CBSE 12th 2015 Chemistry Question Paper Solution

1PAGE # 1

Q 1. Write the formulae of any two oxoacids of phosphorus.

Q 2. Which would undergo SN2 reaction faster in the following pair :

C6H5 � CH2 � CH2 � Br and

Br|

CHCHHC 356

Q 3. Out of AlCl3 and NaCl, which is more effective in causing coagulation of a negative sol and why ?

Q 4. Write the formula of a compound in which the element Y forms ccp lattice and atoms of X occupy 1/3rd

of tetrahedral voids.

Q 5. Write the IUPAC name of the given compound :

3

23

3

CH|

OHCHCCH|

CH

Q 6. Why do transition elements show variable states ? How is the variability in oxidation states of d-blockdifferent from that of the p-block elements ?

Q 7. (i) Write down the IUPAC name of the following complex :

[Pt(NH3)(H2O)Cl2]

(ii) Write the formula for the following complex :tris(ethane-1,2-diamine)chromium (III) chloride

Q 8. Calculate the time to deposit 1.5 g of silver at cathode when a current of 1.5A was passed through the

solution of AgNO3. (Molar mass of Ag = 108 g mol�1, 1 F = 96500 C mol�1)

Q 9. Write the reagents used in the following reactions:

(i) C6H5 � CO � CH3 ? C6H5�CH2 �CH3

(ii) CH3 � COOH ? CH3 �COCl

ORArrange the following compounds in increasing order of their property as indicated :

(i) CH3CHO, C6H5CHO, HCHO

(reactivity towards nucleophilic addition reaction)(ii) 2,4-dinitrobenzoic acid, 4-methoxybenzoic acid, 4-nitrobenzoic acid (acidic character)

Question PaperCBSE 12th Board (Chemistry) Code No. A

Venue: Contact No.:C-13, Jawahar Nagar Main Road, Opp. Scholar Residency, Kota (Raj.)| 0744-2422030, 8302490578

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06 to 12th th

April 2015

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Q 10. (i) Why are aquatic species more comfortable in cold water than in warm water ?(ii) What happens when we place the blood cell in saline water solution (hypertonic solution) ? Given

reason.Q 11. (i) Name the method used for the refining of titanium.

(ii) What is the role of Zn in the extraction of silver ?(iii) Reduction of metal oxide to metal becomes easier if the metal obtained is in liquid state. Why ?

Q 12. (i) E0 value for the Mn3+/Mn2+ couple is positive (+ 1.5 V) whereas that of Cr3+/Cr2+ is negative

(�0.4 V). Why ?

(ii) Transition metals form coloured compounds. Why ?(iii) Complete the following equation :

2

424 OC5H16MnO2

Q 13. (i) What type of isomerism is shown by [Co(NH3)5ONO]Cl2 ?

(ii) On the basis of crystal field theory, write the electronic configuration for d4 ion if 0 < P.

(iii) Write the hybridization and shape of [Fe(CN)6]3�.

Q 14. Predict the products of the following reactions :

(i)

3

3

CH|

OCCH ?NHCONHNH 22

(ii) C6H5�CH2�CH3 ?H)b(

KOH/KMnO)a( 4

(iii)COOH

423 SOH/HNO.conc

Q 15. Write the names and structures of the monomers of the following polymers :(i) Nylon-6,6(ii) Bakelite(iii) Polystyrene

Q 16. (i) Which one of the following is a disaccharide :starch, maltose, fructose, glucose

(ii) What is the difference between acidic amino acid and basic amino acid ?(iii) Write the name of the linkage joining two nucleotides.

Q 17. Vapour pressure of water at 20°C is 17.5 mm Hg. Calculate the vapour pressure of water at 20°C when

15 g of glucose (Molar mass = 180 g mol�1) is dissolved in 150 g of water.

Q 18. Examine the given defective crystal :

X+ Y� X+ Y� X+

Y� X+ Y� X+ Y�

X+ Y� X+ e� X+

Y� X+ Y� X+ Y�



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May 2015May to 0Last 10 Years Question papers will be provided Daily Test

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Answer the following questions :(i) Is the above defect stoichiometric or non-stoichiometric ?(ii) Write the term used for the electron occupied site.(iii) Give an example of the compound which shows this type of defect.

Q 19. How do you convert the following :(i) Prop-1-ene to Propan-2-ol(ii) Bromobenzene to 2-bromoacetophenone(iii) 2-bromobutane to But-2-ene

ORWhat happens when(i) ethyl chloride is treated with NaI in the presence of acetone,(ii) chlorobenzene is treated with Na metal in the presence of dry other

(iii) methyl chloride is treated with KNO2 ?

Write chemical equations in support of your answer.

Q 20. Give reasons for the following :(i) p-nitrophenol is more acidic than p-methylphenol.(ii) Bond length of C � O bond in phenol is shorter than that in methanol.

(iii) (CH3)3C � Br on reaction with sodium methoxide (Na+ �OCH3) gives alkene as the main product

and an ether.

Q 21. Calculate 0cellE and 0

rG for the following reaction at 25°C :

A2+ + B+ AA3+ + B

Given : Kc = 1010, 1F = 96500 C mol�1

Q 22. Define adsorption with an example. Why is adsorption exothermic in nature ? Write the types of adsorption

based on the nature of forces between adsorbate and adsorbent.

Q 23. Seeing the growing cases of diabets and depression among young children, Mr. Lugani, the principal of

one reputed school organized a seminor in which he invited parents and principals. They all resolved

this issue by strictly banning junk food in schools and introducing healthy snacks and drinks like soup,

lassi, milk, etc. in school canteens.

They also decided to make compulsory half an hour of daily physical activities for the students in the

morning assembly. After six months, Mr. Lugani conducted the health survey in most of the schools and

discovered a tremendous improvement in the health of the students.

After reading the above passage, answer the following questions :

(i) What are the values (at least two) displayed by Mr. Lugani ?

(ii) As a student, how can you spread awareness about this issue ?

(iii) What are antidepressant drugs ? Give an example.




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April 2015

4PAGE # 4

(iv) Name the sweetening agent used in the preparation of sweets for a diabetic patient.

Q 24. For the hydrolysis of methyl acetate in aqueous solution, the following results were obtained :

t/s 0 30 60

(CH COOCH 1/mol L 0 30 0 153

-1 . 3 0 60 . .

(i) Show that it follows pseudo first order reaction, as the concentration of water remains constant.(ii) Calculate the average rate of reaction between the time interval 30 to 60 seconds.

OR(a) For a reaction A + B P, the rate is given by

Rate = k [A]2[B]

(i) How is the rate of reaction affected if the concentration of A is doubled ?(ii) What is the overall order of reaction if B is present in large excess ?

(b) A first order reaction takes 23.1 minutes for 50% completion.Calculate the time required for 75% completion of this reaction.(Given : log 2 = 0.301, log 3 = 0.4771, log 4 = 0.6021)

Q 25. (a) Account for the following :

(i) Bond angle in 4NH is greater than that in NH3.

(ii) Reducing character decreases from SO2 to TeO2.

(iii) HClO4 is a stronger acid than HClO.

(b) Draw the structures of the following :

(i) H2S2O8

(ii) XeOF4

OR(a) Which poisonous gas is evolved when white phosphorus is heated with conc. NaOH solution ?

Write tha chemical equation.(b) Write the formula of first noble gas compound prepared by N. Bartlett. What inspired N. Bartlett to

prepare this compound ?(c) Fluorine is a stronger oxidizing agent than chlorine. Why ?(d) Write one use of chlorine gas.(e) Complete the following equation :

CaF2 + H2SO4



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5PAGE # 5

Q 26. An aromatic compound �A� of molecular formula C7H7ON undergoes a series of reactions as shown

below. Write the structures of A, B, C, D and E in the following reactions :

(C H ON) A C H NH B C 7 6 5 27

Br +KOH2

CHCl + NaOH3

CuCNNaNO + HCl2

H O2

D EOR

(a) Write the structures of the main products when aniline reacts with the following reagents :

(i) Br2 water

(ii) HCl

(iii) (CH3CO)2O / pyridine

(b) Arrange the following in the increasing order of their boiling point :

C2H5NH2, C2H5OH, (CH3)3N

(c) Give a simple chemical test to distinguish between the following pair of compounds :

(CH3)2 � NH and (CH3)3N




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6PAGE # 6

Ans 1. (I) H3PO3 (Phosphorous acid)

(ii) H3PO4 (Phosphoric acid)

Ans 2. C6H5 � CH2 �CH2 �Br (due to less stearic hindrence)

Ans 3. AlCl3 is more effective

due to high Positive Charge density on Al+3 as compared to Na+

Ans 4. The no. of atoms Y in CCP = Nno. of tetrahedral voids = 2N

no. of X atoms = 31

N2

= N32

Formula x : y

N32

: N

= 2 : 3

= x y2 3

Ans 5. 2, 2 - Dimethylpropan-1-ol

Ans 6. Transition elements show variable oxidation states since in these elements there is a small energy

difference between 3d and 4s orbital therefore 3d and 4s both e� participate in the bond formation hence

transtion elements shows variable oxidation states.Oxidation State of P block elements both type that is positive and negetivebut d block elements shows only positive oxidation states.

Ans 7. (i) Ammineaquadichloridoplatinum (II)(ii) 33 ClenCr

en =

22

22

NHNH||

CHCH

Solution

CBSE 12th Board (Chemistry) Code No. A



06 1th th


7PAGE # 7

Ans 8. Ag+ + e� Ag(s)

108 gm Ag required = 96500 C

1.5 gm Ag required = 5.1108

96500

= 1340.2 C

t = iQ

t = 5.1

2.1340

t = 893.5 sec.

Ans 9. (i) Zn � Hg / HCl

(ii) PCl5or

(i) C6H5CHO < CH3CHO < HCHO

(ii) 4-methoxybenzoic acid < 4-nitrobenzoic acid < 2, 4-dinitrobenzoic acid

Ans 10. (i) aquatic species is more comfortable in cold water than in warm water it is due to the more dissolution

of O2 in cold water

(ii) Blood cell will be squeeze.

dissolution of gases is a exothermic procees means at low temperature gases more dissolve in

Water

Ans 11. (i) van Arkel method

(ii) Zn displace silver form its salt solution.

)s(2

42 Ag2CNZnZnCNAg2

(iii) Since in the liquid state S = +ve

Ans 12. (i) 23

MnMn

Couple is positive

Mn3+ Mn+2 due to stable half filled (d5) electronic configuration it has reduction tendency..

32 CrCr have oxidation tendency

Cr3+ is more stable than Cr2+

due to stable 3g2t electronic Configuration.

(ii) due to d-d transition

(iii) 4MnO2 + 16H+ + 2

42OC5 10CO2 + 8H2O + 2Mn2+




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Ans 13. (i) it shows linkage isomerism

[ Co (NH3)5 ONO]Cl2 and [Co(NH3)5 NO2] Cl2(ii) If 0 < P then

d4 3

g2t 1ge

(iii) [ Fe (CN)6 ]3�

hybridisation d2sp3

shape actahedral

Ans 14. (i)

3

3

CH|

0CCH 22 NHCONHNH

3

223

CH|

OHNHCONHNCCH

(ii) COOHHCCHCHHC 56H)b(

KMnO)a(3256

4

(iii)

COOH COOH

NO2

Con

H O + H SO3 4N 2

Ans 15. (i) Nylon 6,6Monomer Adipic acid, hexamethylenediamine

HOOC � (CH2)4 � COOH H2N � (CH2)6 � NH2

(ii) Bakelite

Mnoner OHPhenal , formalaldehyde

O

H C H

(iii) Polystyrene Monomer �� Styrene

CH=CH2

Ans 16. (i) Maltose

(ii) acidic amino acid have �COOH > � NH2 group

where as basic amino acid have �NH2 > �COOH group

(iii) Phosphodiester linkage



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9PAGE # 9

Ans 17. P°A = 17.5 mm Hg WA = 150 gm

WB = 15 gm MA = 18 gmmol�1

MB = 180 gm mol�1

AB

AB

A

SA

WM

MW

P

PP

1501801815

517

P517 s

P = 17 . 325 mm HgS

Ans 18. (i) non � stoichiometric

(ii) F - Center (Ferb Centre)(iii) NaCl in presence of excess Na

Ans 19. (i) C CH = CH CH CH CH OH

3 2 3 3 H

H+

H O2

(ii)

Br

Br

O

C C H6 5

C H6 5 COCl

An. AlCl3

(iii) CH CH CH CH CH CH = CH C

Br

3 2 3 3 3

H

Alc KOH

OR

(i) NaClIHCINaClHC 52acetone

52




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10PAGE # 10

(ii) NaCl2HCHCdryetherNa2ClHC2 565656

(iii) KClNOOCHKNOClCH 323

Ans 20. (i) P-nitrophenol

OH

NO2

is more acidic it is due to �I, �M effect of NO2 group.

(ii) due to resonance bond length of C � O bond in phenol is shorter than that is methanol.

(ii) NaOCHBrCCH 333

2

33

3

CH||

OHCHNaBrCCH|

CH

Since 3° alkyl halide gives more preference for elemination reaction as compared to substution reaction

Ans 21. G° = � 2.303 RT log KC

G° = � 2.303 × 8.314 × 298 × log 1010

G° = � 57058.483 J/mol

= -5. 7×104

G° = � nF

cellE

cellE = nFG

965001)107.5(

E4

Cell

1Cell 1095E

V

Ans 22. AdsorptionThe accumulation of molecular species at the surface rather than in the bulk of a solidor liquid is called adsorption.

e.g. water molecules adsorbed by silicagel* during the adsorption process there is a force of attraction between adsorbate and adsorbenthence energy is released.* Two types(a) Physisorption (b) Chemisorption.



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11PAGE # 11

Ans 23. (i) (a) He is very concious towards the health of students.(b) He is very deceplined.

(ii) As a student i am also motivate to my friend.(iii) Phenelzine(iv) Saccharin (ortho-sulphobenzimide)

Ans 24. Case 1

(I) K1 = xa

alog

t303.2

K1 = 30.060.0

log30303.2

K =1 log 22.30330

Case 2

xaa

logt3032

K2

150600

log603032

K2

2log2603032

K2

K =2 × log22.30330

K1 = K2 it means it follows Pseudo first order reaction.

(II) average rate = �tR

=

3060300150

= 30150

= 200

1

= 5 × 10 sec-3

OR

(a) (I) rate1 = K |A|2 |B|

rate2 = K [2A]2 |B|

rate2 = 4K |A|2 |B|

r = 4r2 1




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12PAGE # 12

(II) Second order

(b) For 50% Completion of reaction

K = N

Nlog

t3032 0

N0 = initial amount of the substance

N = amount left after t lime

K = 50

100log

1233032

K = 2log123

3032

___________(1)

For 75% Completion of reaction

K = 25

100log

t3032

K = t3032

log 4

K = 2log2t3032

___________(2)

Divide equation 1 and 2

KK

2log2t3032

2log123

3032

t = 46.2 minuteAns. 25 (a)

(i) in NH4+ and NH3 nitrogen is SP3 hybridised but due to lP�bP replusion bond angle in NH3 but

there is no lP in NH4+ hence its bond angle is 109°28� but in NH3 it is 107°

(ii) due to inert pair effect.

(iii) due to higher oxidation state of Cl and high oxygen content in HClO4 it is more acidic then HOCl.

in HClO4 O.S of Cl = +7

in HClO O.S of Cl = +1



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13PAGE # 13

(b)

(i) S

O

OO

HO

S

OH

OO

O

(ii)Xe

FO

FF

F

OR

(a) P4 + 3NaOH + 3H2O PH3 + 3NaH2PO2

* Poisonous gas is PH3 (Phosphine)

(b) Formula Xe+ PtF6�

N Barlett Prepared the compund O2+ PtF6

� He then realised that the first jonisation enthalpy of

melecular oxygen (1175 KJ mol�1) was almost identical with that of xenon (1170 KJ mol�1) he

made efforts to prepare same type of compound with Xe and was successful in Preparing another

red colour compound Xe+ PtF6�.

(c) due to low dissociation bond enthalpy and High hydration enthalpy F2 is a strong oxidising agent.

(d) Use In sterilising drinking water.

(e) CaF2 + H2SO4 CaSO4 + 2HF

Ans 26. C7 H7OH

N2

+ Cl

_ CN

(A) (B) (C)

O

C NH2

COOH

(D) (E)

N = C




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April 2015

14PAGE # 14

OR

(a) (i)

NH2

OH

Br3 22

NH2

Br

Br

Br

(ii)

NH2

HCl

NH Cl3

+

(iii)

NH2

Py

23 OCOCH NH C CH3

O

(b) C2H5 �OH > C2H5NH2 > (CH3)3 N

(c) (CH3)2 NH react with Hinsberg reagent (C6H5SO2Cl)

2325623 CHClSOHCNHCH

O

N S C H

O6 5

(CH3)3 N does not react with Hinsberg reagent



06 1th th


CBSE 12th 2015 Chemistry Question Paper Solution

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