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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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