SM*(S15-1095-01)MLP

GCE A level

1095/01

CHEMISTRY – CH5

P.M. MONDAY, 15 June 2015

1 hour 45 minutes plus your additional time allowance

Surname

Other Names

Centre Number

Candidate Number 2

© WJEC CBAC Ltd.

2

For Examiner’s use only

QuestionMaximum

Mark

Mark

Awarded

Section A 1. 16

2. 9

3. 15

Section B 4. 20

5. 20

Total 80

3

ADDITIONAL MATERIALS

In addition to this examination paper, you will need:

• acalculator;• an8pageanswerbook;• acopyofthePERIODIC TABLE supplied by WJEC.

RefertoitforanyRELATIvE ATOMIC MASSES you

require.

INSTRUCTIONS TO CANDIDATES

Use black ink, black ball-point pen or your usual

method.

Write your name, centre number and candidate number

inthespacesprovidedonthefrontcover.

SECTION A Answer ALL questions in the spaces

provided.

SECTION B Answer BOTH questions in SECTION B in a

separate answer book which should then

be placed inside this question-and-answer

book.

Candidates are advised to allocate their time

appropriately between SECTION A (40 MARkS) and

SECTION B (40 MARkS).

4

INFORMATION FOR CANDIDATES

Thenumberofmarksisgiveninbracketsattheendofeach question or part-question.

Themaximummarkforthispaperis80.

Youranswersmustberelevantandmustmakefulluseoftheinformationgiventobeawardedfullmarksforaquestion.

TheQWClabelalongsideparticularpart-questionsindicatesthosewheretheQualityofWrittenCommunication is assessed.

5

SECTION A

Answer ALL questions in the spaces provided.

1(a) Copperionscombinewitharangeofligandstoformcomplexions,including[CuCl

4]2−

and

[Cu(H2O)

6]2+

.

(i) State what is meant by a LIGAND.[1]

(ii) Drawthestructuresof[CuCl4]2−

and

[Cu(H2O)

6]2+ions.[2]

6

1(a) (iii) Asolutioncontaining[Cu(H2O)

6]2+

ions is

blue.Explaintheoriginofthiscolour. [3]

7

8

1(a) (iv) When excess ammonia is added to a

solutioncontaining[Cu(H2O)

6]2+

ions, the

colourofthesolutionchangesasanewcomplexionisformed.Givetheformulaofthenewcomplexionandthecolourofthesolutionformed.[2]

(b) Phosphorusformstwochlorides,PCl3 and PCl

5,

and there is a dynamic equilibrium between these

compoundsinthegasphase.Thisisrepresentedby the equation below.

PCl5(g)PCl

3(g)+Cl

2(g)

(i) Writeanexpressionfortheequilibriumconstant, Kp,forthisreaction.[1]

9

1(b) (ii) AsealedvesselisfilledwithPCl5 at a

pressureof3.0×105Pa.Uponheating,thesystemcomestoequilibriumtoforma mixture that contains PCl

3 at a partial

pressureof1.3×105 Pa.

I. StatethepartialpressureofCl2 at

equilibrium. [1]

II. Calculatethevalueoftheequilibriumconstant, Kp,givingitsunits.[3]

Kp =

Units

10

1(b)(ii) III. As the temperature is increased the value

ofKpincreases.Statewhatinformationthisprovidesabouttheenthalpychangeofthisreaction,givingareasonforyouranswer.

[1]

(c) Silicon(Iv) chloride reacts with water whilst CCl4

doesnot.GivetheequationforthereactionofSiCl

4withwaterandexplainwhythebehaviourof

CCl4 and SiCl

4withwaterissodifferent.[2]

Total[16]

16

11

2. Ironisextractedathightemperaturesfromtheorehaematite, which contains iron(III) oxide, Fe

2O

3.

The process can be summarised by the equation

below.

Somethermodynamicdataforthesubstancesinthereactionareshowninthefollowingtable.

Fe2O

3(s)+3CO(g)2Fe(s)+3CO

2(g)∆Hθ =−23kJmol−1

Substance

Standard

enthalpychangeofformation,∆Hθ / kJ mol

−1

Standard

entropy,

Sθ / J k

−1 mol

−1

Fe2O

3(s) −826 90

Fe(s) 0 27

CO(g) 198

CO2(g) −394 213

f

12

2(a) Calculatethestandardenthalpychangeofformationofcarbonmonoxide.[3]

∆Hθ = kJ mol−1

(b) Explainwhythestandardentropiesofcarbondioxideandcarbonmonoxidearesignificantlygreaterthanthoseofiron(III)oxideandiron. [1]

f

13

2(c) Thestandardentropychangeforthisreaction,∆Sθ, is +9 J k

−1 mol

−1.

(i) Calculatethefreeenergychange,∆Gθ,forthisreactionat298K.[2]

∆Gθ = kJ mol−1

14

2(c) (ii) Explainwhythisreactionisfeasibleatalltemperatures.[2]

(iii) Manyindustrialprocessesusehightemperatures even when the reaction is

feasibleatlowtemperatures.Suggestwhyhightemperaturesareused.[1]

Total[9]

9

15

THE CHEMISTRY OF BORON

BoronisanelementatthetopofGroup3.Itformsarangeofcompoundswhosebehaviourisverydifferentfromtheotherelementsinthesamegroup.Boronshowsthepropertiesofanon-metal,howevertheremainingelements,includingaluminium,gallium,indium and thallium all show metallic properties. This

changeissimilartothatseeninothergroupsinthep-blockwithGroup4havingthenon-metalcarbonat the top and the metal lead at the bottom. In its

compounds, boron exhibits the +3 oxidation state

exclusively,formingmaterialssuchasBCl3, BF

3 and

B2O

3. No compounds with a +1 oxidation state are

known. Aluminium also exists only as the +3 oxidation

state, however the +1 oxidation state becomes more

commonasthegroupisdescended.

5

10

15

3. Readthefollowingpassageandthenanswerthequestions in the spaces provided.

16

BORANES

Thereareverymanycompoundsformedbetweenboronandhydrogenandthesearecalledboranes.Theseboranesaregroupedintoseriesandtwoexamplesofthese are:

NIDO-boraneswithageneralformulaofBnH

n+4.

This series includes

pentaborane(9), B5H

9, and decaborane

(14), B10

H14

.

ARACHNO-boraneswithageneralformulaofB

nH

n+6.Thefirstmemberofthisseriesis

tetraborane(10), B4H

10.

Alloftheseboranesareelectrondeficient,whichleadsthem to be very reactive. The majority react explosively

on contact with air, which led to their proposed use as

arocketfuel.TodestroythestockpileofB5H

9 when it

wasnolongerneeded,theUSgovernmenttreatedit withsteamtoformasolutionofboricacid(H

3BO

3) and

hydrogengas.

20

25

30

17

BORON NITRIDE

Boronnitridehasagiantcovalentstructurethathasthesamenumberofelectronsasgraphiteanddiamond.They are said to be isoelectronic. Boron nitride exists in

twoforms:

Hexagonalboronnitridehasastructuresimilartographite,andissometimescalled

‘whitegraphite’becauseofitsexcellentlubricatingproperties.Unlikegraphite,hexagonal

boron nitride is an insulator and has applications

which depend upon this property.

Cubic boron nitride has a diamond structure, and

is the second hardest natural material

known.Ithashighthermalconductivityandischemically inert.

USES OF BORON COMPOUNDS

NearlyallboronoreextractedfromtheEarthisdestinedforrefinementintoboricacidandsodiumtetraborate.Mostboricacidisusedintheproductionofshock-resistantglass,whilstsodiumtetraborateisusedasanadditivetodetergents.Boronisalsousedinnuclearreactors,whereboronshieldingisusedasacontrol,takingadvantageofitshighcross-sectionforneutroncapture.

END OF PASSAGE

35

40

45

50

55

18

3(a) Explainwhyboronformscompoundswiththe+3oxidation state alone, but thallium compounds are

more stable with the +1 oxidation state

(lines10-15).[2]

19

3(b) Boranesarecompoundsmadeupofboronandhydrogenonly(lines17-27).Asampleofagaseousboranewasfoundtocontain78.14%boronand21.86%hydrogenbymass.Asampleofthisboraneofmass1.232goccupiedavolumeof1 dm3 at 273 k and 1 atm pressure.

[Themolarvolumeofagasat273Kand1atmpressureis 22.4 dm3.]

(i) Whatistheempiricalformulaofthisborane?[2]

Empiricalformula

20

3(b) (ii) Whatisthemolecularformulaofthisborane?[3]

Molecularformula

(c) Explain the term ELECTRON DEFICIENT

(line28).[1]

21

3(d) Balancetheequationforthereactionofpentaborane(9), B

5H

9,withsteam(lines29-34). [1]

(e) Thestandardenthalpychangeofformationofpentaborane(9) is +42.8 kJ mol

−1.

Statewhatinformationthisvaluegivesaboutthestabilityofthiscompound.[1]

B5H

9 + H

2O H

3BO

3 + H

2

22

3(f) Hexagonalboronnitrideandgraphitehavesimilarstructures(lines40-45).Describethedifferencesbetween these two isoelectronic materials in

termsoftheirbondingandstructure.[3] QWC[1]

23

3(g) Boron-10absorbsaneutron(line56)toformanintermediate,whichthendecaysbyemissionofanalpha particle.

Givethemassnumberandatomicnumberofthefinalproduct.[1]

Mass number

Atomic number

Total[15]

TOTAlSECTIONA[40]

15

24

SECTION B

Answer BOTH questions in the separate answer book

provided.

4. Theleavesoftherhubarbplantarerichinethanedioic acid (oxalic acid) which is a poisonous

compound.Asolutioncontainingethanedioateionscanbeformedbyboilingrhubarbleaveswithwater. It can be separated and samples titrated

againstacidifiedpotassiummanganate(VII)tofindtheconcentrationoftheethanedioatesolution.

(a) Suggesthowtheethanedioatesolutioncouldbeseparatedfromtherhubarbleaves.[1]

(b) Writeanion-electronhalf-equationforthereductionofacidifiedmanganate(VII)ions,MnO

4−.

[1]

(c) Theion-electronhalf-equationfortheoxidationofethanedioateionsisgivenbelow.

C2O

42−

(aq) 2CO2(g)+2e−

(i) Givetheoxidationstatesforcarbonatthestartandendofthisreaction.[1]

25

4(c) (ii) Writeanequationforthereactionofacidifiedmanganate(VII)ionswithethanedioateions.[1]

(d) Give a reason why an indicator is not needed in

thistitration.[1]

(e) Foursamplesof25.00cm3oftheethanedioatesolutionweretitratedagainstacidifiedpotassiummanganate(VII)solutionofconcentration0.0200 mol dm

−3.Thevolumesofpotassiummanganate(VII)solutionrequiredforcompletereaction are listed below.

1 2 3 4

VolumeofkMnO

4(aq) / cm

3 28.80 27.95 28.00 27.80

Usetheinformationgiventocalculatetheconcentrationoftheethanedioatesolution. [4]

(f) Heatingethanedioicacidinglycerolproducesmethanoic acid, HCOOH.

(i) Writetheexpressionfortheaciddissociation constant, ka,formethanoicacid. [1]

26

4(f) (ii) Thevalueofkaformethanoicacidis 1.8×10−4 mol dm

−3.

CalculatethepHofasolutionofmethanoicacidofconcentration0.2moldm−3.[3]

(iii) Amixtureofmethanoicacidandsodiummethanoatecanbeusedasabuffersolution. State what is meant by a

BUFFER SOLUTION and explain how a

mixtureofmethanoicacidandsodiummethanoateactsasabuffer.[3]QWC[1]

(g) Acidifiedpotassiumdichromate,K2Cr

2O

7 , is also

anoxidisingagent.

(i) Givethecolourchangethatoccurswhenacidifiedpotassiumdichromateactsasanoxidisingagent.[1]

(ii) When sodium hydroxide is added to a

solutionofpotassiumdichromate,acolourchangeoccurswithoutaredoxreactionoccurring.Givetheformulaofthenewchromium-containingionandthecolourofthesolutionformed.[2]

Total[20]

pre

cip

itate

A

Pb

2+

(aq

)

aqueou

ssolutio

nof

po

tassiu

m io

did

eso

lid

B a

nd

bro

wn

so

luti

on

C

Br 2

(aq

)

aqueou

ssolutio

nof

po

tas

siu

m b

rom

ide a

nd

io

din

e

Cu

2+(a

q)

27

5. Thediagramoppositeshowssomeofthereactionsofpotassiumiodidesolution.

(a) IdentifyprecipitateAandgiveitscolour.[2]

(b) WriteanequationforthereactionofCu2+(aq) and

I−(aq),clearlyidentifyingtheprecipitate.[2]

(c) Bromine reacts with aqueous potassium iodide as

shown opposite, however bromine does not react

with aqueous sodium chloride. Use the standard

electrode potentials below to explain these

observations.[3]QWC[1]

Half-equation Eθ / v

I2 + 2e

− 2I− +0.54

Br2 + 2e

− 2Br− +1.09

Cl2 + 2e

− 2Cl− +1.36

(d) Solid potassium iodide reacts with concentrated

sulfuricacidinthesamewayassodiumiodide.

Describetheobservationsmadeduringthisreactionandidentifytheproductsformed.[3]

28

5(e) Hydrogenperoxidereactswithacidifiedpotassiumiodideaccordingtotheequationbelow.

2H+ + 2l− + H

2O

2 I

2 + 2H

2O

(i) Thisreactionwasstudiedusinganiodineclock reaction. Describe the principles

ofhowtherateofaclockreactionisdetermined. Experimental details are not

required.[2]

(ii) TherateofthisreactionwasstudiedbyadifferentmethodforarangeofconcentrationsofH

2O

2(aq) and I−(aq) and

pH values. These are listed in the table

opposite.

Exp

eri

men

t

nu

mb

er

Init

ial

co

nc

en

trati

on

ofH

2O

2(a

q) /

mo

l

dm−3

Init

ial

conc

entrationof

I−(a

q) /

mo

l d

m−3

pH

Init

ial ra

te /

mo

l d

m−3

s−1

10.0

010

0.1

01

2.8×10

−6

20.0

020

0.1

01

5.6×10

−6

30.0

020

0.1

02

5.6×10

−6

40.0

010

0.4

01

11.2×10−

6

29

5(e) (ii) I. Some experiments were undertaken

at pH 1 and some at pH 2. Give the

differenceintheconcentrationsofH

+ionsinthesetwosolutions.[1]

II. Use the data in the table opposite

page28todeducetherateequationforthisreaction,givingyourreasoning.[3]

III. Calculatethevalueoftherateconstant, k,givingitsunits.[2]

IV. Thereactionisrepeatedatahighertemperature. State how the increase

intemperatureaffectstherateequationandrateconstant.[1]

Total[20]

TOTAlSECTIONB[40]

END OF PAPER