Year End Examination O level Pure Chemistry
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O LEVEL CHEMISTRY CONCEPT
YEAR END EXAMINATION
PURE CHEMISTRY PRACTICE PAPER
Paper 1
Answer all twenty questions from this section.
The total marks for this section is 20.
For each question, there are four possible answers, A, B, C and D. Choose the one
you consider correct and record your choice on the separate answer sheet.
1 A student sets up the apparatus as shown. Predict the gas that will be collected
from the set-up and identify a suitable dehydrating agent that can be used.
Name of gas Dehydrating agent
A ammonia gas calcium oxide
B ammonia gas silica gel
C hydrogen chloride calcium oxide
D hydrogen chloride silica gel
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2 Tests on a sample of water polluted by sewage and fertilisers gave the following
results:
Reagent added Result
sodium hydroxide and aluminium foil colourless, pungent gas evolved
aqueous potassium iodide yellow precipitate formed
Which compound is present in the water?
A ammonium carbonate
B ammonium chloride
C lead nitrate
D lead sulphate
3 In the cooling curve shown below, at which stage can both solid and liquid exist
together?
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4 An element, X, has two isotopes, namely X-16 and X-18. Its relative atomic mass
is 16.4. What is the proportion of each isotope?
A 50% X-16 and 50% X-18
B 60% X-16 and 40% X-18
C 70% X-16 and 30% X-18
D 80% X-16 and 20% X-18
5 The diagram below show the structures of two atoms of the elements P and Q
respectively.
Calculate the mass of 1 mole of the compound formed by P and Q.
A 11 g
B 14 g
C 23 g
D 30 g
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6 Which of the following statements explains why magnesium chloride has a very
high melting point?
A Magnesium and chlorine are joined together by very strong covalent bonds.
B Magnesium and chlorine form ions joined together by a crystal lattice.
C The reaction between magnesium and chlorine is highly exothermic.
D The reaction between magnesium and chlorine is fast and vigorous.
7 Which of the following contains the same number of atoms as 9 g of water?
A 2 g of hydrogen gas
B 8 g of methane gas
C 14 g of nitrogen gas
D 22 g of carbon dioxide gas
8 Methane burns completely in oxygen according to the equation:
CH4 (g) + 2 O2 (g) → CO2 (g) + 2 H2O (g)
In an experiment, 40 cm3 of methane from an impure source of petroleum gas
was reacted with excess oxygen. 38.4 cm3 of carbon dioxide was formed. What
was the percentage purity of methane?
A 48%
B 52%
C 91%
D 96%
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9 When calcium is dropped into dilute sulphuric acid, bubbles of gas evolve at the
beginning but eventually stop. What causes the reaction to stop?
A A layer of insoluble calcium sulphate forms around the calcium and
prevents any further reaction.
B A layer of calcium oxide on the surface of the calcium stops the calcium
from reacting with the acid.
C Calcium is above hydrogen in the reactivity series and does not react with
dilute acid.
D The sulphuric acid is not concentrated enough for the reaction to proceed.
10 During the Haber process, how is the ammonia produced separated from the
reaction mixture?
A By cooling the mixture.
B By dissolving the other two gases.
C By filtering out the other two gases through cotton wool.
D By passing the gases through fused calcium oxide.
11 Caesium is a Group I element in the Periodic Table and its relative atomic mass
is greater than that of potassium. Which of the following statements concerning
caesium is INCORRECT?
A Caesium is a weaker reducing agent than potassium.
B Caesium reacts violently with water.
C Caesium is a soft metal.
D Caesium reacts with oxygen to form an oxide, Cs2O.
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12 The table gives information on four metals and some of their compounds.
Metal G H I J
action of dilute sulphuric acid
on metal
hydrogen
evolved no reaction
hydrogen
evolved
hydrogen
evolved
effect of hydrogen on
heated oxide reduced reduced no reaction no reaction
action of metal on a solution
of the sulphate of J no reaction no reaction J formed no reaction
What is the order of reactivity of these metals?
most reactive least reactive
A H G I J
B H J G I
C I J G H
D I H G J
13 The diagram shows the energy profile of a chemical reaction.
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What is the correct description for the reaction?
Sign of ΔH Overall energy change
A negative exothermic
B negative endothermic
C positive endothermic
D positive exothermic
14 Which one of the following reactions would be affected by a chance in pressure?
A C (s) + H2O (g) → CO (g) + H2 (g)
B 3 Fe (s) + 4 H2O (g) → Fe3O4 (s) + 4 H2 (g)
C 2 SO2 (g) + O2 (g) → 2 SO3 (g)
D CO2 (g) + C (s) → 2 CO (g)
15 In which of the following substances does carbon have the smallest oxidation
number?
A CO
B CO2
C CH4
D CaCO3
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16 Chlorine reacts with cold dilute aqueous sodium hydroxide solution according to
the following equation.
Cl2 (g) + 2 NaOH (aq) → NaClO (aq) + NaCl (aq) + H2O (l)
Which of the following statements is correct?
A Chlorine is oxidised and sodium hydroxide is reduced.
B Chlorine is reduced and sodium hydroxide is oxidised
C Chlorine is both oxidised and reduced.
D Sodium hydroxide is both oxidised and reduced.
17 A student is given 5 pieces of unknown metal strips (P, Q, R, S and T). He runs a
test on these metals using the apparatus shown below and recorded the results
in a table.
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Arrange the metals according to their reactivity in decreasing order.
A P > Q > S > R > T
B Q > P > T > S > R
C R > S > Q > T > P
D T > S > R > Q > P
18 In the process shown below, which of the following combinations is correct?
C10H22 C6H14 + 2 X
Process Identity of X
A fractional distillation an alkane
B fractional distillation an alkene
C cracking an alkane
D cracking an alkene
19 A food chemist wants to create the odour of pineapples in a product. An ester
with this odour has the formula C3H7COOC2H5.
Which pair of reactants would produce this ester?
A CH3COOH and C3H7OH
B C2H5COOH and C2H5OH
C C2H5COOH and C3H7OH
D C3H7COOH and C2H5OH
catalyst
heat
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20 A condensation polymer is to be made from the two monomers below.
Which diagram shows the structure of the polymer?
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Paper 2 Section A
Answer all the questions in this section in the spaces provided.
The total marks for this section is 50. A1 Use the following list of substances to answer the question. You may use
each substance once, more than once or not at all. [4]
aluminium chloride ammonium chloride copper(II) chloride
hydrogen chloride sliver chloride sodium chloride
Which substance (a) is a diatomic covalent molecule;
(b) dissolves in water to give a red colour with methyl
orange;
(c) decomposes to form an alkaline and an acidic
gas;
(d) forms a deep blue solution with excess aqueous
ammonia?
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A2 In a light bulb, the tungsten wire may get so hot that it melts and breaks. The
graph below shows the heating curve for tungsten.
(a) From the graph, predict the temperature at which the tungsten wire
breaks. [1]
___________________________________________________________
___________________________________________________________
(b) Describe the arrangement and movement of the particles in tungsten
at 5000°C. [2]
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(c) Using the graph, explain whether the wire is made up of purely tungsten
or an alloy containing mainly tungsten. [2]
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___________________________________________________________
A3 (a) The diagram below shows the arrangement of electrons in the outer
shell of an atom of element E.
(i) State the group in the Periodic Table to which E belongs. [1]
___________________________________________________________
(ii) E forms an ion. State the formula of the ion formed by E. [1]
___________________________________________________________
(iii) E forms a compound with carbon. Draw a 'dot and cross' diagram
to show the bonding you would expect to see in this compound.
You need to show only the outer shell electrons. [2]
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(b) Silicon carbide, SiC, has a very high melting point and has a structure
similar to that of diamond. With respect to its structure, explain why
silicon carbide has a very high melting point. [2]
___________________________________________________________
___________________________________________________________
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A4 Some research students used a detector to compare the air in the city centre
with air in the school playground.
The detector measures how much carbon monoxide there is in a sample of
air. Each student took one measurement in each place. The results from the
four students are shown in the table below.
Amount of Carbon Monoxide in the Air
Student City Centre School Playground
A 67 61
B 71 63
C 33 65
D 70 62
(a) Which student did not use the meter properly at the city centre? [1]
___________________________________________________________
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(b) Suggest one source of carbon monoxide in the air. [1]
___________________________________________________________
(c) What is the general difference in the carbon monoxide level at the city
centre and at the school playground? Suggest a possible explanation for
the difference. [2]
___________________________________________________________
___________________________________________________________
___________________________________________________________
(d) How can the emission of carbon monoxide be limited? [1]
___________________________________________________________
(e) State another air pollutant that could be present and shows a similar
difference between the air samples from the city centre and the school
playground. [1]
___________________________________________________________
___________________________________________________________
A5 An alloy which was known to be a mixture of two metals was divided into tow
samples.
The first sample dissolves completely in an excess of dilute nitric acid to form
a blue solution.
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The second sample was added to an excess of dilute sulphuric acid. A
reddish brown solid and a colourless solution were formed. Addition of
aqueous ammonia to this colourless solution gave a while precipitate which
was soluble in an excess of aqueous ammonia.
(a) Name the reddish brown solid and the blue solution. [2]
___________________________________________________________
___________________________________________________________
(b) Explain why aluminum cannot be present in the alloy. [1]
___________________________________________________________
___________________________________________________________
(c) (i) Name the white precipitate. [1]
___________________________________________________________
(ii) Write the equations for the reactions which lead to its
formation. [2]
___________________________________________________________
___________________________________________________________
___________________________________________________________
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A6 Copper has played a significant part in the history of mankind as it has
excellent ductility and electrical conductivity. Throughout the evolution of
technology, carious methods of extracting and refining copper were devised.
(a) Method 1 involves the electrolysis of molten copper(II) oxide using
graphite electrodes.
(i) State the ions present in molten copper(II) oxide. [1]
___________________________________________________________
(ii) Write the ionic equation for the reactions taking place at the anode
and the cathode. [2]
___________________________________________________________
___________________________________________________________
(iii) Explain why the anode requires frequent replacement. [1]
___________________________________________________________
___________________________________________________________
(b) Method 2 involves the electrolysis of copper(II) sulphate solution using
graphite electrodes.
(i) Besides the frequent replacement of the anode, suggest one other
reason why method 2 is favoured over method 1. [1]
___________________________________________________________
___________________________________________________________
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(ii) One student suggests that copper(II) hydroxide can be used for
method 2. Comment on the feasibility of this student's
suggestion. [1]
___________________________________________________________
___________________________________________________________
(c) Method 3 is illustrated by the diagram below.
(i) Write the ionic equation for the reaction at the anode. [1]
___________________________________________________________
(ii) Will there be a change in the colour of the electrolyte?
Explain your answer. [2]
___________________________________________________________
___________________________________________________________
___________________________________________________________
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A7 Petroleum is a complex mixture of hydrocarbons.
(a) What is meant by the term hydrocarbon? [1]
___________________________________________________________
(b) The components in petroleum are separated by fractional distillation.
Which property of the components allows them to be separated by this
process? [1]
___________________________________________________________
(c) One of the fractions of petroleum, kerosene, is used as a fuel in
intercontinental jet airliners. The formula of kerosene may be taken
as C14H30.
(i) When kerosene burns in an excess of air, carbon dioxide and steam
are formed.
Balance the following equation for the complete combustion of
kerosene. [1]
______ C14H30 + ______ O2 → ______ CO2 + ______ H2O
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(ii) The flight path from Singapore to London is approximately 10 700
km. A typical intercontinental jet airliner burns 115.56 tonnes of
kerosene for the flight. Use your equation in (c)(i) to calculate the
mass of CO2 produced during this flight. [1 tonne = 1 000 kg] [2]
(d) Fractional distillation of petroleum does not produce sufficient quantities
of some fractions to match demand. Cracking is used to concert large
hydrocarbon molecules into smaller molecules that are in greater
demand.
A hydrocarbon of molecular formula C12H26 is cracked. The cracking of
C12H26 produces a gaseous hydrocarbon in which the composition by
mass of carbon is 85.7% while that of hydrogen is 14.3%
(i) Calculate the empirical formula of the hydrocarbon produced. [2]
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(ii) A sample of 0.28 g of this hydrocarbon has a volume of 120 cm3 at
r.t.p. Calculate the relative molecular mass and hence determine the
molecular formula of the hydrocarbon. [2]
A8 Three samples of calcium carbonate are placed in flasks for an investigation.
In flask E is 5 g of large lumps of calcium carbonate.
In flask F is 5 g of medium-sized lumps of calcium carbonate.
In flask G is 5 g of small lumps of calcium carbonate.
An excess of dilute hydrochloric acid of the same volume is added to each
flask. The flasks are placed on three electronic balances. The figure below
shows the change in mass of the flasks plotted against time.
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(a) (i) Why do the three flasks and their contents lose their mass? [1]
___________________________________________________________
___________________________________________________________
(ii) How do the rates of reaction change with time? [1]
___________________________________________________________
___________________________________________________________
(b) (i) Sketch on the same axes the curve you would expect if 10 g of
powdered calcium carbonate is used instead of 5 g of large lumps of
calcium carbonate. Label this curve H. [1]
(ii) Use collision theory to explain why the size of the lumps affects the
rate of reaction. [2]
___________________________________________________________
___________________________________________________________
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Paper 2 Section B
Answer all three questions from this section.
The last question is in the form of either/or and only one of the alternatives should be
attempted.
The total mark for this section is 30.
Write your answers on the separate answer papers.
B9 Walkers and climbers buy 'warm packs'. When these packs are being used,
the packs become hot and remain at a temperature of about 40°C for several
hours. A 'warm pack' contains several chemicals evenly mixed together in a
porous bag. The whole pack is contained in a polythene bag.
The label from one 'warm pack' is shown below.
When the polythene bag is opened, air enters the pack. The iron in the pack
rusts, forming iron(III) oxide.
(a) Write an equation, with state symbols, for the rusting of iron to
produce iron(III) oxide. [2]
(b) A student investigated the reaction occuring in the pack by placing
the opened pack on an electronic balance. The increase in mass of the
opened pack was recorded at regular intevals over a period of several
hours. The results are shown below.
This pack contains
finely powdered iron water and sodium chloride absorbed on
an inert powder carbon catalyst
total mass of pack = 52.2 g
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Time / Hour Total Mass Increase Of The Pack / Grams
0 0.00
4 1.30
8 2.60
12 3.80
16 4.50
20 4.70
24 4.75
28 4.80
32 4.80
36 4.80
40 4.80
(i) The mass of the pack increase by 4.80 g. Explain why the mass of
the pack increased. [1]
(ii) How long would the pack be effective as a hand warmer? [1]
(c) Given that the initial mass of the pack is 52.2 g.
(i) calculate the number of moles of oxygen gas reacted with iron
at the end of 40 hours; [1]
(ii) calculate the percentage by mass of iron in the pack. [2]
(d) (i) Is the reaction taking place in the 'warm pack' exothermic or
endothermic? [1]
(ii) Draw an energy profile diagram for the oxidation of iron. Label on
the diagram the activation energy and the enthalpy change. [2]
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B10 Iron is made by reducing haematite with coke and limestone in the Blast
Furnace.
(a) Name the element and the compound which react to produce the
carbon monoxide required to reduce the haematite in the Blast
Furnace. [2]
(b) Construct a chemical equation, including state symbols, for the
reduction of haematite by carbon monoxide. [2]
(c) Explain why waste gases contain sulphur dioxide and oxides of
nitrogen. [3]
(d) Slag floats above iron in the Blast Furnace before molten iron is
tapped for further use. If the layer of slag was not present, there
would be a lower yield of molten iron collected. Suggest a possible
reason for this. [1]
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(e) Pure iron is not commonly used to manufacture products but their alloys
are.
(i) Give one use for an alloy of iron. [1]
(ii) State a reason why pure iron is not suitable for the use named
in (e)(i). [1]
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EITHER B11 An organic compound, Q, shows a number of reactions as indicated in the
figure below.
(a) Draw the structure formula of the organic product formed in
reaction I. [1]
(b) Reaction II converts the carbon-carbon double bond into single bonds
through the addition of hydrogen. Suggest the conditions necessary for
the reaction to take place. [1]
(c) Draw the structural formula of an organic product in reaction III. [1]
(d) (i) Write the balance chemical equation for reaction IV. [1]
(ii) State two observations for reaction IV. [2]
(e) (i) Compound Q undergoes addition polymerisation in reaction V. Draw
the structural diagram of the polymer formed in reaction V. [1]
(ii) The product formed in reaction V is non-biodegradable. Explain the
meaning of the term 'non-biodegradable'. [1]
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(f) Compound Q is an unsaturated organic compound. Describe a test and
state the positive result to show that compound Q is unsaturated. [2]
OR B11 When potassium chlorate(V), KClO3, is heated at 600°C, it decomposes into
potassium chloride and oxygen.
2 KClO3 2 KCl + 3 O2
Copper(II) oxide acts as a catalyst for the reaction. Some information about
these compounds are shown in the table below.
KCl KClO3 CuO
melting point / °C 772 368 1326
boiling point / °C 1407
(a) (i) Suggest why there is no boiling point stated in the table for
potassium chlorate(V). [1]
(ii) In what physical state will potassium chlorate(V) be when it starts to
decompose? [1]
(iii) Potassium chloride has high melting and boiling points. Explain,
with reference to its chemical bonding, why potassium chloride has
high melting and boiling points. [2]
(iv) If you had a mixture of potassium chloride, copper(II) oxide and
potassium chlorate(V), how would you obtain pure copper(II) oxide
from the mixture? [3]
CuO
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(b) (i) What is the oxidation state of chlorine in KClO3? [1]
(ii) Explain, in terms of oxidation number, why this decomposition
reaction is also a redox reaction. [2]
Check your work! -‐ End of Paper -‐