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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



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?



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



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%



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.



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.



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



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.



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



20 A condensation polymer is to be made from the two monomers below.

Which diagram shows the structure of the polymer?



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?



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]

___________________________________________________________

___________________________________________________________



(c) Using the graph, explain whether the wire is made up of purely tungsten

or an alloy containing mainly tungsten. [2]

___________________________________________________________

___________________________________________________________

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]



(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]

___________________________________________________________

___________________________________________________________

___________________________________________________________

___________________________________________________________

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]

___________________________________________________________



(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.



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]

___________________________________________________________

___________________________________________________________

___________________________________________________________



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]

___________________________________________________________

___________________________________________________________



(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]

___________________________________________________________

___________________________________________________________

___________________________________________________________



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



(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]



(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.



(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]

___________________________________________________________

___________________________________________________________



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



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]



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]



(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]



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]



(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



(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 -‐

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