S3_Chemistry_EOY_08_P2

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Name: __________________________________ ( ) Class: _____

HWA CHONG INSTITUTION

END-OF-YEAR EXAMINATION 2008

CHEMISTRY

Paper 2

Level: Sec 3Time: 1 hour 45 minutes

INSTRUCTIONS TO CANDIDATES

Do not turn the pages over until you are told to do so.

Write your name, index number and class in the spaces at the top of this page.

Section A and B

Answerall questions.

Write your answers in the spaces provided.

All essential working must be shown.

INFORMATION FOR CANDIDATES

The number of marks is given in brackets [] at the end of each question or part question.

A copy of the Periodic Table is printed on page 2.

FOR EXAMINERS USE

Section A

B 8

B 9

B 10

Total

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This question paper consists of14printed pages (including this page)


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Group

I II III IV V VI VII 01

HHydrogen

1

4

HeHelium

2

7

LiLithium

3

9

BeBeryllium

4

11

BBoron

5

12

CCarbon

6

14

NNitrogen

7

16

OOxygen

8

19

FFluorine

9

20

NeNeon

10

23

NaSodium

11

24

MgMagnesium

12

27

AlAluminium

13

28

SiSilicon

14

31

PPhosphorus

15

32

SSulphur

16

35.5

ClChlorine

17

40

ArArgon

18

39

KPotassium

19

40

CaCalcium

20

45

ScScandium

21

48

TiTitanium

22

51

VVanadium

23

52

CrChromium

24

55

MnManganese

25

56

FeIron

26

59

CoCobalt

27

59

NiNickel

28

64

CuCopper

29

65

ZnZinc

30

70

GaGallium

31

73

GeGermanium

32

75

AsArsenic

33

79

SeSelenium

34

80

BrBromine

35

84

KrKrypton

36

85

RbRubidium

37

88

SrStrontium

38

89

YYttrium

39

91

ZrZirconium

40

93

NbNiobium

41

96

MoMolybdenum

42

TcTechnetium

43

101

RuRuthenium

44

103

RhRhodium

45

106

PdPalladium

46

108

AgSilver

47

112

CdCadmium

48

115

InIndium

49

119

SnTin

50

122

SbAntimony

51

128

TeTellurium

52

127

IIodine

53

131

XeXenon

54

133

CsCaesium

55

137

BaBarium

56

139

LaLanthanium

57

178

HfHafnium

72

181

TaTantalum

73

184

WTungsten

74

186

ReRhenium

75

190

OsOsmium

76

192

IrIridium

77

195

PtPlatinum

78

197

AuGold

79

201

HgMercury

80

204

TlThallium

81

207

PbLead

82

209

BiBismuth

83

PoPolonium

84

AtAstatine

85

RnRadon

86

FrFrancium

87

226

RaRadium

88

227

AcActinium

89 +

*58-71 Lanthanoid series

+90-103 Actinoid series

140Ce

Cerium

58

141Pr

Praseodymium

59

144Nd

Neodymium

60

PmPromethium

61

150Sm

Samarium

62

152Eu

Europium

63

157Gd

Gadolinium

64

159Tb

Terbium

65

162Dy

Dysprosium

66

165Ho

Holmium

67

167Er

Erbium

68

169TmThulium

69

173Yb

Ytterbium

70

175Lu

Lutetium

71

Key

a

X

b

a = relative atomic massX = atomic symbol

b = proton (atomic) number

232

ThThorium

90

PaProtactinium

91

238

UUranium

92

NpNeptunium

93

PuPlutonium

94

AmAmericium

95

CmCurium

96

BkBerkelium

97

CfCalifornium

98

EsEinsteinium

99

FmFermium

100

MdMendelevium

101

NoNobelium

102

LrLawrencium

103

The volume of one mole of any gas is 24 dm 3 at room temperature and pressure (r.t.p)

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+ dilute acid T

Section A (40 marks)

Answerall questions in the spaces provided.

A1

Study the following flow chart and answer the questions that follow:

(a) Identify the substances W and T. [2]

(i) W:

(ii) T:

(b) (i) Name the type of reaction that occurred in step II. [1]

(ii) Write the chemical equation for the reaction that occurred in step II. [1]

3

I

Insoluble

Yellow solution

G with noeffervescence

White precipitate

R

Reddish brown

crystal G

Water

Reddish brown

solid W

II

III

+ Ba(NO3)2 (aq)

IV


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(c) Predict the observation which you would make if solution G is added to aqueous sodium

hydroxide until no further change. [2]

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

________________________________________________________________________

(d) Describe briefly how you would carry out step IV in the laboratory to obtain reddish-

brown crystals G. [3]

________________________________________________________________________

A2

Barium oxide dissolves in water to form a strong alkali, barium hydroxide.

(a) (i) What is meant by a strong alkali? [1]

_____________________________________________________________________

_____________________________________________________________________

(ii) Give an example of a weak alkali. [1]

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(b) Conductance is a measure of how well a solution conducts electricity.

The graph below shows the change in conductance of a barium hydroxide solution assulphuric acid is added to it. A white precipitate is formed as sulphuric acid is added to the

barium hydroxide solution.

(i) Write an ionic equation with state symbols for the reaction between aqueous barium

hydroxide and sulphuric acid. [2]

(ii) Explain the shape of the graph, making reference to the ions and molecules present in

the solution. [3]

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

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(iii) Describe the change in pH of the solution as sulphuric acid is added. [1]

5

Conductance/ mA

Volume of H2SO

4(aq) added/ ml


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A3

(a) (i) Explain the term electronegativity. [1]

_____________________________________________________________________

(ii) By using the symbols + and -, indicate the dipole of the covalent bonds shown

below. [2]

C Cl

Cl F

(b) The gases NH3 and HCl combine to form a salt, NH4Cl.

(i) Construct dot and cross diagrams to show the bonding in ammonia and hydrogenchloride gas. [2]

NH3 HCl

(ii) Compare the boiling points and physical states of NH3, HCl and NH4Cl at room

temperature. Explain your answer in terms ofstructure and bonding. [6]

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

____________________________________________________________________

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A4

The table below lists the physical and chemical properties of 8 elements at standard pressure that

correspond to known elements in the Periodic Table. The elements are identified by the code

letters A, B, C, D, E, F, G and H.

Element AMelting point 98 oC

Boiling point 886 oC

Atomic radius 186 pmOxide formula A2O

Element EMelting point 649 oC

Boiling point 1090 oC

Atomic radius 160 pmOxide formula EO

Element B

Melting point -101 oCBoiling point -35 oC

Atomic radius 100 pm

Oxide formula B2O

Element F

Melting point 64 oCBoiling point 774 oC


Oxide formula F2O

Element C



Oxide formula C2O3

Element G



Oxide formula GO2Element D

Melting point 181 oC

Boiling point 1347 oCAtomic radius 150 pm

Oxide formula D2O

Element H

Melting point -189 oC

Boiling point -186 oCAtomic radius 94 pm

Oxide formula (none)

(a) What is the number of valence electrons in an atom of A and B at ground state? [2]

Number of valence electrons in A: ___________________________________________

Number of valence electrons in B: ___________________________________________

(b) Identify, by code letter, the element that is a noble gas in the table. [1]

_______________________________________________________________________

(c) Three of the elements are in the same group of the Periodic Table.

(i) To which group do the elements belong? [1]

_________________________________________________________________

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Section B (30 marks)

Answerall the three questions in the spaces provided. Each question carries 10 marks.

B1

(a) Reactivity series is the order of reactivity of metals with substances such as air, water and

dilute acid. The reactivity series is shown below:

Potassium

Sodium

CalciumMagnesium

Aluminium

ZincIron

Tin

Lead

HydrogenCopper

Silver

Gold

It can be used to predict the reactivity of metals with dilute acid. Metals higher than

hydrogen in the reactivity series react with acid, while those below hydrogen will not reactwith acid.

A student wants to test the validity of the series by comparing the reactivity of calcium,aluminium, iron, lead and copper with dilute hydrochloric acid by setting up the apparatus

as shown in the diagram. As the reaction proceeds, gas produced travels through the tubingto an inverted measuring cylinder filled with water, displacing some of the water in the

measuring cylinder.

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Reactivity

increases

Dilute HCl (aq)

Metal


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(i) Suggest a reason why the set up should not be put close to a flame. [1]

(ii) Why is it necessary to rub the metal pieces with sandpaper before reacting them withdilute hydrochloric acid? [1]

(iii) Suggest how he would compare the reactivity of the metals using the set up above. [1]

(iv) Although lead is above hydrogen in the reactivity series, the student observed that therewas no effervescence when lead was added to the acid.

Explain why lead does not react with hydrochloric acid. [2]

(b) (i) State the number of protons and neutrons in an atom of12

24

Mg. [1]

(ii) Draw the electron-in-box diagram for a magnesium ion. [1]

(iii) Write the formula of an atom which is isoelectronic with magnesium ion. [1]

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(iv)Calcium reacts with nitrogen to form calcium nitride, which has a melting point of

1195 oC. Draw the dot and cross diagram of calcium nitride. [2]

B2

The following is the percentage composition by mass of ascorbic acid.

40.90 % Carbon4.55 % Hydrogen

54.55 % Oxygen

(a) (i) Determine the empirical formula of ascorbic acid. [3]

(ii) Given that relative molecular mass (Mr) of ascorbic acid is 176, determine themolecular formula of ascorbic acid. [2]

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(b) A brand of vitamin C contains ascorbic acid and zinc as active ingredients. A student

carried out an experiment to determine the percentage of ascorbic acid in a tablet of vitaminC by carrying out the following steps.

1) Weigh 1 tablet of vitamin C.2) Crush the tablet in a conical flask and add 50 ml of deionised water.

3) Titrate aqueous vitamin C with 1.00 mol/dm3 aqueous NaOH using phenolphthalein

indicator.4) Stop when indicator changes colour. Record reading.

The results he obtained were as follows:

Mass of one tablet of vitamin C = 4.00 g

Average volume of aqueous NaOH required = 17.6 cm3

(i) Calculate the number of moles of aqueous NaOH in 17.6 cm3 of 1.00 mol/dm3 NaOH

solution. [1]

(ii) Assuming that ascorbic acid is a monobasic acid, calculate the number of moles of

ascorbic acid which reacts with 17.6 cm3 of 1.00 mol/dm3 NaOH. [2]

(iii) Given that Mr of ascorbic acid is 176, calculate the mass of ascorbic acid in 1 tablet of

vitamin C. [1]

(iv) Hence calculate the percentage by mass of ascorbic acid in 1 tablet of vitamin C. [1]

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B3

The relative amount of nitrogen dioxide in the air over Singapore over a 10-year period is shown

below.

0

1

2

3

4

5

6

7

1981 1982 1983 1984 1985 1986 1987 1988 1989 1990

Year

Relativeamountofnitrogen

dioxide

Urban

(a) Explain

(i) the general increase in the amount of urban nitrogen dioxide in the air between 1981

and 1987. [1]

_____________________________________________________________________

(ii) the change in the amount of urban nitrogen dioxide in the air after 1987. [1]

(iii) how nitrogen dioxide is formed. [2]

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(b) Acid rain is a problem in industrialized countries around the world. Acid rainoften has a pH of 4.0 or lower. This level of acidity can damage trees andplants, leach minerals from the soil, and cause the death of aquatic animalsand plants.

(i) Name a gas, other than nitrogen dioxide, which may cause acid rain. [1]

(ii) State a possible source of the gas named in b (i). [1]

(iii) Explain how the gas in b (i) causes acid rain and why such rain causes damage tobuildings. Include at least one equation in your answer. [4]

--END OF PAPER

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S3_Chemistry_EOY_08_P2

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