GCE ASChemistryJanuary 2008

Mark SchemesIssued: April 2008

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

MARK SCHEMES (2008)

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 finding 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 satisfied before the question papers and mark schemes are finalised.

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 final 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.

iii

CONTENTS

Page

AS 1: Module 1 1

AS 2: Module 2 9

v

ADVANCED SUBSIDIARY (AS)General Certificate of Education

January 2008

MARKSCHEME

ASC1W8 3429.01

ChemistryAssessment Unit AS 1

assessing

Module 1: General Chemistry

[ASC11]

THURSDAY 17 JANUARY, MORNING

1

2ASC1W8 3429.01

Quality of written communication:

2 marks The candidate expresses ideas clearly and fluently 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 fluently. 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 sufficiently intrusive to disrupt the understanding of the passage.

3ASC1W8 3429.01

AVAILABLEMARKS

AVAILABLEMARKS

Section A

1 D

2 C

3 A

4 B

5 B

6 C

7 B

8 B

9 C

10 D

[2] for each correct answer [20] 20

Section A 20

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Section B

11 (a) Green [1] Red/Crimson [1] [2]

(b) Electron (excited) to higher energy level [1] Electron falls back to lower energy level [1] Diagram

(Energy) emitted (as a quantum of) light [1] [3] 5

12 (a) Only 4 electrons around the central beryllium atom [1] instead of 8 Atom gain/lose share electrons to obtain 8 electrons in the outer shell [1] [2]

(b) (i) Both electrons in a (covalent) bond come from the same atom [1]

(ii)

H

H

H

HN

X•

X•

••X

•

[–1] for each mistake [2] 5

13 (a) (i) Starch [1]

(ii) A solution the concentration of which is known (accurately) [1]

(iii) Any four: Pipette known volume of the iodine solution into a (conical) flask [1] Titrate with the thiosulphate [1] until the colour of the solution is pale yellow then add starch [1] Continue adding the thiosulphate until the solution goes from blue/black to colourless [1] [4]

Quality of written communication [2]

(b) (i) 2Na2S2O3 + I2 → Na2S4O6 + 2NaI accept ionic equation ([–1] for each mistake) [2]

+

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(ii) Carry any error from the equation through

(0.1 × 22.5)/1000 = 2.25 × 10–3

(2.25 × 10–3)/2 = 1.125 × 10–3

1.125 × 10–3 1.125 × 10–3 × 10 = 0.01125 0.01125 × 34 = 0.3825 (0.3825/25) × 1000 = 15.3 (g dm–3). (Award full marks directly for the correct answer. Carry any errors through, [–1] for each mistake) [4] 14

14 (a) (i) C12H26 + 1812O2 → 12CO2 + 13H2O

([–1] for each mistake) [2]

(ii) y-axis labelled enthalpy [1] reactants and products correctly shown [1] [2]

(iii) Enthalpy of the reactants is greater than the enthalpy of the products [1]. (Difference) given out as heat [1]. (Or correct explanation in terms of breaking and making bonds.) [2]

(b) (i) Enthalpy of combustion: Enthalpy change on the complete combustion in oxygen [1] of 1 mole [1] (under standard conditions) [2]

(ii) Hess’s Law: The overall enthalpy change for a reaction is independent of the number of steps taken [1] provided the conditions remain the same [1] [2]

(iii) 250.0 + ∆H = 8(–393.5) + 9(–286.0) ∆H = –5472 (kJ mol–1) ([–1] for each mistake) [3]

(c) (i) The energy required to break (1 mole of) bonds in the gaseous state to form the gaseous atoms [1]

(ii) (16 × 750) + (18 × 463) = 20 334 [1] 16 548 – 20 334 = –3786 [1] [2]

(iii) Bond enthalpy is an average term/Hess’ Law refers to a specific compound [1]/varies in compounds [2] 18

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15 (a) (i)

+ + + +

+ + + +

+ + + +

e– e–e– e–e–

e–e–

e–

e–

e–

e–

[2]

(ii) Malleable: Layers can slide over one another (and the bonds reform without breaking) [1] [1]

Conducts electricity: Delocalised (valence) electrons [1] are free to move [1] [2]

(b) (i) 2Na(s) + F2(g) → 2NaF(s) [2]

(ii)

x x

xxx

x

x x

xx

+ –

Na F

x x

Na

x x

F

([–1] for each mistake) [3]

(iii) To help reduce tooth decay [1]

(iv) Lack of freedom of choice (or suitable alternative) [1]

(c) (i) Shielding remains constant/electrons add to same shell [1] Nuclear charge increases giving a greater attraction for the outer electrons [1] [2]

(ii) 12 to 13: The outer electron is being added to the p-subshell which is slightly further from the nucleus making it easier to remove the electron/stability of shell [1]

15 to 16: The outer electron is forming the first pair in the p-subshell and it is slightly easier to separate a pair of electrons/ stability of shell [1] [2]

e–

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(iii)

([–1] for each mistake) [2] 18

16 (a) The ability of an atom in a covalent bond to attract the electrons [1]

(b) (i) H2 + F2 → 2HF [1]

(ii) [1]

(iii) Thermal stability decreases down the Group [1] as strength of the HHal bond decreases down the Group [1] [2]

(iv) HAt > HI > HBr > HCl > HF [1]

(c) (i) * Make a solution of the solid [1] Add silver nitrate White precipitate for chloride [1] Giving a cream ppt for bromide [1] White ppt soluble in dilute ammonia solution [1] Cream ppt insoluble in ammonia solution [1]

either

(maximum of [4]) [4]

(ii) NaBr + H2SO4 → NaHSO4 + HBr [2]

(iii) Steamy fumes/purple vapour/smell of rotten eggs/heat produced/ (yellow) solid formed (any two, [1] each) [2]

(d) (i) Cl2: 0 [1] NaCl: –1 [1] NaOCl: +1 [1] [3]

(ii) (ON of Cl changes from) 0 to –1 = Reduction [1] (ON of Cl changes from) 0 to +1 = Oxidation [1] [2]

(iii) Disproportionation [1] 20

Section B 80

Total 100

δ+

Hδ–

F

ADVANCED SUBSIDIARY (AS)General Certificate of Education

January 2008

MARKSCHEME

ASC2W8 3442.01

ChemistryAssessment Unit AS 2

assessing

Module 2: Organic, Physical and Inorganic Chemistry

[ASC21]

TUESDAY 22 JANUARY, MORNING

9

Quality of written communication:

2 marks The candidate expresses ideas clearly and fluently 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 fluently. 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 sufficiently intrusive to disrupt the understanding of the passage.

10ASC2W8 3442.01

11ASC2W8 3442.01

AVAILABLEMARKS

AVAILABLEMARKS

Section A

1 B

2 B

3 C

4 A

5 B

6 A

7 B

8 A

9 D

10 C

[2] for each correct answer [20] 20

Section A 20

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Section B

11 (a) C ═ C

H── H─

CH3H3C─

C ═ CH

── H─

CH3

H3C

─

cis trans [2]

(b) Restricted rotation [1] about C═C [1] [2] 4

12 (a) l-iodobutane [1]

(b) C─I bond [1] is weaker/weakest [1] (than C─Br and C─Cl) Breaks more easily [1] [2]

(c) (i)

[1]

(ii)

H ─ C ─ C ─ C ═ C ─ H│H

│H

H│

H│

CH3│

H│

[1] 5

13 (a) (i) Rate of forward reaction = rate of reverse reaction Concentration of any reactant or product constant [2]

(ii) Equilibrium shifts to RHS [1] 4 moles (g) LHS → 2 moles (g) RHS [1] [2]

(iii) Negative [1] When temperature increases shifts in endothermic direction/reverse reaction is endothermic [1] [2]

(b) Increases the rate of the forward reaction and reverse reactions equally [1] 7

H ─ C ─ C ─ C ─ C ─ H│H

│H

H│

H│

CH3│

H│

│H

│OH

13ASC2W8 3442.01

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14 (a) (i)

Correct dipole [1] [3]

(ii) electrophilic [1] addition [1] [2]

(b) Moles of ethene = 120 ÷ 24 000 = 0.005 moles 1:1 ratio Moles of bromine (Br2) = 0.005 moles Mass of bromine (Br2) = 0.005 × 160 = 0.8 g Volume of pure liquid bromine Volume (cm3) = mass (g) ÷ density (0.8 ÷ 3.2) = 0.25 cm3 [4] 9

15 (a) (i) White flame/white solid [1]

(ii) 2Mg + O2 → 2MgO [2]

(b) Moles of HCl = 2 × 0.05 = 0.1 moles 2:1 ratio Moles of H2 = 0.05 moles Volume of H2 = 0.05 × 24 = 1.2 dm3 or 1200 cm3 [3]

(c) (i) White [1] precipitate [1] [2]

(ii) Mg2+(aq) + CO32–(aq) → MgCO3(s) [2]

(d) (i) Decreases down the group [1] Use of lattice enthalpy (X) [1] Use of hydration enthalpy (Y) [1] Variation in Y is greater than variation in X down the group [1] [4]

(ii) Barium chloride (or nitrate) [1] 15

C ═ CH

── H─

HH ─Hδ+

Brδ–│

→ H ─ C ─ C ─ H

H│

H│

│H Br–

+→ H ─ C ─ C ─ H

H│

H│

│H

│Br

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16 (a) T [1]

H C C C OH

H│

CH3│

│H

│H

H│

│H

[1] P [1]

H C C C C H

H│

OH│

│H

│H

H│

│H

H│

│H

[1] S [1]

Butan-2-ol [1] [6] (b) (i) Molecules which have the same molecular formula but different structural formula [2]

(ii) An alcohol which has 3 carbons directly attached to the same carbon as the hydroxyl group [2]

(iii) Heat each alcohol (separately) [1] with acidified (potassium) dichromate (APD)/acidified (potassium) manganate VII [1] with butan-1-ol APD orange to green/purple to colourless [1] with 2-methylpropan-2-ol APD remains orange/remains purple [1] Maximum [3] [3]

Quality of written communication [2]

(c) (i) methyl group and a hydrogen attached to the same carbon as the hydroxy group [1]

(ii)

or Butan-2-ol

[1]

H C C C C H

H│

OH│

│H

│H

H│

│H

H│

│H

(iii) Alkaline solution [1] of iodine [1] yellow ppt [1] [3] 20

17 (a) (i) carbon dioxide and nitrogen [2]

(ii) 2CO + 2NO → N2 + 2CO2 [1]

(iii) Platinum/Rhodium/Palladium [1]

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(iv) Maximum surface area/efficiency [1] minimises cost [1] better catalysis [1] Any two from three [2]

(v) The catalyst is in a different physical state (solid) [1] than the reactants (gases) [1] [2]

(vi) Adsorbs to surface [1] Weakens bonds (in the reactants)/correct orientation/d-orbitals argument [1] [2]

(vii) The lead compounds bond very strongly (chemisorb) to the catalytic surface [1] poisoning the catalyst/preventing catalysis [1] [2]

(b) (i) y-axis = number of molecules [1]

(ii) The minimum amount of energy required for reaction [1]

(iii) Most collisions (between molecules of CO and NO) have energy less than activation energy [1]

(iv)

Numberof

molecules

Peak to RHS+

Lower

Broadening

Kinetic energy

T1

EA

Peak to RHS + Lower [2] Broadening [1] [3]

(v) A greater fraction of all collisions (between CO and NO) [1] have energy greater than or equal to the activation energy [1] [2] 20

Section B 80

Total 100