GCE A2ChemistrySummer 2007

Mark SchemesIssued: October 2007

iii

NORTHERN IRELAND GENERAL CERTIFICATE OF SECONDARY EDUCATION (GCSE) AND NORTHERN IRELAND GENERAL CERTIFICATE OF EDUCATION (GCE)

MARK SCHEMES (2007)

Foreword

Introduction

Mark Schemes are published to assist teachers and students in their preparation for examinations. Through the mark schemes teachers and students will be able to see what examiners are looking for in response to questions and exactly where the marks have been awarded. The publishing of the mark schemes may help to show that examiners are not concerned about fi nding out what a student does not know but rather with rewarding students for what they do know.

The Purpose of Mark Schemes

Examination papers are set and revised by teams of examiners and revisers appointed by the Council. The teams of examiners and revisers include experienced teachers who are familiar with the level and standards expected of 16- and 18-year-old students in schools and colleges. The job of the examiners is to set the questions and the mark schemes; and the job of the revisers is to review the questions and mark schemes commenting on a large range of issues about which they must be satisfi ed before the question papers and mark schemes are fi nalised.

The questions and the mark schemes are developed in association with each other so that the issues of differentiation and positive achievement can be addressed right from the start. Mark schemes therefore are regarded as a part of an integral process which begins with the setting of questions and ends with the marking of the examination.

The main purpose of the mark scheme is to provide a uniform basis for the marking process so that all the markers are following exactly the same instructions and making the same judgements in so far as this is possible. Before marking begins a standardising meeting is held where all the markers are briefed using the mark scheme and samples of the students’ work in the form of scripts. Consideration is also given at this stage to any comments on the operational papers received from teachers and their organisations. During this meeting, and up to and including the end of the marking, there is provision for amendments to be made to the mark scheme. What is published represents this fi nal form of the mark scheme.

It is important to recognise that in some cases there may well be other correct responses which are equally acceptable to those published: the mark scheme can only cover those responses which emerged in the examination. There may also be instances where certain judgements may have to be left to the experience of the examiner, for example, where there is no absolute correct response – all teachers will be familiar with making such judgements.

The Council hopes that the mark schemes will be viewed and used in a constructive way as a further support to the teaching and learning processes.

v

CONTENTS

Page

A2 1: Module 4 1

A2 2: Module 5 7

A2 3A: Module 6A 15

ADVANCEDGeneral Certifi cate of Education

2007

MARKSCHEME

A2C1S7P

Chemistry

Assessment Unit A2 1assessing

Module 4: Further Organic, Physical and Inorganic Chemistry

[A2C11]

FRIDAY 25 MAY, MORNING

A2C11S

1

AVAILABLEMARKS

2A2C1S7

Section A

1 C

2 C

3 A

4 D

5 A

6 A

7 B

8 A

9 A

10 A

[2] for each correct answer [20] 20

Section A 20

3A2C1S7

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Section B

11 (a) Change in volume/change in pressure with time [1] [1]

(b) (i) Plotting and line of best fi t [1] Rate = k[N2O5] [1] [2]

(ii) k = Rate/[N2O5] = e.g. (11.2 × 10–6)/(20.4 × 10–3) = 5.49 × 10–4 [1] s–1 [1] [2] 5

12 (a) Aluminium Al2O3 amphoteric ionic

Phosphorus P2O5/ P4O10 acidic covalent

Silicon SiO2 acidic covalent

[1]

[1]

[1]

[1] for each correct line [3]

(b) (i)

es between Al atoms – [0] each error [–1] i.e. not using both × and • not showing dative bonds/×× or •• not showing all outer es on Cl atoms [3]

(ii) Al2Cl6 + 3H2O → Al2O3 + 6HCl ([2], [–1] for each mistake) or Al2Cl6 + 6H2O → 2Al(OH)3 + 6HCl [2]

(c) (i)

([2], [–1] for no labels) [2]

(ii) A – (Heat of) atomisation of magnesium [1] B – 1st and 2nd ionisation (energies) for magnesium [1] [2]

(iii) 150 + 2186 + 12 (596) +650 = ∆Hlat + (–602) ∆Hlat = 3886 (kJ mol–1) ([2], [–1] for each mistake) [2] 14

rocksil soakedwith water magnesium ribbon

HEAT

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13 (a) (i) Pentan-2-one [1]

(ii) B will turn H+/MnO4– [1] from purple to colourless [1]

or B will turn H+/Cr2O2– [1] (from orange) to green [1]

or B will turn Fehling’s solution [1] (from blue) to red/brown (solid) [1] or B will give a silver mirror [1] with Tollen’s Reagent [1] state no reaction with A 2,4-dinitrophenylhydrazine [1] – compare mpts [2] Also accept A will give a positive iodoform test [1] Yellow crystals [1] No reaction with B [1] [3]

(iii) RFM of B = 86 Moles of B: (1 × 10–13)/86 = 1.16 × 10–15

Number of molecules of B = 7.0 × 108

each error [–1] [3]

(b) (i) Place a mixture of (sulphuric) acid and potassium dichromate (in a pear fl ask) or acidifi ed permanganate (VII) [1] Add 3-methylbutan-1-ol slowly/anti bump [1] Heat the mixture under refl ux [1] Distil off the 3-methylbutanoic acid [1] [4]

Quality of written communication [2]

(ii) [H+]2 = Ka × [Acid] = 1.5 × 10–4

[H+] = 0.01225 [1] pH = 1.91 [1] [2]

(iii) Bubbles/effervescence PCl5 gets smaller/dissolves Vigorous reaction/heat evolved (Any two, [1] each) [2]

(iv) (CH3)2CHCH2COOH + PCl5 → (CH3)2 CHCH2COCl + POCl3 + HCl ([2], [–1] for each mistake/unbalanced) [2] 19

14 (a) (i)

([2], [–1] for each mistake) [2]

(ii) C3H5(OOCC17H35)3 + 3OH–

→ CH2(OH)CH(OH)CH2OH + 3C17H35COO–

([2], [–1] for each mistake) [2]

O

CH2 O C C17H35 O

CH O C C17H35 O

CH2 O C C17H35

5A2C1S7

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(b) (i) The number of milligrams of potassium hydroxide [1] needed to neutralise the fatty acids formed by the complete hydrolysis of 1 gram of fat [1] [2]

(ii) Moles of HCl used = 1.33 × 10–3 [1] Moles of reacted KOH = (5 × 10–3) – (1.33 × 10–3) = 3.67 × 10–3 [1] Mass of KOH used = (3.67 × 10–3) × 56 = 0.2055 g = 205.5 mg [1] Saponifi cation value = 205.5/1.05 = 195.7 [1] [4]

(c) (i) The number of grams of iodine [1] which will react/saturate with 100 g of a fat [2]

(ii) Addition of hydrogen [1] across the double bonds [1] [2]

(d) Concept of the relationship between saturated fats and coronary heart disease/obesity [1] 15

15 (a) (i) Catalyst: Vanadium(V) oxide/V2O5

Temperature: 450 °C Pressure: 1–10 atmospheres ([1] each) [3]

(ii) The catalyst speeds up (both the forward and the reverse) reactions equally [1] A high pressure will favour a high yield of SO3, as there are fewer molecules on the product side (move equation to RHS). However the conditions chosen give a high yield without needing the expense of a high pressure [1] (The reaction is exothermic,) therefore a high yield is favoured by a low temperature. (450 °C is a compromise)/low temperature the reaction is too slow/the catalyst works best at this temperature [1] [3]

(iii) Kp =

p(SO3)2

p(SO2)2 × p(O2) [1]

(iv) Initial moles: SO2 = 2.0; O2 = 2.0; SO3 = 0 Equilibrium moles: SO2 = 0.2; O2 = 1.1; SO3 = 1.8 Mole fraction: SO2 = 0.0645; O2 = 0.3548; SO3 = 0.5806 Partial pressure: SO2 = 0.1148 × 108; O2 = 0.6315 × 108; SO3 = 1.0335 × 108

Kp = 1.28 × 10–6

([3], [–1] for each mistake, carry error through) Units = N–1 m2 [1] [4]

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(b) (i) Ca3(PO4)2 + 2H2SO4 → Ca(H2PO4)2 + 2CaSO4

([2], [–1] for each mistake) [2]

(ii) 62/234 = 26.5% ([2], [–1] for each mistake) [2]

(iii) Advantages: Increases crop yield Applies nutrients required (Any one or any suitable alternative [1])

Disadvantages: Expensive Pollution of water supply/Eutrophication (Any one or any suitable alternative [1]) [2] 17

Section B 70

Total 90

ADVANCEDGeneral Certifi cate of Education

2007

MARKSCHEME

A2C2S7P

ChemistryAssessment Unit A2 2

assessing

Module 5: Analytical, Transition Metals andFurther Organic Chemistry

[A2C21]

WEDNESDAY 30 MAY, AFTERNOON

A2C21S

7

Quality of Written Communication:

2 marks The candidate expresses ideas clearly and fl uently through well-linked sentences and paragraphs. Arguments are generally relevant and well-structured. There are few errors of grammar, punctuation and spelling.

1 mark The candidate expresses ideas clearly, if not always fl uently. Arguments may sometimes stray from the point. There may be some errors of grammar, punctuation and spelling, but not such as to suggest a weakness in these areas.

0 marks The candidate expresses ideas satisfactorily, but without precision. Arguments may be of doubtful relevance or obscurely presented. Errors in grammar, punctuation and spelling are suffi ciently intrusive to disrupt the understanding of the passage.

8A2C2S7

9A2C2S7

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Section A

1 C

2 D

3 D

4 B

5 C

6 D

7 C

8 B

9 B

10 B

[2] for each correct answer [20] 20

Section A 20

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Section B

11 (a) C3H7+ [1]/CH2CHO+ [1]

CH3CO+ [1] [2]

(b) C O/carbonyl [1]

(c) CH3CH2CH2COCH3 /CH3CH2CH2CH2CHO [1] 4

12 (a) (i) sodium nitrite [1] hydrochloric acid [1] [2]

(ii) diazonium ion formed is unstable/prevent decomposition [1]

(b) (i)

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each error [–1] [2]

(ii) conjugated system/delocalised electrons/chromophore [1] absorbs visible radiation/light/energy levels close together/ to promote electrons (to a higher level) [1] Penalise inclusion of emission [–1] [2] 7

13 (a) (i) loss of electrons [1]

(ii) green [1] to red-brown/yellow/violet [1] 2Fe2+ + Cl2 → 2Fe3+ + 2Cl– [1] [3]

(iii) 1s22s22p63s23p63d6 [1] 1s22s22p63s23p63d5 [1] [2]

(iv) iron(III) more stable due to half-fi lled d (sub)shell [1]

(v) dissolve in conc. hydrochloric acid [1] add H2O2/conc. nitric acid to oxidise iron(II)/Fe [1] add (excess) potassium thiocyanate solution [1] obtain concentration from absorbance/transmission (using calibration curve) [1] [4]

Quality of written communication [2]

11A2C2S7

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(b) (i) [Co(CH3COO)2(H2O)4] [2]

(ii) oxidising agent/to oxidise [1] cobalt(II) to cobalt(III) [1] [2]

(iii) octahedral [1]

(iv) six/6 [1]

(v) 1 dm3 of peroxide produces 20 dm3 of oxygen gas = 20/24 mole oxygen = 0.833 mole = 0.833 mol dm–3

2:1 ratio ∴ 1.67 mol dm–3 [3]

(c) (i) Co2+ → Co3+ + e– or reversible equation [1] ClO– + H2O + 2e– → Cl– + 2OH– [1] 4OH– → 2H2O + O2 + 4e– [1] [3]

(ii) (homogeneous) catalyst and chlorate ions each in solution/same phase [1] 26

14 (a) (i) coordinate/dative [1]

(ii) 1 mole Au ≡ 2 moles cyanide 1000 g Au = 5.076 moles 5.076 moles Au ≡ 10.152 moles cyanide volume of 2M potassium cyanide = 10.152 × 1000/2 = 5076 cm3 or 5.076 dm3 [3]

(b) (i)

each error [–1], e.g. using all crosses [2]

(ii) linear [1] electrons move as far apart as possible [1] [2]

(iii) 2Cu(CN)2 → 2CuCN + C2N2 Unbalanced = [1] [2]

(c) (i) CH3I + KCN → CH3CN + KI [1]

(ii)

[1]

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(iii) A = lithium aluminium hydride/lithium tetrahydridoaluminate [1] B = hydrochloric acid [1] C = sodium hydroxide (solution) [1] [3]

(d) (i) known concentration [1]

(ii) (blood) red [1]

(iii) [Fe(SCN)(H2O)5]2+ [1]

(iv) AgNO3 + KSCN → AgSCN + KNO3 [1]

(v) moles of excess thiocyanate = 14.3 × 0.05/1000 = 0.000715 moles of excess silver nitrate = 0.000715 moles of silver nitrate at start = 25.0 × 0.05/1000 = 0.00125 moles of silver nitrate reacting with chloride = 0.00125 – 0.000715 = 0.000535 mass of chloride in cheese = 0.000535 × 35.5 = 0.019 g mass in 1 g = 0.019/1.48 = 0.01284 g

or

volume of silver nitrate solution required to react with chloride = 25 – 14.3 = 10.7 cm3

moles = 10.7 × 0.05/1000 = 0.000535 mass of chloride in cheese = 0.000535 = 0.000535 × 35.5 = 0.019 g mass in 1 g = 0.019/1.48 = 0.01284 g

Award [4] directly for correct answer Each error [–1], carry error through [4] 23

15 (a) forms hydrogen bonds [1] between NH2 group and water [1] [2]

(b) (i) strongest: dopamine weakest: phenylamine [1] dopamine – electrons pushed towards nitrogen/lone pair more available [1] phenylamine – electrons withdrawn by aromatic ring/less available [1] [3]

(ii)

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[1]

(c) (i) C9H11O4N [1]

(ii) carbon atom joined to 4 different [1] atoms or groups [1] [2] or (two) non superimposable [1] mirror images [1]

13A2C2S7

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(iii)

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[1] 10

Section B 70

Total 90

ADVANCEDGeneral Certifi cate of Education

2007

MARKSCHEME

A2C3S7P

ChemistryAssessment Unit A2 3A

assessing

Module 6A: Synoptic Paper

[A2C31]

FRIDAY 1 JUNE, MORNING

A2C31S

15

Quality of Written Communication:

2 marks The candidate expresses ideas clearly and fl uently through well-linked sentences and paragraphs. Arguments are generally relevant and well-structured. There are few errors of grammar, punctuation and spelling.

1 mark The candidate expresses ideas clearly, if not always fl uently. Arguments may sometimes stray from the point. There may be some errors of grammar, punctuation and spelling, but not such as to suggest a weakness in these areas.

0 marks The candidate expresses ideas satisfactorily, but without precision. Arguments may be of doubtful relevance or obscurely presented. Errors in grammar, punctuation and spelling are suffi ciently intrusive to disrupt the understanding of the passage.

16A2C3S7

17A2C3S7

AVAILABLEMARKS

Section A

1 (a) C6H5NH2 + HNO2 → C6H5OH + H2O + N2 or C6H5NH2 + HNO2 + HCl → C6H5N2

+Cl– + 2H2O [2]

(b) carcinogenic so wear gloves/fume cupboard [1]

(c)

[3]

(d) 7.2/144 = 0.05 moles of napthol

5.0/93 = 0.054 moles phenylamine

0.5 × 0.05 moles of Sudan–I = 0.025 × 248 = 6.2 g [4]

(e) benzene diazonium chloride decomposes above 5 °C [1]

(f) Dissolve in the minimum amount [1] of hot solvent/ethanol [1] Filter (while hot) and cool to crystallise [1] [3]

Quality of written communication [2]

(g) crystals in capillary tube [1] heat slowly in electric block/hot oil [1] (record) temperature when it melts [1] [3]

(h) crude product will have lower m.pt/range of temperatures [1] 20

Section A 20

sodium nitrite solution

thermometer [1]

phenylammonium chloride

ice bath [1]

[1]

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18A2C3S7

Section B

2 (a) (i) K = [C6H11O5NH2][H+]/[C6H11O5NH3+] [1]

(ii) pKa= –log108.12 × 10–5 = 4.09 [1]

(iii) pH = –log10 √8.12 × 10–5 × 0.2 = 2.39 [3]

(b) C (atom) has 4 different groups/atoms attached [2] non superimposable [1] on its mirror image [1] [2]

(c) (i) white ppt [1]

(ii) Ba2+ + SO42– → BaSO4 [1]

(d) (i) Coordinate or dative bond [1]

(ii) species which donates electrons [1] through several points of attachment [1] [2]

(e) (i) blue solution turns to red ppt [1] Cu(II) → Cu(I) [1] [2]

(ii) hydrolysis/disaccharide becomes two monosaccharides [1] 15

3 (a) (i) same molecular formula but different structures [1]

(ii) CH3CH2OCH2CH3 CH3OCH2CH2CH3

CH3OCHCH3 CH3 any two from three [2]

(iii) CH3CH2OCH2CH3 [1]

ratio 3:2 therefore CH3:CH2 [1]

triplet from CH2 [1] quartet from CH3 [1] two environments [1] [4]

any two from three

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(b) (i) C2H5OH + CH3COOH → CH3COOC2H5 + H2O [2]

(ii) Kc = [1]

(iii)

accept endothermic curve [2]

(c) (i) + 0.3 V [1]

(ii) purple to colourless [2]

2MnO4– + 2H2O + 5SO2 → 2Mn2+ + 5SO4

2– + 4H+ [2] [4] 17

4 (a) (i) known mass of soy milk [1] add Wij’s solution and leave in the dark [1] two from three add KI [1]

titrate with standard thiosulphate [1] starch, blue/black to colourless [1] two from three blank titration [1] [4]

(ii) moles of fat = 4.6858

= 5.36 × 10–3

moles of hydrogen = 5.36 × 10–3 × 2 = 1.07 × 10–2

volume of hydrogen = 1.07 × 10–2 × 24 = 0.257 dm3 [2]

(iii) fi nely divided [1] Ni [1] [2]

(b) (i) eriochrome (black T) [1] red to blue [2] [3] solochrome (black)

(ii) Moles edta = 20.5 × 0.01/1000 = 2.05 × 10–4

Moles MgCl2 in 100 cm3 = 2.05 × 10–3 Mass MgCl2 = 2.05 × 10–3 × 95 = 0.195

% MgCl2 in Tofu = (0.195/3.00) × 100 = 6.49% [4] 15

extent of reaction

enthalpy

[CH3COOC2H5] [H2O][C2H5OH].[ CH3COOH]

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20A2C3S7

5 (a) (i) +4 [1]

(ii) 6 [1]

(iii) Pt + 4 HNO3 → Pt(NO3)2 + 2NO2 + 2H2O [2]

(b) (i) Anti-cancer drug [1]

(ii)

[1]

(iii) (56/168 ) × 100 = 33% [2] error loses [1]

(iv) Primary structure = sequence/order of amino acids [1] Secondary structure = coiling of chain/formation of α-helix/ formation of β pleated sheets [1]

(c) (i) adsorbed/bonded to surface [1] weakens bonds/lowers activation energy/comment on d-orbitals/ orientation [1] [2]

(ii) C6H14 → C6H6 + 4H2 [1] 13

Section B 60

Total 80