the west african examinations council - qanda

THE WEST AFRICAN EXAMINATIONS COUNCIL

West African Senior School Certificate Examination

for School Candidates

SC 2018 CHEMISTRY 2&1 3 hours

Do not open this booklet until you are told to do so. While you are waiting, read and observe the following

instructions carefully. Write your name and index number in the spaces provided above.

This booklet consists of two papers. Answer Paper 2 which comes first, in your answer booklet and Paper 1

in your Objective Test answer sheet. Paper 2 will last for 2 hours after which the answer booklet will be

collected. Do not start Paper 1 until you are told to do so. Paper 1 will last for 1 hour.

© 2020 The West African Examinations Council

SC5052&1

WASSCE 2018

CHEMISTRY 2 & 1

Essay and Objective

3 hours

The West African Examinations

Council

Senior High School Certificate

Examination

Literature-In-English

Name: …………………………………………………….

Index Number: ……………………………………………

2

Study Materials for QANDA Liberia | Created by: SMART Liberia | Powered by: British Embassy (Monrovia)

PAPER 2 2 hours

ESSAY

[100 marks]

Answer four questions in all: Question 1 in Section A and three questions from Section B.

All questions carry equal marks.

Credit will be given for clarity of expression and orderly presentation of material.

SECTION A

Answer all the questions in this section.

1. (a) What is a functional group? [2 marks]

Answer:

Functional groups are specific groupings of atoms within molecules that have their own

characteristic properties, regardless of the others atoms present in molecules.

(b) Define each of the following terms:

(i) aliphatic compound;

Answer:

An aliphatic compound -- Any chemical compound belonging to the organic class in

which the atoms are connected by single, or triple bonds to form nonaromatic

structures.

(ii) aromatic compound.

[4 marks]

Answer:

Aromatic compounds -- are chemical compounds that consist of conjugated planar

ring systems accompanied by delocalized pi electron clouds in place of individual

alternating double and single bonds.

(c) Draw the structure of each of the following compounds:

(i) 3-chloro-3 methylbutan-2-ol;

Answer:

3


(ii) 3-methylbutanoic acid.

Answer:

[2 marks]

(d) State three properties of carbon that is responsible for its ability to form

many compounds. [3 marks]

Answer:

Chemical Formula: C

Oxidation: Combines with oxygen to produce carbon dioxide (CO₂) and carbon monoxide

(CO)

Reactivity: Carbon does not dissolve in, or react with water or acids.

(e) Why is it lot advisable to react a metal trioxocarbonate (IV) with a mineral acid

in a sealed glass flask? [2 marks]

Answer:

It is not advisable to react with a metal trioxocarbonate (IV) with a mineral acid in a sealed

glass flask because when metals (Cu, Na, Zn) react with mineral acids like HCl and H₂SO₄

hydrogen gas results. Nitric acid is an acid that decomposes very quickly. When metals react

with mineral acids except nitric acid, the respective salt H₂ gas is involved.

(f) If 10.2 g of a salt Q dissolves in 15.4 cm3 of distilled water at 40°C, calculate the

solubility of Q in mol dm3 at 40°C. [Mr Q =331] [4 marks]

Answer:

Data Soln:

Mass of Salt= 10.2g Solubility= mole of solute volume of solution

V= 15.4cm³ mol= mass of salt molecular weight

Solubility = ?

4


(g) Explain briefly why an increase in temperature causes the rate of a chemical

reaction to increase. [3 marks]

Answer:

An increase in temperature increases reaction rates because of the disproportionately large

increase in the number of high energy collisions.

(h) State two functions of a salt-bridge in an electrochemical cell. [2 marks]

Answer:

The two functions of the salt bridge in electrochemistry are:

• It maintains electrical neutrality within the electrochemistry circuit.

• Preventing the cell from rapidly running its reactions to equilibrium.

(i) State two large-scale uses of hydrogen in the chemical industry. [2 marks]

Answer:

• It is used as a fundamental building block for the manufacturer of ammonia.

• It is used in the manufacture of many polymers.

(j) State one environmental effect of burning fuels. [1 mark]

Answer:

When fuels are burned, they release carbon dioxide and other greenhouse games which in turn

trap heat in our atmosphere, making them the primary contributors to global warming and

climate change.

5


SECTION B

Answer three questions only from this section.

2. (a) Consider the following compounds:

NaH, B2O3, CH4, SnO

Choose from the list one:

(i) amphoteric substance,

Answer:

Amphoteric ------------------------------------------------- CH₄.

An amphoteric substance is one that can act as either an acid or a base, depending on

the medium.

(ii) substance whose aqueous solution is acidic;

Answer:

Substance whose aqueous solution is acidic ----------- SnO.

iii) substance whose aqueous solution is basic;

Answer:

Substance whose aqueous solution is basics ----------- NaH.

iv) substance which is a reducing agent.

Answer:

Substance which is a reducing agent --------------------- B₂O₃.

[4 marks]

(b) (i) The enthalpy of neutralization of sodium hydroxide with hydrochloric acid is

57.5 kJ mo1-1, the same as the enthalpy of reaction between H3O+(aq) and OH-

(aq).

Give reasons why this is so.

Answer:

It is always the same as the enthalpy of the reaction because when the standard

enthalpy change of neutralization is the enthalpy change when the solutions of an

acid and an alkali under standard condition produce 1 mole of water.

(ii) The enthalpy of neutralization for the following systems are:

CH3COOH — NaOH 55.2 kJ mol-1

6


HCN—NaOH 11.7kJ mol-1

Give reasons why the values are different from that given in 2(b)(i).

Answer:

For every weak acid, like ethanoic acid and hydrogen cyanide the enthalpy change of

neutralization may be much less.

[6 marks]

(d) (i) Outline the principles involved in partition chromatography.

Answer:

• The separation of the components from the sample mixture is carried out by the

process of partition of the components between 2 phases.

• Both phases are in liquid form.

• The liquid surface is immobilized by a stationary phase which results in making

its stationary phase.

(ii) Describe briefly how you would use-the principle of partition to separate

a sample of kerosene which is known to be. contaminated with water.

Answer:

I would use the principle of position to separate kerosine and water by using a

separating funnel to separate the mixture of two immiscible liquids. Note: Kerosine,

oil, and water do not mix with each other and form two separate layers.

[5 mark].

(e) An isotope of an element Q is represented by the symbol 𝑄1531 .

What does the superscript indicate? [1 mark]

Answer:

The superscript represents the number of protons.

3. (a) (i) Would the concentration of the products formed in any chemical reaction

increase with increasing temperature?

Answer:

Yes, the concentration of the products formed in any chemical reaction increase with

increasing temperature.

(ii) Give reasons for your answer in 3(a)(i).

7


Answer:

With an increase in temperature, there is an increase in the number of collisions.

[3 marks]

(b) (i) Which two of the following gases would show the greatest deviation from

the ideal behavior? H2, N2, O2, Cl2, SO2 and NCl3

Answer:

Cl₂ and SO₂.

(ii) Give reasons for your answer in 3(b)(i).

Answer:

They do not interact like H₂ & N₂ in a reaction.

[4 marks]

(c) Explain briefly:

(i) why the first ionization energies of the group (VII) elements decrease

down the group;

Answer:

This ionization energy decreases down the group because going down a group, the

ionization energy decreases.

(ii) the trend in the boiling points of the group (VII) elements down the group.

Answer:

The melting points and boiling points of the halogens increase going down group VII.

This is because, going down group VII; the molecules become larger and the

intermolecular forces become stronger.

[7 marks]

(d) In an experiment to determine the solubility of KCLO3 at different temperatures, the

following results were obtained:

(i) Draw a graph of temperature (x-axis) against solubility (y-axis);

Temperature/oC 0 10 20 30 40 50 60

Solubility in g/dm3 14 17 20 24 29 34 40

8


Answer:

(ii) Use your graph to determine:

(I) the solubility of KClO3 at 55 °C;

Answer:

The solubility of KCl03 at 55oC is approximately 37.5g/dm³.

(II) how much of the KClO3 will crystallize out when a saturated solution of the

salt is cooled from 55 °C to 25 °C.

Answer:

37.5g/dm³ - 22.5g/dm³ = 15g/dm³

Therefore, g/dm³ will be crystallize and when a saturated solution of the salt

is cooled from 55⁰C to 25⁰C

[9 marks]

(e) Explain briefly the term end-point as used in titrations. [2 marks]

Answer:

Endpoint: The point during titration when an indicator shows that the amount of

reactant necessary for a complete reaction has been added to a solution.

9


4. (a) Name one metal that could be extracted by:

(i) electrolysis;

Answer:

The metal Zn can be extracted from electrolysis.

(ii) reduction with carbon.

Answer:

Copper can be extracted by the reduction with carbon.

[2 marks]

(b) Draw and label a set-up that could be used for the electrolytic purification of copper.

Answer:

.

[4 marks]

(c) Copy and complete the table below:

Process Products Major raw material(s)

Haber Process

Solvay Process

[7 marks]

10


Answer:

Process Products Major raw material(s)

Haber Process Ammonia Methane

Solvay Process Calcium Chloride Sodium Carbonate (Na₂CO₃)

(d) An electric current of 100 A is passed’ through a molten liquid of sodium chloride

for 5 hrs. Calculate the volume of chlorine gas liberated at s.t.p.

[1 Faraday = 96,500 C Mv = 22.4 dm3]

Answer:

2Cl⁻ → Cl₂ + 2e⁻

100×96500 coulomb

Q= I ×t = 100×5×60×60 coulomb

The amount of chlorine liberated by passing 100×5×60×60 coulomb of electric charge.

Volume of Cl₂ liberated at STP = 9.3254 x 22.4 = 208.01 L

[6 marks]

(e) Describe briefly:

(i) what should be observed sodium reacts with water,

Answer:

When sodium reacts with water, you will observe a colorless solution of sodium

hydroxide (NaOH) and hydrogen gas (H₂).

(ii) a chemical test for water.

Answer:

Pure cooper(ii) sulfate is white. It is also known as anhydrates cooper (II) sulfate

because it has no water in it. When water is present in a sample of copper (II) Sulfate

it turns blue.

[6 marks]

5. (a) (i) Name three sources of water.

Answer:

Three sources of water include: ground water, surface water, and rain water.

(ii) State two sources of water pollution.

Answer:

1

2 x 9500 x 100 x 5 x 60 x 60 = 9.3264mole

11


Two sources of water pollution are sewage and agriculture pollution.

(iii) State the effect of

(I) boiling a temporary hard water,

Answer:

Hard water is the water that contains soluble salts of bivalent ions like

calcium and magnesium principally in the form of bicarbonates, chlorides

and sulfates. Upon heating the bicarbonate salts decompose and precipitates

out in the form of scaling white deposition. Therefore, water hardness that is

caused by calcium/magnesium bicarbonates is known as temporary.

(II) adding sodium trioxocarbonate (IV) crystals to permanent hard water.

Answer:

Sodium carbonate is also known as a washing soda removes temporary and

permanent hardness from water. The water is softened because it no longer

contains dissolved calcium ions and magnesium ions. It will form lather

more easily with soap.

[7 marks]

(b) Consider the following reaction scheme:

(i) What type of reaction is taking place in reaction I?

Answer:

Endothermic decomposition reaction.

(ii) Name substances X and Y.

Answer:

X= NaHSO₄

Y= NaNO₃

12


(iii) Why should NaNO3 be heated strongly to produce X and Y?

Answer:

NaNO₃ should be heated strongly because it undergoes decomposition reaction and

liberates oxygen & convert into Sodium Nitrate.

2NaNO₃₍heat₎→2NaNO₂ + O₂

(c) (i) Write a chemical equation for the laboratory preparation of ammonia

Answer:

2NH₄Cl + Ca (OH)₂ → CaCl₂ + 2H₂O + 2NH₂.

(ii) State the method of collecting the gas prepared 5 (c)(i)

Answer:

The ammonia gas is dried by passing through a drying tower containing lumps of

quicklime (CaO).

(iii) Name two compounds that are used as drying agents for gases

Answer:

The two compounds that are used as drying agents for gases are calcium chloride and

potassium chloride.

[5 marks]

(d) Ammonia is manufactured in the industry by the Haber process.

(i) State the source of the raw materials,

Answer:

Methane.

(ii) Name two impurities removed during the purification of the raw materials,

Answer:

The two types of impurities removed are natural and added impurities.

(iii) In what state is the final product collected?

Answer:

Final State.

13


(iv) Explain briefly your answer in 5(d)(iii)

Answer:

The final product will be collected during the final state where the reaction

experiments come to an end.

[6 marks]

(e) Explain briefly why a solution of trioxonitrate (V) acid turns yellowish on storage

for some time [2 marks]

Answer:

Nitric acid is colorless. concentrated nitric acid undergoes decomposition as it is very unstable

to heat. On decomposition they form reddish brown nitrogen dioxide gas which when

dissolved in the acid appears yellow in color.

END OF ESSAY TEST

14


DO NOT TURN OVER THIS PAGE

UNTIL YOU ARE TOLD TO DO SO.

YOU WILL BE PENALIZED SEVERELY IF YOU ARE

FOUND LOOKING AT THE NEXT PAGE BEFORE

YOU ARE TOLD TO DO SO.

PAPER 1 1 hour

OBJECTIVE TEST

[50 MARKS]

1. Use 2B pencil throughout.

2. On the pre-printed answer sheet, check that the following details are correctly printed:

(a) In the space marked Name, check your surname followed by your other names.

(b) In the spaces marked Examination, Year, Subject and Paper, check ‘WASSCE’,

‘SC2020’, ‘CHEMISTRY’, and ‘1’ in that order.

(c) In the box marked Index Number your index number has been printed vertically in

the spaces on the left-hand side, and each numbered space has been shaded in line

with each digit. Reshade each of the shaded spaces.

(d) In the box marked Subject Code, the digits 505113 are printed vertically in the spaces

on the left-hand side. Reshade the corresponding numbered spaces as you did for

your index number.

3. An example is given below. This is for a female candidate whose name is Julia S. BLAMUH.

Her index number is 7102143958 and she is offering Chemistry 1.

THE WEST AFRICAN EXAMINATIONS COUNCIL-LIBERIA ANSWER SHEET

PRINT IN BLOCK LETTERS

Name: BLAMUH JULIA S. LIB Examination: WASSCE Year: SC 2018

Subject: CHEMISTRY Paper: 1

INDEX NUMBER

7 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

1 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

0 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

2 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

1 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

4 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

3 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

9 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

5 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

8 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

For Supervisors only.

If a candidate is absent

Shade this space.

INSTRUCTIONS TO CANDIDATES: 1. Use grade 2B pencil throughout.

2. Answer each question by choosing one letter and shading it like this. [ A ] [ B ] [ C ] [ D ] [ E ]

3. Erase completely any answer you wish to change.

4. Leave extra spaces blank if the answer spaces provided are more than you need.

5. do not make any markings across the heavy black marks at the right-hand edge of your answer sheet.

SUBJECT CODE

5 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

0 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

5 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

2 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

1 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

3 [ 0 ] [ 1 ] [ 2 ] [ 3 ] [ 4 ] [ 5 ] [ 6 ] [ 7 ] [ 8 ] [ 9 ]

15


Answer all the questions.

Each question sis followed by four options lettered A to D. find the correct option for each question

and shade in pencil on your answer sheet, the answer space which bears the same letter as the option you have

chosen. Give only one answer to each question. An example is given below.

Which of the following elements react with water?

A. Carbon

B. Iodine

C. Sulphur

D. Sodium

The correct answer is Sodium, which is lettered D, and therefore answer Space D would be shaded.

[ A ] [ B ] [ C ] [ D ] [ E ]

Think carefully before you shade the answer spaces; erase completely any answers you wish to change.

Do all rough work on this question paper.

Now answer the following questions.

1. Which of the following raw materials is used in the plastic industry?

A. Methane

B. Ethene

C. Sulphur

D. Hydrogen

The correct answer is Ethene., which is lettered B.

Ethene is used in the plastic industry because It is the building block for a vast range of chemicals from

plastics to antifreeze solutions and solvents

2. Which of the following organic compounds can undergo both addition and substitution reactions?

A. Pentane

B. Hexane

C. Propane

D. Benzene

The correct answer is Benzene., which is lettered D.

Benzene addition reaction is the of cyclohexane by a mix of benzene vapor and hydrogen passed over the

nickel catalyst; while chlorobenzene is formed by substitution reaction.

3. Which of the following equations represent a redox reaction?

A. AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)

B. HNO3(aq) + NaOH(aq) → NaNO3(aq) + H2O(l)

C. 2HS(g) + SO2(g) → 2H2O(1) + 3S(g)

D. CaCO3(s) → CaO(s) + CO2(g)

16


The correct answer is “2HS(g) + SO2(g) → 2H2O(1) + 3S(g”, which is lettered C.

In the reaction 2H₂S + SO₂→3S + 2H₂O identify the oxidizing and reducing agents. In the above reaction

Sulphur (S) is oxidized and oxygen (O) is reduced.

4. The process of extraction of iron from its ore is

A. decomposition.

B. oxidation.

C. sublimation.

D. reduction.

The correct answer is reduction., which is lettered D.

Iron is extracted from iron ore in a huge container called a blast furnace. Iron are such as hematite contain

iron (II) oxide, Fe2O₃. The oxygen must be removed to form the iron (III) oxide in order to leave the iron

behind.

5. What is the solubility of a salt, if 0.4 g of it is obtained on evaporating 200 cm’ of its saturated solution to

dryness?

A. 0.8 g dm-3

B. 8.0 g dm-3

C. 2.0 g dm-3

D. 80 g dm-3

The correct answer is “2.0gdm⁻³”, which is lettered C.

1000 cm3 = 1dm3

200 cm3= 0.2 dm3

0.2 dm3 contains 0.4g

hence, solubility of the salt which is the amount of the salt dissolvable in 1 dm3 = 0.4 𝑔

0.2𝑑𝑚3 = 2.0𝑔𝑑𝑚−3

6. An acidic salt has

A. double anions in its aqueous solution.

B. hydrogen ions in its aqueous solution.

C. a single cation in its aqueous solution.

D. hydrogen atoms in its aqueous solution.

The correct answer is “hydrogen ions in its aqueous solution.”, which is lettered B.

It implies that aqueous solution possesses hydrogen ions.

7. A reaction is endothermic if the

A. enthalpy change is negative.

17


B. reaction vessel feels cool during the reaction.

C. bond forming energy exceeds bond breaking energy.

D. heat of formation of reactants exceeds heat of formation of products.

The correct answer is “reaction vessel feels cool during the reaction.”, which is lettered B.

If the system becomes colder as the forward reaction occurs, the reaction is said to be endothermic.

8. In which of the following compounds does hydrogen form ionic compounds?

A. CH4

B. HCl

C. NaH

D. NH3

The correct answer is NaH., which is lettered C.

The bonding between a non-metal and a metal is an ionic bonding.

9. Consider the following reaction equation:

Br2 + 2KI → 2KBr + I2

Bromine is acting as

A. a reducing agent.

B. an oxidizing agent.

C. an acid.

D. a base.

The correct answer is “an oxidizing agent.”, which is lettered B.

In the equation bromine is acting as an oxidizing agent because it reduced from O in Br, to 1 in KBr

This is the oxidation-reduction (redox) reaction:

2 Br0 + 2 e- → 2 Br-I (reduction)

2 I-I - 2 e- → 2 I0 (oxidation)

Br2 is an oxidizing agent, KI is a reducing agent.

10. An organic compound has the empirical formula CH2. If its molar mass is 42 gmol-1, what is its molecular

formula?

[H=1.0, C = 12.0]

A. C2H4

B. C3H4

C. C4H8

D. C3H6

The correct answer is “C3H6.”, which is lettered D.

18


Given the molecular formula. CH₂. The empirical formula will be (CH₂)n = 42

= (12+(2×1)n = 42

= 14n=42

=14n/14= 42/14

n=3

Hence, the empirical formula is C₃H₆

11. Ethene is produced from ethanol by

A. decomposition.

B. hydrolysis.

C. dehydration.

D. ozonolysis.

The correct answer is dehydration., which is lettered C.

When ethanol is heated in presence of concentration. H₂SO₄, dehydration takes place to give ethylene. The

reaction of ethene with steam to form ethanol can be reversed. This allows ethanol to be converted into

ethene. This process is called a dehydration reaction.

12. Consider the following equilibrium reaction:

2AB2(g) + B2(g) ⇌ 2AB3(g) ∆𝑯 = −𝒙𝒌𝑱 𝒎𝒐𝒍−𝟏

The backward reaction will be favoured by

A. an increase in pressure.

B. a decrease in pressure.

C. a decrease in temperature.

D. an introduction of a positive catalyst.

The correct answer is “a decrease in pressure.”, which is lettered B.

The equilibrium position is shifted to the left with a decrease in pressure in this system because the number

of gaseous molecules on the right is less. (Le Chatelier Principle).

13. What is the mass of solute in 500 cm3 of 0.005 mol dm-3 H2SO4?

[H=1.0, O=16.0, S=32.0]

A. 0.490 g

B. 0.049g

C. 0.0245g

D. 0.245g

The correct answer is “0.245g.”, which is lettered D.

Data Soln

V= 500cm3= 5000cm3/1000= 0.5L M= n/V

M=0.005mol n = 0.005 x 0.5= 0.0025

mass=? Mass = 0.0025 x 98g/mol = 0.245g

19


14. Pure water can be made to boil at a temperature lower than 100°C by

A. decreasing the external pressure.

B. reducing its quantity.

C. distilling it.

D. increasing the external pressure.

The correct answer is “decreasing the external pressure.”, which is lettered A.

The easiest and most drastic ways to change the boiling point is by tampering with the pressure above your

water. To lower the boiling point, you need to simply decrease its external pressure.

The pressure of gas above a liquid affects the boiling point. In an open system this is called atmospheric

pressure. The greater the pressure, the more energy required for liquids to boil, and the higher the boiling

point.

20


15. Consider the following sketch of the solubility curve of some substances

At what temperature is the solubility of KNO3 equals that of NaNO3?

A. A. 0°C

B. B. 40°C

C. C. 30°C

D. 20°C

The correct answer is 20oC., which is lettered D.

The graph shows that at 20⁰C the solubility of KNO₃ equal that of NaNO₃ because it is at the point KNO₃

and NaNO₃ interest with each other.

16. When a salt is added to its saturated solution, the salt

A. dissolves and the solution become super satu’rated.

B. precipitates and the solution remains unchanged.

C. dissolves and the solution become unsaturated

D. dissolves and crystals are formed

The correct answer is “precipitates and the solution remains unchanged.”, which is lettered B.

The point of saturation is the stage at which no more of a substance can be absorbed into a vapor or

dissolved into a solution. The stage beyond which no more of something can be absorbed or accepted.

Hence, the solution can no longer take in the salt anymore/ From this point, it begins to form precipitate

while the solution remains unchanged.

17. When substance X was added to a solution of bromine water, the solution became colourless X is likely to

be

A. propane

B. propanoic acid

C. propanol

D. propyne

The correct answer is propyne., which is lettered D.

21


Thus, bromine water will be decolorized by alkynes due to the presence of two pi bonds available for the

reactions.

18. the preferential discharge of ions during electrolysis is influenced by the

A. mechanism of electrolysis.

B. nature of the electrode.

C. electrolytic reactions.

D. type of electrolytic cell.

The correct answer is nature of the electrode., which is lettered B.

The following influence the preferential discharge of ions during electrolysis:

• The position of the ions in the electrochemical series

• The concentration of the ions in the electrolyte

• The nature of the electrode

19. The valence electrons of 12Mg are in the

A. 2s orbital.

B. 2px orbital.

C. 3s orbital.

D. 1s orbital.

The correct answer is “3s orbital.”, which is lettered C.

₁₂Mg = 2,8,2

=1s²2s²2p⁶3s²

Valence electron is the electron in the outermost shell of an atom. When we do the electron configuration of

₁₂Mg the outermost shell is 3s. Therefore, 3s contain the valence electron.

20. Stainless steel is an alloy comprising of

A. Fe and C.

B. Fe and Ni.

C. Fe, C and Al.

D. Fe, C and Ni.

The correct answer is “Fe, C and Ni.”, which is lettered D.

Stainless steel comprises iron (Fe) chromium (Cr) Manganese (Mn) Silicon (Si) Carbon (C) and in many cases

significant amounts of nickels (Ni) and Molybdenum (Mo).

21. The number of hydrogen ions in 1.0 dm3 of 0.02 mol dm3 tetraoxosulphate (VI) acid is

[NA = 6.02 x 1023]

A. 1.2 x 1022

B. 2.4 x 1022

C. 1.2 x1023

D. 2.4 x 1023

22


The correct answer is “1.2 x 1022.”, which is lettered A.

1mole = 6.02x10²³ion

0.02mol dm⁻³=0.02 x 6.02x10²³

= 1.2×10²²

22. The most suitable substance for putting out petrol fire is

A. carbon (IV) oxide.

B. water.

C. fire blanket.

D. sand.

The correct answer is “carbon (IV) oxide.”, which is lettered A.

In order to extinguish a petrol fire, you have to cut off the oxygen. This can be done by using carbon dioxide

gas to dilute the oxygen available and stop the burning.

23. The following factors will contribute to environmental pollution except

A. production of ammonia.

B. photosynthesis.

C. manufacture of cement.

D. combustion.

The correct answer is photosynthesis., which is lettered B.

Photosynthesis is the process where green plants use sunlight to make their own food. So it does not pollute

the environment.

24. The position of equilibrium in a reversible reaction is affected by

A. particle size of the reactants.

B. vigorous stirring of the reaction mixture.

C. change in concentration of the reactants.

D. presence of a catalyst.

The correct answer is “change in concentration of the reactants.”, which is lettered C.

The factors that affect the equilibrium position of a reversible reaction are:

(i) Temperature (ii) Pressure, (iii) Concentration, (iv) Catalyst.

25. The diagram below illustrates a conical flask containing water and ice.

Which of the following statements about the diagram is correct?

A. The water is at lower temperature than the ice.

B. Energy is released when the ice changes to water.

C. Energy is absorbed when the ice changes to water.

D. The water molecules vibrate about a fixed point.

The correct answer is “Energy is absorbed when the ice changes to water.”, which is lettered C.

23


Heat energy near the ice gets absorbed into the ice. The energy breaks the bonds of the ice, causing it to melt

into liquid water. In other words, when ice melts, the energy gets absorbed into the water.

26. Which of the following statements best explains the differences between a gas and a vapour?

A. Unlike gases, vapour can easily be condensed into liquids.

B. Unlike gases, vapours are liquids at room temperature.

C. Unlike gases vapour is readily converted into solids.

D. Vapours are generally denser than gases.

The correct answer is “Vapour are generally denser than gases.”, which is lettered D.

Vapour is the equilibrium state between the gases and liquid, and it can bounce back to its original form,

liquid with constant temperature and pressure exerted on it.

27. Consider the following reaction equation:

2HCl + Ca (OH)2 → CaCl2 +H2O.

What volume of 0.1 mol dm3 HC1 would completely neutralize 25 cm3 of 0.3 mol dm3 Ca (OH)2?

A. 30 cm3

B. 75 cm3

C. 150 cm3

D. 25cm3

The correct answer is “150 cm3.”, which is lettered C.

The goal here is firstly compare the moles owing to the fact that the equation should be balanced. Next, we

compare the difference in concentration and use it against the volumes but making sure it’s in dm³.

28. Cu and HNO3 are not suitable for preparing hydrogen gas because of their

A. conductivity and corrosiveness respectively.

B. reactivity and oxidation respectively.

C. melting point and reduction respectively.

D. electronegativity and solubility respectively.

The correct answer is “conductivity and corrosiveness respectively.”, which is lettered A.

Copper is not active enough to replace hydrogen in an acid. Also, nitric acid is a strong oxidizing agent that

quickly oxidizes hydrogen to water.

29. Which of the following formulae cannot be an empirical formula?

A. CH

B. CH2

C. N2O4

D. P2O5

The correct answer is “N₂O₄.”, which is lettered C.

24


The empirical formula is always in the ratio of the smallest positive integer, hence, N₂O₄ has an empirical

formula NO₂.

30. One of the criteria for confirming the purity of benzene is to determine its

A. boiling point

B. heat capacity

C. mass

D. color

The correct answer is “boiling point.”, which is lettered A.

Any pure substance will have a specific melting and boiling point. The presence of impurities alers the

boiling points.

31. When chlorine is passed through a sample of water, the pH of the water sample would be

A. >7

B. <7

C. =7

D. 0

The correct answer is “<7”, which is lettered B.

Cl₂+H₂O → HCl + HOCl

The two compounds in the product end are acidic; hence, the mixture is acidic. Therefore, the pH is < 7.

32. How many atoms are contained in 0.2 moles of nitrogen?

[NA = 6.02 x 1023]

A. 1.20 x 1023

B. 4.82 x 1023

C. 3.62 x 1023

D. 2.41 x 1023

The correct answer is “1.20 x 1023.”, which is lettered A.

0.02mol N₂ x 6.02x10²³

= 1.2×10².

33. The strength of metallic bonds depends on the

A. charge density of the atoms.

B. number of valence electrons.

C. ductility of the metal.

D. total number of electrons in the atom.

The correct answer is “number of valence electrons.”, which is lettered B.

It is determined by the difference in the electron structures of the atoms. These primarily are: The number of

outer electrons, i.e.: The number of valence shell electrons released during a metallic bond.

25


34. When zinc is added to AgNO3 solution, crystals of silver form on the zinc surface.

This indicates that zinc is

A. reduced.

B. oxidized.

C. decomposed.

D. dissociated.

The correct answer is “oxidized.”, which is lettered B.

2AgNO₃+Zn → Zn (NO₃)₂+2Ag

The oxidation number of Zn in the reactant is O, and in the product is +2. Therefore, it is oxidized.

35. The empirical formula of a compound containing 0.067 mol Cu and 0.066 mol 0 is

[Cu = 63.5, O = 16.0]

A. Cu2O.

B. Cu2O2.

C. CuO2.

D. CuO.

The correct answer is CuO., which is lettered D.

Cu:O

0.067:0.066

More ratio 0.067/0.066 : 0.0066/0.066

= 1:1

CuO

36. The change in the oxidation state of iron in the reaction represented by the equation below is

2FeCl3 + H2S → 2FeCl2 + 2HCl + S

A. +2 to +3.

B. +3 to +0.

C. 0 to +2.

D. +3 to +2.

The correct answer is “+3 to +2.”, which is lettered D.

The oxidation number of irons in FeCl₃ = +3

The oxidation number in FeCl₂ = +2.

37. Which of the following methods can be used to separate blood cells from plasma?

A. Chromatography

B. Filtration

C. Centrifugation

D. Distillation

The correct answer is Centrifugation., which is lettered C.

Centrifugation is the method use in the separation of blood cells from plasma of the cell through circulation.

26


38. Which of the following statements about ionic radius is correct? Ionic radius

A. increases as nuclear charge increases.

B. decreases as nuclear charge decreases.

C. decreases as nuclear charge increases.

D. remains constant as nuclear charge increases.

The correct answer is “decreases as nuclear charge increases.”, which is lettered C.

In the ironic radius, whenever the nuclear of the charge increase, the ironic radius of the charge decreases.

Therefore, the radius of the charge is in direct proportion to its radius.

39. Analysis of hydrocarbon shows that it contains 0.93 g of carbon per gram of the compound. The mole ratio

of carbon to hydrogen in the compound is

[H=l.0, C=12.0]

A. 2: 1

B. 1: 2

C. 1: 1

D. 2: 3

The correct answer is “1: 1”, which is lettered C.

The mole ratio of hydrogen to carbon in the compound of

H → C

1 → 1

Ratio = 1:1.

40. The law of definite proportions states that

A. chemical compounds are pure because they contain the same elements.

B. pure samples of substances are in the same proportion by mass.

C. pure samples of the same compound contain the same elements combined in the same proportion

by mass.

D. matter can neither be created nor destroyed.

The correct answer is “pure samples of the same compound contain the same elements combined in the

same proportion by mass.”, which is lettered C.

The law of definite proportions states samples of a compound will always contain the same proportion of

elements by mass. The mass ratio of elements is fixed no matter where the elements came from, how the

compound is prepared, or any other factor.

41. What is the relative molecular mass of a compound which has empirical formula CH2O?

[H= 1.0, C= 12.0, O=16.0]

A. A. 42

B. 180

C. 126

D. 45

27


The correct answer is 180., which is lettered B.

(Emp)x= 180

30x= 180

30x/30 = 180/30

x= 6

Therefore, 30 x 6 = 180

42. Atoms are electrically neutral because they

A. contain equal number of protons and electrons.

B. do not conduct electricity.

C. are composed of neutrons and electrons.

D. cannot be attracted by electromagnetic field.

The correct answer is “contain equal number of protons and electrons.”, which is lettered A.

Atoms are electrically neutral because they contain equal quantities of positively charged protons and

negatively charged electrons.

43. Common salt (NaCl) is used for preserving foods. Which of the following properties could be used to

determine its purity before use?

A. Solubility in water

B. Relative density

C. Melting point

D. Crystalline nature

The correct answer is “Crystalline nature.”, which is lettered D.

The crystalline nature is used to observe it purity before used because NaCl is a solute which constitute a

write crystalline.

44. Which of the following electron configuration represents the transition element chromium (24Cr)?

A. 1s22s22p63s23p64s23d4

B. 1s22s22p63s23p64s13d5

C. 1s22s22p63s23d44s1

D. 1s22s22p63s23p63d6

The correct answer is “1s22s22p63s23p63d6.”, which is lettered D.

It represents the transitional element chromium because the last energy level of the electron occupied 3p and

3d energy level.

45. The atomic number of an isotope of hydrogen is equal to its mass number because it

A. does not contain neutrons.

B. has a high charge to mass ratio.

C. has a totally filled valence shell.

D. exhibits isotropy.

28


The correct answer is “does not contain neutrons.”, which is lettered A.

Hydrogen as an element that is critical. The nucleus has only protons. Since the mass number is the sum of

protons and neutrons, we can clearly see that the result is the number of protons. Mass number = Number of

protons + Number of Neutron

Mass Number= Number of protons.

46. The total number of shared pair of electrons in the compound below is

A. 5

B. 12

C. 10

D. 6

The correct answer is 6., which is lettered D.

It shares the total of 6 pairs of electrons because hydrogen gave out le and carbon gave out le which

constitute a lone pair of electrons.

47. The bonding pairs of electrons in a hydrogen chloride molecule is pulled towards the chlorine atom because

A. chlorine has a larger atomic size.

B. chlorine is more electronegative.

C. chlorine has a larger atomic mass.

D. there is no bonding orbitals within the hydrogen atom

The correct answer is “chlorine is more electronegative.”, which is lettered B.

The chlorine atom has a very high electronegative which caused it to pull the hydrogen chloride molecule

towards it.

48. The solubility of CO2 in water can be accounted for by

A. van der Waal’s forces

B. ionic attraction.

C. covalent bonding.

D. dipole attraction.

The correct answer is “van der Wall’s forces.”, which is lettered A.

In CO₂, due to electronegativity difference oxygens have slight negative charge, hence surrounded by polar

water molecules forming cage structure. This leads to its solubility.

29


49. Which of the following properties would not influence electrovalent bond formation?

A. Electronegativity

B. Catalytic ability

C. Ionization potential

D. Electron affinity

The correct answer is “Catalytic ability.”, which is lettered B.

Every other factor influences the formation of electrovalent or ionic bonds except catalytic.

50. Particles in a solid exhibit

A. vibrational and random motion

B. vibrational and translational motion

C. vibrational motion only.

D. random and translational motion.

The correct answer is “vibrational motion only.”, which is lettered C.

Solid vibrates but generally do not move from place to place.

END OF PAPER

30


THE WEST AFRICAN EXAMINATIONS COUNCIL

West African Senior School Certificate Examination

for School Candidates

SC 2018 CHEMISTRY 3 1 hour 30 minutes

Write your name and index number in ink in the spaces provided at the top right-hand corner of this

paper.

Answer all the question sin your answer booklet in ink.

Marks will be awarded mainly for details that show that you have ha d the required practical experience in

the laboratory and for clarity of expression and orderly presentation of material.

© 2018 The West African Examinations Council

SC5053/D

WASSCE 2018

CHEMISTRY 3

Alternative to

PRACTICAL

1 hour 30 minutes

The West African Examinations

Council

Senior High School Certificate

Examination

Literature-In-English

Name: …………………………………………………….

Index Number: ……………………………………………

31


1. In a titration experiment, 29.70 cm3 of a solution of mineral acid A, containing 0.025 moles in 250 cm3

of solution neutralized 25.0 cm3 of NaOH solution B. Solution B contained 4.76 g dm-3 of solution.

(a) From the information given, calculate the:

Data:

𝑉𝐴𝐶𝐼𝐷 = 29.70𝑐𝑚3

𝑁𝐴𝐶𝐼𝐷= 0.025moles

𝑉𝑁𝑎𝑂𝐻 = 25.0𝑐𝑚3

𝐷𝑁𝑎𝑂𝐻 = 4.76𝑔/𝑑𝑚3

𝑀𝐴𝐶𝐼𝐷 = 0.025𝑚𝑜𝑙𝑒𝑠

250𝑐𝑚3 .1𝑚𝑜𝑙

1𝑐𝑚3 ×1𝑑𝑚3

1000𝑚𝑙 .

= 0.025𝑚𝑜𝑙

0.25𝑑𝑚3 = 0.1M .

(i) number of moles of acid in the average litre;

Answer:

Moles of acid = 0.1 = 𝑚𝑜𝑙

𝑑𝑚3

0.1 = 𝑥

29.70𝑐𝑚3 .1𝑑𝑚3

1000𝑐𝑚3

0.1

1 =

𝑥

0.0297

x = 0.00297moles.

(ii) number of moles of NaOH in the volume of alkali used;

Answer:

Mole NaOH = 25.0𝑐𝑚3 × 1𝑑𝑚3

1000𝑐𝑚3 × 4.76𝑔

1𝑑𝑚3 × 1𝑚𝑜𝑙

40𝑔= 𝟎. 𝟎𝟎𝟐𝟗𝟖𝒎𝒐𝒍𝒆𝒔.

(iii) mole ratio of acid to base in the reaction.

Answer:

The ratio is 1:1.

(b) (i) Suggest what the acid in 1(a) could be;

Answer:

The acid in 1(a) could be HCL (Hydrochloric Acid).

(ii) Give a reason for your answer in 1(b)(i);

Answer:

The acid could be hydrochloric acid because of the mole-to-mole ratio of acid to base

in the reaction.

(iii) Write an equation for the reaction between NaOH(aq) and the suggested acid.

32


Answer:

𝑯𝑪𝑳(𝒂𝒒) + 𝑵𝒂𝑶𝑯(𝒂𝒒) → 𝑵𝒂𝑪𝑳(𝒂𝒒) + 𝑯𝟐𝟎(𝒍).

(c) If the indicator in the experiment was methyl orange, state the color of the indicator:

(i) in solution B before the titration;

Answer:

The color is Yellow.

(ii) at the end-point. [H = 1, O = 16, Na = 23]

Answer:

The color is Orange.

[16 marks]

2. C is a simple salt. The tests below were performed on portions of C. Copy and complete the table.

TEST

OBSERVATION

INFERENCE

(a) (i) C + heat Colorless, ordorless gas

evolved

……………………

……………………

(ii) Gas tested with

glowing splint

Glowing splint rekindled

……………………

(iii) C + strong heating Brown gas evolved which

turned damp blue litmus

paper red.

Residue left was yellow

when hot and white when

cold.

……………………

……………………

(b) (i) Solution of C

+ FeSO4(aq)

+ conc. H2SO4

……………………

……………………

(ii) Solution of C

+ NH3(aq) in drops

and then in excess

White gelatinous

precipitate formed.

Precipitate dissolved.

……………………

……………………

……………………

33


TEST

OBSERVATION

INFERENCE

(a) (i) C + heat Colorless, ordorless gas

evolved

Carbonate (𝐶𝑂32−) may be

present

(ii) Gas tested with

glowing splint

Glowing splint rekindled

Confirmation of oxygen

gas (02)

(iii) C + strong heating Brown gas evolved which

turned damp blue litmus

paper red.

Residue left was yellow

when hot and white when

cold.

Nitrogen dioxide (02) may

be present

(b) (i) Solution of C

+ FeSO4(aq)

+ conc. H2SO4

Dark brown ring is

formed at the junction of

the layer of two solutions

𝑁𝑂3− may be present

(ii) Solution of C

+ NH3(aq) in drops

and then in excess

White gelatinous

precipitate formed.

Precipitate dissolved.

𝑍𝑛2+ may be present

(c) (i) Write the formula of C;

Answer:

Zn𝑪𝑶𝟑 .

(ii) Name C.

Answer:

Zinc (II) Carbonate.

3. (a) State one reagent with the necessary condition that could be used to distinguish between:

(i) secondary alkanol and tertiary alkanol;

Answer:

Lucas Reagent – is used to distinguish secondary and tertiary alkanol.

(ii) terminal alkyne and non-terminal alkyne.

Answer:

Ammoniacal Silver Nitrate/Ammoniacal Cuprous Chloride.

[4 marks]

34


(b) Outline the technique that could be used to purify a sample of potassium chloride

contaminated with sand. [4 marks]

Answer:

- Firstly, mix the sample with water

- Filter the solution by using filter paper

- The sand will be left on the filter paper

- Potassium Chloride (KCL) will sublimate and stick to the funnel.

(c) Give a reason for each of the following laboratory practices:

(i) Alkaline solutions are not stored in glass stoppered reagent bottles;

Answer:

Alkaline solutions are not stored in glass stoppered reagent bottles because alkali can

cause the stopper to corrode and fuse to the bottle neck. Also, the glass contracts with

changes in temperature.

(ii) reactions involving organic solvents are heated on a water bath rather

than over Bunsen flame.

Answer:

Reaction involving organic solvents are heated on a water bath rather over Bunsen

flame because water bath provides a larger surface area for heating and there is no

temperature fluctuations when heating many sample at the same time. Also, water

bath is the best for flammable chemical.

[2 marks]

(d) (i) List four pieces of apparatus that could be used in the determination

of heat of neutralization;

Answer:

Calorimeter, thermometer, graduated cylinder, and beaker.

(ii) Name two gases that could be collected over water;

Answer:

Hydrogen gas (𝐻2) and Nitrogen gas (𝑁2).

(iii) Give a reason for your answer in 3(d)(ii).

Answer:

These gases are insoluble in water.

Because water displacement is a convenient way to collect a gas.

35


[7 marks]

(e) (i) State two uses of activated charcoal.

Answer:

- Teeth whitening and oral health

- Water filtration.

(ii) In a titration experiment to determine the number of moles of water of

crystallization given two solutions, state two precautions that should be

taken in carrying Out the experiment.

Answer:

- Gentle heating should be carried out to reduce the risk of decomposing. Use a well-

ventilated lab.

- Wear safety googles

[4 marks]

END OF PAPER

36


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