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QuestionPaper2015Set-1

Class-12Chemistry

Time:3Hours,MaximumMarks:70

GeneralInstructions:

1.Allquestionsarecompulsory.

2.Q.No.1to5areveryshortanswerquestionsandcarry1markeach.

3.Q.No.6to10areshortanswerquestionsandcarry2markseach.

4.Q.No.11to22arealsoshortanswerquestionsandcarry3markseach.

5.Q.No.23isavaluebasedquestionandcarry4marks.

6.Q.No.24to26arelonganswerquestionsandcarry5markseach.

7.Uselogtablesifnecessary,useofcalculatorisnotallowed.

1.Whatistheno.ofatomsperunitcell(z)inabody-centredcubicstructure?

Ans.2

2.Inreferencetosurfacechemistry,definedialysis.

Ans.Itisaprocessofremovingadissolvedsubstancefromacolloidalsolutionbymeansof

diffusionthroughasuitablemembrane.

3.WhatistheIUPACnameofthecomplex[Ni(NH ) ]Cl ?

Ans.Hexaamninenickel(II)chloride

4.Drawthestructureof3-methylpentanal.

Ans.

5.Completethefollowingreactionequation:

C H N Cl+H PO +H O

Ans.

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(whereArisC6H5)

6.Defineosmoticpressureofasolution.Howistheosmoticpressurerelatedtothe

concentrationofasoluteinasolution?

Ans.Theexternalpressurewhichisappliedonsolutionsidetostoptheflowofsolvent

acrossthesemi-permeablemembrane.Theosmoticpressureisdirectlyproportionalto

concentrationofthesolution. =CRT

7.Definethefollowingterms:

(i)Half-lifeofareaction(t½)

(ii)Rateconstant(k)

Ans.(i)Thehalf-lifeofareactionisthetimeinwhichtheconcentrationofareactantis

reducedtoonehalfofitsinitialconcentration.

(ii)Rateconstantistherateofreactionwhentheconcentrationofthereactantisunity.

8.Drawthestructuresofthefollowing:(i)H SO

(ii)

Ans.(i)

(ii)

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9.Whatismeantby‘disproportionation’?Giveanexampleofadisproportionation

reactioninaqueoussolution.

OR

Suggestreasonsforthefollowingfeaturesoftransitionmetalchemistry:

(i)Thetransitionmetalsandtheircompoundsareusuallyparamagnetic.

(ii)Thetransitionmetalsexhibitvariableoxidationstates.

Ans.Disproportionation:Thereactioninwhichanelementundergoesself-oxidationand

selfreduction

simultaneously.Forexample:

2Cu+(aq) +(aq)+Cu(s)

10.Explainthemechanismofdehydrationstepsofethanol:-

Ans.

11.Definethefollowing:

(i)Schottkydefect

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(ii)Frenkeldefect

(iii)F-centre

Ans.(i)Thedefectinwhichequalnumberofcationsandanionsaremissingfromthelattice.

(ii)Duetodislocationofsmallerionfromitsnormalsitetoaninterstitialsite.

(iii)Anionicvacanciesareoccupiedbyunpairedelectron.

12.45gofethyleneglycol(C H O )ismixedwith600gofwater.Calculate

(i)thefreezingpointdepressionand

(ii)thefreezingpointofthesolution

(Given:Kfofwater=1.86Kkgmol )

Ans.(i)

2.325Kor2.325

(ii) =2.325

O - =2.325

=-2.325 or270.675K

13.Therateconstantsofareactionat500Kand700Kare0.02s and0.07s

respectively.Calculatethevalueofactivationenergy,Ea.(R=8.314JK mol )

Ans. =

log =

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0.544= 5.714 /19.15

=0.544 19.15/5.714 =18230.8K

14.Definethefollowingterms:

(i)Electrophoresis

(ii)Adsorption

(iii)Shapeselectivecatalysis

Ans.(i)Themovementofcolloidalparticlesunderanappliedelectricpotentialtowards

oppositelychargedelectrodeiscalledelectrophoresis.

(ii)Theaccumulationofmolecularspeciesatthesurfaceratherthaninthebulkofasolidor

liquidistermedadsorption.

(iii)Thecatalyticreactionthatdependsupontheporestructureofthecatalystandthesize

ofthereactantandproductmoleculesiscalledshape-selectivecatalysis.

15.Outlinetheprinciplesofrefiningofmetalsbythefollowingmethods:

(i)Distillation

(ii)Zonerefining

(iii)Electrolysis

OR

Writedownthereactionstakingplaceindifferentzonesintheblastfurnaceduring

theextractionofiron.Howispigirondifferentfromcastiron?

Ans.(i)Theimpuremetalisevaporatedtoobtainthepuremetalasdistillate.

(ii)Thismethodisbasedontheprinciplethattheimpuritiesaremoresolubleinthemelt

thaninthesolidstateofthemetal.

(iii)Theimpuremetalismadetoactasanode.Astripofthesamemetalinpureformisused

ascathode.Theyareputinasuitableelectrolyticbathcontainingsolublesaltofthesame

metal.Themorebasicmetalremainsinthesolutionandthelessbasiconesgototheanode

mud.

OR

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3 +CO +

(Ironore)

+CO

(limestone)

CaO (Slag)

FeO+CO Fe+

C+ Fe+

Coke

FeO+C Fe+CO

Castironhaslowercarboncontent(about3%)thanpigiron/castironishard&brittle

whereaspigironissoft.

16.Whatislanthanoidcontraction?Whataretheconsequencesoflanthanoid

contraction?

Ans.ThesteadydecreaseinatomicradiifromLatoLuduetoimperfectshieldingof4f–

orbital.

Consequences–

(i)Membersofthirdtransitionserieshavealmostidenticalradiiascorespondingmembers

ofsecondtransitionseries.

(ii)Difficultyinseparation.

17.Indicatethetypesofisomerismexhibitedbythefollowingcomplexes:

(i)[Co(NH ) (NO2)]

(ii)[Co(en) ]Cl (en=ethylenediamine)

(iii)[Pt(NH )2Cl ]

Ans.(a)Linkageisomerism

(b)Opticalisomerism

(c)Cis-trans/Geometricalisomerism

18.NamethefollowingaccordingtoIUPACsystem:

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(i)

(ii)

(iii)

Ans.(a)Butan–2–ol

(b)2–bromotoluene

(c)2,2-dimethylchlorpropane

19.Howarethefollowingconversionscarriedout?

(i)Propenetopropane-2-ol

(ii)BenzylchloridetoBenzylalcohol

(iii)Anisoletop-Bromoanisole

Ans.(i)

(ii)

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(iii)

20.Anaromaticcompound‘A’ontreatmentwithaqueousammoniaandheatingforms

compound‘B’whichonheatingwith andKOHformsacompound‘C’ofmolecular

formula .WritethestructuresandIUPACnamesofcompoundsA,BandC.

Ans.A-BenzoicAcid

B-Benzamide

C-Aniline

21.Howarevitaminsclassified?Namethevitaminresponsibleforthecoagulationof

blood.

Ans.Fatsolublevitamin-VitaminA,D

Watersolublevitamin-VitaminB,C

VitaminK

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22.Writethenamesandstructuresofthemonomersofthefollowingpolymers:

(i)Buna-S

(ii)Neoprene

(iii)Teflon

Ans.(i) =CH=CH= and

=

1,3-ButadieneStydrene

(ii)

Chloroprene/2-Chloro-1,3-Butadine

(iii)

Tetrafluroethene

23.Rameshwenttoadepartmentalstoretopurchasegroceries.Ononeofshelveshe

noticedsugar-freetablets.Hedecidedtobuythemforhisgrandfatherwhowasa

diabetic.Therewerethreetypesofsugar-freetablets.Rameshdecidedtobuysucrolose

whichwasgoodforhisgrandfather’shealth.

(i)NameanothersugarfreetabletwhichRameshdidnotbuy.

(ii)Wasitrighttopurchasesuchmedicineswithoutdoctor’sprescription?

(iii)WhatqualityofRameshisreflectedabove?

Ans.(i)Aspartame,Saccharin(anyone)

(ii)No

(iii)Socialconcern,empathy,concern,socialawareness.

24.a)Definethefollowingterms:

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(i)Molarconductivity(^m)

(ii)Secondarybatteries

(iii)Fuelcell

(b)Statethefollowinglaws:

(i)Faradayfirstlawofelectrolysis

(ii)Kohlrausch’slawofindependentmigrationofions

OR

(a)Definethetermdegreeofdissociation.Writeanexpressionthatrelatesthemolar

conductivityofaweakelectrolytetoitsdegreeofdissociation.

(b)Forthecellreaction

Ni(s)| (aq)|| (aq)|Ag(s)

Calculatetheequilibriumconstantat25°C.Howmuchmaximumworkwouldbe

obtainedbyoperationofthiscell?

E° /Ni=0.25VandE°

Ag+/Ag=0.80V.

Ans.(a)(i)Molarconductivityofasolutionatagivenconcentrationistheconductanceofthe

volumeVofsolutioncontainingonemoleofelectrolytekeptbetweentwoelectrodeswith

areaofcrosssectionAanddistanceofunitlength.

(ii)Secondarybattery-canberechargedbypassingcurrentthroughitinoppositedirection

sothatitcanbeusedagain.

(iii)Galvaniccellsthataredesignedtoconverttheenergyofcombustionoffuelslike

hydrogen,methane,methanol,etc.directlyintoelectricalenergyarecalledfuelcells.

(b)(i)Theamountofchemicalreactionwhichoccursatanyelectrodeduringelectrolysisby

acurrentisproportionaltothequantityofelectricitypassedthroughtheelectrolyte(solution

ormelt).

(ii)Limitingmolarconductivityofanelectrolytecanberepresentedasthesumofthe

individualcontributionsoftheanionandcationoftheelectrolyte.

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OR

(a)Degreeofdissociationistheextenttowhichelectrolytegetsdissociatedintoits

constituentions.

(b) cell= Ag+/Ag- Ni2+/Ni

=0.80V–0.25V

=0.55V

logKc=

=

logKc=18.644

=-nF cell

=-2 96500C 0.55V

=-106,150J

Max.work=+106150J

or106.150kJ

25.(a)Completethefollowingchemicalreactionequations:

(i)Cu+HNO (dilute)

(ii)P +NaOH+H2O

(b)(i)WhydoesR P=OexistbutR N=Odoesnot?(R=alkylgroup)

(ii)Whyisdioxygenagasbutsulphurasolid?

(iii)Whyarehalogenscoloured?

OR

(a)Writebalancedequationsforthefollowingreactions:

(i)Chlorinereactswithdryslakedlime.

(ii)CarbonreactswithconcentratedH SO .

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(b)Describethecontactprocessforthemanufactureofsulphuricacidwithspecial

referencetothereactionconditions,catalystsusedandtheyieldintheprocess.

Ans.(a)(i)

(ii)C+ (conc.)

(b)i)Duetoabsenceofd-orbital,nitrogencannotexpanditsvalencybeyondfour.

(ii)Becauseofpπ–pπmultiplebondingindioxygenwhichisabsentinsulphur.

(iii)Duetoexcitationofelectronbyabsorptionofradiationfromvisibleregion.

OR

(a)(i)

(ii)C+ (conc.)

b)ItismanufacturedbyContactProcesswhichinvolvesfollowingsteps:

(i)burningofsulphurorsulphideoresinairtogenerate .

(ii)conversionof to bythereactionwithoxygeninthepresenceofacatalyst(

)

(iii)absorptionof in togiveOleum( ).Theoleumobtainedisdilutedto

givesulphuricacid

Reactioncondition–pressureof2barandtemperatureof720K

Catalystusedis

Yield–96–98%pure

26.(a)Describethefollowinggivingchemicalequations:

(i)De-carboxylationreaction

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(ii)Friedel-Craftsreaction

(b)Howwillyoubringaboutthefollowingconversions?

(i)BenzoicacidtoBenzaldehyde

(ii)Benzenetom-Nitroacetophenone

(iii)Ethanolto3-Hydroxybutanal

OR

(a)Describethefollowingactions:

(i)Acetylation(ii)Aldolcondensation

(b)Writethemainproductinthefollowingequations:

(i)

(ii)

(iii)

Ans.(a)(i)Carboxylicacidslosecarbondioxidetoformhydrocarbonswhentheirsodium

saltsare

heatedwithsodalime(NaOHandCaO).

(ii)Whenthealkyl/acylgroupisintroducedatorthoandparapositionsbyreaction

withalkylhalide/acylhalideinthepresenceofanhydrousaluminiumchloride(aLewis

acid)ascatalyst.

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(b)(i)

(ii)

(iii)

OR

(a)(i)Whentheacylgroupsareintroducedatorthoandparapositionsbyreactionwithacyl

halideinthepresenceofanhydrousaluminiumchloride(aLewisacid)ascatalyst.

(ii)Aldehydesandketoneshavingatleastone-hydrogenundergoareactioninthepresence

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ofdilutealkaliascatalysttoform -hydroxyaldehydes(aldol)or -hydroxyketones

(ketol),respectively.

(b)(i)

(ii)

(iii)

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