chemistry a-level edexcel 2008 jan (qp+ms)

8/9/2019 Chemistry A-Level Edexcel 2008 Jan (QP+MS)

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Mark Scheme January 2008

GCE

GCE Chemistry (8080/9080)

Edexcel Limited. Registered in England and Wales No. 4496750Registered Office: One90 High Holborn, London WC1V 7BH


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Edexcel is one of the leading examining and awarding bodies in the UK andthroughout the world. We provide a wide range of qualifications including academic,vocational, occupational and specific programmes for employers.

Through a network of UK and overseas offices, Edexcels centres receive the support

they need to help them deliver their education and training programmes to learners.For further information please call our Customer Services on + 44 1204 770 696, orvisit our website at www.edexcel-international.org.uk.

January 2008

All the material in this publication is copyright

Edexcel Ltd 2008


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Contents

1. Unit 6241/01 Mark Scheme 1


3. Unit 6243/01A Mark Scheme 23




7. Unit 6246/01A Mark Scheme 63


i


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General Marking Guidance

x All candidates must receive the same treatment. Examinersmust mark the first candidate in exactly the same way as theymark the last.

x Mark schemes should be applied positively. Candidates must berewarded for what they have shown they can do rather thanpenalised for omissions.

x Examiners should mark according to the mark scheme notaccording to their perception of where the grade boundariesmay lie.

x There is no ceiling on achievement. All marks on the markscheme should be used appropriately.

x All the marks on the mark scheme are designed to be awarded.Examiners should always award full marks if deserved, i.e. ifthe answer matches the mark scheme. Examiners should alsobe prepared to award zero marks if the candidates response isnot worthy of credit according to the mark scheme.

x Where some judgement is required, mark schemes will providethe principles by which marks will be awarded andexemplification may be limited.

x When examiners are in doubt regarding the application of themark scheme to a candidates response, the team leader mustbe consulted.

x Crossed out work should be marked UNLESS the candidate has

replaced it with an alternative response.

Using the mark scheme

1 / means that the responses are alternatives and either answer should receive full credit.2 ( ) means that a phrase/word is not essential for the award of the mark, but helps the

examiner to get the sense of the expected answer.3 [ ] words inside square brackets are instructions or guidance for examiners.4 Phrases/words in bold indicate that the meaning of the phrase or the actual word is

essential to the answer.5 ecf/TE/cq (error carried forward) means that a wrong answer given in an earlier part of a

question is used correctly in answer to a later part of the same question.

Quality of Written Communication

Questions which involve the writing of continuous prose will expect candidates to:

x show clarity of expressionx construct and present coherent argumentsx demonstrate an effective use of grammar, punctuation and spelling.

Full marks will be awarded if the candidate has demonstrated the above abilities.Questions where QWC is likely to be particularly important are indicated QWC in

the mark scheme BUT this does not preclude others.

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6241/01

QuestionNumber

Correct Answer Acceptable Answers Reject Mark

1.(a)(i) Copper

.3d

10

4s

1Subscripts/ignore capitals

4s inside 3d

3d94s2

1

QuestionNumber


1.(a)(ii) Bromide ion.3d104s24p6

Subscript/ignore capitals4s inside 3d

4p inside 3d

1

QuestionNumber


1.(b) The average mass (taking into account

the abundance of each isotope) of theatoms (of that element) (1)

relative to 1/12th the (mass of a)carbon 12 atomOrrelative to 12C = 12 (exactly) (1)second mark stand alone

Weighted/mean in place of

average

Atoms must be mentionedat least once to score (2)

Average mass of a mole ofatoms of an elementrelative to 1/12th mole ofC12 /relative to one mole of 12C= 12 (exactly) (2) 2

QuestionNumber


1.(c) [62.93 x 69.17] + [64.93 x 30.83] (1)100

= 63.55 (1)must be to 2 decimal places

cq only on transcription error e.g.69.71 provided answer to 2 d.p.

63.54 with some workingscores (1)

Correct answer alonescores (2)

Answer should have nounit, but allow unit ofg mol-1 but not grams

or g

2

1


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QuestionNumber


1.(d)(i)

Empirical formula Cu2CO5H2(1) for dividing by atomic mass(1) stating empirical formula

Cu C O H

57.563.5

5.4012

36.216

0.9001

0.906 0.450 2.26 0.9002.01 1 5.02 2.00

Correct answer withoutworking scores (2)

Use of atomicnumber scores 0

2

QuestionNumber


1.(d)(ii) Empirical formula mass = 221 = MrMolecular formula Cu2CO5H2

Must show use of 221

If use atomic number in(i)allow mark for Cu2CO5H and220

Allow any formula thatadds up to the correctmolecular formula

1

QuestionNumber


1.(e) (Highest = 65Cu + 2 37Cl) = 139 (1)(Lowest = 63Cu + 2 35Cl) = 133 (1)Ignore units 2

2


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QuestionNumber


2.(a) Lithiumcarmine/ red/ magenta/ crimson

Any combination of these or prefacedby deep or dark

Potassium: lilac

Sodium: yellow

All three correct 2 marksTwo correct 1 mark

scarlet

mauve or purple

orange or yellow-orange

Brick-red

2

QuestionNumber


2.(b) Electrons (absorb heat energy and) arepromoted (to higher level) (1)

They drop back and emitlight/radiation (of characteristiccolour) (1)

Excitedany phrase that impliesmovement to higherlevel

ignore references toshells, sub-shells, etc.

If answer based onabsorption spectrascores zero

Colour or energy

2

QuestionNumber


2.(c)(i) LiCl + H2SO4 o LiHSO4 + HCl

Ignore state symbols

Multiples

2LiCl +H2SO4 o Li2SO4+2HCl

1

QuestionNumber


2.(c)(ii) K2CO3 + 2HNO3 o 2KNO3 + H2O + CO2

CO32- + 2H+ o H2O + CO2 /H2CO3

CO32- + H+ o HCO3

-

Ignore state symbols and spectatorions

Multiples

K2CO3 + 2HNO3 o2KNO3 + H2CO3

K2CO3 +HNO3 o KNO3 +KHCO3

1

3


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QuestionNumber


2.(c)(iii) NaI + AgNO3 o AgI + NaNO3

Ignore state symbols and spectator

ions

Multiples

Ag+ + I o AgI

1

QuestionNumber


2.(d)(i) The beryllium ion would be (very)small (1)

and would polarise chloride ions(producing sharing of electrons /

covalency) (1)

ORDifference in electronegativity small/similar (1)Therefore share (pair of) electrons /no electron transfer (1)

If both routes given. Mark both out of2 and then score higher hark.

Allow Be2+ has a largecharge to sizeratio/large chargedensity

Distort for polarise

Anion for chloride ion

Answers that referto polarisation ofatoms score zero

Answers that referto electronegativityof ions score zero

2

QuestionNumber


2.(d)(ii) .. ..:Cl : Be: Cl:.. ..

Ignore shape and inner electrons ifcorrect

All dots or all crossesor mixture of both

Polymer withcontinuation bonds

DimerIonic formula

1

4


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QuestionNumber


3.(a) x Diagram showing correct covalentand hydrogen bonds (1)

x Linear around at least two H andwater shown as v shaped (1)

x +

H and

O (1) must be shownacross at least one hydrogen bond

If only two watermolecules shown max 2

marks

Blobs for O and H

provided correct +/

shown

Ignore a slip in partialcharges provided not partof hydrogen bond

If use O2H allowthird mark only

If any H bondshown betweentwo oxygens ortwo hydrogens

3

H

O

H

H

O

H

HG-

G+G+

G+

G+ G+

G-

G+H

G -

O

5


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QuestionNumber


3.(b) Each water can form more hydrogenbonds (than each hydrogen fluoride

molecule) (1)

So more energy is needed to break thehydrogen bonds in water/separatemolecules (hence higher boilingtemperature) (1)

2nd mark is stand alone unless wrongintermolecular force identified in firstpart e.g. vdw

Each water moleculecan form two hydrogen

bonds, HF can onlyform one

Each water moleculecan form four hydrogenbonds HF can only formtwo

Intermolecular forcefor hydrogen bond

Just H bonds inwater are stronger

Is not good enoughto score the mark

Any reference tobreaking covalentbonds/bonds in themolecule scores

zero.

2

QuestionNumber


3.(c)(i)O

H H H HH H

Must attempt to draw as a pyramid wedge or dash or both. If three linesdrawn must not look planar

Ignore name unless planar

Ignore omission of +sign in diagram

1

+ +O

QuestionNumber Correct Answer Acceptable Answers Reject Mark

3.(c)(ii) Any number from 105 to 108 inclusive.Mark independently of (c)(i) 1

QuestionNumber


3.(c)(iii) Repulsion between the H3O+ and the H+ They are both cations

so repulsionORThey are both positive

so repulsion 1

6


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QuestionNumber


4.(a) Substance that can lower/reduce theoxidation number (of an element in

another substance)

Ignore references to loss or gain ofelectrons unless contradictory.

Substance containingan element whose

oxidation number isincreased (in areaction)ORCauses a decrease inthe oxidation numberof themolecule/species itreacts withORThe reducing agentsoxidation number

increases

The oxidationnumber goes down

A definition of redox

1

QuestionNumber


4.(b)(i) 2ClO + 4H+ + 2e()o Cl2 + 2H2O

Ignore state symbols and

Or multiples

-2e()on RHS1

QuestionNumber


4.(b)(ii) 2Cl- o Cl2 + 2e()


Or multiples

-2e() on LHS1

QuestionNumber


4.(c) ClO + Cl + 2H+ o Cl2 + H2O

Stand alone not consequential on (b)


Or multiples

1

7


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QuestionNumber


4.(d) White/misty/steamy fumes

Mauve/purple/violet/ (iodine)vapour/gas/fumes

Black solid

Any two of above

Ignore any yellow solid/bubbling/fizzing

Ignore non-visible observations e.g.getting hot

lilac

(shiny) grey solid

White smoke

Just dark solid

precipitate

2

QuestionNumber


4.(e)(i) 2KClO3 o 2KCl + 3O2 Or multiples1

QuestionNumber


4.(e)(ii) Oxidation numbers all correct (1)

Cl OStart +5 -2End -1 0

Chlorine reducedas oxidation number decreases/changes from +5 to -1 (1)

Oxygen oxidised asoxidation number increases/changesfrom -2 to 0 (1)

Oxidation number mark may beawarded if included withinexplanations.

Penalise omission of reference tooxidation or reduction once

2nd and 3rd marks are consequential onstated oxidation numbers.

Allow 5+, 2-, 1-Allow V, -II, -I

Correct identification ofO as oxidised and Cl asreduced scores (2)provided oxidationnumber change is in thecorrect direction forboth even if actualnumbers wrong.

Cl5+ , Cl-1 , O-2

3

8


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QuestionNumber


5.(a)(i) The ability of an atom/element/species to attract the electrons (1)

in a covalent bond/bond pair/sharedelectrons (1)

Power/extentinstead of ability

pulls toward/drawsinstead of attract

Molecule

2

QuestionNumber


5.(a)(ii) The molecule is symmetrical /tetrahedral (1)

So bond polarity/dipoles cancelsORcentres of positive and negativecharge coincide (1) stand alone

Diagrams showingvectors

Too small adifference in

electronegativity

Charge cancels

2

QuestionNumber


5.(a)(iii) Dispersion/Induced dipole /LondonORtemporary/instantaneous dipole

van der Waals/vdw Dipole-dipole

Hydrogen bond

1

9


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QuestionNumber


5.(b)(i) Ignore sig. figs UNLESS rounded to 1SF

700 g TMP = 700 (1) = 6.14 mol114

Moles of oxygen = 12.5 x 6.14 (1) =76.75

Volume of oxygen = 12.5 x 6.14 x 24=1842 dm3 (1)

Units essentialWorking must be checked i.e.3.07 x 25 x 24 = 1842 dm3 (2)3.07 x 12.5 x 24 = 921 dm3 (1)

OR228 g of TMP need 25 x 24 dm3 ofoxygen (1)

700 g of TMP need 25 x 24 x 700 of228

oxygen(1)

= 1842 dm3(1)

Units essential[Working must be checked]

1840/1800 dm3

1830 if 6.14 rounded to6.1

Moles 2C8H18 = 700228= 3.07

3

QuestionNumber


5.(b)(ii) Ignore sig. figs UNLESS rounded to 1SF

Moles of CO2 = 8 x6.14 (1) = 49.12

Mass of CO2 = 8 x6.14 x44 = 2161 g (1)Units essential but dont penalise if

already penalised in (i)

OR228 g of TMP give 44 x 16 g CO2 (1)

700g of TMP give 44 x 16 x 700 g228

of CO2= 2161 g (1)

Could be consequential on (i)

2160/2200or 2147 / 2150 / 2100

if 6.14 rounded to 6.1

2

10


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QuestionNumber


6.(a) Energy/Enthalpy/heat change per mole forthe (1)

Removal of one electron (per atom) (1)

From 1 mole of gaseous atoms (1)

If wrong equation given with a correctdefinition (max 2)

Required instead ofchange

X(g) o X+(g) + e() canscore last 2 marks

3

QuestionNumber


6.(b) Increase in shielding/screening (1)

Increase in nuclear charge/moreprotons/atomic number (1)

Increase in distance (of outermostelectron)/larger atomic radiusOR(increase in) shielding outweighs nuclearcharge (increase) (1)

Ignore references to:

effective nuclear charge OR nuclearattraction

Electron at higherenergy level

3

QuestionNumber


6.(c)(i) Na:Mg:Almetallic (structure)

Sigiant atomic (structure)

P:S:Cl:Arsimple molecularAll three correct 1 mark 1

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QuestionNumber

Correct Answer AcceptableAnswers

Reject Mark

6.(c)(ii) strong covalent bonds (1)

(throughout the lattice and lots ofenergy) need to break many bonds (1)2

QuestionNumber

Correct Answer AcceptableAnswers

Reject Mark

6.(c)(iii) Aluminium supplies more electrons(per atom)/Al ion is more highlycharged/Al ion is smaller/ Al ion has ahigher charge density (1)

The (attractive) forces between thealuminium ions and the electrons arestronger/require more energy to breakthan in the case of sodium. (1)

Reverse for Na

Any reference tobonding other thanmetallic bond/sea of electrons/delocalised system 2

chemistry a-level edexcel 2008 jan (qp+ms)

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