Al Chemistry 2002 Paper 2

2002-AL CHEM PAPER 2

HONG KONG EXAMINATIONS AUTHORITY HONG KONG ADVANCED LEVEL EXAMINATION 2002

CHEMISTRY A-LEVEL PAPER 2 1.30 pm – 4.30 pm (3 hours) This paper must be answered in English

1.

There are TWO sections in this paper, Section A and Section B.

2.

Section A carries 60 marks and Section B carries 40 marks.

3.

Answer THREE questions from Section A and TWO questions from Section B.

4.

Answers to questions in Sections A and B are to be written in the AL(C)1 and AL(E) Answer Books respectively.

5.

Some useful constants and a Periodic Table are respectively printed on pages 16 and 17 of this question book.

香 港 考 試 局

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2002-AL-CHEM 2–1

SECTION A Answer any THREE questions, using the AL(C)1 Answer Book. 1.

(a)

(i)

17 8O

+ 42 He →

(ii)

15 1 7 N + 1H

→ 42 He + Y

(iii)

234 90 Th

234 91 Pa

→

20 10 Ne

+X

+Z

(3 marks)

Elements A and B form a compound with molecular formula AB3. A sample of the compound was injected into a mass spectrometer and the mass spectrum shown below was obtained.

relative intensity

(b)

Identify species X, Y and Z in the nuclear reactions below:

0

19

50

31

69

88

mass/charge ratio (i)

A molecular ion AB3+ was formed in the mass spectrometer. Suggest how AB3+ was formed.

(ii)

The peaks at mass/charge ratios 69 and 50 are due to cations formed from detaching one and two atoms of B from AB3+ respectively. Account for the presence of the peaks at mass/charge ratios 19 and 31.

(iii)

Suggest what compound AB3 is.

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(5 marks)

1.

(c)

You are provided with a sample of blackboard chalk made from hydrated calcium sulphate(VI) powder. (i)

(ii)

(d)

The presence of calcium in the sample can be shown by conducting a flame test. (I)

Give the essential steps in a flame test.

(II)

State the origin of the flame colour.

Devise an experiment, using chemicals and apparatus commonly available in a school laboratory, to determine the number of water of crystallization per formula unit of CaSO4 in the sample of blackboard chalk. (8 marks)

Ammonia (NH3) and phosphine (PH3) are hydrides of nitrogen and phosphorus respectively. Account for each of the following phenomena: (i)

The bond angle between two N–H bonds in NH3 (about 107°) is greater than that between two P–H bonds in PH3 (about 94°).

(ii)

NH3 is very soluble in water but PH3 is sparingly soluble. (4 marks)

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2.

(a)

The table below lists the standard enthalpy changes of combustion __

(∆Hco, 298 ) of three substances.

Substance

___

∆Hco,298 / kJ mol−1

C (graphite)

– 394

H2(g)

– 286

C3H6(g) cyclopropane

– 2090

(i)

Calculate the standard enthalpy change of formation of cyclopropane.

(ii)

The standard enthalpy change of atomization of graphite is +715 kJ mol–1, and the average C–H and H–H bond enthalpies are +413 kJ mol–1 and +436 kJ mol–1 respectively. Estimate the C–C bond enthalpy in cyclopropane.

(iii) Explain why the C–C bond enthalpy estimated in (ii) deviates significantly from the average C–C bond enthalpy of +346 kJ mol–1 in straight chain alkanes. (8 marks) (b)

The electronic arrangement of a magnesium atom is 2, 8, 2. Suggest how you would use experimental data available from scientific literature to establish the above electronic arrangement. (3 marks)

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2.

(c)

The graph below shows the variations of melting points and boiling points of the Period 3 elements.

temperature / K →

3000

boiling point 2000

1000

melting point 0 Na

Mg

Al

Si

P

S

Cl

Ar

Explain why (i)

silicon, a metalloid, has a very high melting point;

(ii)

the boiling points of the metals are in the order: Al > Mg > Na;

(iii)

there is generally a larger difference between the melting point and the boiling point for metals than for non-metals;

(iv)

the melting point of sulphur is the highest among the non-metals. (9 marks)

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3.

(a)

An experiment was conducted to study the hydrolysis of benzenediazonium chloride at 298 K and 1 atm. C6H5N2+Cl–(aq) + H2O(l) → C6H5OH(aq) + N2(g) + HCl(aq) The progress of the hydrolysis was followed by measuring the volumes of N2(g), v, liberated at different times, t. The table below lists the experimental results.

(b)

t/s

0

5

10

15

25

3600

5400

v / cm3

0

33

56

73

92

110

110

(i)

By plotting a suitable graph, show that the hydrolysis is first order with respect to benzenediazonium chloride.

(ii)

Using your graph in (i), determine the rate constant of the hydrolysis at 298 K.

(iii)

Suggest how the activation energy of the hydrolysis can be determined. (You are not required to give the experimental details.) (8 marks)

A hydrogen-oxygen fuel cell uses concentrated potassium hydroxide solution as electrolyte and nickel as electrodes. (i)

Draw a labelled diagram to show the design of the above fuel cell.

(ii)

Briefly describe how the cell works, giving the equations for the electrode half reactions.

(iii)

State one advantage of using fuel cells over using batteries. (5 marks)

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3.

(c)

At 298 K, the equilibrium constants, Kc , for reactions (1) and (2) below are 1.8 × 107 mol–2 dm6 and 2.0 × 10–10 mol2 dm–6 respectively. Ag+(aq) + 2NH3(aq) AgCl(s)

Ag(NH3)2+(aq)

(1)

Ag+(aq) + Cl–(aq)

(2)

(i)

For each of the reactions (1) and (2), write an expression for its Kc.

(ii)

Calculate the Kc at 298 K for the following reaction : Ag(NH3)2+(aq) + Cl–(aq)

AgCl(s) + 2NH3(aq) 　 (iii)

Using your result in (ii), calculate the solubility, in mol dm–3, of AgCl(s) in 0.10 M NH3(aq) at 298 K. (7 marks)

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4.

(a)

(b)

Mixtures of methanol and ethanol behave as ideal solutions. At 298 K, the vapour pressures of methanol and ethanol are 17.2 kPa and 8.4 kPa respectively. (i)

Suggest why mixtures of methanol and ethanol behave ideally.

(ii)

A solution is formed by mixing the same mass of methanol and ethanol. Calculate the vapour pressure of the solution at 298 K.

(iii)

Some of the vapour in equilibrium with the solution in (ii) at 298 K is condensed. Calculate the mole fraction of methanol in the condensate.

(iv)

Suggest one method that can be used to separate a mixture of methanol and ethanol. (7 marks)

Both MgO(s) and NaF(s) have a face-centred cubic structure. The table below lists the melting points and solubilities in water of the two compounds. MgO(s)

NaF(s)

2800

995

6.2 × 10–4

9.8 × 10–2

melting point / °C solubility / g (100 cm3 H2O)–1

(i)

Draw the unit cell of MgO(s).

(ii)

Account for the following phenomena: (I)

The melting point of MgO(s) is higher than that of NaF(s).

(II)

The solubility of NaF(s) is higher than that of MgO(s). (6 marks)

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4.

(c)

(d)

Complexes are formed by both s-block elements and d-block elements. (i)

What is the meaning of the term ‘complex’ ?

(ii)

Why do d-block elements form more complexes than s-block elements ? (4 marks)

Suggest why 2,4,6-trinitrotoluene (TNT) is an explosive. CH 3 O 2N

NO 2

NO 2 TNT

(3 marks)

END OF SECTION A

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SECTION B Answer any TWO questions, using the AL(E) Answer Book. 5.

(a)

(b)

The reaction of 1,6-dichloro-6-methylheptane with concentrated sodium hydroxide solution gives compound A (C8H17OCl) as the major product. On the other hand, 1,6-dichloro-6-methylheptane reacts slowly with hot water to give compound B, which has the same molecular formula as A. (i)

Draw the structure of 1,6-dichloro-6-methylheptane.

(ii)

Give the structure of A and outline a mechanism for its formation.

(iii)

Give the structure of B and outline a mechanism for its formation.

(iv)

Suggest why A is formed under strongly basic conditions while B is formed under neutral conditions. (8 marks)

Suggest a synthetic route, in not more than four steps and using LiAlD4 or NaBD4 as a source of deuterium, for the following transformation. OH

D

(4 marks)

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5.

(c)

Consider the substances listed below: butane ethanoic acid propanone

benzoic acid hexane tetrachloromethane

dichlorodifluoromethane polystyrene triethylamine

For each of the descriptions of physical properties from (i) to (viii) below, choose from the above list, one substance which best fits the description. (i)

a colourless, flammable gas

(ii)

a colourless liquid with a sour odour

(iii)

a colourless, water miscible, flammable liquid

(iv)

a colourless, non-flammable liquid

(v)

a colourless liquid with a fishy smell

(vi)

a colourless, water immiscible, flammable liquid

(vii)

a white solid which is insoluble in both cold and hot water

(viii)

a white solid which is insoluble in cold water, but soluble in hot water (8 marks)

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6.

(a)

Study the information given below: Compound D (C8H14) is an acyclic hydrocarbon having one chiral carbon centre and one methyl side-chain. The reaction of D with excess hydrogen in the presence of palladium gives compound E (C8H18), which does not have any chiral carbon centres. D undergoes ozonolysis to give three products, methanal, ethanal and compound F (C5H8O2), which has one chiral carbon centre. Deduce all possible structures of D, E and F. (8 marks)

(b)

Based on the fact that the pKa of carboxylic acids (RCO2H) is about 5 and that the pKb of amines (RNH2) is about 10, answer the questions below: (i)

For each of the compounds G, H and J below, NH 2

NH 2 CH 3(CH2) 2CO 2H G

(ii)

H

CO 2H J

(I)

draw the structure of the predominant species in a pH 3 buffer solution, and

(II)

draw the structure of the predominant species in a pH 11 buffer solution.

Two electrodes are dipped into an aqueous solution of G, H and J maintained at pH 7, and are connected to the two poles of a battery. Which of these compounds, under such conditions, will remain almost stationary ? Explain your answer. (6 marks)

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6.

(c)

Both compounds K and L are natural fats that exist in human body. CH2OCO(CH2)16CH3 CHOCO(CH2)7CH=CH(CH2)7CH3 CH2OCO(CH2)16CH3 K CH2OCO(CH2)16CH3 CHOCO(CH2)3(CH=CHCH2)4(CH2)3CH3 CH2OH L

(i)

Draw structures of all products formed from the complete hydrolysis of K.

(ii)

Suggest, with explanation, whether infra-red spectroscopy can be used to differentiate the products formed from the complete hydrolysis of K.

(iii)

Which compound, K or L, has the greater iodine value ? Explain. (6 marks)

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7.

(a)

Catalytic converters incorporated in car exhaust systems can reduce the emission of air pollutants into the atmosphere. The catalysts commonly used are platinum (Pt) and rhodium (Rh). (i)

With the help of equations, briefly describe the reactions inside a catalytic converter.

(ii)

The table below lists the relative levels of Pt and Rh in uncontaminated underground ice samples, and in surface snow samples collected from 1973 to 1976 in central Greenland. Samples

Relative level Pt

Rh

uncontaminated underground ice samples

1

0.04

surface snow samples collected during 1973

6

1.5

surface snow samples collected during 1974

5

1.8

surface snow samples collected during 1975

40

5

surface snow samples collected during 1976

45

7

Source : Chemistry in Britain, April 2001

(iii)

(I)

Suggest a possible kind of human activity that was responsible for the medium-high levels of Pt and Rh in snow in central Greenland prior to 1975.

(II)

Suggest why there was a sudden increase in levels of Pt and Rh in snow in central Greenland after 1975.

Suggest one measure that can help reduce the levels of Pt and Rh contamination. (8 marks)

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7.

(b)

For each of the following pairs of molecules, identify their relationship as identical, enantiomeric, geometrical isomeric or structural isomeric.

(i)

CH3CH2

CH2CH3

HO2C C

and

C

H

C

CH3

H

and O

H

O

HO2C

CH3

HO2C

CH3

CH3

(iv)

and

HO2C

H

H3C

C H3C

N H

H3C H

H3C C

C C

H CH3

CH3

and

and

C C

CH3

CO2H

H3C

NH

H

CO2H

O

(ii)

(v)

C

CH3CH2

CH2CH3

O

(iii)

H

CH3

H3C

(5 marks)

(This question is continued on the next page.)

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7.

(c)

A mixture of 2.8 g of butane-1,4-diol and 6.3 g of benzene-1,3-dicarbonyl chloride was heated at 215oC for 30 minutes to give 6.4 g of a polymer M. COCl HO(CH2)4OH COCl butane-1,4-diol

benzene-1,3-dicarbonyl chloride

(i)

Draw the repeating unit of M.

(ii)

What type of polymerization is involved in the formation of M ?

(iii)

Calculate the percentage yield of M. (5 marks)

(d)

Suggest a synthetic route, in not more than three steps, for the transformation of 3-methylbenzoic acid to N,N-diethyl-3-methylbenzamide, a substance commonly used in mosquito repellant. CON(CH2CH3)2

CO2H

CH3

CH3 3-methylbenzoic acid

N,N-diethyl-3-methylbenzamide

(2 marks)

END OF PAPER

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Useful Constants Gas constant, R = 8.31 J K–1 mol–1 Faraday constant, F = 9.65 × 104 C mol–1 Avogadro constant, L = 6.02 × 1023 mol–1 Planck constant, h = 6.63 × 10–34 J s Speed of light in vacuum, c = 3.00 × 108 m s–1 Ionic product of water at 298 K, Kw = 1.00 × 10–14 mol2 dm–6 Specific heat capacity of water = 4.18 J g–1 K–1

Characteristic Infra-red Absorption Wavenumber Ranges (Stretching modes) Bond

Compound type

C=C C=O C≡C C≡N O–H C–H O–H N–H

Alkenes Aldehydes, ketones, carboxylic acids, esters Alkynes Nitriles Acids (hydrogen-bonded) Alkanes, alkenes, arenes Alcohols, phenols (hydrogen-bonded) Amines

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Wavenumber range /cm–1 1610 to 1680 1680 to 1750 2070 to 2250 2200 to 2280 2500 to 3300 2840 to 3095 3230 to 3670 3350 to 3500

2002-AL-CHEM 2–18

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– 17 –

Be 9.0 12 Mg 24.3 20 Ca 40.1 38 Sr 87.6 56 Ba 137.3

88 Ra (226)

87 Fr (223)

**

*

4

Li 6.9 11 Na 23.0 19 K 39.1 37 Rb 85.5 55 Cs 132.9

II

族

3

I

GROUP

58 Ce 140.1 90 Th 232.0

21 Sc 45.0 39 Y 88.9 57 * La 138.9 89 ** Ac (227)

59 Pr 140.9 91 Pa (231)

104 Rf (261)

22 Ti 47.9 40 Zr 91.2 72 Hf 178.5

H

60 Nd 144.2 92 U 238.0

105 Db (262)

23 V 50.9 41 Nb 92.9 73 Ta 180.9

1.0

1

61 Pm (145) 93 Np (237)

24 Cr 52.0 42 Mo 95.9 74 W 183.9

62 Sm 150.4 94 Pu (244)

25 Mn 54.9 43 Tc (98) 75 Re 186.2

63 Eu 152.0 95 Am (243)

26 Fe 55.8 44 Ru 101.1 76 Os 190.2

64 Gd 157.3 96 Cm (247)

27 Co 58.9 45 Rh 102.9 77 Ir 192.2

週期表

65 Tb 158.9 97 Bk (247)

28 Ni 58.7 46 Pd 106.4 78 Pt 195.1

66 Dy 162.5 98 Cf (251)

29 Cu 63.5 47 Ag 107.9 79 Au 197.0

相對原子質量

原子序

relative atomic mass

atomic number

PERIODIC TABLE

67 Ho 164.9 99 Es (252)

30 Zn 65.4 48 Cd 112.4 80 Hg 200.6

68 Er 167.3 100 Fm (257)

B 10.8 13 Al 27.0 31 Ga 69.7 49 In 114.8 81 Tl 204.4

5

III

69 Tm 168.9 101 Md (258)

C 12.0 14 Si 28.1 32 Ge 72.6 50 Sn 118.7 82 Pb 207.2

6

IV

70 Yb 173.0 102 No (259)

N 14.0 15 P 31.0 33 As 74.9 51 Sb 121.8 83 Bi 209.0

7

V

71 Lu 175.0 103 Lr (260)

O 16.0 16 S 32.1 34 Se 79.0 52 Te 127.6 84 Po (209)

8

VI

F 19.0 17 Cl 35.5 35 Br 79.9 53 I 126.9 85 At (210)

9

VII

0 He 4.0 10 Ne 20.2 18 Ar 40.0 36 Kr 83.8 54 Xe 131.3 86 Rn (222)

2

2002 A-Level Chemistry Paper 2 Section A 2.

3.

4.

(a)

(i)

+50 kJ mol–1

(ii)

+308 kJ mol–1

(a)

(ii)

0.073 s–1

(c)

(ii)

3.6 × 10–3

(iii)

5.3 × 10–3 mol dm–3

(a)

(ii)

13.59 kPa

(iii) 0.75 Section B 7.

(c)

(iii)

94

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