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QuestionPaper2016DelhiSet-1

Class-12Chemistry

TimeAllowed:3HoursMaximumMarks:100

GeneralInstructions

(i)Allquestionsarecompulsory.

(ii)Q.no.1to5areveryshortanswerquestionsandcarry1markeach.

(iii)Q.no.6to10areshortanswerquestionsandcarry2markseach.

(iv)Q.no.11to22arealsoshortanswerquestionsandcarry3markseach.

(v)Q.no.23isavaluebasedquestionandcarry4marks.

(vi)Q.no.24to26arelonganswerquestionsandcarry5markseach.

(vii)Uselogtablesifnecessary,useofcalculatorsisnotallowed.

SectionA

Q1Outof and whichismorereactive

towards reactionandwhy?

Ans:Sinceformationofcarbocationistherate-determiningstepinthe reaction,the

stabilityofcarbocationwoulddetermineitsreactivity.

Theorderofstabilityofcarbocationisasfollows:

Tertiary>Secondary>Primary>Methyl

Here,1-chloro-1-methylpropanewouldformsecondarycarbocation,while1-chloro-2-

methylpropanewillformprimarycarbocation,whichislessstablethansecondary

carbocation.Hence,reactivitytowardstheSN1reactionwouldbehigherfor1-chloro-1-

methylpropane.

Q2OnaddingNaOHtoammoniumsulphate,acolourlessgaswithpungentodouris

evolved,whichformsablue-colouredcomplexwithCu2+ion.Identifythegas.

Ans:OnaddingNaOHtoammoniumsulphate,ammoniagasisevolved.Ithasapungent

odourandformsablue-colouredcomplexwiththeCu2+ion.

Theconcernedchemicalreactionsareasfollows:

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Q3Whattypeofmagnetismisshownbyasubstanceifmagneticmomentsofdomains

arearrangedinsamedirection?

Ans:Ferromagnetismisshownbythesubstancesforwhichthemagneticmomentsof

domainsarearrangedinthesamedirection.

Q4WritetheIUPACnameofthegivencompound:

Ans:TheIUPACnameofthegivencompoundis2,4,6-tribromoaniline.

Q5Writethemainreasonforthestabilityofcolloidalsols.

Ans:Therearetwomainreasonsforthestabilityofcolloidalsols:

1.Electrostaticstabilisation:Presenceofequalandsimilarchargesonthecolloidalparticles

preventscoagulationofthecolloidalsol.

2.Solvation:Colloidalparticlesarecoveredbyasheathofliquidinwhichtheyare

extensivelysolvated,therebyprovidingstability.

SectionB

Q6Fromthegivencells:

Leadstoragecell,Mercurycell,FuelcellandDrycell

Answerthefollowing:

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(i)Whichcellisusedinhearingaids?

(ii)WhichcellwasusedinApolloSpaceProgramme?

(iii)Whichcellisusedinautomobilesandinverters?

(iv)Whichcelldoesnothavelonglife?

Ans:(i)Mercurycellisusedinhearingaids.

(ii)FuelcellwasusedintheApollospaceprogramme.

(iii)Leadstoragecellisusedinautomobilesandinverters.

(iv)Drycelldoesnothavealonglife.

Q7Whenchromiteore isfusedwithNaOHinpresenceofair,ayellow-

colouredcompound(A)isobtained,whichonacidificationwithdilutesulphuricacid

givesacompound(B).Compound(B)onreactionwithKClformsanorangecoloured

crystallinecompound(C).

(i)Writetheformulaeofthecompounds(A),(B)andC.

(ii)Writeoneuseofcompound(C).

OR

Completethefollowingchemicalequations:

Ans:Chromiteore,onfusionwithNaOH,formssodiumchromate(yellow-coloured

compound):

Sodiumchromate,onacidification,givessodiumdichromate(B):

Sodiumdichromate,onreactionwithKCl,formspotassiumdichromate(orange-

colouredcrytallinecompound):

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Oneuseofpotassiumdichromateisthatitisapowerfuloxidisingagent.Itisusedin

preparationofazocompounds.Itisalsousedinleatherindustry.

Disclaimer:Studentscanwriteanyoneuseofpotassiumdichromate.

OR

Q8Whenaco-ordinationcompoundCrCl3.6H2OismixedwithAgNO3,2molesofAgCl

areprecipitatedpermoleofthecompound.Write

(i)Structuralformulaofthecomplex.

(ii)IUPACnameofthecomplex.

Ans:AstwomolesofAgClareobtained;therefore,thestructuralformulawouldcontaintwo

Cl−ionssatisfyingtheprimaryvalencies,whilefiveH2OmoleculesandoneCl−ionare

presentinsidethecoordinationsphere,makingthecoordinationnumber6.OneH2O

moleculewillbepresentasthemoleculeofhydration.

Structuralformula:[CrCl(H2O)5]Cl2.H2O

IUPACnameofthecompound:Pentaaquachloridochromium(III)chloride

Q9Forareaction:

(i)Writetheorderandmolecularityofthisreaction.

(ii)Writetheunitofk.

Ans:(i)ThisreactioniscatalysedbyPtathighpressure.So,itisazero-orderreactionwith

molecularity2.

(ii)Theratelawexpressionforthisreactionis

Rate=k

Hence,theunitofkismolL−1s−1.

Q10Writethemechanismofthefollowingreaction:

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Ans:Themechanismofthegivenreactionisasfollows:

(i)Protonationofanalcoholmolecule

(ii)Attackofotheralcoholmoleculeontheprotonatedmolecule

(iii)Deprotonation

SectionC

Q11Givenreasons:

(i)C–ClbondlengthinchlorobenzeneisshorterthanC–ClbondlengthinCH3–Cl.

(ii)Thedipolemomentofchlorobenzeneislowerthanthatofcyclohexylchloride.

(iii)SN1reactionsareaccompaniedbyracemizationinopticallyactivealkylhalides.

Ans:(i)Inchlorobenzene,theC−Clbondgetspartialdoublebondcharacterbecauseofthe

+MeffectshownbytheClgroup.Duetodoublebondcharacter,thebondlengthdecreasesin

chlorobenzeneascomparedtothenormalCH3−Clbondlength.Therefore,theC–Clbond

lengthinchlorobenzeneisshorterthantheC–ClbondlengthinCH3–Cl.

(ii)Reasonsbehindthedipolemomentofchlorobenzenebeinglowerthanthatofcyclohexyl

chloridearefollows:

(a)Inchlorobenzene,theC−Clbondisshorterduetopartialdoublebondcharacter.

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(b)HybridisationsofCinC−Clin?chlorobenzeneandcyclohexylchloridearesp2andsp3,

respectively(sp2Cbeingmoreelectronegativethansp3C).

Asdipolemomentistheproductofchargeandbonddistance,boththefactorsin

chlorobenzenearelowerascomparedtocyclohexylchloride.Therefore,thedipolemoment

ofchlorobenzeneislowerthanthatofcyclohexylchloride.

(iii)InSN1reaction,formationofcarbocationasanintermediatetakesplace.This

carbocationhassp2-hybridisedandplanarstructure.Thisplanarcarbocationisattackedby

nucleophilefromboththesidesequallytoformdandlisomersinequalproportion.Such

productsarecalledracemicmixture.Hence,SN1reactionsareaccompaniedbyracemisation

inopticallyactivealkylhalides.

Q12Anelementcrystallizesinaf.c.c.latticewithcelledgeof250pm.Calculatethe

densityif300gofthiselementcontain2×1024atoms.

Ans:Given:

a=250pm=250×10−12m

z=4

m=300g

(Mismolarmass.)

Molarmass,

Density,

Therefore,thedensityofthegivenelementis38.4g/cm3

Q13Therateconstantforthefirst-orderdecompositionofH2O2isgivenbythe

followingequation:

CalculateEaforthisreactionandrateconstantkifitshalf-lifeperiodbe200minutes.

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(Given:R=8.314JK–1mol–1)

Ans:Given:

Orderofthereaction=Firstorder

t1/2=200minutes=200×60=12,000seconds

Therelationbetweent1/2andkisgivenby

t1/2=0.693/k

k=0.693/12000=5.7×10−5

Therateconstantforthefirst-orderdecompositionofH2O2isgivenby

ByArrheniusequation

Comparing(i)and(ii),weget

Q14(i)Differentiatebetweenadsorbtionandabsorption.

(ii)Outof and ,whichoneismoreeffectiveincausingcoagulationof

negativelychargedsolandwhy?

(iii)Outofsulphursolandproteins,whichoneformmultimolecularcolloids?

Ans:(i)Adsorptionisasurfacephenomenonthatcausestheaccumulationofmoleculesofa

substanceatthesurfaceofasolidorliquidratherthaninthebulk.Inadsorption,the

substancegetsconcentratedatthesurfaceonly.Itdoesnotpenetratethroughthesurfaceto

thebulkofthesolidorliquid.Forexample,whenachalkstickisdippedintoaninksolution,

onlyitssurfacebecomescoloured.

Ontheotherhand,theprocessofabsorptionisabulkphenomenon.Inabsorption,the

absorbedsubstancegetsuniformlydistributedthroughoutthebulkofthesolidorliquid.

(ii)AccordingtotheSchulze-Hardyrule,theeffectivenessofthesaltcausingflocculation

dependsonthechargeontheionofoppositesigntothechargeonthesolparticles.The

greaterthemagnitudeoftheoppositecharge,thehighertheabilityofasalttocoagulatethe

sol.

Thus,trivalentsaltAlCl3ismoreeffectiveincausingthecoagulationofanegativelycharged

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solthandivalentsalt .

(iii)Outofsulphursolandproteins,sulphursolformsmultimolecularcolloids.Sulphursol

consistsofparticlescontainingathousandormoreS8molecules.Ontheotherhand,

proteinsformmacromolecularcolloids.

Q15(i)NamethemethodofrefiningofmetalssuchasGermanium.

(ii)IntheextractionofAl,impureAl2O3isdissolvedinconc.NaOHtoformsodium

aluminateandleavingimpuritiesbehind.Whatisthenameofthisprocess?

(iii)Whatistheroleofcokeintheextractionofironfromitsoxides?

Ans:(i)Zonerefiningmethodisthemostsuitablemethodforrefiningmetalslike

germanium(semiconductor).

(ii)Intheextractionofaluminium,impure isdissolvedinconcentratedNaOHtoform

NaAlO2.Thismethodisknownasleachingofalumina.

(iii)Cokereducestheironoxidetomoltenironmetal.Also,coke,whenburntintheblast

furnace,suppliestheheatrequiredforcarryingouttheextractionofironfromitsoxide.

Q16Calculatee.m.fofthefollowingcellat298K:

Ans:Thebalancedchemicalreactioncanbewrittenasfollows:

Thecellcanberepresentedasfollows:

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canbecalculatedasfollows:

Q17Givereasons:

(i)Mnshowsthehighestoxidationstateof+7withoxygenbutwithfluorine,itshows

thehighestoxidationstateof+4.

(ii)Transitionmetalsshowvariableoxidationstates.

(iii)Actinoidsshowirregularitiesintheirelectronicconfigurations.

Ans:(i)Mnshowsthehighestoxidationstateof+7withoxygenbecauseitcanformppi−dpi

multiplebondsusing2porbitalofoxygenand3dorbitalofMn.Ontheotherhand,Mnshows

thehighestoxidationstateof+4withflourinebecauseitcanformsinglebondonly.

(ii)Thevariableoxidationstatesoftransitionelementsareduetotheparticipationofnsand

(n−1)d-electronsinbonding.Loweroxidationstateisexhibitedwhenthens-electronstake

partinbonding.Higheroxidationstatesareexhibitedwhenthe(n−1)d-electronstakepart

inbonding.

(iii)Actinoidsshowirregularitiesintheirelectronicconfigurationsbecausetheenergy

differencesbetween5f,6dand7ssubshellsareverysmall;hence,anelectroncanbe

occupiedinanyofthesubshells.Theyhavetheelectronicconfigurationof7s2withvariation

ofoccupancyin5fand6dorbitals.

Q18Writethemainproduct(s)ineachofthefollowingreactions:

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(i)

(ii)

(iii)

Ans:(i)

(ii)

(iii)

Q19WritethestructuresofA,BandCinthefollowing:

(i)

(ii)

Ans:(i)

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(ii)

Q20(i)Whatistheroleoft-butylperoxideinthepolymerizationofethene?

(ii)Identifythemonomersinthefollowingpolymer:

(iii)Arrangethefollowingpolymersintheincreasingorderoftheirintermolecular

forces:Polystyrene,Terylene,Buna-S

OR

Writethemechanismoffreeradicalpolymerizationofethene.

Ans:(i)Inpolymerisationofethene,sourceoffreeradicalisneededtoinitiatethechain

reaction.Suchfreeradicalsareusuallyproducedbydecompositionofperoxidesliket-butyl

peroxideorbenzoylperoxide.

(ii)Thegivenpolymerisnylon6,6.

Monomersofnylon6,6areadipicacid(HOOC(CH2)4COOH)andhexamethylenediamine

(H2N(CH2)6NH2).

(iii)Elastomersofrubbershavetheweakestintermolecularforcesofattraction,whilefibres

havethestrongestintermolecularforcesofattraction.Plasticshaveintermdiateforcesof

attraction.

Theincreasingorderofintermolecularforcesofattractionofthegivenpolymersisas

follows:Terylene>Polystyrene>Buna-S

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Or

Freeradicalmechanismforpolymerisationofethane

Chain-initiatingstep

Chain-propagatingstep

Chain-terminatingstep

Q21(i)Writethenameoftwomonosaccharidesobtainedonhydrolysisoflactosesugar.

(ii)WhyVitaminCcannotbestoredinourbody?

(iii)Whatisthedifferencebetweenanucleosideandnucleotide?

Ans:(i)Uponhydrolysis,lactoseproducesonemoleculeofD-glucoseandonemoleculeofD-

galactose.

(ii)VitaminCiswater-solubleinnature.Itcannotbestoredinthehumanbodyasit

repeatedlygetseliminatedthroughurine.

(iii)Anucleosideisformedbytheattachmentofpurineorpyrimidinebasetothe1-position

ofapentosesugar.

Ontheotherhand,anucleotideisaunitformedbytheattachmentofnucleosideto

phosphoricacidatthe5′-positionofthesugarmoiety.

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Q22(a)Forthecomplex[Fe(CN)6]3–,writethehybridizationtype,magneticcharacter

andspinnatureofthecomplex.(At.number:Fe=26).

(b)Drawoneofthegeometricalisomersofthecomplex[Pt(en)2Cl2]2+whichis

opticallyactive.

Ans:(a)

Hybridisation:d2sp3

Magneticcharacter:Paramagnetic

Spinnatureofcomplex:Low-spincomplex

(b)cis-isomerof[Pt(en)2Cl2]2+isopticallyactive.

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SectionD

Q23Duetohecticandbusyschedule,Mr.Angadmadehislifefulloftensionsand

anxiety.Hestartedtakingsleepingpillstoovercomethedepressionwithoutconsulting

thedoctor.Mr.Deepak,aclosefriendofMr.Angad,advisedhimtostoptakingsleeping

pillsandsuggestedtochangehislifestylebydoingYoga,mediationandsomephysical

exercise.Mr.Angadfollowedhisfriend'sadviceandafterfewdayshestartedfeeling

better.

Afterreadingtheabovepassage,answerthefollowing:

(i)Whatarethevalues(atleasttwo)displayedbyMr.Deepak?

(ii)Whyisitnotadvisabletotakesleepingpillswithoutconsultingdoctor?

(iii)Whataretranquilizers?Givetwoexamples.

Ans:(i)ThefollowingvaluesaredisplayedbyMr.Deepak:

(a)Careandconcern:Hecaredforthewell-beingofhisfriendMr.Angad.

(b)Knowledge:Hesuggestedhisfriendeffectivemeasurestocounterstressandanxiety.

(ii)Sleepingpillsareprescribedbydoctorstopatientsinstress,painordepression.Itshould

notbetakenwithoutaprescriptionoradoctor'sconsultancybecausethesepillshaveseveral

sideeffects.Sleepingpillsslowdownthefunctioningofthebrainandthenervoussystem.

(iii)Tranquillisersarethoseclassoforganiccompoundsthatareneurologicallyactivedrugs.

Theyperformtheirfunctionbyinhibitingthemessagetransfermechanismfromnerveto

receptor.Theyinduceasenseofwell-beingandareusedinthetreatmentofstress,anxiety,

irritabilityandmentaldiseases.Theirexamplesarechlordiazepoxide,iproniazid,

phenelzine,meprobamateandequanil.

SectionE

Q24(a)Accountforthefollowing:

(i)Ozoneisthermodynamicallyunstable.

(ii)SolidPCl5isionicinnature.

(iii)FluorineformsonlyoneoxoacidHOF.

(b)Drawthestructureof

(i)

(ii)

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OR

(i)ComparetheoxidizingactionofF2andCl2byconsideringparameterssuchasbond

dissociationenthalpy,electrongainenthalpyandhydrationenthalpy.

(ii)WritetheconditionstomaximizetheyieldofH2SO4bycontactprocess.

(iii)Arrangethefollowingintheincreasingorderofpropertymentioned:

(a)H3PO3,H3PO4,H3PO2(Reducingcharacter)

(b)NH3,PH3,AsH3,SbH3,BiH3(Basestrength)

Ans:(a)(i)OzonedecomposesintoO2withtheevolutionofheat,i.e.ΔHisnegative

(exothermic). =negative

SincethedecompositionofO3increasesthenumberandfreedomofparticles,entropyalso

increases.

Therefore, =positive

Now,ΔG=ΔH–TΔS

Both−?Hand (since?Sispositive)resultintolargenegative?G.Hence,O3becomes

thermodynamicallyunstableanddecomposesintooxygeneasily.

(ii)PCl5isionicinsolidstatebecauseitexistsas[PCl4]+[PCl6]−inwhichthecationhas

tetrahedralgeometryandtheanionhasoctahedralgeometry.

(b)(i)BrF5

(ii)XeF4

OR

(i)Althoughelectrongainenthalpyoffluorineislessthanthatofchlorinebecauseofthe

smallsizeoffluorine,buttheoxidisingpowerdependsonotherfactorslikebond

dissociationenergyandhydrationenergy.Thesmallerthesizeoftheatom,thegreaterthe

hydrationenthalpy.Fluorinebeingsmallinsizehashigherhydrationenthalpyascompared

tochlorine.Also,fluorinefacesgreaterinter-electronicrepulsionamongitslonepairsof

electronsbecauseofitssmallsize,whilethereisverylessrepulsioninchlorine.Hence,the

bonddissociationenthalpyoffluorineislowerthanthatofchlorine.

Thus,thehighhydrationenthalpyandlowbonddissociationenthalpyoffluorineresultinits

higheroxidisingpowerascomparedtothatofchlorine.

(ii)Manufacturingofsulphuricacidviathecontactprocessinvolvesthreesteps:

(1)BurningoforestoformSO2

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(2)ConversionofSO2toSO3usingV2O5asacatalyst

(3)AbsorptionofSO3inH2SO4togiveoleum

Thesecondstep,i.e.conversionofSO2toSO3isthekeystep.Sincethisreactionis

exothermicinnatureandtwomolesofgaseousreactantgiveonemoleofgaseousproduct.

Thus,inaccordancewithLeChatelier'sprinciple,toobtainthemaximumamountofSO3,

lowtemperatureandhighpressurearerequired.

(iii)(a)Reducingcharacter:H3PO4<H3PO3<H3PO2

Thistrendcanbeexplainedonthebasisofstructuresofoxyacidsofphosphorus.

ThehigherthenumberofP−Hbond,thehigherthereducingpoweroftheoxyacidof

phosphorus.TherearetwoP−HbondsinH3PO2,oneP−HbondinH3PO3andnoP−Hbond

inH3PO4.So,thisexplainsthereducingtrendofthegivenoxyacidsofphosphorus.

(b)Basestrength:BiH3<SbH3<PH3<NH3

Onmovingdownthegroup,thesizeofthecentralatomincreases.Thisdecreasesthe

electrondensityonthecentralatomandtherebyaffectingtheelectron-donatingabilityof

theatom.Hence,thebasicstrengthdecreasesonmovingdownthegroup.

Q25WritethestructuresofA,B,C,DandEinthefollowingreactions:

OR

(a)WritethechemicalequationforthereactioninvolvedinCannizzaroreaction.

(b)Drawthestructureofthesemicarbazoneofethanal.

(c)WhypKaofF-CH2-COOHislowerthanthatofCl−CH2−COOH?

(d)Writetheproductinthefollowingreaction:

(e)Howcanyoudistinguishbetweenpropanalandpropanone?

Ans:

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OR

(a)Cannizzaroreaction

(b)Semicarbazoneofethanol

(c)Fluorineismoreelectronegativethanchlorine.Thepresenceoffluorineinamolecule

willmakeitmoreacidic.Thus,thepKaofF−?CH2−COOHislowerthanthatofCl−CH2−?

COOH.

(d)

(e)

Propanal Propanone

ItformssilvermirroronreactionwithTollen's

reagent.

ItisnotoxidisedbyTollen's

reagent.

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Itdoesnotreactwithiodoform. Itgivespositiveiodoformtest.

OnreactingwithSchiff'sreagent,itgivespink

colour.

ItdoesnotreactwithSchiff's

reagent.

Q26(a)Calculatethefreezingpointofsolutionwhen1.9gofMgCl2(M=95gmol−1)was

dissolvedin50gofwater,assumingMgCl2undergoescompleteionization.

(Kfforwater=1.86Kkgmol−1)

(b)(i)Outof1Mglucoseand2Mglucose,whichonehasahigherboilingpointand

why?

(ii)Whathappenswhentheexternalpressureappliedbecomesmorethantheosmotic

pressureofsolution?

OR

(a)When2.56gofsulphurwasdissolvedin100gofCS2,thefreezingpointloweredby

0.383K.Calculatetheformulaofsulphur( ).

( for =3.83Kkgmol−1,Atomicmassofsulphur=32gmol−1]

(b)Bloodcellsareisotonicwith0.9%sodiumchloridesolution.Whathappensifwe

placebloodcellsinasolutioncontaining

(i)1.2%sodiumchloridesolution?

(ii)0.4%sodiumchloridesolution?

Ans:(a)Given:

Therefore,

Molalityofthesolution,m=

m=0.4m

Also,MgCl2undergoescompleteionisationandtherebyyielding3molesofconstituentions

foreverymoleofMgCl2.

∴i=3

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Now,depressioninfreezingpointisgivenas

Hence,thenewfreezingpointofthesolutionis270.92K.

(b)(i)Theelevationintheboilingpointofasolutionisacolligativeproperty;therefore,itis

affectedbythenumberofparticlesofthesolute.Sincetheamountofsoluteishigherin2M

glucosesolutionascomparedto1Mglucosesolution,theelevationintheboilingpointis

higher.Hence,2Mglucosesolutionhasahigherboilingpointthan1Mglucosesolution.

(ii)Whentheexternalpressureexertedonthesolutionishigherthantheosmoticpressure,

thepuresolventstartsflowingoutofthesolutionthroughthesemi-permeablemembrane.

Thisprocessisknownasreverse-osmosis.

OR

(a)Given:

Therefore,

Molalityofthesolution,

m=0.8m

Thedepressioninfreezingpointofasolutionisgivenas

Hence,8sulphuratomsareundergoingassociation,asshownbelow:

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(b)(i)1.2%sodiumchloridesolutionishypertonicwrt0.9%sodiumchloridesolution.

Therefore,whenthebloodcellsareplacedin1.2%sodiumchloridesolution,waterflowsout

ofthecellsandthecellsshrink.

(ii)0.4%sodiumchloridesolutionishypotonicwrt0.9%sodiumchloridesolution.Therefore,

whenthebloodcellsareplacedin0.4%sodiumchloridesolution,waterflowsintothecells

andthecellsswell.

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