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Mark Scheme (Results)January 2008

GCE

GCE O Level Chem ist ry (7081) Paper 2

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

w w w .Xt r em ePaper s.n et
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General Marking Guidance

Al l candidates must receive the same tr eatment . Examiners must mark t hefirst candidate in exactly the same way as they mark the last.

Mark schemes should be appl ied posit ivel y. Candidates must be rew arded f orwhat t hey have shown t hey can do rather t han penalised f or om issions.

Examiners should mark according to the mark scheme not according to theirperception of where the grade boundaries may l ie.

There is no cei l ing on achievement. Al l marks on the mark scheme should beused appropriat ely.

All the marks on the mark scheme are designed to be awarded. Examinersshould always award ful l marks i f deserved, i .e. i f the answer matches themark scheme. Examiners should also be prepared to award zero marks i f t hecandidate s response is not w ort hy of credit according t o the m ark scheme.

Where some judgement is required, mark schemes wil l provide the principlesby which marks wi l l be awarded and exempl i f i cat ion may be l imi t ed.

When examiners are in doubt regarding the application of the mark schemet o a candidate s response, t he team l eader must be consult ed.

Crossed out work should be marked UNLESS the candidate has replaced itwith an alternative response.

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SECTION A

QuestionNumber

Answer Rej ect Mark

1 (a) suit able met al carbonate + suit able acid

concentr ated sulphuri c acid / anhydrous calcium chlori de(accept fomulae)

downward del ivery / upward d isplacement of a i r

NOT

c H2SO4

(1)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

1 (b) any ammonium salt + a st rong alkal i

ca lc ium oxide / CaO / quick l ime

upward del ivery / downward d isplacement of a i r

(1)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

1(c) hydrochloric acid + potassium manganat e(VII) / pot assiumpermanganat e / KMnO4 / manganese(IV) oxide / manganesedioxide / MnO2

concentrat ed acid (dependent on HCl)

concentrat ed sulphuri c acid / anhydrous calcium chlori de(accept f ormulae)

downward del ivery / upward d isplacement of a i r

(1)

(1)

(1)

(1)


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QuestionNumber

Answer Rej ect Mark

2 (a)(i) opposit ely charged ions

att ract ion between ions

Formation of an ionicbond by electron transfer

(1)

(1)

QuestionNumber

Answer Rej ect Mark

2 (a)(ii) a shared pair of elect rons / elect ron pair sharing

att ract ion betw een bond pair and ( tw o) nucle i

(1)

(1)

Question

Number

Answer Rej ect Mark

2 (b)(i) Na+ and Cl -

Correctly placedALLOW: correctlyplaced Na and C1atoms or +/ -charges

Na+ Cl - Na+ Cl -Cl - Na+ Cl - Na+Na+ Cl - Na+ Cl -

(1)

(1)

Question

Number

Answer Rej ect Mark

2 (b)(ii) M1 3 bond pair s

M2 ot her elect rons correct (dependent on M1)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

2 (c) weak intermolecular forces / weakatt ract ions betw een molecules

l i t t le heat / energy needed t o overcomet hem / separate molecules easi ly broken

(1)

(1)


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QuestionNumber

Answer Rej ect Mark

3 (a) f rac t ional d ist i l la t ion / f rac t ionat ion

l iquid a i r

(1)

(1)

QuestionNumber

Answer Rej ect Mark

3 (b)(i) magnesium dissolves / react s, (but copper rem ains) (1)

QuestionNumber

Answer Rej ect Mark

3 (b)(ii) Mg + H2SO4

MgSO4 + H2 (or ionic)Allow Cu on both sides of t he equation

(1)

QuestionNumber

Answer Rej ect Mark

3 (b)(iii) Fi l t r a t ion / cent r i f uge / decant (1)

Question

Number

Answer Rej ect Mark

3 (c)(i) Niger Red (1)

QuestionNumber

Answer Rej ect Mark

3 (c)(ii) Sudan Orange (1)

QuestionNumber

Answer Rej ect Mark

3 (c)(iii) correct measurements for dye (3.0-3.5) and solvent front

(3/ 6) = 0.5 (3.5/ 6) = 0.58

or any value in betw een 3 and 3.5

(1)

(1)

QuestionNumber

Answer Rej ect Mark

3 (c)(iv) t wo cir cles wi t h (Chad) Yellow outside (Mali) Blue.Ignore circle w hich represents t he solvent f ront

(1)


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QuestionNumber

Answer Rej ect Mark

4 (a)(i) long-chain contains many carbon at oms / bonds(ignore ref erence t o hydrogen atom s, penali se H2)

hydrocarbon contains carbon and hydrogen only

Cont inuous chai ns.Long chains of C

atoms

(1)

(1)

QuestionNumber

Answer Rej ect Mark

4 (a)(ii) cracking

h igh tempera ture / 450C to 900C /

cata lyst (zeol i t e / a luminosi l icate / SiO2 / Al 2O3)

M2 depend ant on M1

(ignore any ref erence t o pressure)

heat / su f f ic ien ttempera tureany other catalyst

(contradict ion)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

4 (a)(iii ) M1 C2H4 + C3H6

M2 C13H28 C2H4 + C3H6 + C8H18

(a l low balance equat ion i f M1 incorrect , provided formulaegiven in M1 are correct form ulae for an a lkane / a lkene)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

4 (b)(i) 50 100 at mos (or 5000-10000 kPa)

acid cata lyst / H3PO4 / phosphor ic acid( Ignore any reference to t emperature)

High pressure (1)

(1)

QuestionNumber

Answer Rej ect Mark

4 (b)(ii) C2H4 + H2O C2H5OH

(Accept CH3CH2OH, ignore state symbols)

C2H6O (1)

QuestionNumber

Answer Rej ect Mark

4 (b)(iii) fast r eact ion / cont inuous / pure product

( ignore reference to cost)

High yieldAnswers based on adisadvantage of

fe rmenta t ion

(1)


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QuestionNumber

Answer Rej ect Mark

5 (a)(i) Buret t e ONLY Biuret t e / b i ret t eBuret te wi th any other

piece of apparatus egburet t e and p ipet t e

(1)

QuestionNumber

Answer Rej ect Mark

5 (a)(ii) ( fa in t ) p ink / (pale ) p inkaccept colour less t o pink

Any reference t o red (1)

QuestionNumber

Answer Rej ect Mark

5 (a)(iii ) add dropwise (near t he end-point )

swir l t he f lask / wash down t he inside of t he f l ask /use of whi t e t i l e /

repeat t i t ra t ion (1)

(1)

any 1forM2

QuestionNumber

Answer Rej ect Mark

5 (b)(i) m oles NaOH = 0. 0246 x 0.50= 0.0123(0. 123 scores (1) only)

(1)(1)

QuestionNumber

Answer Rej ect Mark

5 (b)(ii) mol es HX = 0.0123 (al low t e) (1)

QuestionNumber

Answer Rej ect Mark

5 (b)(iii) M1 Mr = 1.50 / 0.0123 (a l low t e)M2 Mr = 121.95 / 122 (dependent on correct expression f or M1)

(1)(1)

QuestionNumber

Answer Rej ect Mark

5 (c) To obt ain accurat e / average / concordant t i t rat ions / values (1)

TOTAL FOR SECTION A: 50 MARKS


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SECTION B

QuestionNumber

Answer Rej ect Mark

6 (a)(i) subst ance t hat speeds up / alt ers t he rate of a

react ion

wi t hout being used up itself / rem ains unchanged /does not t ake part

Specific

catalystother thanMnO2

(1)

(1)

QuestionNumber

Answer Rej ect Mark

6 (a)(ii) (re)l ights a glow ing spl int (1)

QuestionNumber

Answer Rej ect Mark

6 (b)(i) Sealed f l ask / glass t ube + cork / connections(al low dropping funnel / t h ist le funnel below t hesurface of t he l iquid)

sui table col lect ion met hod (syr inge / label ledgraduated t ube over wat er)

(If flask is heated negates M1)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

6 (b)(ii) Scale using over half of t he graph paper.

7 or 8 correct p l ots

smoot h curves

(1)

2x1 = (2)

2x1 = (2)

QuestionNumber Answer Rej ect Mark

6 (b)(iii) 32 36 seconds (1)


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QuestionNumber

Answer Rej ect Mark

6 (c)(i) gradient decreases wi t h t ime

concentrat ion of H2O2 decreases / few er part ic les insame volum e

few er col l isions in uni t t ime / less f r equent col l isions

(1)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

6 (c)(ii) gradient increases as concentration increases

mor e part icles ( in a given volume)

more f requent col l is ions

NOTE f requent in e i ther ( i ) or ( i i )DO NOT PENALISE OMISSION TWICE

(1)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

6 (d) Exper iment 3

gradient l ess t han Experim ent 1fi nal volume 30 cm3

Exper iment 4gradient great er t han Exper iment 2fi nal volume 90 cm3

(1)(1)

(1)(1)

QuestionNumber

Answer Rej ect Mark

6 (e) M1 60/ 24000 = 0.0025 mol

M2 0.005 mol H2O2

M3 Mr H2O2 = 34

M4 mass H2O2 = 0.005 x 34 = 0.17g

If 24000 not used in M1, scor e M3 and M4 onl yI f rat io 1 : 2 not used in M2, scor e M1, M3 and M4If genuine arithmetical error made lose 1 mark.

(1)

(1)

(1)

(1)


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QuestionNumber

Answer Rej ect Mark

7 (a) M1 sulphur burnt / heated in a i r

M2 S + O2 SO2

M3 SO2 mixed wi t h a i r

M4 at 350 t o 500C

M5 at pressure of 1 atm t o 3 atm

M6 use catalyst of vanadium (V) oxide / V2O5

M7 2SO2 + O2 2SO3

M8 SO3 dissolved i n 98% / conc sulp huri c acid

M9 wat er added (t o give conc H2SO4 / r equ i redconcentrat ion)

M10 SO3 + H2SO4 H2S2O7

H2S2O7 H2O 2H2SO4

OR SO3 + H2O H2SO4

oxygen

oxygen

atmosphericpressure/ 1at m

(1)

(1)

(1)

(1)

(1)

(1)

(1)

(1)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

7 (b) M1 H+ SO42- OH -

M2 2H+ + 2e - H2

M3 4OH- 2H2O + O2 + 4e-

M4 H+ gains elect rons / are reduced

M5 OH- lose elect rons / are oxidised

M6 H2 at cathode / O2 at anode

(1)

(1)

(1)

(1)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

7 (c)(i) M1 add zinc oxide to acid unt i l in excess / no more dissolves

M2 heat / warm

M3 fi l t er off excess / (or excess underst ood fr om M1)

M4 part ial ly evaporate and cool / leave t o cryst al l ise

M5 ZnO + H2SO4 ZnSO4 + H2O

(1)

(1)

(1)

(1)

(1)


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QuestionNumber

Answ er Rej ect Mark

7 (c)(ii) M1 2.52 g of wat er

M2 mol es ZnSO4 = 3.22 / 161 = 0.02

M3 mol es H2O = 2.52 / 18 = 0.14

M4 x= 0.14 / 0.02 = 7

If M1 incor rect , score M2 and M3 (conseq, mass/ 18)

If M2 incor rect , score M1 and M3

If M1 and M2 incor rect , score M3 only (conseq, mass/ 18)

Al ternat ive

M1 5.74 / Mr hydrate = 3.22 / 161

M2 Mr = 287

M3 xH2O = 287 161 = 126

M4 x = 126 / 18 = 7

(1)

(1)

(1)

(1)

(1)

(1)

(1)

(1)


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QuestionNumber

Answer Rej ect Mark

8 (a) Group I

M1 1 elect ron in outer shell

M3 lose 1 elect ron

M5 shiny/ grey met als/ sol ids

M9 more react ive down group

M11 inc re ase size /outer e lectron fur therfr om nucleus /increased shielding/more shell s

M12 less at t ract ion for outerelectron

M13 outer e- lost more easi ly

Need reference to out er e - t oscore al l 3 m arks M11 t o M13

M9 incorrectLose M11,12,13

Group VII

M2 7 elect rons in outer shell

M4 gain 1 elect ron

M6 chl ori ne green gasM7 bromi ne brow n l iq uidM8 iodine grey/ black sol id

Alternative if M6,7,8 not

scored.Gas t o li quid t o solid (1)Colour darkens (1)

M10 less reactive down group

M14 small est at om hasst rongest at t ract ion f ore lectron

M15 easier t o gain anElectron

M10 incorrectLose M14 and M15

M5Solidsonly

(1)(1)

(1)(1)

(1)(1)(1)(1)

(1)(1)(1)

(1)

(1)(1)

(1)


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QuestionNumber

Answer Rej ect Mark

8 (b) There must be contrasting statements to score.

Potassium Calcium

ignit es / explodes does not ignit e

moves on surf ace sinks /does not move on surface

mel t s does not mel t

f izzes vigorously f izzes less vigorously

If no compar isons al low 1 mark f or 3 correct observati ons ofpot assium in calcium

2K + 2H2O 2KOH + H2 formulaebalance

Ca + 2H2O Ca(OH)2 + H2 fo rmulabalance

Any3 by(1)markeach

(1)(1)

(1)(1)

QuestionNumber

Answer Rej ect Mark

8 (c) M1 8 electrons in outer shel l (He = 2) / complete octet /

Ful l out er shell

M2 do not gain or lose elect rons(ref erence t o both gain and lose)

M3 use: l ight bulbs / in bags for food preservat ion /iner t at mosphere for weld ing / steel m akingmanufacture of t i taniumdating rocks

Stable

conf igurat iononly

(1)

(1)

(1)


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QuestionNumber

Answer Rej ect Mark

9 (a)(i) M1 di f f erent forms of the same element

M2 in t he same physical st at e (M2 depend ent on M1)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

9 (a)(ii) M1 macromolecular / g iant molecule

M2 (carbon atom s) covalentl y bonded

(1)

(1)

QuestionNumber

Answer Rej ect Mark

9 (a)(iii ) diamond t et rahedral

graphite layers/ hexagonalAllow 1 mark for each C in diamond bonds to 4 other andeach C in graphite bonds to 3 other, i f no marks awardedabove

(1)

(1)

Question

Number

Answer Rej ect Mark

9 (a)(iv) diamond covalent bonds bet ween al l atom s

covalent bonds are st rong / d i f f icu l t t o break / r ig id st ructure

graphite w eak for ces (of att ract ion) bet ween layers

so layers slide

(1)

(1)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

9 (b)(i) carbon dioxide / CO2

plent i f u l supply / excess of a i r

C + O2 CO2

carbon monoxide / CO

l imi t ed / smal l supply of a i r

2C + O2 2CO / C + O2 CO

suf f ic ien t / r igh t amount/ good / enou gh

bad / less

(1)

(1)

(1)

(1)

(1)

(1)


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QuestionNumber

Answer Rej ect Mark

9 (b)(ii) either CO2 t u rns l imewater m i lky

but CO has no effect

or CO burns when l ighted t aper is appli edCO2 ext inguishes t he t aper

(1)

(1)

(1)(1)

QuestionNumber

Answer Rej ect Mark

9(b)(iii) Carbon monoxide is the reducing agent (can scorefr om equat ion)

(b lack) goes t o red brown / p ink brown / p ink

CuO + CO Cu + CO2

red OR brown

(1)

(1)

(1)

QuestionNumber

Answer Rej ect Mark

9 (c) M1 Mr MgCO3 = 84 and Mr Na2CO3 = 106

M2 mol MgCO3 = 3.36/ 84 = 0.04

M3 mol Na2CO3 = 0.04

M4 mass = 0. 04 x 106 = 4. 24g

If 1 incorrect Mr in M1 tr eat as ar i thm et ic err or , l ose 1 markI f both Mr incorrect m ax 2 for quest ion.

If 1: 1 rat io not used score M1, M2 and M4.

M2 and M3 could be scored as 3.36 x 10684

(1)

(1)

(1)

(1)

TOTAL FOR PAPER: 100 MARKS

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