
H  (aq ) which reacts with calcium carbonate to give gas ( CO2 )
bubbles.
CaCO3  2H   Ca 2   CO2  H2O
(ii)
1
1
1

2
(DO NOT accept CO3  2H  CO2  H2O
(1) Formula mass of CaCO 3 = 40 + 12 + 16×3 = 100
1 mole of CaCO 3 gives 1 mole of CO 2
No. of moles of CO 2 evolved
= No. of moles of CaCO 3 present
625  103
100
 6.25  103

3
3
Theoretical volume of gas = 6.25  10  24 dm
3
3
= 150 cm (0.15 dm )
1
1
1
(Deduct 1 mark for wrong/no units)
(2) Some of the CO 2 produced dissolved in water/ CO 2 is
(fairly) soluble in water
(iii) (Keep) out of moisture (water)/(keep) in a dry place
Reason:
The amount of active ingredients will decrease/the tablet
will lose function/the active ingredients of the tablet will
react in the presence of water.
or, (Keep) out of heat/(keep) in a cool place
Reason:
at high temperatures, vitamin C deteriorates/ CaCO 3
undergoes decomposition/the amount of active
ingredients will decrease/the tablet will lose function.
or, (Keep) away from sunlight
Reason:
vitamin C may decompose
CaCO 3 can be decomposed by sunlight
1
1
1
(1)
(1)
(1)
(1)
(0)
(The warning statement and the reason must match each other.
7.
(b)
The following flow diagram shows the conversion of a compound X to an acid Y.
oxidation
X
Ethanol
Y
X can rapidly decolourize a solution of bromine in 1,1,1-trichloroethane.
(i) What is X? Name the industrial process by which X is converted to ethanol.
(ii) Write a chemical equation for the reaction between X and bromine.
(iii) (1) Give the systematic names of Y.
(2) Draw a labelled diagram of the laboratory set-up for the conversion of
ethanol to Y.
(iv) Ethanol can be detected in the breath of a drunken driver. Suggest ONE
chemical test to show the presence of ethanol in his breath and state the
observable change produced by the test.
(9 marks)
(b)
(i)
(ii)
ethene/ CH 2  CH 2 / C 2 H 4
†catalytic hydration
CH 2  CH 2  Br2  CH 2 BrCH 2 Br
or, C2 H 4  Br2  CH 2 BrCH 2 Br
(iii) (1)
(2)
†Ethanoic acid
1
1
1
1
3
or
(If more than 1 diagram is drawn, only the first diagram will be
marked.)
deduct 1 mark for wrong reagents/incomplete indication of reagents.
deduct 1 mark for closed/open system
deduct 1 mark for wrong/no indication of direction of water flow
deduct 1 mark for no indication of heat
(maximum mark deducted = 3)
(iv) pass the breath into acidified potassium dichromate (solution). The
colour of the solution will change from orange to green.
†correct spelling is required
8.
(a)
1
1
The fumes emitted from a factory using diesel fuel contain several gaseous pollutants.
One of these pollutants, Z, has a choking smell and can decolourizes bromine water.
(i)
(1) What is Z?
(2) What is the effect of Z on the environment?
(3) Suggest ONE way reduce the amount of Z in the fumes.
(ii) (1) Suggest ONE other pollutant that is present in the fumes.
(2) Explain how this pollutant is formed.
(3) What is the effect of this pollutant on the environment?
(4) Suggest ONE way to reduce the amount of this pollutant in the fumes.
(iii) If a fire is caused by the burning of diesel fuel, what type of fire extinguisher
should not be used to put out the fire?
(8 marks)
8.
(a)
(i)
(1)
(2)
(3)
(ii)
(1)
(2)
(3)
(4)
Sulphur dioxide/ SO 2
attacks respiratory system/produces acid rain/causes smog/toxic
(DO NOT accept harmful/air pollutant)
installation of scrubbers (pass fumes through alkalis)/use fuel of
low sulphur content
carbon monoxide/CO/particulate/carbon particles/nitrogen
oxides/ NO x /unburnt hydrocarbons
CO/carbon particles (particulates)/unburnt HCs: incomplete
combustion (of fuel)
NO x : combination of N 2 and O 2 at high temperature
CO: poisonous/toxic
or, unburnt HCs/carbon particles: causes smog
or, unburnt HCs/particulates: carcinogenic/causes smog
or, NO x : poisonous/toxic/produces acid rain/(photochemical)
smog
CO/C particles/unburnt HCs: ensure that there is sufficient
supply of air during combustion of fuel/installation of catalytic
converter.
or, particulates: installation of electrostatic precipitator/bag
filtration/centrifugation
or, NO x : installation of scrubber/catalytic converter
(iii) water type fire extinguisher
(Award 0 mark if fire extinguisher other than water type is given)
(b)
1
1
1
1
1
(1)
1
(1)
(1)
(1)
1
(1)
(1)
1
Small swimming pools usually use sodium hypochlorite solution rather than chlorine
gas to sterilize the pool water.
(i) Suggest ONE reason for using sodium hypochlorite solution rather than
chlorine gas in small swimming pool.
(ii) Suggest ONE chemical test to show the presence of hypochlorite ions in a
sample of pool water. State the observable change in the test.
3
(iii) A 100 cm sample of pool water contains 5.0 g of sodium hypochlorite.
3
Calculate the concentration, in moldm , of sodium hypochlorite in the
sample.
(iv) What would be observed if a petal of red flower was put into a sodium
hypochlorite solution? Using an equation, explain this observation.
(v) Briefly describe how sodium hypochlorite solution can be produced industrially.
(Relative atomic masses: O = 16.0, Na = 23.0, Cl = 35.5)
(10 marks)
8.
(b)
(i)
(ii)
sodium hypochlorite solution is easy to handle/leakage of toxic
chlorine gas may require the evacuation of people living
nearby/chlorine is stored in heavy steel cylinder which is difficult to
transport.
Test with litmus paper (solution)/dye/pH paper, the colour of the
indicator/dye will be bleached
(DO NOT accpet blue litmus turn red and then white.)
or, Add dilute acid to the sample, greenish yellow chlorine gas will be
given off.
or, add some pool water to a test tube containing potassium iodide
1
1
1
(1+1)
solution, brown colour of iodine will appear
(iii) Formula mass of NaOCl = 23 + 16 + 35.5 = 74.5
Molarity of sodium hypochlorite = (5 ÷ 74.5) × 10
= 0.67 (M)
(Accept also 0.7 M, 0.671 M, 0.6711 M)
(iv) the red colour of the petal is bleached/faded/turn pink/turn
white/decolourized


OCl  dye  Cl  (dye  O)
NaOCl
 dye  NaCl  (dye  O)
or,
(DO NOT accept HOCl  dye  HCl  (dye  O)
(v)
9.
(a)
Electrolysis of brine/concentrated solution of NaCl, produces chlorine
gas (at the anode) and NaOH solution (from the electrolysis). Allow
chlorine and NaOH to react to give NaOCl.
(1+1)
1
1
1
1
1
1
1
Sodium hydroxide can be used as a raw material in the manufacture of both soapy
and soapless detergents.
(i) Briefly describe how a soapy detergent can be prepared from a vegetable oil in
a school laboratory.
(ii) The formula of a certain soapy detergent is C n H 2 n 1COONa and its formula
mass is between 300 and 310. Calculate the value of n.
(iii) The structure of a certain soapless detergent is shown below:
CH3
CH3 CH3 CH3 CH3
H
H
H
C
C
C
C
+
C
C
C
SO3 Na
H
H
H
H
CH3 CH3 CH3
(1)
What other raw materials, apart from sodium hydroxide, are required in
the manufacture of this soapless detergent?
(2) Give ONE advantage and ONE disadvantage of using this soapless
detergent for domestic cleaning compared with using a soapy detergent.
(Relative atomic masses: H = 1.0, C = 12.0, O = 16.0, Na = 23.0)
(10 marks)
9.
(a)
(b)
(i)
Heat/boil vegetable oil with sodium hydroxide solution.
Add concentrated NaCl solution/salt solution/brine/salt out the soap.
Separate (filter) the soap from the solution.
(ii) Formula mass of the soap
= 12(n+1) + (2n+1) + 2×16 + 23
= 14n + 68
300 < 14n + 68 < 310
16.6 < n < 17.3
∴ n = 17
(iii) (1) petroleum (fraction)
(concentrated) sulphuric acid/oleum
(DO NOT accept dilute sulphuric acid)
(2) advantage: the soapless detergent can be used in hard
water/acidic solution.
(DO NOT accept can be used in sea water.)
disadvantage: the soapless detergent is non-biodegradable/may
causes water pollution/may cause skin allergies/can kill marine
lives
1+1
1
1
1
1
1
1
1
1
When the circuit in the set-up shown above is closed, the acidified potassium
permanganate solution loses its colour gradually.
(i) Write a half equation for the reaction that occurs in the acidified potassium
permanganate solution. Explain whether the permanganate ion is oxidized or
reduced.
(ii) What would be observed in the potassium iodide solution after some time?
Write a half equation for the reaction that would occur.
(iii) Identify the direction of electron flow in the external circuit.
(iv) Write an ionic equation for the reaction that occurs when an acidified potassium
permanganate solution and a potassium iodide solution are mixed together.
(v) (1) What is the function of the salt bridge in the set-up?
(2) Explain whether a sodium sulphite solution can be used instead of a
potassium nitrate solution in the salt bridge.
(8 marks)
9.
(b)
(i)
(ii)
MnO4   8H   5e  Mn2  4H2O
1
MnO4  is reduced because it receives electrons/the oxidation
number of Mn changes from +7 to +2/the oxidation number of Mn
decreases
The solution turns (pale) brown/yellow.
(DO NOT accept iodine/brown solid/violet (gas) is formed.)
2I   I2  2e
1
1
1


or, 2I  2e  I2
(iii) From KI solution to KMnO 4 solution/from RHS to
LHS/counterclockwise
(DO NOT accept from -ve carbon electrode to +ve carbon electrode)
(iv) 2MnO   16H   10I   2Mn2  8H O  5I
4
(v)
(1)
(2)
2
2
To allow migration of ions between the two beakers.
(Accept to complete the circuit.)
(DO NOT accept migration of electrons/conduction of
electricity)
No. Sodium sulphite can be oxidized/react with permanganate
ions.
END OF PAPER
1
1
1
1