Bonding in Organic Compounds_Organic Synthesis Marks Scheme

7/22/2019 Bonding in Organic Compounds_Organic Synthesis Marks Scheme

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1. (i) When calcium oxide and coke are heated in an electric furnace, the products are carbonmonoxide and calcium dicarbide (CaC2). Write the equation for this reaction.

CaO + 3C CaC2+ CO (1)

(ii) Addition of water to calcium dicarbide leads to the formation of calcium hydroxide andethyne (ethyne has the formula C2H2and is the starting point for the manufacture of a

variety of substances, including rayon and PVC). Write the equation for the productionof ethyne.

CaC2+ 2H2O Ca(OH)2/CaO2H2+ C2H2(1)

(iii) Until recently most ethyne was made in industry by the method in (ii). Today, ethyne isproduced in industry by heating methane (CH4) alone at a high temperature for 0.01

second. Write an equation for this reaction.2CH4C2H2+ 3H2(1)

(iv) Draw a diagram showing the electron arrangement in the dicarbide ion C22.

Triple bond with co rrect total number of electrons (2)

(5)

2. (a) The enthalpy change for the reaction

CH2 =CH2+ H2 CH3CH3

is - 120 kJ mol-1, whereas that for the reduction of benzene, C6H6, to cyclohexane, C6H12,is -208 kJmol-1. What may be deduced from the fact that this value is not three times

the first one?delocalised bonding in benzene (1) benzene does not have 3 (localised) C=Cbonds (1) benzene ring has high stabili ty (1) less susceptib le to addition (1)

(2)

(b) (i) State the conditions under which benzene may e nitrated to formmononitrobenzene.less than 60 C (1)

(ii) Both of the reagents that are used to nitrate benzene are usually regarded as acids.However, in this instance, one of them behaves as a base. Show how this is so.HNO3+ 2H2SO4 NO2+ 2HSO3-+ H3O+(2)

OR HNO3+ H2SO4 H2NO3++ HSO4-

OR HNO3+ H2SO4 NO2++ HSO4-+ H2O (1)sulphuric acid donates H+to HNO3(1)

Khalid Mazhar Qureshi www.edexcel-cie.com


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(iii) Give the mechanism for the nitration of benzene

NO

2

HNO2 NO2

+

+H

(1) allow this mark also for H at end

(1) for plus charge

incomplete ring delocalisationand

+

OR equivalent using Kekule forms - intermediate should have two doublebonds only

(iv) Explain why benzene tends to undergo substitution rather than addition reactions.addition destroys delocalisation OR substitution does not (1)

(8)(Total 10 marks)

3. (i) State the conditions under which benzene may e nitrated to form mononitrobenzene.

less than 60 C (1)

(ii) Both of the reagents that are used to nitrate benzene are usually regarded as acids.However, in this instance, one of them behaves as a base. Show how this is so.

HNO3+ 2H2S04 N02+ 2HSO3-+ H30+(2)

OR HNO3+ H2SO4 H2N03++ HS04-

OR HNO3+ H2SO4 N02++ HSO4-+ H20 (1)

sulphuric acid donates H+to HNO3(1)

(iii) Give the mechanism for the nitration of benzene

NO

2

H

NO2 NO2+

+H

(1) allow this mark also for H at end

(1) for plus chargeincomplete ring delocalisationand

+

OR equivalent using Kekule forms - intermediate should have two doublebonds only

(iv) Explain why benzene tends to undergo substitution rather than addition reactions.addition destroys delocalisation OR substitut ion does not (1)

4. Low density (poly(ethene) is used for packaging and plastic bags. The exothermic reaction bywhich poly(ethane) is made is shown by the following equation:

nC2H4(C2H4)n

(a) Write the structural formulae, showing all the bonds, of



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H H

H H

C C C C C C C C

H H H H H H

H H H H H H(1)(1)

n

(ii)(i)

(2)

(b) Typical conditions used in the process are a high pressure of 2000 atmospheres and a

relatively low temperature of 200 C.Suggest reasons for these conditions.

Pressure: formation of poly(ethene) occurs with volume decrease (1)favoured by pressure increase / suitable reason (1)If rate award (2)

Temperature: forward reaction, being exothermic (1)favoured by low temperature / suitable reason (1)Al low economic reason with justi fi cationAl low Le Chatel ier

(4)

(c) The reaction proceeds via a free radial mechanism. The production of poly(ethane) may

be initiated by the reaction.

R + CH = CH RCH CH2 22 2

Suggest an equation to show how

(i) a subsequent stage occurs;

RCH2CH2+ H2C=CH2RCH2CH2CH2CH2(1)

(ii) the polymerisation might terminate.

R(CH2CH2)nCH2CH2+ R(CH2CH2)nCH2CH2

R(CH2CH2)nCH=CH2+ R(CH2CH2)nCH2CH3(2)or

R(CH2CH2)n+CH2CH2CH2CH2(CH2CH2)nRFor 2 plausible radicals reacting (2) For R

+ R

R2(1)for H(0)

(1)for single-headed curly arrows in (i) or (ii)

(4)

(d) High density poly(ethane), used for articles such as buckets and crates, is made underother conditions, using a catalyst.

(i) Suggest why this form of poly(ethene) has a higher density.polymer chains more closely packed (1)allow 'crystallites'not less branched or cross-linked

(2)

(ii) Other than density, suggest ONE physical property which would be different forhigh density poly(ethene).more rigid, higher softening point (1)allow tensile strength, Tm, hard,

elasticity not boiling po int (ignore comparative remarks)



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(e) Draw a representative length of the molecule of poly(2-methylpropene), showing threerepeating units.

C C C C C C

H H H

H H H

CH

CH

CH

CH

CH

CH

3

3

3

3

3

3 (1)(1)

(f) (i) Write the structural formula, showing all covalent bonds, for the product obtainedby reacting 2-methylpropene with bromine.

C

C

C

C

C

C

C

C

C

C

H

H

H

H

H

H

H

H

H

H

H

H

H

H

Br

OH

Br

OH

Br

OH

Br

OH

(1)

(1)

HCH

HCH

CH

CH

(ii)

accept

accept

3

3

3

3

H C

H C

H

H

consequential from (i)

(2)(Total 15 marks)

5. Phenylethene (styrene),

CH CH2

is used in large quantities to make poly(phenylethene). A possible synthetic route from benzeneto phenylethene is shown below.

CH CH2

+ CH Br AStep 1

Step 6

Step 2 Step 3

Step 4 Cr O /H

Step 5

Cl , u.v.23

CH Cl CH OH

CHO

2 2

B

Conc H SO

heat2 4 (1) CH MgBr

(2) H

3+

2 72 +

phenylethene



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(a) (i) Give the name of a suitable catalyst for step 1 and give the structure of compound A.aluminium chloride / aluminium bromide / iron(III) bromide (or any that is used) (1)

CH3(1)

(ii) Why is ultraviolet light necessary in step 2?to split the chlorine or homolysis (1)generation of free radicals (1)

(iii) Suggest a suitable reagent and conditions for step 3.aqueousKOH / NaOH (1)heat (1)(correct reagent but no heat (1)heat but incor rect reagent (0))

(iv) The oxidation step 4 has to be done with care to obtain a\ good yield of aldehyde.Suggest how this is achieved.avoid excess oxidising agent (1)add oxidising agent to organiccompound and not the other way round (1)(recognition of avoiding the second stage if neither first point scored (1))

(v) How would you prepare the Grignard reagent, methylmagnesium bromide,CH3MgBr used in step 5?Mg + CH3Br (1)in dryether (1)OR with iodine catalyst (1)(max 2)

(vi) Give the structural formula of B.3CHCH

OH all hydrogen atoms must be shown except ring (1)

(10)

(b) (i) What type of polymerisation does phenylethene undergo?

addition (1)OR free radical (1)

(ii) Draw the structure of the polymer chain showing at least TWO monomer units.

C C C C

H C H C HH

H H H Hn

6 65 5

(open ends but no [ ]n(1))

(2)

(4)



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(c) Commercially, pheynylethene is made by the series of reactions:

AlCl3

900 K

Fe O2 3

CH CH2 3

2CH CH2

CH CH2

2+ + H

Suggest two reasons why this method id better than the route given earlier.better yield / shorter cheaper / useful by product H2/ no Grignard reagent

not cheaper on its own

(2)(Total 16 marks)

6. The following is adapted for a textbook of practical chemistry which gives practical details forthe preparation of the azo dye phenylazo-2-naphthol.

Dissolve 2.5 g of phenylamine in a mixture of 8 cm3of concentrated hydrochloric acid and 8cm3of water in a small beaker. Place in an ice bath; ignore any crystals that may appear.When the temperature is between 0 C and 5 C, add drop by drop a solution of 2 g of sodiumnitrite dissolved in 10 cm3of water, not allowing the temperature to rise above 5 C. Additionof the sodium nitrite solution should continue until, after a wait of 3-4 minutes, a drop of the

reaction mixture given an immediate blue colouration with starch-iodine paper.

Prepare a solution of 3.9 g of 2-naphthol in 10% aqueous sodium hydroxide solution in a 250cm3beaker, and cool in ice bath to below 5 C; add 10-15 g of crushed ice to this solution. Stirthe mixture, and add the diazonium salt prepared as above very slowly; red crystals of the azocompound will separate. When addition is complete, allow the mixture to stand in ice for 10minutes and then filter the product, using gentle suction on a Buchner funnel. Wash with water;the product may be recrystallised from glacial ethanoic acid. it has a melting point of 131 C.

(a) Phenylamine is toxic by inhalation and skin absorption; concentrated hydrochloric acid iscorrosive and gives harmful fumes. What specific precautions would you therefore takewhen doing this experiment?

fume cupboard (1)gloves (1)(safety requirements must be specific to question)

(2)

(b) Write the equation for the reaction between phenylamine and hydrochloric acid.C6H5NH2+ HCI C6H5NH3+CImust have correct chargesignore CIif H+on the L.H.S.

(1)

(c) (i) Why should the reaction mixture be kept between 0 C and 5C?< 0 C too slow (1)> 5 C product decomposes (1)

(ii) Is the diazotisation reaction exothermic or endothermic? How do you know?exothermic (1)have to keep temperature below 5 C (1)

(iii) Why should you wait before testing with starch-iodide paper for the presence ofexcess nitrite ions?

reaction sl ow so NO2

needs time to be used (1)

(5)



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(d) Give the equation, using structural formulae, for the diazo coupling reaction betweenbenzene diazonium chloride and 2-naphthol.

N Cl + N=N

OH

ignore HCl

+

2

reactants (1) products (1)

+ HCl

allow N N or NN but not N

=N or N=N

CInot essential

(2)

(e) The aqueous solution of the diazo compound prepared as in the first paragraph will, ifallowed to warm up, turn from very pale yellow to a turbid orange-red, and will evolvenitrogen. Why is this?

diazo compound gives phenol (1)which reacts with diazo compound to gi ve dye (1)

(2)(Total 12 marks)

7. (a) (i) What are isotopes?atoms with same Z different A (1) notmass no. / atomic no.

(ii) The oxygen isotope 19O is formed by bombardment of 18O with another particle;the only other product is -radiation. Write the equation for this reaction.

O + n188

10

198O + (1)

(iii) 19O is a -emitter; give the equation for its decay.O + F + (1)19

8199

01

01

e OK, enot

(iv) The table below gives the count-rate of a sample of 19O measured at various times.Show that the decay of 19O is first order and determine graphically or otherwise thehalf-life of this nuclide.

time/s

counts/s

0

2000

10

1550

20

1200

30

930

40

720

50

550

60

430

70

330

80

2601

plot either raw data vs. t showing constant tand relating this to first order

kinetics; orplot ln (counts) vs. t. showing straight line and relating this to fir storder.

In either case: points (1)

labelled axes right way round (1)line (1)

{Value of t= 27 s (1)

{Statement recognising graph as arising from 1st order process (1)

One or other showing a mean determination of t for both marks



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(v) The rate of decay of the radioactive species 40K is given by

rate of decay = N

whereNis the number of atoms of 40K present at time tand is the decay constant.The human body contains about 4 moles of potassium, of which 0.012% is theradioactive isotope 40K.If the decay constant for this nuclide is 1.6 1017s1, how many potassium atomsdecay per second in the average human? (Avogadro constant = 6.0 1023mol1)

no. of 40K atoms N = 4 6.0 1023 )1(1000

012.0

= 2.88 1020 (1)

rate = = 1.6 1017 2.89 1020 (1)= 4600 (s1) (1)

(12)

(b) The rate equation describing the reaction of some halogenoalkanes with nucleophiles isalso first order; eg:

(CH3)3CBr + OH(CH

3)3COH + BrWrite the rate equation for this reaction and show how it

is related to the mechanism for the reaction.rate = k[(CH3)3CBr] (1)

(CH ) CBr (CH ) C + :Br

:OHdo not allow if arrow is from negative charge no need for lone pair

(1)

3 3 3 3r.d.s.

(1)

+

fast (1)

3 3(CH ) COHfor process leadingto carbonium ion

(1)

mech:

OHfast can score if somehow the non-involvement of OHin r.d.s.is made explicit

(5)(c) An estimate of the relative rates of reaction of halogenoalkanes RX (where X is Cl, Br

or I) with aqueous hydroxide ions can be obtained by reacting a sample of each separatelywith silver nitrate dissolved in aqueous ethanol.

(i) What would you see as the reaction proceeds? Give reasons for your answer.precipitate (1)of silver halide (1)ionic equation + states for pptn of AgX (1)

(ii) why do you think aqueous ethanol is used as the solvent for the silver nitrate in thereaction with halogenoalkanes?improves miscibility of reagents (1)orsolvent for both reagents (or words tothat effect)

(iii) Write the halogenoalkanes Rbr, RI and RCI in order of rate of reaction, fastest first.iodide > bromide > chloride (1)

(iv) Give your reasons for this order.CI bond weakest (1)

(6)



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(d) By considering the importance of the shapes of both reactants and intermediates in SN1

and SN2 reactions, suggest why the compound 1-bromotypticene (below) is virtually inert

to nucleophilic attack.

Br

C

C

H

SN1 needs coplanar carbocation; not achievable (1)SN2 needs backs ide

approach blocked by rings (1)or repulsion of OHby electrons in benzenerings

(2)(Total 25 marks)

8. An estimate of the relative rates of reaction of halogenoalkanes RX (where X is Cl, Br or I) withaqueous hydroxide ions can be obtained by reacting a sample of each separately with silvernitrate dissolved in aqueous ethanol.

(i) What would you see as the reaction proceeds? Give reasons for your answer.precipitate (1)of silver halide (1)ionic equation + states for pptn of AgX (1)

(ii) why do you think aqueous ethanol is used as the solvent for the silver nitrate in thereaction with halogenoalkanes?

improves miscibility of reagents (1)orsolvent for both reagents (or words tothat effect)

(iii) Write the halogenoalkanes Rbr, RI and RCI in order of rate of reaction, fastest first.

iodide > bromide > chloride (1)

(iv) Give your reasons for this order.CI bond weakest (1)

(Total 6 marks)

9. Propranolol is a chiral compound used in some 40 pharmaceutical preparations for the treatmentof high blood pressure and cardiac pain. It is a base and is usually used as its hydrochloridesalt, which is a white powder soluble to the extent of 50 g dm3in cold water and much more soin hot.

Propranolol is manufactured from blycidyl butanoate.

CH CH CH C O CH CH CH

O

O

3 2 22 2

which is a chiral ester. This is made from glycidol, which has a boiling point of 56 C, andbutanoyl chloride, the latter being made from butan-1-ol via butanoic acid.



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The esterification gives a racemic mixture of the ester but proporanolol requires only one of theoptical isomers in this mixture.

Butan-1-ol is made commercially from natural gas; it can also be made from an aldehyde and aGrignard reagent, but this is not economic. The alcohol is oxidised to butanoic acid, which isthen converted to the acid chloride and then the ester.

(a) (i) What is meant by the term chiral?compound non-superimposable on mirror image (1)

(not bonded to 4 different groups...)

(ii) Draw the two stereoisomers of glycidol, CH CHCH OH

O

2 2 .

H H

C C

CH2 CH2

CH2CH OH &

CH OH

2

2CH2

O O

O Oor

3D structure (1)mirror image (1)

(iii) How is chirality detected experimentally?rotate plane of plane-polarised light (1)not bend, nor reflect, nor refract

(5)

(b) Write the equations, stating briefly the necessary conditions, to show how you wouldbring about the following:

(i) conversion of butan-1-ol to butanoic acid;

CH CH CH CH OH CH CH CH COOHCr O / H

3 2 2 2 3 2 2

2 72 +

heat reagents (1)Heat (1)equations (1)

(ii) conversion of butanoic acid to butanoyl chloride;

CH CH CH COOH + SOCl CH CH CH COCl + SO + HCl3 2 2 2 3 2 2 2r.t.

PClPCl

H POPOCl + 2HCl

3 3 3

5 3

3

4 equation with appropriate stoichiometry (1)conditions (1)

(iii) reaction of butanoyl chloride with glycidol.

CH CHCH OH + ClOCCH CH CH

CH CHCH O CCH CH CH + HCl

2

2

2

2

2

2

2

2

3

3

O

O

O

formulae of reactants (1)products (1)(full structures not necessary)consequential on acid chloride

(6)



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(c) (i) Suggest how butan-1-ol could be prepared using a Grignard reagent andan aldehyde.

CH CH CH MgBr + HCHO (1)3 2 22 23CH CH CH

C

H H

OMgBr(1)

+(1) H

butan 1 ol

(ii) State how the Grignard reagent you have suggested can be prepared from ahalogenoalkane.

CH CH CH Br + Mg3 2 2 2 23CH CH CH MgBrdry

ether

(1) (1)

or (1)I catalyst2

(5)

(d) Suggest why only one of the optical isomers of propranolol is effective as a drug.enzymes chiral reagents so reagent and ester only fit if stereochemistrycorrect (1)or metabolism stereochemically sensitive

(1)

(e) Give experimental details of how you could purify propranolol hydrochloride byrecrystallisation. How would you assess its purity?

dissolve in min vol (1)boiling water (1)filter hot (1)cool and filter (1)wash with small vol cold water (1)dry (in desiccator) (1)determine melting temperature and compare with data book value or mixed

m.p. (1)(7)

(f) How would you liberate the base propranolol from its hydrochloride salt?add sodium hydroxide solution (1)

(1)(Total 25 marks)

10. Consider the following reaction scheme, then answer the question which follow.

CCH CO H HOCH CH CO H ClCH CH CO H CH CHCO H

H

O A B C D

step 1 step 2 step 3

2 2 2 2 2 2 2 2 22



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(a) From your knowledge of the characteristic reactions of functional groups, how would youshow the presence of:

(i) The CHO group in A;eg Fehlings solutions / Benedicts / ammoniacal silver nitrate (1)not 2,4-DNP unless an oxidation is also carried outwarm (1)red / orange / brown precipitate (1)or cor rect result for reagent

(ii) The CO2H group in B?Add Na2CO3(aq) / NaHCO3 or a named carbonate orMg (1)

CO2(H2if Mg used) evolved / effervesces / fizzes (1)

neutral iron(III) (1) red / brown colour (1)allow named indicator (1) and correct co lour (1)but indicator and no colour (0)

or alcohol(1)+ conc H2SO4and warm (1)produce sweet smell (1)but(max 2)

(5)

(b) Give the reagents and conditions required to carry out:

(i) Step 1:eg NaBH4/ LiBH4(1)if NaBH4(aq) (2)

followed by acid / in solution (1)or any reducing agents that workeg lithium aluminium hydride (1) in dry ether (1)hydrogen (1) with platinum (1)sodium (1) in ethanol (1)

(ii) Step 2:ethanolic(1)KOH / NaOH(1)notOH ionsheat/followed by acidification(1)

(4)

(c) Name the type of reaction occurring in:

(i) Step 1:reduction / nucleophilic addition-elimination / hydrogenation / addition (1).

(ii) Step 3:elimination / dehydrohalogenation(1)

(2)

(d) Give the essential structural features necessary for geometrical isomerism to occur insample organic molecules. Hence deduce whether or note this type of isomerism existsin compound D.

C=C / C = N double bond(1)this can be implied in a diagram

correct orientation of groups required(1)or something about groups on agiven carbon not being the same

does not occur in D (1)

(3)

(Total 14 marks)



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11. Suggest the conditions under which ammonia could be used to convert CH3CHCICO2H to

CH3CH(NH2)CO2H.concentrated (ammonia) / sealed tube / metal bomb / high pressure / alcoholi c(ammonia) (1)not gaseousheat/warm / heat under reflux (1)reflux only (0)

(Total 2 marks)

12. (a) Give the reagents and conditions necessary to convert nitrobenzene to phenylamineeg tin / iron / zinc (1)+ concentrated HCI / ethanoic acid (with iron only)(1)HCI only ()heat / reflux(1)if LiAIH4(1)and dry ether(1)(max 2)

(3)

(b) In order to prepare a diazonium salt, phenylamine is dissolved in excess hydrochloricacid. A solution of sodium nitrite is added in small quantities to this solution until inexcess, maintaining the temperature between 0 and 10 C, preferably around 5C.The diazonium salt is formed in solution according to the equation:

C H NH + 2HCl + NaNO C H N NCl + NaCl + 2H O6 5 2 2 6 5+

2

(i) what structural feature of the phenylamine molecule allows it to dissolve readily inhydrochloric acid? Give the formulae of the species formed and hence explain, inenergetic terms, why phenylamine is soluble in hydrochloric acid but not verysoluble in water despite its ability to form hydrogen bonds.lone pair of electrons on N/NH2group (allows phenylamine to act as a base (1)

C6H5NH4+(and CI) (1)ionic water solub le (1)

hydration energy of ions > lattice energy (1)large hydrophobic phenyl group makes phenylamine less soluble in water (1)

(ii) The function of the sodium nitrite is to react wit excess hydrochloric acid to formnitrous acid. Write an ionic equation for this reaction. Identify the acid/base

conjugate pairs.H3O++ NO2

H2O + HNO2(1) must be an ionic equationA1 B2 B1 A2 1 mark for each conjugate pair (2)if acid and bases are indicated but not paired then (1)

if H++ NO2HNO2get equation mark only

(iii) Suggest why the sodium nitrate solution is added in small quantities.exothermic (1)

temperature may rise about 5 C/10 C / other reactions may occur (1)(10)



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(c) If the solution of the diazonium salt is warmed to about 50 C, it decomposes as follows:

C H N NCl + H O C H OH + N + HCl6 5+

2 6 5 2

Describe in detail an experiment you would perform in order to measure the rate of thisreaction. Include in your account how the measurements taken could be used todetermine the rate at a particular time during the decomposition.

diagram(1)suitable container(1)

suitable method of collecting gas(1)apparatus leak proof(1)(thistle funnel negates)thermometer in reacting mixture(1)start cold(1)

warm up to 50 C(1)maintain constant temperature(1)start clock at correct point (1) (max 8)note gas volume at various time intervals(1)plot graph: Volume N2vs time(1)

shape of graph shown(1)find gradient at given time(1)

OR pH method (max 3)plus (4) marks for: measure pH

plot [H+]

shapegradient

(12)

(Total 25 marks)

13. Give the reagents and conditions necessary to convert nitrobenzene to phenylamineeg tin / iron / zinc (1)+ concentrated HCI / ethanoic acid (with iron only) (1)HCI only ()heat / reflux (1)if LiAIH4(1)and dry ether (1)(max 2)

(Total 3 marks)

14. In order to prepare a diazonium salt, phenylamine is dissolved in excess hydrochloric acid.A solution of sodium nitrite is added in small quantities to this solution until in excess,maintaining the temperature between 0 and 10 C, preferably around 5C.The diazonium salt is formed in solution according to the equation:

C H NH + 2HCl + NaNO C H N NCl + NaCl + 2H O6 5 2 2 6 5+

2

(a) what structural feature of the phenylamine molecule allows it to dissolve readily inhydrochloric acid? Give the formulae of the species formed and hence explain, inenergetic terms, why phenylamine is soluble in hydrochloric acid but not very soluble inwater despite its ability to form hydrogen bonds.

lone pair of electrons on N/NH2group (allows phenylamine to act as a base (1)

C6H5NH4

+

(and CI

) (1)ionic water solub le (1)

hydration energy of ions > lattice energy (1)large hydrophobic phenyl group makes phenylamine less soluble in water (1)



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(b) The function of the sodium nitrite is to react wit excess hydrochloric acid to form nitrousacid. Write an ionic equation for this reaction. Identify the acid/base conjugate pairs.

H3O++ NO2H2O + HNO2(1) must be an ionic equation

A1 B2 B1 A2 1 mark for each conjugate pair (2)if acid and bases are indicated but not paired then (1)

if H++ NO2HNO2get equation mark only

(c) Suggest why the sodium nitrate solution is added in small quantities.exothermic (1)

temperature may rise about 5 C/10 C / other reactions may occur (1)(Total 10 marks)

15. (a) Explain why light is essential for the reaction between methane and chlorine to formchloromethane at room temperature. Explain also why this method is not regarded as agood way of synthesising pure chloromethane.

light a form of energy / hv(1)required to break the CI-Cl bond / split thechlorine molecule(1)

into free radicals (OR equation CI22CI.)(1) (Cl2 2Cl.(2))homolytic fission earns the 2nd and 3rd marks ie (2)accept if the rest of theanswer demonstrates a lack of understanding

mechanism: CI+ CH4CH3+ HCl(1)

.CH3+ CI2CH3CI + CI.(1)

or the equivalent in words for the above equationrepetition of process gives dichlo romethane etc. (or chain reaction goesfurther) / or termination step showing product other than CH3CI(1)

hence product not pure(1)

(7)

(b) Explain why the first ionisation energy of phosphorus is greater than that of both silicon

and sulphur.(implied) definition of first ionisation energy(1)(P > Si) since nuclear charge P > Si(1)and shielding by inner shells same / outer electrons in same shell/orbital(1)(P > S) since S has paired electrons in 3p shell (1)greater repuls ion between these makes them easier to remove /or given a half filled p shell which conveys some stability(1)

(5)

(c) An acidic solution of potassium manganate (VII) will liberate chlorine from dilute sodiumchloride solution but an acidic solution of potassium dichromate (VI) will not. Solidpotassium dichromate (VI) will liberate chlorine gas from concentrated hydrochloric acid.

Explain these observations with reference to the data below.

E / V

MnO4 (aq) + 8H+(aq) + 5e Mn2+(aq) + 4H2O + 1.52

Cl2(g) + 2e-2Cl (aq) + 1.36

Cr2O72(aq) + 14H+(aq) + 7e2Cr3+(aq) + 7H2O + 1.33



16/96

liberation of CI2is oxidation (implied)(1)

2CI 2eCI2(1)oxidant having a more positive E values will do this(1)hence manganate(VII) will and dichromate(VI) will not(1)

but E values refer to molar solutions /standard conditions(1)concentrated HCI not 1 mol dm-3(1)

difference in concentration makes up for small dif ference in E values(1)

(7)

(d) By application of the concept of bond energy, predict a value for H for the reaction:

C2H5OH + CH3CO2H CH3CO2C2H5+H2O

Hence predict the effect of an increase in temperature on the equilibrium constant forthis reaction.

same bonds broken as are formed(1)1 C O and 1 H-O bonds are broken and formed(1)

total H = 0(1)marked consequentially on bonds

deducing Kc= constant from H = 0 (2)

just if ication (1)egtemperature change has no effect on the equilibrium posit ion

or

Kc =[ ][ ]

[ ][ ]

ester water

acid alcoholimplied

orle Chatelier argument

if H = +ve or ve, mark Kcand justifi cation consequentially for full (3)

(6)(Total 25 marks)

16. Explain why light is essential for the reaction between methane and chlorine to formchloromethane at room temperature. Explain also why this method is not regarded as a goodway of synthesising pure chloromethane.

light a form of energy / hv (1)required to break the CICl bond / split thechlorine molecule (1)

into free radicals (OR equation CI22CI.) (1) (Cl2 2Cl.(2))homolytic fission earns the 2nd and 3rd marks ie (2)accept if the rest of theanswer demonstrates a lack of understanding

mechanism: CI.+ CH4.CH3+ HCl (1)

.CH3+ CI2CH3CI + CI.(1)

or the equivalent in words for the above equationrepetition of process gives dichlo romethane etc. (or chain reaction goesfurther) / or termination step showing product other than CH3CI (1)

hence product not pure (1)

(7)



17/96

17. Consider the following series of reactions and answer the questions which follow.

NaOH (aq)

NaOH(aq)

ethanolic KOH

HCl(aq)

C H O6 12 2 C H O4 10 CH CO Na3 2 +

C H4 8

C H4 10

2H /Pt

C H Br4 9 CH CO H3 2

+A B C

DEF

G

(a) (i) What type of reaction is represented by the conversion of Eto F?elimination (1)

ignore nucleophilic or electrophilic

(1)

(ii) The product Fexists in two steroisomeric forms. Draw them, and state the featureof the molecule which makes this isomerism possible.

H H H

CH CH3 3 CH H

CH

3

3

C C C C allow stick for Hs

(1) (1) restricted/no/stops rotation about C=C (1)this mark is conditional on twocorrect cis/trans structures being given

(3)

(iii) Give a simple chemical test, stating what you would se, for the functional group

present in F.bromine (water) (1)

yellow / brown / orange colourless (notclear) (1)just decolour ise without stat ing original colour ()or any suitable equivalent:

eg potassium manganate(VII) purple brown/ colourless/green is OK(2)

(iv) Fis more reactive than G. Suggest in terms of the bonding of these compoundswhy this is so.alkenes have accessible / high electron density / description of and bonding (1)or C=C has bond which is weaker than bond so alkenes react(2)

if jus t alkene has a bond is given then (1)onlyif double bonds add on and single bonds undergo substitution isgiven then (1)only

(2)



18/96

(b) Compound Edisplays optical isomerism.

(i) State what this means.rotates (plane of polarisation of ) plane-polarised (monochromatic) light (notbends/ twists) or non-superimposable mirror image (1)if contains chiral carbon is given this must be explained or indicated on thediagram for (1)

(1)

(ii) Sketch the optical isomers of E.

CH CH CH CH

H H

C CBr Br

2 23 3

CH3 CH3structure (1)correct mirror image (1)must be 3D drawing for (2) if it is drawn flat (1)onlyif a correct mirror image of an incorrect bu t chiral compound (1) the chiralcompound must be feasible to get this mark

(2)

(c) The reaction of Eto give Bis a nucleophilic substitution.(i) What is meant by the term nucleophile?

species with lone pair () to donate ()seeks positive centres () onlynot seeks protons in nucleus or nucleus lovingnot has a negative charge

(1)

(ii) Give the structural formula for B.

H C C C C H

H H H H

H H OH H

(1)

consequential alcohol on (b)(ii)the structure must be sufficient to show butan-2-olCH3CH2CH(OH)CH3is OK

(1)

(iii) Give a simple chemical test for the functional group in B, and say what youwould see.+PCI5(1)(steamy) (acid) fumes / whi te gas (1)if evolut ion of HCI given () if

PCI5(aq) then (0)

any other suitable test and result acceptable e.g.

sodium (1) Bubbles (1)if H2formed is given ()

or potassium dichromate (VI (1)green (1)

or potassium manganate(VII) (1)brown/colourless (1)

or add carboxylic acid and conc. sweet smell (1)if ester formed given then()sulphuric acid) (1)

or ZnCI2/HCI (1)white ppt (1)

or I2/NaOH or KI/NaCIO (1)yellow ppt (1)if forms CH3 ()

consequential on answer given to (c)(iii)

(2)

(d) The type of reaction exemplified by A B + C is important in the manufacture of soap.



19/96

(i) What type of reaction is this?hydrolysis / saponification (1)not substitution

(1)

(ii) Acould be reacted with aqueous acid to give Band D. If the same quantity of Awas treated with aqueous acid, instead of aqueous alkali, how would the yield of Bdiffer? Explain your answer.

yield falls; () reaction with acid is an equilib rium ()(1)

(e) Consider the reaction C D.(i) Name D.

acetic/ethanoic acid (1)

(1)

(ii) Identify the acid-base conjugate pair in this reaction.CH3COOH / CH3COO (1)CH3COONa given ()

ifCand Dgiven () only

(1)

(iii) Explain why the reaction occurs.HCI/H3O+is a stronger acid (1)than

ethanoic acid (1)orCH3COO strong base (1)whereas

CI weaker base (1)

(2)

(iv) A quantity of Awas reacted with NaOH, acidified and the volatile acid Ddistilledout. Dwas then added to a solution containing 0.0250 mol (an excess) of NaOH.The excess NaOH from this reaction required 28.7 cm3of 0.100 mol dm3HCl forcomplete reaction. What mass of awas reacted with NaOH in the first place?

NaOH left mol 28 7

100001 1 2 87 103

.. ( ) .

NaOH used = 0.025 2.87 10-3(1)= 0.0221 mol

0.0221 mol o f A

mass of A = 0.0221 116 (1)= 2.56/7 g (1)

(4)(Total 25 marks)

18. Polymers may be naturally occurring or synthetic. Name

(a) a synthetic polyalkeneany suitable (1)must contain C and H only eg polythene

(1)



20/96

(b) a synthetic polyamidenylon (1)not acrylic

(1)

(c) a natural polyalkeneprotein or a natural protein such as keratin / gelatine / silk / (1)not hair / wool / fingernails

(1)

(d) a synthetic polymer containing no hydrogenPTFE / Teflon (1)must be names

(1)(Total 4 marks)

19. Terylene is a polymer made from ethane 1,2-diol and benzene 1,4-dicarboxylic acid. It is acondensation polymer.

(a) Draw the structural formulae of the two compounds which are used to make Terylene.

COOH

COOH

(1)

HOCH2CH2OH (1)

(2)

(b) Give a structural formula for the polymer.

( OCH CH OCO2 2

OC )n correct structure (1)minor fault ()but ester link must be presentline through bracket and n (1)

(2) 2nd mark conditional on 1st

(2)

(c) Explain the meaning of the term condensationin this context.2 molecules joined together by loss of water (1)

(1)

(d) Suggest why polyesters are not suitable for use under strongly alkaline conditions.hydrolyses (easily) / saponification (1)

(1)(Total 6 marks)



21/96

20. Carvone

C

C

C

O

CH

CH

CH3

CH2 CH2

CH2H C3

O

CH3

CH2H C3

which may alsobe shown as

is the main flavouring material in spearmint oil.

(a) Draw the structure of the product obtained when carvone reacts with

CH

(2)

3

3

NNH 2

2

NO

2NO

any NN link at carbonyl (1)

CH BrBr

Br

Br

CH

O

(2) (1)

(2)

for each double bond that has been reactedif use bromine water if get addition to give ignore relative positions of these

(i)

(ii)

Br OH

(4)

(b) Explain why carvone does not react with ammoniacal silver nitrate.ketone so not easily oxidised (and therefore no reaction)/

no reducing group present / no aldehyde group present (1)

(1)



22/96

(c) Carvone is chiral and shows optical activity.

(i) Explain the meaning of chiral.mirror-image and or iginal non superimposable /two non-superimposable mirror images /molecule can be left handed or right handed /molecule with a carbon atom attached to 4 different groups (1)

(1)

(ii) Circle on the structure of carvone the features of the molecule which makesit chiral.

CH3

O

(1)

(1)

(iii) What is optical activity?ability to rotate (plane of polarisation) (1)

(of plane) polarised (monochromatic) light (1)

(2)

(d) Suggest a synthetic method, including reference to reagents and conditions, by whichcarvone could be converted to

Cl

CH3

CH2H C3

C

route (1)(ie state the C=O group is reduced or give the intermediate)

C=O to CHOH: reagent (1)conditions (1)

CHOH to CHCl: reagent (1)conditions (1)

eg reduce C=O to CHOH: LiAIH4(1)(dry) ether (1)

convert CHOH to CHCI: PCI5(1)heat/warm/room temperature (1)

(5)(Total 14 marks)



23/96

21. Alkanes and alkenes differ strikingly in their reactivity, for example with chlorine; this is aconsequence of their structure.

(a) Using a charge-cloud representation of the and conds show the structures of ethaneand ethene.

ignore in CH concentrate on CCignore absence of charge cloud heremark for co rrect representation of

(2)

(b) (i) Give the equation for the reaction of one mole of ethane with one mole of chlorine.

CH CH + Cl CH CH Cl + HCl allow C H / C H Cl etc(1)3 3 2 3 2 2 6 2 5 (1)

(ii) Give the mechanism for this reaction.

Cl 2Cl

(1)

CH CH + Cl CH CH + HCl

(1)

CH CH + Cl CH CH Cl + Cl (1)

2

3 3 3 2

3 2 2 3 2 (3)

(iii) Butane is a by-product by this reaction. How does it arise?

2CH CH butane (1)

if start with methane then ( for the Cl 2Cl and(max 2) (1)

(1)for a consequentially correct 2nd propagation step)

3 2

2

if start with methane then (max 2) (1)for the CI22 CIand(1)for a consequentially correct 2nd propagation step)

(1)

(c) (i) Give the mechanism for the reaction of chlorine with ethene.

C C

ClCl :Cl

C CC C

Cl Cl Cl

each arrow ()(1)for intermediate(1)for arrow from chlorine the lone pair does not haveto be drawn in but the arrow must notcome from thenegative charge

(3)

(ii) Explain in terms of their structures why the reactions of ethane and of ethene withchlorine are so different.ethene has more accessible electron density (1)which polarises CI2to form electrophile (1)

in ethane strong bonds need to be broken / bond less strong than (1)(or explain in terms of saturation of ethane)

(3)



24/96

(iii) Why are alkenes not used as fuels?too valuable as synthetic intermediates / used to make polymers (1)

not H values as these are about the same

(1)

(d) Alkynes such as ethyne

HCCH

are unsaturated compounds and undergo addition reactions in a similar fashion to alkenes.Under suitable conditions ethyne will react with water, and the reaction might be expectedto be

HCCH + H2O CH2==CHOHethenol

(i) Using the bond enthalpies given below, suggest why the product of this reaction isnot in fact ethenol, but its structural isomer ethanal, CH3CHO.

H/kJ mol1: CH412, C==C612, CO 360, C==O 743, OH 463

CC 348, C837.sum of bond enthalpies of ethenol= 3 412 + 612 + 360 + 463 = 2671 kJ mol1(1)

sum of bond enthalpies of ethanal= 4 412 + 348 + 743 = 2739 kJ mol1(1)

production of ethanal more exothermic (1)so thermodynamically favoured / product more stable (1)if answers incorrect but in correct order or calculation not attempted last 2marks can still be scored

(4)

(ii) The catalyst used for the reaction is mercury(II) sulphate. The process wasresponsible for a serious pollution incident in Japan in the 1950s, when mercury(II)sulphate effluent was converted by bacteria in river muds into methylmercury,(CH3)2Hg. This then entered the food chain via fish caught locally. HgSO4is a

typical inorganic compound, (CH3)2Hg is typically organic and is very much more

toxic. Suggest a reason why?Me2Hg covalent and fat-soluble (. retained in body) (1)

allow similar argument based on solubil ity of HgSO4

(1)

(e) Alkanes are obtained by the fractional distillation of crude oil; this system is complex, butit does not form any azeotropes. The boiling-point/composition diagram shown is for apair of liquids Aand Bwhich doe form an azeotrope:

0 1

Temperature

Mole fraction of A

X

(i) State and explain what would happen if a mixture of composition was fractionally



25/96

distilled.distillate richer in B / residue richer in A (1)pure B distils off first (1)until azeotropic composit ion reached (1)when azeotrope distils unchanged (1)

(4)

(ii) Does this system show a positive or negative deviation from Raoults Law?

State how this deviation arises.negative (1)interactions between molecules/intermolecular forces in mixture greater thanin either of pure substances (1)

(2)(Total 25 marks)

22. (a) Give the equation for the reaction of one mole of ethane with one mole of chlorine.

CH CH + Cl CH CH Cl + HCl allow C H / C H Cl etc(1)3 3 2 3 2 2 6 2 5 (1)

(b) Give the mechanism for this reaction.

Cl 2Cl

(1)CH CH + Cl CH CH + HCl

(1)

CH CH + Cl CH CH Cl + Cl(1)

2

3 3 3 2

3 2 2 3 2 (3)

(c) Butane is a by-product by this reaction. How does it arise?

2CH CH butane (1)

if start with methane then ( for the Cl 2Cl and(max 2) (1)

(1)for a consequentially correct 2nd propagation step)

3 2

2

if start with methane then (max 2) (1)for the CI2 2 CIand(1)for a consequentially correct 2nd propagation step)

(1)

(Total 5 marks)



26/96

23. Phenylamine, C6H5NH2, can be made in several ways from benzene. The flowchart shows two

of these in outline.

NO2

2

Step 1

Step 2

Step 3

NH

C H8 10

C H O7 6 2

C H OCl7 5

C H NO7 7

A

B

C

D

MnO /OH4

phenylamine

AlCl /C H Cl3 2 5

(a) (i) Give the reagents and conditions needed for step 1.concentrated nitric + (concentrated) sulphuric (1)40 60 C/heat/warm to max 60 C (1)

(2)

(ii) Write the mechanism for this reaction.

HNO + 2H SO 2HSO + H O + NO

or HNO + H SO HSO + H O + NO (1)

(1)3 2 4 4 3 2

3 2 44 2 2 +

NO2

HNO2 NO2

+

+H

(4)

(iii) Give the reagents and conditions for step 2.tin / iron (1)+ concentrated HCI (1)allow ethanoic acid for ironheat (1)not refluxnot LiAIH4

(3)



27/96

(b) (i) In the alternative pathway identify the compounds Aand Dinclusive.

CH CH

COCl

COOH

CONH

2

2

3A

C

B

D

(1)each = (4) allow correct unambiguous names ieA ethylbenzene / phenylethane B benzenecarboxylic acid/benzoic acidC benzenecarbonyl chloride/benzoyl ch loride D benenecarboxamide/benzamide

(4)

(ii) State the reagents and conditions needed for step 3.bromine (1)alkal i / NaOH (1)heat (1)

(3)

(iii) Why is the first pathway commercially preferable for the manufacture of

phenylamine?quicker formation of product/simplest path best because yields higher / moreeconomic (1)

(1)

(c) Phenylamine reacts with nitrous acid in the presence of concentrated hydrochloric acid at05C to produce benzenediazonium chloride.If the temperature of the solution rises, this compound reacts with the solvent water togive phenol, C6H5OH, and nitrogen gas. The rate of the reaction can be followed by

measuring the volume of nitrogen produced at various times, pressure and temperatureremaining constant. The amount of benzenediazonium chloride remaining in the solutionis proportional to V Vt, where Vtis the volume of gas at time tand Vis that at the end

of the reaction.

(i) Give the equation for the reaction between benzenediazonium chloride and water.

N Cl2 OH

2 2+ H O + N + HCl

+

allow C6H5or kekule

if no charges (1)

(2)



28/96

(ii) Some results of this experiment are shown below.

250

200

150

100

50

00 500 1000

t/s

(

)/cm

V

V

3

t

gets half-life from graph at least two readings (2)half-life constant (1)characteristic of firs t order reactions (1)if say not constant but then say not1st order award the last mark

Deduce the order of reaction with respect to benzenediazonium chloride fromthe graph.

(4)

(iii) Is the reaction necessarily of this order overall? Explain your answer.the other reagent/water present (1)which may / may not contribute to theoverall order (1)

(2)(Total 25 marks)



29/96

24. (a) Phenylamine, C6H5NH2, can be made in several ways from benzene. The flowchart

shows two of these in outline.

NO2

2

Step 1

Step 2

Step 3

NH

C H8 10

C H O7 6 2

C H OCl7 5

C H NO7 7

A

B

C

D

MnO /OH4

phenylamine

AlCl /C H Cl3 2 5

(i) Give the reagents and conditions needed for step 1.concentrated nit ric + (concentrated) sulphuric (1)40 60 C/heat/warm to max 60 C (1)

(2)

(ii) Write the mechanism for this reaction.

HNO + 2H SO 2HSO + H O + NO

or HNO + H SO HSO + H O + NO (1)

(1)3 2 4 4 3 2

3 2 44 2 2 +

NO2

HNO2 NO2

+

+H

(4)

(iii) Give the reagents and conditions for step 2.tin / iron (1)+ concentrated HCI (1)allow ethanoic acid for ironheat (1)not refluxnot LiAIH4

(3)



30/96

(b) (i) In the alternative pathway identify the compounds Aand Dinclusive.

CH CH

COCl

COOH

CONH

2

2

3A

C

B

D

(1)each = (4) allow correct unambiguous names ieA ethylbenzene / phenylethane B benzenecarboxylic acid/benzoic acidC benzenecarbonyl chloride/benzoyl ch lori de D benenecarboxamide/benzamide

(4)

(ii) State the reagents and conditions needed for step 3.bromine (1)alkal i / NaOH (1)heat (1)

(3)

(iii) Why is the first pathway commercially preferable for the manufacture of

phenylamine?quicker formation of product/simplest path best because yields higher / moreeconomic (1)

(1)(Total 17 marks)

25. An organic compound X contains 82.75% carbon and 17.25% hydrogen by mass.

(a) (i) Calculate the empirical formula of X.82.75

12

17.25

1

=6.9

6.9 =

17.25

6.9

= 1 = 2.5 (1) (ie for correct ratio)

empirical formula = C2H5 (1)

if just C2H5 then (0)

(2)



31/96

(ii) Deduce from the mass spectrum below the relative molecular mass of X, giving areason for your choice. Hence show that the molecular formula of X is C4H10.

20

40

60

80

100

605040302010

58

43

29

15

Relativeintensity

m/e 58

highest m/e molecular ion / parent ion / molecule / parent peak (1)

which corresponds toC4 H10( = 48 + 10) = 58(1)

(2)

(b) There are two possible structures A and B for this molecule:

C C C C

H H H H

H H H H

H H C C

C

C

H H H

H H H

H H

3

A B

(i) Identify the species responsible for the peaks in the mass spectrum at 43, 29 and 15.43: +C3 H7 (1)

29: +C2 H5 (1)

15: +CH3 (1)

penalise (1) once if any +s are omitted

(3)

(ii) Hence deduce which of the structures Aor Bis present, giving a reason foryour answer.A + reason pinpoint ing +C2H5(2)

A + reason which is vague in terms of species (1)

(2)

(c) Complete combustion of Xin oxygen gives carbon dioxide and water only.

(i) Write an equation for this combustion reaction.C4H10+ 6O2 4CO2+ 5H2O (or doubled)(1)

(1)



32/96

(ii) Calculate the total volume of the gaseous mixture produced when 2 cm of gaseousC4H10is mixed with 15 cm of oxygen and completely burned. All volumes are

measured at room temperature and pressure.2 vols 13 vols 8 vols (1) which can be implied

hence 8 cm3CO2(1)

+ 2 cm3O2 in excess 10 cm3in total(1)

if calculationincludes 10 cm3gas for H2O to get 20 cm3as answer then(2)only

marked consequentially on equation

allow cor rect method using 24000 or 22400cm3 mol1

(3)

(Total 13 marks)

26. (a) Give the formulae of the three structural isomers of C4H8which are non-cyclic.CH3CH2CH=CH2(1)

CH3CH=CHCH3(1)

(CH3)2C=CH2 (1)

(3)

(b) One of these isomers show a type of stereoisomerism.

(i) Give the structure of stereoisomers and name them.clear structures of both isomers () each

names: cis and trans ()but-2-ene ()

(2)

(ii) Suggest how these stereoisomers might be distinguished.different melting / boiling points or difference in i.r. spectra

or difference in n.m.r. or difference in dipoles (1)

(1)

(c) One of the isomers of C4H8in (a) reacts with HBr to give two different products, the

major one of which is a chiral molecule.

(i) Identify this isomer of C4H8.but-1-ene (1)allow name or correct formula

(1)



33/96

(ii) Give the mechanism for the reaction of this isomer with HBr.

CH CH CH=CH CH CH CHCH CH CH CHCH3 2 2 3 2 2 3 2 3

BrH H Br()

()

:Br(1)

+

the arrow from the double bond can point to the H

the arrow from the Brmust not po int to the positive charge or come from the

ve sign.

the arrows must not be straight or v-shaped

allow triangular structured intermediate

the intermediate must have a + charge not +(3)

(iii) Why is the major product chiral but the minor one not so?the product has a carbon atom with four different groups attached/ has anon-superimposable minor image (1)

not just assymetryric carbon

allow inverse argument (ie the minor product does not have....)

(1)

(iv) Why is the chiral product the major one, and the non-chiral product the minor one?intermediate secondary carbocation more stable than primary (1)

allow inverse argument (ie in minor product intermediate....)

statement of Markownikof rule alone (0)

(1)

(v) The major product of this addition reaction is found to be optically inactive.Explain why this is so.both d and I forms / optical isomers are present (1)

in equal (molar) quantities / racemic mixture formed (1)

(2)(Total 14 marks)

27. The characteristic reactions of benzene can be classified as electrophilic substitution reactions.

(a) Select a reaction of benzene which illustrates this type of reaction. Give the reagents andthe equation for this reaction, the conditions under which it occurs and the name of theorganic product.

I II III

reagent conc()

HNO3/H2SO4()

Br2/RHal/RCOHal ()

+ AlCI3() allow iron

bromide

conc/fuming()H2SO4()

equation correct equation (1) correct equation (1) correct equation (1)

conditions warm/heat () to maxof 60C()or4060Cas specifictemperature range (1)

anhydrous heat (1) heat (1)

name of organicproduct

nitrobenzene (1) any unambiguousname (1)

benzene sulphonic acid(1)

(4)

(b) For the reaction selected in (a):



34/96

(i) identify the electrophile;electrophile for reaction in (a)

eg No2+/ RCO

+/ R

+/ Br

+(1)name or formula

(1)

(ii) give an equation to show its formation;equation for reaction in (a)

eg HNO3+ 2H2SO42HSO4+ H3O++ NO2+(2)if onl y HNO3+ H2SO4 HSO4+ H2O then H2O + NO2+then (2)but if w ritten in 2 stages ie H2NO3+then H2O + NO2+then (2)eg RHal + AICI3 R++ AICI4(2)penalise (1)for each error

(2)

(iii) give the mechanism for the substitution reaction.arrow to electrophile (1)

must be from ring or inside the ring

not to +ve sign or to oxygen

intermediate with incomplete ring and oneposit ive charge

or correct position of one positive charge if Kekule (1)

loss of proton ie arrow on CH bond (1)

(+ve charge can be outside bracket but if show TWO positive charges on

intermediate (max 1))

eg

NO2+

+ +NO

NO2

2H

H+

(3)

(c) Give two specificsafety precautions you would need to take in carrying outthereaction in (a).

specific safety precautions 2 (1) any two of:

gloves

fume cupboard or ventilation

indirect heating

benzene carcinogenic and talk about risk assessment or replacement

(ignore other suggestions such as safety goggles or lab coats as these

are not specific to these systems

however if the suggestions are patently absurd in these cases (1))

(2)



35/96

(d) Give one reaction of the functional group which was introduced into the benzene ring as aresult of the reaction performed in (a). give the reagents, conditions and equation forthis reaction.

the answers in th is section must relate to the functional group not to thebenzene ring

Reagent (1)name or formula of compound(s)eg for reduction of NO2 Sn/HCI (not LiAIH4)

conditions (1)applicable for the reagent statedeg heat (under reflux) not jus t reflux equation (1)will accept [H} or H2but must be balanced

(3)

(Total 15 marks)

28. (a) When excess methane reacts with chlorine, the main product is chloromethane.

(i) Under what conditions does this reaction occur?sunlight / UC (1)

(1)

(ii) Give the mechanism for this reaction.

(initiation) CICI CI+ CI(1)(propagation) CI + HCH3 CIH + CH3(1)

CICI + CH3 CI+ CICH3(1)(termination) eg CI+ CI CI2(1)if correct use of half arrow these take place of

does not have to be on the C atom ie CH3is acceptable.

(4)

(b) Heptane and octane are liquids at room temperature with boiling points of 98C and126C respectively.

(i) What type of intermolecular forces of attraction are present in such liquids?van der Waals/dispersion / induced dipole-induced dipole /

instantaneous dipole (1)

(1)



36/96

(ii) On the axes below, sketch a graph of how the boiling points of various mixtures ofthese two liquids vary with composition. Show clearly the composition of theliquid and vapour phases.

0

Temperature

mole fraction of heptane 1

lines correct shape ()and labels ()

there must be 2 curves without a max or min in the diagram

the liquid line must notbe straight

correct orientation according to axes (1)

(2)

(iii) By what process would a mixture containing a mole fraction of 0.5 heptane beseparated into pure heptane and pure octane?fractional distillation (1)

(1)

(c) Liquid alkanes such as heptane and octane occur in petrol used as fuel to drive cards.

(i) Give two reasons why liquid fuels are generally preferred to gaseous ones.any TWO from:

liquids have smaller volume can carry more fuel OWTTE (1)

(ie some reference to volume and consequence)

gases would need high pressures and therefore more likely escape (1)

(ie some reference to pressure and reason)

liquids easier to transfer (1)(max 2)

(2)

(ii) The combustion characteristics of fuels for internal combustion engines in cars canbe considerably improved by adding branched chain alkanes, cycloalkanes,aromatic hydrocarbons or tetraethyl lead(IV) (lead tetraethyl). Two of these arenow considered to be hazardous to health. Select these two and identify the healthhazard with which each is associated.aromatics () carcinogenic ()

lead compounds () lead poisoning etc ()

hazard is consequential on compound chosen

(2)

(Total 13 marks)



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29. This question relates to the following reaction scheme

step 1 step 2 step 3

C2H5Br C2H5CN C2H5CH2NH2 C2H5CH2OH

(a) Give the reagents, the conditions required and the equation for step 1 and step 2.

(i) Step 1KCN / NaCN (1)or name

not HCN

ethanolic / aqueous ethanol/alcoholic ()

boil/heat (under reflux) ()

equation (1)molecular or ionic

(3)

(ii) Step 2Na in EtOh / LiAIH4/ hydrogen (1)not sodium borohydride

correct condition for reagent used ieroom temp or warm (for Na in EtOH) / dry ether (for LiAIH4) /

Pt or Ni catalyst (for hydrogen) (1)

equation (using [H] or H2acceptable but if using hydrogen gas must

show as H2)(1)

(3)

(b) (i) give a mechanism for step 1.mechanism SN2

(1):CN

C C Br

(1)

C CC C

CN CN

Br Br

+..

-

the arrow from CNmust not come from the lone pair on the nitrogen

arrows must not be straight or vshaped

do not need to show the lone pair

the intermediate must show an overall negative charge

if no Bron ri ght hand side then penalise ()

(3)

(ii) What type of mechanism is this?nucleophilic substitution (1)

(1)



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(c) The conversion of C2H5Br to C2H+5+CH2OH by this method is ineffective, not least

because step 3 gives a very poor yield of only 7%. Outline an alternative synthetic route,stating clearly the reagents and conditions of the steps you suggest.

There are several alternatives for this part of the question. The two mostlikely are listed below. If a candidate suggests an alternative route which isfeasible the schemes below should act as a guide as how the marks shouldbe apportioned.

Mg (1)dry ether (1)

(C2H5Br + Mg) C2H5MgBr (1)ie mark for product name or formulamethanal (1)name or formuladil HCI or water (1)hydrolyse(1)

OR Step 1 of question the same (1)dil HCI / Na OH (1)boil/heat (under reflux) (1)some reference to the need to remove water or purify the acid (1)LiAIH4(1)

dry ether (1)

(6)(Total 16 marks)

30. The following are some common ions of chromium together with their characteristic colours.

[Cr(H2O)63+Green CrO42Yellow

[Cr(H2O)6]2+Blue Cr2O72Orange

A green solution of chromium(III) sulphate on treatment with dilute sodium hydroxide gave agreen precipitate A, which dissolved in excess sodium hydroxide to give a dark green solution B.Treatment of solution Bwith hydrogen peroxide. H2O2, gave a yellow solution Cwhich on

acidification with dilute sulphuric acid, gave an orange solution D.

(a) (i) Write equations for the formation of Aand B.FORMATION OF A:

[Cr(H2O)6]3+ + 3OHCr(OH)3(H2O)3+ 3H2Ospecies (1)

balancing (1) conditional on correct species

if products given as Cr(OH)3+ 6H2O then (1)only

if Cr3+(aq) + 3OH(aq) Cr(OH)3(s)2(1)onlymolecular equation equivalent to:

Cr2(SO4)3+ 6NaOH 2Cr(OH)3+ 3Na2SO4(1)only



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FORMATION OF B:

[Cr(OH)4(H2O)2](1)

also allow [Cr(OH)5(H2O)]2 or[Cr(OH)6]3

not CrO3(aq)

if give Cr(OH)3+ OH [Cr(OH)4](1)

[Cr(OH5]2

(1)[Cr(OH)6]3(1)

allow molecular formula if molecular equation given for A

(3)

(ii) What type of reaction is shown in both equations?deprotonation / acid base (1)

(1)

(iii) What is the function of sodium hydroxide?base / proton acceptor (1)

(1)

(b) (i) What ion is responsible for the colour of solution C?CrO42/ chromate(VI) (1)not Cr6+or Cr(VI)

(1)

(ii) What type of reaction is the conversion of Bto C?redox / oxidation (1)

(1)

(iii) What is the function of the hydrogen peroxide in this reaction?oxidant / oxidising agent (1)

(1)

(c) (i) Write an equation for the conversion of Cto D

2CrO42+ 2H+ Cr2O72+ H2O (2)if correct species but not balanced then (1)only

allow molecular equation

if give 2CrO42+ H+ Cr2O72+ OHthen (1)only(2)

(ii) Is this a redox reaction? Give a reason for your answer.no (1)conditional on correct reason

no change in oxidation number/state (of chromium) (1)

(2)

(d) Acidified potassium dichromate(VI) is frequently used as an oxidising agent inorganic chemistry.

(i) Identify the organic product of the reaction between acidified potassiumdichromate(VI) and butan-2-ol.butanone (1)

OR clear structural formula

CH CH CCH

O

3 32

(1)

(ii) Give the reagents and the observable result of a single reaction which is common toboth butan-2-ol and the organic product in (d)(i)



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iod ine + NaOH / KI + NaCIO (1)

full names or formulae required

notiodine and alkali / iodide and hypochlorite

cream / pale yellow / yellow ppt (1)

(2)

(Total 15 marks)

31. (a) The following data concerns the redox chemistry of halogen elements and sodiumthiosulphate.

E /V

Cl2+ 2e 2Cl +1.36

Br2+ 2e 2Br +1.07

2SO42+ 10H + 8E S2O32+ 5H2O +0.57

I2+ 2e 21 +0.54

S4O62 2S2O32 +0.09

(i) What is the maximum change in oxidation number of sulphur which can be broughtabout by the action of sodium thiosulphate with iodine and chlorine:

Write full ionic equations for each reaction.reaction with iodine: +2+2.5 or 0.5 (1)I2+ 2S2O32S4O62+ 2I(1)allow S4O62+ 2II2+ 2S2O32but not S4O62+ 2II2+ 2S2O32

reaction with chlorine: +2 +6 OR 4 (1)4XCI2+ S2O32+ 5H2O 8CI+ 25042+ 10Hallow 8CI+ 2SO42+ 10H+4CI2+ S2O32+ 5H2Obut not 8CI+ 2SO42+ 10H+4CI2+ S2O32+ 5H20species (1)

balanced (1)this mark is conditional on correct species

if the equations are given the wrong way round with an but the oxidationnumber changes are given correctly for these equations as 0.5 and 4 thenthe 2 oxidation s tate marks can be given (ie (2))

(5)

(ii) Suggest a reason why bromine cannot be estimated by direct titration with sodiumthiosulphate in the same way that iodine can.the colour change is not sharp / not easy to see (1)

no suitable indicator (1)

OR

bromine is volatile / is lost from the system (1)

therefore results are not accurate / reliable (1)

(2)



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(b) Bromine can be used to convert ethene to 1,2-dibromoethane which can then undergofurther reactions as shown below:

CH CH BrCH CH Br NCCH CH CN2 2 2 2 2 2Step 1 Step 2

Step 3

Step 4

2 2 2 2HO CCH CH CO H

C

2 2 2 2 2 2H NCH CH CH CH NH

D

A B

(i) Give the reagents and conditions required for each of steps 2, 3 and 4, clearlyidentifying the step to which you are referring.STEP 2:

KCN/NaCN in ethanol / propanone / alcohol / aq ethanol (1)

not HCN

heat / boil (under reflux) (1)

not just reflux / warm

STEP 3:

dil HCI / conc HCI (1)NaOH followed by acid is acceptable

not conc. H2SO4


if warm is given in bothsteps 2 and 3 orif reflux is given in both Steps 2 and

3 then penalise only once

STEP 4:

Na + EtOH / LiAIH4/ H2(1)

not NaBH4/ Sn/HCI

room temperature (for Na + EtOH) / dry ether (for LiAIH4)

Pt or Ni or Pd (for H2) (1)

for all steps conditi ons are conditional on correct reagents

(6)



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(ii) Write a mechanism for the reaction in step 2. Give the type of mechanism andidentify the rate of determining step.substitut ion of just one Br is enough

SN1:

arrow on CBr (1)must start on bond and end on Br:C Br

correct carbonium ion (1)

production of carbonium ion marked as rate determining step (1)

arrow from CNto carbonium (1)C :CN

+

must be from C and notfrom the charge or from N

lone pairs not essential

nucleophilic substitution (1)

SN1 alone is not adequate

formation of Br(1)

OR SN2:

arrow from CN(1)(as above)

arrow on CBr (1)(as above)

this can appear in the transition state

structure of transition state including charge (1)

formation of Br(1)

nucleophillic substitution (1)


formation of transition state as r.d.s. or single step so this is r.d.s. (1)

(6)

(iii) Cand Dcan react together to give a polymer. Give the structural formula of thispolymer showing clearly the repeat unit.

CC C C N C C C C N

O OH H H H H H

H H H H H H H H peptide link (1)

correct total unit (1)must be multiple of the above unit

open ended (1)

if no Hs(max 2)

(3)



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(iv) The polymer in (b)(iii) could be made more rapidly in the laboratory if Cwas firstconverted into another more reactive compound. Give the formula of thiscompound and show how it could be formed from Cformula of acyl chloride (1)

PCI5/ PCI3/ SOCI2(1)

equation (for whichever of the 3 reagents given above) (1)

RCOOH + PCI5etc is acceptable.

(3)

(Total 25 marks)

32. Bromine can be used to convert ethene to 1,2dibromoethane which can then undergo furtherreactions as shown below:

CH CH BrCH CH Br NCCH CH CN2 2 2 2 2 2Step 1 Step 2

Step 3

Step 4

2 2 2 2HO CCH CH CO H

C

2 2 2 2 2 2H NCH CH CH CH NH

D

A B

(i) Give the reagents and conditions required for each of steps 2, 3 and 4, clearly identifyingthe step to which you are referring.

STEP 2:

KCN/NaCN in ethanol / propanone / alcohol / aq ethanol (1)

not HCN


not just reflux / warm

STEP 3:

dil HCI / conc HCI (1)NaOH followed by acid is acceptable

not conc. H2SO4


if warm is given in bothsteps 2 and 3 orif reflux is given in both Steps 2 and

3 then penalise only once

STEP 4:

Na + EtOH / LiAIH4/ H2(1)

not NaBH4/ Sn/HCI

room temperature (for Na + EtOH) / dry ether (for LiAIH4)

Pt or Ni or Pd (for H2) (1)

for all steps conditions are conditional on correct reagents

(6)



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(ii) Write a mechanism for the reaction in step 2. Give the type of mechanism and identifythe rate of determining step.

substitut ion of just one Br is enough

SN1:

arrow on CBr (1)must start on bond and end on Br:C Br

correct carbonium ion (1)

production of carbonium ion marked as rate determining step (1)

arrow from CNto carbonium (1)C :CN

+

must be from C and notfrom the charge or from N

lone pairs not essential

nucleophilic substitution (1)


formation of Br(1)

OR SN2:

arrow from CN(1)(as above)

arrow on CBr (1)(as above)

this can appear in the transition state

structure of transition state including charge (1)

formation of Br(1)

nucleophillic substitution (1)


formation of transition state as r.d.s. or single step so this is r.d.s. (1)

(6)

(iii) Cand Dcan react together to give a polymer. Give the structural formula of thispolymer showing clearly the repeat unit.

CC C C N C C C C N

O OH H H H H H

H H H H H H H H peptide link (1)

correct total unit (1)must be multiple of the above unit

open ended (1)

if no Hs(max 2)(3)



45/96

(iv) The polymer in (b)(iii) could be made more rapidly in the laboratory if Cwas firstconverted into another more reactive compound. Give the formula of this compound andshow how it could be formed from C

formula of acyl chloride (1)

PCI5/ PCI3/ SOCI2(1)

equation (for whichever of the 3 reagents given above) (1)

RCOOH + PCI5etc is acceptable.

(3)

(Total 18 marks)

33. (a) A buffer solution of pH =3.87 contains 7.40 g dm3 of propanoic acid together with aquantity of sodium propanoate. Ka for propanoic acid = 1.35 x 105mol dm3at 298 K.

(i) Explain what a buffer solution is and how this particular solution achieves its bufferfunction.resists changes in pH (1)not pH is constant when (contaminated by) smallamounts of acid or base (1)

weak (ionisation of) acid (1)must be stated

equation for ionisation (1)

HA allowed butis required(suppressed by) strong ionisation of salt / completely ionised (1)

hence giving solution with relatively high concentrations of anion and acidmolecules (1)

equation fo r removal of H+(1)

OR DESCRIBED IN WORDS

equation for removal of OH(1)

allow correct interpretation of the Henderson equation for the last 2 marks

(8)

(ii) Calculate the concentration in g dm3of sodium propanoate, C2H5CO2Na, in the

solution, stating any assumptions made.pH = 3.87 [H+] = 1.35 104(1)

1.35 105= 1.35 104[

.

SALT

01 (1)

[SALT] = 0.01 mol dm3(1)

[SALT] = 0.01 96 = 0.96 g dm3(1)(if correct answer and some working (4))

assumptions:

all anion comes from salt (1)

ionisation of acid negligible (1)

(6)



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(iii) If the sodium propanoate were to be replaced by anhydrous magnesium propanoatecalculate the concentration of magnesium propanoate in g dm3, required to give abuffer of the same pH.magnesium propanoate has two propanoate ions per mole (1)

half the molar concentration requi red = 0.005

0.005 170 = 0.85g dm3(1)(2)

(b) Suggest a sequence of reactions by which propanoic acid, C2H5CO2H, could be converted

into 2-animopropanoic acid, stating the important conditionschlorine / bromine (1)

u.v. with sunlight / phosphorus (red) (1)

intermediate ie 2chloropropanoic acid or the bromo i f bromine used (1)

(conc excess) ammonia (1)

2 equations (2)OR free radical mechanism (1)and reference to necessity ofseparation of mixtures at stage 1 (1)

(5)

(c) Pure 2-aminopropanoic acid has a relatively high melting point and is insoluble inhydrocarbon solvents.

(i) Sketch a structure for this compound which would account for these observations.

2

3

|

CHCOCH

NH

3 (1) must show charges

(1)

(ii) Write ionic equations to show the action of an aqueous solution of2-aminopropanoic acid with:

A. an excess of acid;

B. an excess of alkali.

CH3CH(N

H3)CO2+ H+ CH3CH(N

H3)CO2H

CH3CH(N

H3)CO2+ OH+ CH3CH(N

H2)CO2+ H2

mark consequentially on the answer to (i) but can allow both equations tostart with the molecule

(2)

(iii) Hence explain how 2-aminopropanoic acid might behave as a buffer in solution.thus product of amino acid and OHor H+will be mixture of salt + acid/base (1)

removes excess acid or alkali so that pH changes lit tle / able

to react with H+and OHand control pH (1)(max 4)

(consequential on first statement)

(1)

(Total 25 marks)



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34. Suggest a sequence of reactions by which propanoic acid, C2H5CO2H, could be converted into

2-animopropanoic acid, stating the important conditionschlorine / bromine (1)

u.v. with sunlight / phosphorus (red) (1)

intermediate ie 2chloropropanoic acid or the bromo i f bromine used (1)

(conc excess) ammonia (1)

2 equations (2)OR free radical mechanism (1)and reference to necessity ofseparation of mixtures at stage 1 (1)

(Total 5 marks)

35. A red solid A(Pb3O4) on treatment with dilute nitric acid gave a brown solid B and a colourless

solution. Solid Bwhen treated with concentrated hydrochloric acid gave a greenish-yellow gasC, which bleached damp red litmus paper. The resulting solution, on cooling, gave a whiteprecipitate D.

Identify B, Cand Dand write equations for the conversion of Ato Band Bto C. What can youdeduce about the nature of A from its reaction with dilute nitric acid?

B = PbO2(1)allow cor rect name

C = CI2(1)allow cor rect name

D = PbCI2(1)allow correct name

equation A to B:

species (1)balancing (1)conditional on co rrect species

equation B to C:

PbO2+ 4HCI PbCI2+ CI2+ 2H2OOR with 6HCI PbCI42+ 2H+species (1)balancing (1) conditional on correct species

mixed oxide / compound oxide / two oxidation states for l ead (1)

(8)



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(b) A purple solid salt Fdissolved in water to form a purple solution G.When excessacidified iron(II) sulphate solution was added to Gand the precipitate allowed to settle thepurple solution was seen to have changed to a pale yellow solution II. F imparted anapple-green colour to a bunsen flame.

Identify the species responsible for the colours in F, Gand H and explain, with the aid ofequations, any reactions occurring. What is the formula of F?

F = MnO4(1)G = MnO4(1)allow names

H = [Fe(H2O)6]3+(1)(must be hexaaquo)

apple green flame shows barium (1)

F is Ba(MnO4)2(1)formula only

manganate(VII) oxidises iron(II) to iron (III) (1)

Ba2++ SO2+ BaSo4

MnO4+ 5Fe2++ 8H+Mn2++ 5Fe3++ 4H2O (1)can get oxidation of iron(II) to iron(III) mark from equation

OR

Ba(MnO4)2+ 10FeSO4+ 8H2SO45Fe2(SO4)3+ 2MnSO4+ 8H2O + BaSO4(2)(8)

(c) Compound L(molecular formula C5H1002) on boiling with dilute sodium hydroxide gave

two substances MandNwhich both contain carbon. After separation from the mixture, Nwas found to produce steamy acidic fumes when treated with PCI5. Nalso gave a pale

yellow precipitate when treated with iodine and dilute sodium hydroxide. Ncontains anasymmetric carbon atom.

Identify L, Mand N, giving your reasoning.PCI5shows OH / OH group / hydroxyl group (1)

not OH

undergoes hydrolysis (1)

L is an ester (1)

I2/ NaOH shows CH3CH(OH)R (1)

chiral R must be CH3CH2/ can not be CH3CH2CH2 / can not be CH3 (1)

+ reason eg can not be latter since Mmust contain carbon (1)

Nis CH3CH(OH)C2H5(1)allow correct name

Mis HCO2Na (1)allow correct names

Lis HCO2CH(CH3)C2H5(1)allow cor rect names

(9)(Total 25 marks)

36. A red solid A(Pb3O4) on treatment with dilute nitric acid gave a brown solid B and a colourless

solution. Solid Bwhen treated with concentrated hydrochloric acid gave a greenish-yellow gasC, which bleached damp red litmus paper. The resulting solution, on cooling, gave a whiteprecipitate D.



49/96

Identify B, Cand Dand write equations for the conversion of Ato Band Bto C. What can youdeduce about the nature of A from its reaction with dilute nitric acid?

B = PbO2(1)allow cor rect name

C = CI2(1)allow cor rect name

D = PbCI2(1)allow correct name

equation A to B:

species (1)balancing (1)conditional on co rrect species

equation B to C:

PbO2+ 4HCI PbCI2+ CI2+ 2H2OOR with 6HCI PbCI42+ 2H+species (1)balancing (1) conditional on correct species

mixed oxide / compound oxide / two oxidation states for l ead (1)

(8)

37. A purple solid salt Fdissolved in water to form a purple solution G.When excess acidifiediron(II) sulphate solution was added to Gand the precipitate allowed to settle the purple solutionwas seen to have changed to a pale yellow solution II. F imparted an apple-green colour to abunsen flame.

Identify the species responsible for the colours in F, Gand H and explain, with the aid ofequations, any reactions occurring. What is the formula of F?

F = MnO4(1)G = MnO4(1)allow names

H = [Fe(H2O)6]3+(1)(must be hexaaquo)

apple green flame shows barium (1)

F is Ba(MnO4)2(1)formula only

manganate(VII) oxidises iron(II) to iron (III) (1)

Ba2++ SO2+ BaSo4

MnO4+ 5Fe2++ 8H+Mn2++ 5Fe3++ 4H2O (1)can get oxidation of iron(II) to iron(III) mark from equation

OR

Ba(MnO4)2+ 10FeSO4+ 8H2SO45Fe2(SO4)3+ 2MnSO4+ 8H2O + BaSO4(2)(8)



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38. Compound L(molecular formula C5H1002) on boiling with dilute sodium hydroxide gave two

substances MandNwhich both contain carbon. After separation from the mixture, Nwas foundto produce steamy acidic fumes when treated with PCI5. Nalso gave a pale yellow precipitate

when treated with iodine and dilute sodium hydroxide. Ncontains an asymmetric carbon atom.

Identify L, Mand N, giving your reasoning.PCI5shows OH / OH group / hydroxyl group (1)

not OH

undergoes hydrolysis (1)

L is an ester (1)

I2/ NaOH shows CH3CH(OH)R (1)

chiral R must be CH3CH2/ can not be CH3CH2CH2 / can not be CH3 (1)

+ reason eg can not be latter since Mmust contain carbon (1)

Nis CH3CH(OH)C2H5(1)allow correct name

Mis HCO2Na (1)allow correct names

Lis HCO2CH(CH3)C2H5(1)allow cor rect names

(9)

39.

H C C C C Br

H C C C C OH

H C C C C

H C C C C H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

H

Br

H

H

H

A

B

C

E

OH

O

(1) allow CH CH CH CH Br

(1)

(1)

(1)

3 2 2 2

NoteifAis 2 bromobutane Band Ealso consequential to maximum of 2 marksif tertbut then Bconsequentially to maximum of 1 markifAis 1bromo2methylpropane Band Cconsequential to maximum of 2 marksif noAis given then B, C, Ecan score a maximum of 2 marks 4

(b) (solution) of bromine (1)decolourised / loses its colour (1)notgoes clear notdiscolouredOR

alkalinemanganate (VII) (1)green (1) 2



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(c) CH3CH2CH2COOH + NaHCO3CH3CH2CH2COONa + N2O + CO2formula of sodium salt (1)notC4H7O2Na but C3H7CO2Na is permissible

equation (1)equation mark may be awarded if use C4H7O2Naif correct acid structure for Cis given in (a) R can be used for CH3CH2CH2 2

(d) CH CH CH COCH CH CH CH

O

3 22

2 2 2 3

(1)

allow C3H7for CH3CH2CH2allow C4H9for CH3CH2CH2CH2the use of RCOOR' is permissible here if Cis given correctly in (a) 1

(e) potassium (di)chromate ()+ dilute namedstrong acid ()OR

potassium manganate (VII) ()+ dilute H2SO4() notHCl

allow correct formulae but notjust ions or acidified' heat under reflux (1)condition mark conditional on an oxidising reagent 2

(f) (i) [H+] = cKa orKa = d][

]][[

Aci

AH

(1)

= 0.11051.1 5 (1)

= 1.23 103mol dm3pH = 2.9 or2.91 (1) 3

(ii) buffer (1)oran explanation of pH protectionnotpH constant 1

(iii) Number of moles of salt = 1105.5

(1)

[salt] =

110

5.5 0.5 = 0.1 (1)

either pH = pKa + lg]acid[]salt[

or[H+] =][

][

Salt

AcidaK (1)

pH = 4.8(2) (1) 4[19]

40. (a) (i) use of mixed acid increases concentration of NO2+/ creates NO2+ (1)

electrophile orsome comment on the way H2SO4does this (1)

OR

full equation (2) 2

(ii) (reaction exothermic and) temperature must not rise (1)

some indication that the temperaturemust be kept down nottoo exothermic 1

(iii) too much conversion to dinitrobenzene otherwise /to prevent further nitration (1)if this is not mentioned in (iii) but then given in(iv) the mark can be awarded 1



52/96

(iv) optimum rate / good yield (1) 1

(v) acid and benzene immiscible / there are 2 layers / maintain mixing of reactants (1)so rate slow if not mixed orensure reactants are in contact (1) 2

(vi) removes/dilutes most of the acid remaining (1)if this is notmentioned in (vi) but then given in(vii) the mark can be awarded 1

(vii) removes residual acid dissolved in nitrobenzene (1) 1(viii) separates nitrobenzene from other volatile constituents / this is the temperature over

which pure nitrobenzene will distill (1) 1

(b) tin / tin(II) chloride / Fe (1)

(concentrated) HCl (1)ignore any reference to concentration of HCl this mark isconditional on tin / tin(II) chloride / Fe or Sn2+being given heat (1)this mark isconditional on both reagents being correct not LiAlH4which gives other products 3

(c) (i)

NH CONHCO

enough to make structure clearamide links (1)correct 1,3 position of ring (1)some idea of extension required (ie the end groups must notbe terminated)brackets not necessary 2

(ii) polyamide orcondensation (1) 1

(iii) acid chlorides (much) more reactive / more easily reacted (1)give faster polymerisation / better yield (1) 2

(iv) add SOCl2/ PCl5/ PCl3(1)COCl

COCl

(1)

2[20]

41. (a) (i) >C=C< / carboncarbon double bond / alkene (1) 1

(ii)

CH CH CHH

CHH H HC C C C

3 3 3

3

(1) (1)

if the structure of but1ene is given as well as one (or both) stereoisomer(s) ofbut2ene then (max 1) 2



53/96

(iii) no/restricted rotation about C=C bond (1)some reference to the relevance of bonds or overlapping porbitals/ substit groupson each carbon atom not the same (1) 2

(iv) CH3CH2CH=CH2(1)accept C2H5CH=CH2 1

(b) (i)

CH CH

CH

C O

23

3

(1)accept C2H5for CH3CH2

1

(ii)

CH C O3 and CH CH3

OH

(1) (1) 2

(iii) (D:) CH3CH2COO(Na+) (1)

(E:) CH3CH2COOH (1)

Dand Elabels not required 2

(c) (i)3 32

OH

CH CH CHCH

1

(ii) CH3CH2+/ C2H5+ 29 (1)

CH3CHOH+ 45 (1) notC2H4OH+or C2H5O+

if charge(s) is (are) absent or incorrect then penalise (1)since t

Bonding in Organic Compounds_Organic Synthesis Marks Scheme

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