�

Topic 8 Chemistry of Carbon Compounds

Part A Unit-basedexercise

Unit 29 An introduction to the chemistry of carbon compounds

Fillintheblanks

� carbon-carbondouble bond

2 hydroxyl

3 carbonyl

4 carboxyl

5 O

C O

6 O

C N

7 permanent dipole-permanent dipole attractions

8 hydrogen bonds

Trueorfalse

9 F

�0 T

�� F

�2 F

�3 T

�4 F

�5 T

�6 T

�7 T

�8 T

2

Multiplechoicequestions

�9 B

20 A

2� A

22 D

23 B

24 C

25 C

26 D

27 D

28 D

29 A

30 C

3� A

32 D

33 C

34 C

35 B

36 D

37 B

38 C

39 A

40 B

4� D

3

42 A

43 B

44 D

45 A

46 C

47 D

48 C

49 C

50 B

5� D

52 A

53 B

54 B

55 D

56 C

57 D

58 C

59 C

60 C

6� D

62 A

63 C

64 B

65 B

66 C

4

67 A

68 B

69 B

70 D

7� B

72 D

73 C

74 B

75 A

76 D

Unit 30 Isomerism

Fillintheblanks

� structural

2 stereoisomers

3 Enantiomers

4 chiral

5 opposite; optically active

Trueorfalse

6 T

7 F

8 F

9 T

�0 T

�� F

�2 T

5

�3 F

�4 T

�5 F

Multiplechoicequestions

�6 B

�7 D

�8 B

�9 B

20 C

2� D

22 A

23 D

28 C

25 B

26 C

27 B

28 C

29 C

30 D

3� B

32 A

33 B

34 B

35 B

6

36 B

37 B

38 A

39 D

40 B

4� C

42 C

43 B

44 A

45 A

46 D

47 B

48 B

49 C

50 D

5� B

52 A

53 B

54 A

55 B

56 B

57 C

58 C

59 B

7

60 B

6� A

62 A

63 C

64 B

65 C

66 D

67 C

68 B

69 D

70 A

7� D

72 D

73 C

74 C

Unit 31 Typical reactions of selected functional groups

Fillintheblanks

� addition / hydrogenation

2 substitution / hydrolysis

3 substitution

4 dehydration / elimination

5 oxidation

6 reduction

7 esterification / condensation

8 hydrolysis

8

Trueorfalse

9 T

�0 F

�� F

�2 F

�3 T

�4 T

�5 T

Multiplechoicequestions

�6 C

�7 C

�8 B

�9 D

20 D

2� C

22 C

23 A

24 C

25 B

26 D Thereactionmixture isheated ina flaskconnectedtoa refluxcondenser. In the refluxcondenser,all thevapour is condensedback into the flask. This prevents any loss of the reactionmixture.

27 B

28 C

29 C

30 D

9

3� A

32 A

33 D

34 C Option A— The acidifiedpotassiumdichromate solution acts as anoxidizing agent.

Option B— Propanoic acid is the final product.

Option C— Propan-�-ol is first oxidized to propanal and then to propanoic acid.

Option D— The reactionmixture changes fromorange togreenas thedichromate ions are reduced tochromium(III) ions.

35 C

36 B

37 C

38 B

39 C

40 A

4� B

42 C

43 A

44 D

45 A

46 D

47 C

48 A

49 C

50 C

5� D Thereactionmixture isheated ina flaskconnectedtoa refluxcondenser. In the refluxcondenser,all thevapour is condensed back into the flask. This prevents any loss of the reaction mixture and favours theoxidationof ethanol to propanoic acid rather than to propanal.

�0

52 D

53 B

54 D Ethanol in thewine is oxidized to ethanoic acid. The acidmakes thewine tastes sour.

55 B

56 C

57 C

58 D

59 B

60 C

6� A

62 C

63 D

64 A

65 B

66 A An ester is formed when a carboxylic acid reacts with an alkanol. The reaction is known asesterification.

67 D Therateofesterification is slow.Henceconcentratedsulphuricacid isusedasacatalyst tospeedupthereaction.

68 B C O H +

O

CH3 C O CH3

O

CH3O CH3H + H2O

+ +carboxylic acid alcohol ester water

69 D The flavoursand fragrancesofmany fruitsaredue toamixtureofnaturalesters.Estersarealsoused inartificial flavourings.

70 B

7� C

72 D

73 C

��

74 A

75 B

76 C

77 B

78 A

79 A

80 C

8� C

82 B

83 B

84 D

85 B

86 A

87 A

88 D

89 C CompoundXisanalcoholanditundergoesoxidationinthereaction.Thereactionmixturechangesfromorange to green as thedichromate ions are reduced to chromium(III) ions.

90 A

9� D

92 A The compound is ethyl ethanoate.

(3) It is produced fromethanol and ethanoic acid.

93 B

94 D

95 A

96 D

�2

97 A

98 B

99 D

�00A

�0�B

�02C

�03B

�04C

�05C

�06C The reactionbetween ethanoic acid and ethanol is esterification.

�07D The rateof esterification is slow.A catalyst such as concentrated sulphuric acid is used to speedup thereaction.

�08B

�09A

��0D

Unit 32 Synthesis of carbon compounds

Fillintheblanks

� a) i) Br2 (in organic solvent) (�)

ii) Br2 (aq) (�)

ii) H2 /Ni catalyst (�)

iii) HBr(g) (�)

iv) MnO4– /OH– (�)

b) i) conc.H2SO4 or conc.H3PO4 orAl2O3, heat (�)

ii) refluxwith conc.HCl, ZnCl2 catalyst; ormix with PCl5; or refluxwith SOCl2 (�)

iii) refluxwithNaBr+ conc.H2SO4; or reflux with red P+Br2 (�)

iv) refluxwithNal + conc.H3PO4; or refluxwith red P+ I2 (�)

v) heatwithK2Cr2O7 /H3O+, distil off theproduct (�)

vi) CH3COOH, conc.H2SO4, heat (�)

�3

c) i) refluxwithK2Cr2O7 /H3O+ (�)

ii) � LiAlH4 / ethoxyethane; 2H3O+ (�)

iii) concentratedH2SO4, heat (�)

iv) refluxwithNaOH(aq) (�)

v) �NH3(aq); 2 heat (�)

vi) HCl(aq), heat (�)

vii)refluxwithNaOH(aq) (�)

Trueorfalse

2 F

3 T

4 T

5 F

6 F

Multiplechoicequestions

7 A

8 A

9 D

�0 A

�� C

�2 D

�3 C

�4 D

�5 C

�6 D

�7 C

�8 C

�9 C

�4

20 C

2� D

22 B

23 D

24 B

25 B

26 D

27 D

28 B

29 A

30 D

3� C

32 D

33 C

34 C

35 A

36 A

37 C

38 C

39 B

40 B

4� A

42 D

43 C

44 A

�5

45 A

46 D

47 B

48 B

49 A

50 B

5� C

52 A

53 C

54 C

Unit 33 Important organic substances

Fillintheblanks

� fats; oils; saponification

2 calcium;magnesium

3 scum

4 non-biodegradable

5 hydrogen

6 condensation

7 monosaccharides

8 glucose; frustose

9 triglyceride

�0 amino acid

Trueorfalse

�� T

�2 F

�6

�3 F

�4 F

�5 T

�6 T

�7 F

�8 T

�9 T

20 F

Multiplechoicequestions

2� B

22 C

23 D The hydrocarbon ‘tail’ is soluble in grease and oil, i.e. hydrophobic. The ionic ‘head’ is soluble in water,i.e. hydrophilic.

24 C When fats or oils are heated with an alkali, they are hydrolyzed first to form glycerol and carboxylicacids. Theacids then reactwith thealkali (sodiumhydroxideorpotassiumhydroxide) to form sodiumorpotassium saltswhich are soaps. Such reactions are called saponification.

25 A Concentrated sodium chloride solution lowers the solubility of soap in water. The soap separates fromthe solution and floats on the surface.

26 D

27 B

28 A Detergents I and IV are soaps. Theywould form scumwithhardwater.

29 C Detergent III is non-biodegradable.

30 B Detergents II and III are soapless detergents.

3� B

32 C

33 D The ionic ‘head’ of a soapparticle is usually a C O–

O

group.

�7

34 A Option A — Seawater is hardwater and contains a relatively high concentrationofmagnesium salts.

Major elements found in sea water

Element Content (parts per million, ppm)

Chlorine �9500

Sodium �0770

Magnesium �290

Sulphur 905

Asoapsolutionformsscumwithseawater.Aproper lathercannotformuntil thesoaphasreactedwith all themagnesium salts in the seawater.

Option B — The tapwater inHongKong is softwater.

35 A

36 D The calcium carbonate deposit canbe removedby an acid.Vinegar contains ethanoic acid.

CaCO3(s) + 2H+(aq) Ca2+(aq)+CO2(g) +H2O(l)

37 B

38 D

39 B

40 D

4� B

42 A

43 A

44 A

45 D

46 A

47 D

48 D

49 B

50 A

�8

5� B (�) Hardwater contains a great amount of dissolved calcium andmagnesium salts.

(2) Sea water contains a relative high concentration of magnesium salts. Therefore sea water is hard water.

(3) The tapwater inHongKong is softwater.

52 D (�) The ionic ‘head’ of a soapless detergent particle is usually a sulphonate –SO2–O– or sulphate–O–SO2–O– group.

53 B

54 A

55 A (�) When the phosphates go into rivers and seas, they become the nutrients of the algae. As a result,algae will grow suddenly. Sometimes algae may grow so that they form a thick layer on the watersurface. Light cannot enter the deeper level of the water. As a result, the plants underneath cannotcarry out photosynthesis and they die.

56 B

57 A

58 C (2) Nylon is a condensationpolymer.

59 B

60 B (�) Poly(ethylene terephthalate) is common polyester. It is formed by the condensation of a diol and adioic acid.

(2) Poly(ethylene terephthalate) is a thermoplastic. There is no covalent bondbetweenpolymer chains.

6� D

62 D

63 A

64 C

65 B

66 D

67 B

68 B The correct explanation is that soap acts as an emulsifying agent.

69 D Thehydrocarbon tail of soaps is hydrophobic. Soaps aremade fromnatural fats andoils.

�9

70 C Bacteria use up oxygen in the water during the decomposition of detergents. This makes the water ofsome streams, rivers and seas smells badly due to oxygendepletion.

7� D Detergents with branched-chain hydrocarbons are non-biodegradable. They cause more harm to theenvironmentwhen compared to thosewith straight-chain hydrocarbons.

72 A

73 B Soapless detergents donot form scumwith either softwater or hardwater.

74 D

75 C Nylon softens uponheating.

76 D

77 C

Part B Topic-based exercise

Multiplechoicequestions

� C

2 D

3 C

4 B

5 A

6 C

7 A

8 A

9 A

�0 A

�� B

�2 A

20

�3 B

�4 D

�5 D

�6 C

�7 A

�8 B

�9 B

20 C

2� C

22 B

23 C

24 B

25 C

26 C

27 D

28 C

29 B

30 D

3� C

32 C

33 D

34 D

35 C

36 C

2�

37 D

38 B

39 D

40 D

4� C

42 C

43 C

44 B

45 A

46 C

47 B

48 A

49 B

50 D

5� B

52 A

53 C

54 C

55 D

56 A

57 C

58 B

59 C

60 B

22

6� D

62 A

63 A

64 D

65 D

66 A

67 A

68 C

69 D

70 B

7� C

72 D

73 A

74 C

75 A

76 C

77 D

78 B

79 D

80 A

8� B

82 B

83 D

84 A

23

85 A

86 B

87 C

88 A

Shortquestions

89 a) 4-methylpent-2-ene (�)

b) 3-bromobut-�-ene (�)

c) 2-chloro-2-methylhexane (�)

d) pentan-2-ol (�)

e) 2-ethylbutan-�-ol (�)

f) hex-3-enal (�)

g) 3-oxobutanoic acid (�)

h) 4-methylpentan-2-one (�)

i) 2-methylpropylmethanoate (�)

j) 2-aminopropanoic acid (�)

90 a)

(�)CH3CHCH2CHCH3

CH3CH3

b) CH3

CH2CH3

(�)

c)

C

O

CH3

(�)

d)

CH3CH2CH

CH3

CH2CH3OC

O

(�)

e) CH2=CHCONH2 (�)

24

9� a) functional group isomers (�)

b) chain isomers (�)

c) position isomers (�)

d) position isomers (�)

e) functional group isomers (�)

f) functional group isomers (�)

92 a) no (�)

b) yes (�)

c) no (�)

d) no (�)

e) yes (�)

f) yes (�)

93 a)

C

Cl

C*

H H

C

H

HH

C

H

C H

H

H

H

H

2-chloropentane

(�) (�)

b)

OH

C*

H H

C

H

HH

C

H

C HH

H

butan-2-ol

(�) (�)

c)

C

H

C

CH3 H

C*

H

HH

C C H

H

H

H 3-methylpent-�-ene

(�) (�)

e)

C COOH

CH3

C*

H

HH

C

H

H

H 2-methylbutanoic acid

(�) (�)

f)

H CHO

Br

C*

H

HH

C 2-bromopropanal

(�) (�)

94 a) propane (�)

b) ethanoic acid (�)

25

c) ethyl ethanoate (�)

d) butanamine (�)

e) cyclohexene (�)

f) butanal (�)

95 a) and b)

Test Observation(s)Type of reaction

involved

ShakeafewdropsofXwithaqueous bromine.

The aqueous bromine changes from yellow-brown to colourless quickly. (�)

addition (�)

AddphosphoruspentachloridetoX.Testanygasevolvedwithmoist blue litmuspaper.

Steamy fumes are observed. (�)The moist blue litmus paper turns red. (�)

substitution (�)

Add acidified potassiumdichromate solution to Xandheat themixture.

The acidified potassium dichromate solution changes from orange to green. (�)

oxidation (�)

96 a) Anyoneof the following:

• Add solid sodiumhydrogencarbonate (or solution). (�)

X gives a gas that turns limewatermilky. (�)

• Usemoist blue litmuspaper / pHpaper for testing. (�)

X turnsmoist blue litmuspaper / turns pHpaper orange (or red). (�)

b) Any one of the following:

• Add aqueousbromine. (�)

Y turns aqueousbromine from yellow-brown to colourless quickly. (�)

• Add cold acidifieddilute potassiumpermanganate solution. (�)

Y turns thepermanganate solution frompurple to colourless quickly. (�)

• Heatwith acidifiedpotassiumdichromate solution. (�)

Y turns thedichromate solution fromorange to green. (�)

26

97 a) Cl2 / ultraviolet; light (�)

b) CH3

(�)

c) red P+ I2; reflux (�)

d) conc. H2SO4 heat (�)

e)COOH

(�)

f) CH3CH(OH)CH2CH3 (�)

g) �NH3; 2 heat (�)

h) � LiAlH4 / ethoxyethane; 2H3O+ (�)

i) NaOH(aq); heat (�)

j)

OH

COOH

(�)

98 a) CH3CH(OH)CH2OH (�)

b)

C H

CH2CH3

H

C

H3CH2C

Br

H3C

(�)

c)

C

CH2CH3

C CH3

Br

H

D

H

(�)

d)O (�)

e)Cl

(�)

f) CH3CH2CH2I (�)

g)

CHCH2CH3C

CH3

CH3 (�)

27

h) OH

CH3

(�)

i)NH2 (1)

(1)

CH3CH2O

+ CH3COO–Na+

99 a) i)

H

HC

C

C OH

O

HO

C

H

H

C

OH

H

CH2OH

OH

(�)

ii) Carbonyl group (�)

Hydroxyl group (�)

b) i) Carboxyl group (�)

ii)

C NC OH

H

CH3

HO

H

H

C

CH3

O

C

O

(�)

C OC OH

H

CH3

H2N

H

C

CH3

O

C

O

(�)

iii) Anyoneof the following:

• Peptide link / amide functional group (�)

• Ester functional group (�)

Structuredquestions

�00a)

H

CH3CH2

C CH2(1)

H

CH3

H

CH3

C C(1)

H

CH3

CH3

HC C

(1)

CH3

CH3

C CH2(1)

28

b) i) H

CH3

H

CH3

C CH

CH3

CH3

HC Cand are cis-trans isomers.

(1)

ii) In order for the intermolecular forces to work well, the molecules must be able to pack together efficiently in the solid. (�)

Molecule of the trans isomer has a more regular and symmetrical structure than molecule of the cis isomer. (�)

Molecules of the trans isomer canpackmore compactly in the solid.

Moreheat is required to overcome the intermolecular forces between themolecules. (�)

Hence the trans isomer has a highermeltingpoint than the cis isomer.

�0� a) 2-hydroxybenzaldehyde (�)

b) Position isomerism (�)

c) X can form intramolecular hydrogenbonds. (�)

Y formsmore intermolecular hydrogenbonds thanXdoes. (�)

Thus themeltingpoint ofY ismuchhigher than that ofX.

�02a) Anyone of the following:

• Warmeach compoundwith acidifiedpotassiumdichromate solution. (�)

A turns thedichromate solution fromorange to green. (�)

There is noobservable change for B. (�)

• Warmeach compoundwith acidifiedpotassiumpermanganate solution. (�)

A turns thepurple permanganate solution colourless. (�)

There is noobservable change for B. (�)

b) Put about 2 cm3of ethanol and� cm3of silver nitrate solution in eachof two test tubes. (�)

Place the test tube in awater bath at 60 °C. (�)

Add several drops ofC andD separately to each test tube.

A yellowprecipitate forms rapidly in the test tube containingD. (�)

Awhite precipitate forms slowly in the test tube containingC. (�)

c) Warmeach compoundwith acidifiedpotassiumdichromate solution. (�)

F turns thedichromate solution fromorange to green. (�)

There is noobservable change for E. (�)

29

d) Add aqueousbromine to each compound separately. (�)

Gdecolorizes aqueousbrominequickly. (�)

There is noobservable change forH. (�)

�03a) i) hydroxyl group (�)

ii) carbonyl group (�)

iii) carboxyl group (�)

b) � LiAlH4 / ethoxyethane (�)

2 H3O+ (�)

c) Excess concentrated sulphuric acid (�)

�80 °C (�)

d) V (�)

K2Cr2O7 /H3O+ (�)

e) Anyone of the following:

• Warmeach compoundwith acidifiedpotassiumdichromate solution. (�)

U turns thedichromate solution fromorange to green. (�)

There is noobservable change forY. (�)

• Mix each compoundwithphosphorus pentachloride. (�)

Ugives steamy fumesof hydrogen chloride. (�)

There is noobservable change forY. (�)

f) Heat V and Z under reflux in thepresenceof concentrated sulphuric acid. (�)

CHCH2CH3O

CH3

CH3CH2CH2C

O

(�)

g) V (�)

* CH2CH(OH)CH2CH3 (�)

30

�04a) i) Condenser (�)

ii) CompoundX is flammable. (�)

iii) To ensure evenboiling. (�)

iv) Propanoic acid (�)

[O] v) CH3CH2CH2OH CH3CH2COOH (�)

vi) As an oxidizing agent (�)

vii)

(�mark foracorrectset-up;�mark forcorrect labels;�mark for thecorrectdirectionofwater flowin condenser; award0mark if the set-up is notworkable) (3)

b) i) Ethyl propanoate (�)

ii) As a catalyst (�)

iii) Heatingunder reflux can reduce the loss of volatile reactants / products by evaporation. (�)

�05a) i) substitution (�)

ii) dehydration / elimination (�)

iii) addition (�)

b) i) Cl2 (�)

ultraviolet light / sunlight (�)

ii) sodiumhydroxide solution (�)

reflux / heat (�)

iii) excess concentrated sulphuric acid (�)

�80 °C (�)

c) i) Structural isomers are compoundswith the samemolecular formula, (�)

but differ in theorder inwhich atoms are linked. (�)

3�

ii) Alcohol Classification

CH3CH2CH2CH2OHprimary

(0.5)

CH3CH2CHCH3

OHsecondary

(0.5)

CH3CHCH2OH

CH3

(�)

primary

(0.5)

CH3COH

CH3

CH3 (�)

tertiary

(0.5)

d) Any oneof the following:

• HCl(g) (�) in thepresenceof ZnCl2 catalyst (�)

• refluxwith concentratedhydrochloric acid (�) using ZnCl2 as catalyst (�)

• reflux (�)with sulphur dichloride oxide (�)

• mix (�)with phosphorus pentachloride (�)

e) i) Dehydration (�)

ii) CH3CH=CHCH3 (�)

�06a) Carbon-carbondouble bond (�)

Hydroxyl group (�)

b)

C CH2CH2OH

CH3

H

C

H

H

H 3-methylbutan-�-ol

(�) (�)

C CH2CH2OH

CH3

Br

C

H

Br

H 2,3-dibromo-3-methylbutan-�-ol

(�) (�)

c) i) 3-methylbut-3-enoic acid (�)

ii) Heat under reflux (�)

with acidified potassiumdichromate solution (�)

32

iii)

H

H

CH3

CH2CHOC C or 3-methylbut-3-enal (�)

d)H

H

CH3

CH2CH2OHC C +

H

CH3

Br

CH C CH2CH2Br

H

2HBr (1) + H2O (1)

�07a)

C Br

H

H

C

H

H

H (�)

b) i) Heat under reflux (�)

with acidified potassiumdichromate solution (�)

ii) Reactwith aqueous ammonia to forman ammonium salt. (�)

Evaporate thewater and subsequently heat thedry salt. (�)

c) i) Substitution (�)

ii) Oxidation (�)

iii) Reduction (�)

d) CH3COOH>CH3CH2OH>CH3CH2NH2 (�)

The boilingpoint of a compounddependson itsmolecular attractions. (�)

All the compounds can formhydrogenbonds.

Molecules ofCH3COOH can formmore extensive hydrogenbonds than thoseofCH3CH2OH. (�)

Thus theboiling point ofCH3COOH is higher than that ofCH3CH2OH.

Sinceoxygen ismoreelectronegative thannitrogen, theO–Hbond inCH3CH2OH ismorepolar than theN–Hbond inCH3CH2NH2.

As a result, stronger hydrogenbonds exist betweenmolecules ofCH3CH2OH. (�)

Thus theboiling point ofCH3CH2OH is higher than that ofCH3CH2NH2.

�08a) Carbon-carbondouble bond (�)

Carbonyl group (�)

b) i) Stereoisomers have their atoms linked in the sameway, (�)

but they differ in the spatial arrangement of their atoms. (�)

ii) Geometrical isomerism (�)

33

iii) Due to the restricted rotation about a carbon-carbondouble bond. (�)

iv) Identicalmethyl groups attach to oneof the carbon atomsof theC=Cbond. (�)

c) i) CHCH2CH2C

CH3

CHCH2OH(H3C)2C

(�)

ii) Primary alcohol (�)

There is one alkyl group attached to the carbonbearing the –OHgroup. (�)

iii) � LiAlH4 / ethoxyethane

2H3O+ (�)

iv) (�)

CHCH2CH2C

CH3

CHCH2(H3C)2C O CH3C

O

(�)

(2)Esterification

�09a)

CH3CHCH2Br

CH3

(�)

b)

C

CH3

CH2CH3 (�) methylpropene (�)

c) i)

CH3CBrCH3

CH3

(�) 2-bromo-2-methylpropane (�)

ii) Structural isomers are compoundswith the samemolecular formula, (�)

but differ in theorder inwhich atoms are linked. (�)

iii) CH3CH2CH2CH2Br (�)

CH3CH2CHBrCH3 (�)

��0a)

C

H

C H

H

H

Br

C

H

Br (�)

34

b) X, Y and Z are formed from thedehydrationof alcoholW.

Thus they are alkenes. (�)

X and Y reactwith bromine to give �,2-dibromo-�-phenylpropane, i.e. C

H

C H

H

H

Br

C

H

Br

.

It canbe deduced that the structures ofX andY are as follows:

H H

(1)

CH3

C CH CH3

(1)

HC C

Z reactswith bromine to give 2,3-dibromo-�-phenylpropane, i.e. C

H

C H

Br

H

Br

C

H

H

.

It canbe deduced that the structure of Z is as follows:

C

H

C H

H

C

H

H (�)

Wundergoes dehydration to giveX,Y and Z. It canbededuced that the structure ofW is as follows:

C

H

C H

H

H

OH

C

H

H (�)

c) X and Y exhibit geometrical isomerism. (�)

X, Y and Z exhibit structural / position isomerism. (�)

d) i) Thepurple permanganate solutionbecomes colourless quickly. (�)

ii)

C

H

C H

H

H

OH

C

H

OH (�)

35

���a) i) Suppose we have �00 g of compound X, so there are 40.0 g of carbon, 6.65 g of hydrogen and 53.3 gof oxygen.

Carbon Hydrogen Oxygen

Massofelementin thecompound

40.0g 6.65g 53.3g

Number ofmoles ofatoms thatcombine

40.0g�2.0gmol–� = 3.33mol

6.65g�.0gmol–� = 6.65mol

53.3g�6.0gmol–� = 3.33mol (�)

Simplestratio ofatoms

3.33mol3.33mol

=� 6.65mol3.33mol

=23.33mol3.33mol

=� (�)

∴ the empirical formula ofX isCH2O.

ii) Let (CH2O)n be themolecular formula ofX.

Relativemolecularmass ofX=n(�2.0+2 x �.0+�6.0) = 30n i.e. 30n = 90.0 n = 3

∴ themolecular formula ofX isC3H6O3. (�)

b) Effervescence occurs when X is mixed with sodium hydrogencarbonate solution. Thus it should be acarboxylic acid and contain a –COOH group. (�)

X undergoes esterificationwith ethanoic acid. Thus it should contain a –OHgroup. (�)

X is chiral. Thus it should contain at least one chiral carbon. (�)

Structure ofX:

2-hydroxypropanoic acid

OH

C

O

C OHH

H chiral carbon

C

H

H (�)

(�)

c) O

C

O

C OHH C

H

H (�)

36

d)

O

C

C

O

O

CO

CHH

CH3

CH3

(�) Ester functional group (�)

��2SinceW canbehydrolyzed to give an acidX and a neutral compoundY, soW shouldbe an ester. (�)

Relativemolecularmass ofW=�0 x �2.0+�2 x �.0+2 x �6.0=�64.0

Relativemolecularmass ofY=�64.0+�8.0 – �22.0=60.0 (�)

Let themolecular formula ofYbeCnH2n+�OH.

i.e. �2n + 2n+�+�6.0+�.0=60.0 n = 3

∴ the molecular formula ofY isC3H7OH (�) and that ofX isC7H6O2 orC6H5COOH. (�)

The structure ofX is

COOH

. (�)

Y canbeoxidized to Z, so Z shouldbe an aldehydeor a ketone.

As Z does not reactwith acidifiedpotassiumdichromate solution, thus Z shouldbe a ketone. (�)

Z is propanone,CH3COCH3. (�)

∴ Y is a secondary alcohol, CH3CHCH3

OH

. (�)

W is

COOCH(CH3)2

. (�)

��3a) CH3CH2CH2CH2Br CH3CH2CH2CH2OHNaOH(aq)

reflux(1) (1)

CH3CH2CH2COOHK2Cr2O7 / H3O

+

reflux(1)

37

b) conc. H2SO4

heat(1) (1)

CH2CH2OH CH CH2

HBr(g)

(1) (1)

NaOH(aq)

reflux(1) (1)

CHBrCH3 CH(OH)CH3

K2Cr2O7 / H3O+

(1)reflux

CCH3

O

c)

CH3CHCH2OHcold alkaline

dilute KMnO4

(1) OH

CH3CHCH3 CH3CHconc. H2SO4

heat(1) (1)

CH2

OH

d) NaOH(aq)

reflux(1)

CH2CH2Br K2Cr2O7 / H3O+

reflux(1)(1)

CH2CH2OH

CH3OH / conc. H2SO4

heat(1)

CH2COOCH3

(1)

CH2COOH

e)CH2CONH2 CH2COOH

H3O+

(1) (1)

CH2CH2OH1 LiAlH4 / ethoxyethane

2 H3O+heat

(1)

f) NaOH(aq)

reflux(1)

conc. H2SO4 or conc. H3PO4

heat(1) (1)

Cl OH

(1)

Br2 (in organic solvent)

(1)

Br

Br

38

��4a) Pressurebuildsup in theset-upwhenthemixture isheated. Itwasdangerous toconductanexperimentusing a closed system.An explosion mayoccur. (�)

Modification – add a receiver adaptor between the condenser and the round-bottomed flask. (�)

b) i) Use a teat pipette to remove the bottom layer. / Use a separating funnel and run off the bottom layer. (�)

ii) Todry theorganic layer. (�)

iii) Anyoneof the following:

• Add aqueousbromine to thedistillate. (�)

The yellow-brownaqueousbromine changes to colourless quickly. (�)

• Add cold acidifieddilute potassiumpermanganate solution to thedistillate. (�)

Thepurple permanganate solution changes to colourless quickly. (�)

iv) • Addphosphorus pentachloride to thedistillate. (�)

• Steamy fumeswouldbeobserved. (�)

��5a) Theprocess is exothermic. (�)

b) i) To remove the excess dilute sulphuric acid. (�)

ii)

(� mark for correct drawing of separating funnel with tap; � mark for showing �-bromopropane layer onbottom; award0mark if the funnel is notworkable) (2)

iii) Toprevent pressure building updue to the formationof carbondioxidegas. (�)

c) To dry theproduct. (�)

d) Use an electric heatingmantle / awater bath / anoil bath for heating (�)

because propan-�-ol / �-bromopropane is flammable. (�)

39

e) i)

(� mark for correct set-up; � mark for correct labels; � mark for correct drawing of fractionating column; �mark for correct directionofwater flow in condenser; award0mark if the set-up is not workable) (4)

ii) 70 °C – 72 °C (�)

f) i) Number ofmoles of propan-�-ol = 9.�2g60.0gmol–�

= 0.�52mol

According to the equation, �mole of propan-�-ol gives �mole of �-bromopropane.

Theoretical yield of �-bromopropane=0.�52mol x �22.9gmol–�

= �8.7g (�)

Percentage yield of �-bromopropane= �0.8g�8.7g

x �00%

= 57.8% (�)

ii) Anyoneof the following:

• The reaction is incomplete. (�)

• Someof thepropan-�-ol dehydrate to forman alkene. (�)

• Someof theproduct stay in the aqueous layer. (�)

��6a) Methanol (�) andpropanoic acid (�)

b) As a catalyst (�)

c) CH3OH(l) +CH3CH2COOH(l) CH3CH2COOCH3(l) +H2O(l) (�)

d)

C O

O H

C

H

H

C C H

H

H

H

H (�)

40

e) Methanol is flammable and it catches fire easily. (�)

f) Any two of the following:

A pleasant smell could be detected. (�) / An insoluble layer formed on the sodium carbonate solution.(�) / Effervescenceoccurred. (�)

g) B (�)

h) Anyone of the following:

propyl methanoate

(1)(1)

(1) (1) (1)(1)C OCH2CH2CH3

O

H ethyl ethanoateC OCH2CH3

O

CH3

methylethyl methanoateC OCH(CH3)2

O

H

i)

(1) (1)butanoic acid

C

H

H

C

H

H

C OH

H

H

H

O

C

(1) methylpropanoic acid (1)

C

CH3

H

C OH

H

H

H

O

C

��7a)

(�mark forcorrect set-up;�mark forcorrectdirectionofwater flow incondenser;award0mark if theset-up is notworkable) (2)

b) To prevent any loss of the volatile substance / ester by evaporation. (�)

c) To convert sodiumbenzoate intobenzoic acid. (�)

4�

d) Dissolve the crude sample inminimumamount of hotwater. (�)

Filter themixturewhile hot. (�)

Allow the filtrate to cool and collect the crystals by filtration. (�)

e) i) Number ofmoles of ethyl benzoate= 4.50g�50.0gmol–�

= 0.0300mol

According to the equation, �mole of ethyl benzoate gives �mole of benzoic acid onhydrolysis.

Theoretical yield of benzoic acid=0.0300mol x �22.0gmol–�

= 3.66g (�)

Percentage yield of benzoic acid= 2.29g3.66g

x �00%

= 62.6% (�)

ii) Hydrolysis is not complete. / Benzoic acid is slightly soluble inwater. (�)

��8a) 3-methylbutyl ethanoate (�)

b) (CH3)2CH(CH2)2OH (�) 3-methylbutan-�-ol (�)

c) Reagent Y is concentrated sulphuric acid. (�)

Heat the reactionmixture under reflux. (�)

d) Esterification

e) Any two of the following:

• Isoamyl acetate (�)

• Acetic acid (�)

• Water (�)

d) • Shake themixturewith sodiumhydrogencarbonate solutionuntil nomoregas is evolved. (�)

• Extract the isoamyl acetate from theorganic layer using ethoxyethane. (�)

• Remove the ethoxyethaneby simple distillation. (�)

��9a) i) Causebleeding in the stomach lining (�)

ii) Paracetamol (�)

b) i) 2-hydroxybenzoic acid (�)

ii) Heatwithmethanol (�)

and a little concentrated sulphuric acid. (�)

42

iii) COO–Na+

OH

(�)

c) Number ofmoles of salicylic acid used=8.28g

�38.0gmol–�

= 0.0600mol (�)

Number ofmoles of aspirin obtained =7.20g

�38.0gmol–�

= 0.0400mol (�)

Percentage conversion=0.0400mol0.0600mol

x �00%

= 66.7% (�)

d) To show the presence of the –COOH group, add sodium hydrogencarbonate solution to thecompound. (�)

Evolutionof colourless gas bubbles indicates thepresenceof the –COOHgroup. (�)

To show thepresenceof the ester group, heat the compoundwithdilute acid. (�)

Smell of vinegar is noted. (�)

e) i) Ca(OH)2 (�)

ii) Aspirin is a covalent compound with intramolecular hydrogen bonds. This reduces the extent ofhydrogenbonding withwater, thusmaking aspirin insoluble inwater. (�)

The largehydrophobic benzene ring also leads to lowwater solubility. (�)

The calcium salt is ionic. Strong interactions exist betweenwater and the ions. (�)

�20a) Saponification (�)

b)

O C C17H33

O

H2C

O C C17H33 + 3NaOH

O

HC

O C C17H33

O

H2C

OHH2C

OH + 3C17H33COO–Na+HC

OHH2C (2)

c) LabelC (�)

43

d) Any oneof the following:

• Wear safety glasses. (�)

• Wear protective gloves. (�)

e) To lower the solubility of soap inwater. (�)

f) To prevent the soap fromdissolving in thewater. (�)

g) Perfume (�) and colouring (�)

h) Not suitable (�)

Seawatercontainsa lotofmagnesium ionsandcalcium ions.Thesoapwould reactwith themetal ionsto form scumand thus reduce the cleaning effectiveness of soap. (�)

�2�a) Any two of the following:

• Hydrocarbonsobtained frompetroleum (�)

• Concentrated sulphuric acid (�)

• Sodiumhydroxide (�)

b) i)

O S O–

O

O (�)

ii) CH3(CH2)�0CH2— (�)

c) When mixed with a mixture of water and paraffin oil, the hydrophobic parts of the detergent particlesdissolve in theoilwhile thehydrophilic parts dissolve inwater. (�)

Uponshaking,oildropletsform.Eachdropissurroundedbydetergentparticleswiththehydrophilicpartsin thewater. (�)

The hydrophilic parts carry negative charges and prevent the oil droplets from coming together again.Hence an emulsion is formed. (�)

d) Detergent X can emulsify the crudeoil into droplets and (�)

the droplets canbe carriedout awaybywater currents. (�)

e) i) Yes (�)

ii) Duringthedecompositionofthedetergent,bacteriauseupoxygeninthewater.Thismakesthewatersmell badly due to oxygendepletion. (�)

f) i) Calcium ion (�)

Magnesium ion (�)

ii) DetergentX can functionwell in hardwater (�)

because it does not form scumwithhardwater. (�)

44

�22a) i) Carboxyl group (�)

ii) Hydroxyl group (�)

b) Sodium hydroxide solution (�)

c)

O CH2 CH2 O

O

C

O

C

(�)

d) Condensation polymerization (�)

e) Permanent dipole-permanent dipole attractions between PETpolymer chains are stronger (�)

than the instantaneousdipole-induceddipole attractions betweenpolythenepolymer chains. (�)

f) i) Hydrolysis (�)

ii) HO CH2 CH2 OH (�)

O–Na+

O

C

O

CNa+O–

(�)

�23a i) Themolecule of valine contains one carbon atombonded to four different groups of atoms. (�)

ii)

(1)

(CH3)2HCNH2

COOHC

H

(1)

CH(CH3)2H2N

HOOC C

H

iii) (�)Rotationof planeof plane-polarized light (�)

(2)Rotate theplaneof plane-polarized light in opposite directions. (�)

b)

CH N

O CH(CH3)2

C CH COOH

CH3

H

H2N

(�)

CH N

O CH3

C CH COOH

CH(CH3)2

H

H2N

(�)

45

c) CH3

H3N+CHCOOH

(1)

CHCOO–

CH3

H2N(1)

�24a) Amine functional group (�), carboxyl group (�), amide functional group (�), ester functional group (�)

b) O

C NHH2N CH

CH2

CO2H

*

O

C OCH3CH

CH2

*

(2)

c)

C OH

O

C

H

CH2COOH

H2N

(�)

CHCH2

COOH

H2N (�)

d) Silicon dioxide increases thebulkmass of the sweetener. (�)

e) Phenylketonurics are unable to metabolize the phenylalanine produced from the hydrolysis ofaspartame. (�)

Ahigh level of phenylalanine in thebrain is extremely harmful and sometimes fatal. (�)

�25a) Condensationpolymerization (�)

b)

N (CH2)6 N H

H

H

H (�)

O (CH2)4

O

C CH HO

O (�)

46

c)

(CH2)4

O

C C

O

N (CH2)6 N

H

H (�)

d) Any one of the following:

Lighter inweight (�)

Does not corrode easily (�)

e) There are hydrogenbondsbetween thepolymer chains of nylon. (�)

Only weak instantaneous dipole-induced dipole attractions exist between the polymer chains ofpolythene. (�)

Hencenylon is stronger thanpolythene.

f) Aholewould appear (�)

because the acid hydrolyzes the amide linkages in nylon. (�)

g) Method I:

The waste contains dichromate ionswhich is toxic. (�)

Method II:

Concentrated nitric acid is a strong acid. Discharge of the waste into waterways leads to environmentalpollution. (�)

�26a) Any two of the following:

Burning fossil fuels produces a lot of air pollutants. (�)

The resources of fossil fuels are limited. (�)

Supplyandpriceofpetroleummaybecomeunstableintimesofpoliticalunstabilityinpetroleum-producingcountries. (�)

Petroleumspillsduringdrillingor transportationcausemajordamage toecosystemsbothon landandatsea. (�)

b) Burning ethanol returns carbondioxide (�)

whichhas been recently removed from the atmosphere during thephotosynthesis of plants. (�)

c) More energy canbeobtained. (�)

d) Any two of the following:

Farmers use fossil-fuel-powered equipment to plant,maintain andharvest the corn. (�)

47

Fossil-fuel-poweredmachines are required to process the corn into ethanol. (�)

Ethanol is transported to collectionpoints via fossil-fuel-powered transport. (�)

e) Anyone of the following:

Thismay lead to diversionof investment from foodproduction, resulting in increased foodprices. (�)

Ethanal is alsoproducedduring the combustionof ethanol. It canharmvegetation, irritate the skin andeyes, anddamage the lungs at high concentrations. (�)

f) As a solvent (�)

�27Any three of the following properties:

Physical properties

• Hydrogenbonds exist between ethanolmolecules. (�)

Thustheboilingpointofethanolishigherthanthoseofalkanes/haloalkanesofsimilarrelativemolecularmasses. (�)

• Due to thehydrogenbonding between ethanolmolecules andwatermolecules, (�)

ethanol ismisciblewithwater in all proportions. (�)

Chemical properties

• Ethanol reactswith hydrogenhalides to formhaloethanes. (�)

Bromoethanecanbepreparedbyheatingamixtureofethanol,sodiumbromideandconcentratedsulphuricacidunderreflux.Concentratedsulphuricacidreactswithsodiumbromidetoproducehydrogenbromide.Hydrogenbromide then reactswith ethanol to give bromoethane. (�)

OR

Bromoethane can be prepared by heating a mixture of ethanol, red phosphorus and bromine underreflux. Phosphorus first reacts with bromine to give phosphorus tribromide. The tribromide then reactswith ethanol to give bromoethane. (�)

• Ethanol canbedehydrated to formethene. (�)

This is done by heating ethanol at �80 °C with excess concentrated sulphuric acid / passing ethanolvapour over aluminiumoxide at 300 °C. (�)

• Ethanol canbeoxidized to ethanal, and then to ethanoic acid. (�)

This is done by heating ethanol with acidified potassium dichromate solution under reflux. The refluxcondenserpreventsanylossofthereactionmixtureandfavourstheoxidationofethanoltoethanoicacidrather than to ethanal. (�)

• Ethanol reactswith carboxylic acid in thepresenceof concentrated sulphuric acid to forman ester. (�)

For example, heating ethanol with methanoic acid in the presence of concentrated sulphuric acid givesthe ester ethylmethanoate. (�)

(3marks for organization andpresentation)

48

�28Addwater to the liquids. (�)

Both butanoic acid andpropanone canmixwithwater in all properties. (�)

Add a pieceof pHpaper to the aqueous solutions. (�)

Solution of butanoic acid is acidicwhile that of propanone is not. (�)

Add aqueousbromine to the remaining two compounds. (�)

Only cyclohexene candecolorize the aqueousbrominequickly. (�)

OR

Add silver nitrate solution to the remaining two compounds. (�)

Only �-bromobutanegives a pale yellowprecipitate slowly. (�)

(3marks for organization andpresentation)

�29Soaps are mainly made from the reaction between fats (or vegetable oil) and sodium hydroxidesolution. (�)

Soaplessdetergentsaremade fromhydrocarbonsobtained frompetroleum,concentratedsulphuricacidandsodium hydroxide. (�)

Both of themhavegood cleaning ability in softwater. (�)

However, soaps form scumand lose cleaning ability in hardwaterwhile soapless detergents donot. (�)

Branch-chained soapless detergents are non-biodegradable. They form thick foam which prevents oxygenfrom dissolving intowater and leads to thedeathof aquatic life. (�)

Soapsandstraight-chainedsoaplessdetergentsarebiodegradable.Whentheyaredecomposedbybacteriainrivers or sea, oxygen in water is used up. This leads to oxygen depletion and thus causes death of aquaticlives. (�)

Ingeneral,soapsandstraight-chainedsoaplessdetergentscausefewerpollutionproblemsthanbranch-chainedsoapless detergents.

(3marks for organization andpresentation)