Chemistry A-Level Edexcel 2008 Jan (QP+MS)
Transcript of 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
2. Unit 6242/01 Mark Scheme 13
3. Unit 6243/01A Mark Scheme 23
4. Unit 6243/02 Mark Scheme 29
5. Unit 6244/01 Mark Scheme 37
6. Unit 6245/01 Mark Scheme 53
7. Unit 6246/01A Mark Scheme 63
8. Unit 6246/02 Mark Scheme 69
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
Correct Answer Acceptable Answers Reject Mark
1.(a)(ii) Bromide ion.3d104s24p6
Subscript/ignore capitals4s inside 3d
4p inside 3d
1
QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
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
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QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
1.(e) (Highest = 65Cu + 2 37Cl) = 139 (1)(Lowest = 63Cu + 2 35Cl) = 133 (1)Ignore units 2
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QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
2.(c)(i) LiCl + H2SO4 o LiHSO4 + HCl
Ignore state symbols
Multiples
2LiCl +H2SO4 o Li2SO4+2HCl
1
QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
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QuestionNumber
Correct Answer Acceptable Answers Reject Mark
2.(c)(iii) NaI + AgNO3 o AgI + NaNO3
Ignore state symbols and spectator
ions
Multiples
Ag+ + I o AgI
1
QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
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
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QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
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QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
3.(c)(iii) Repulsion between the H3O+ and the H+ They are both cations
so repulsionORThey are both positive
so repulsion 1
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QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
4.(b)(i) 2ClO + 4H+ + 2e()o Cl2 + 2H2O
Ignore state symbols and
Or multiples
-2e()on RHS1
QuestionNumber
Correct Answer Acceptable Answers Reject Mark
4.(b)(ii) 2Cl- o Cl2 + 2e()
Ignore state symbols and
Or multiples
-2e() on LHS1
QuestionNumber
Correct Answer Acceptable Answers Reject Mark
4.(c) ClO + Cl + 2H+ o Cl2 + H2O
Stand alone not consequential on (b)
Ignore state symbols and
Or multiples
1
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QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
4.(e)(i) 2KClO3 o 2KCl + 3O2 Or multiples1
QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
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QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
5.(a)(iii) Dispersion/Induced dipole /LondonORtemporary/instantaneous dipole
van der Waals/vdw Dipole-dipole
Hydrogen bond
1
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QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
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
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QuestionNumber
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
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
Correct Answer Acceptable Answers Reject Mark
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