chem_xii_cbse_board_2015.pdf

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Studymate Solutions to CBSE Board Examination 2015-2016

Series : ONS/1

Candidates must write the Code on

the title page of the answer-book.

Code No. 56/1/1/D

Roll No.

4 Please check that this question paper contains 11printed pages.

4 Code number given on the right hand side of the question paper should be written on the title

page of the answer-book by the candidate.

4 Please check that this question paper contains 26questions.

4 Please write down the Serial Number of the questions before attempting it.

4 15 minutes time has been allotted to read this question paper. The question paper will be

distributed at 10.15 a.m. From 10.15 a.m. to 10.30 a.m., the student will read the question

paper only and will not write any answer on the answer script during this period.

CHEMISRY (Teory)[Time allowed : 3 hours] [Maximum marks : 70]

General Instructions:

(i) All questions are compulsory.

(ii) Questions number 1 to 5are very short answer questions and carry 1mark each.

(iii) Questions number 6 to 10are short answer questions and carry 2marks each.

(iv) Questions number 11 to 22are also short answer questions and carry 3marks each.

(v) Questions number 23 is a value based question and carry 4marks.

(vi) Questions number 24 to26 are long answer questins and carry 5 marks each.

(vii) Use log tables, if necessary. use of calculations is not allowed.


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1. Out of CH CH

CH

CH C and CH CH CH

CH

C3 2 3 2

3 3

| |

l l , which is more reactive towards SN1

reaction and why? [1]

Ans. CH CH CH Cl3 2

CH3Secondary Alkyl halide

2. On adding NaOH to ammonium sulphate, a colourless gas with pungent odour is evolved which

forms a blue coloured complex with Cu2+ion. Identify the gas. [1]

Ans. The gas is NH3.

Cu2+(aq) + 4NH3(aq)[Cu(NH

3)4]2+(deep blue)

3. What type of magnetism is shown by a substance if magnetic moments of domains are arranged

in same direction? [1]

Ans. Ferromagnetism, magnetic moments are oriented in same direction.

4. Write the IUPAC name of the given compound: [1]

Ans. 2, 4, 6Tribromoaniline

5. Write the main reason for the stability for colloidal sols. [1]

Ans. Due to solvation and charge present.

6. From the given cells: [2]

Lead storage cell, Mercury cell, Fuel cell and Dry cell

Answer the following:

(i) Which cell is used in hearing aids?

(ii) Which cell was used in Apollo Space Programme?

(iii) Which cell is used in automobiles and inverters?

(iv) Which cell does not have long life?

Ans. (i) Mercury cell (ii) Fuel cell

(iii) Lead storage cell (iv) Dry cell

7. When chromite ore FeCr2O

4is fused with NaOH in presence of air, a yellow coloured compound

(A) is obtained which on acidication with dilute sulphuric acid gives a compound (B) Compound(B) on reaction with KClforms a orange coloured crystalline compound (C). [2]

(i) Write the formulae of the compounds (A), (B) and (C)

(ii) Write one use of compound (C).

OR

Complete the following chemical equations

(i) KMnO4+ 3S

2O

32+ H

2O

(ii) Cr2O

72+ 3Sn2++ 14H+

Ans. (i) 4FeCr2O

4+ 8NaOH + 7O

2 8Na

2CrO

4[A] + 2Fe

2O

3+ 8H

2O

2Na2CrO

4[A] + H

2SO

4 Na

2Cr

2O

7[B] + Na

2SO

4+ H

2O


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Na2Cr

2O

7[B] + 2KCl K

2Cr

2O

7[C] + 2NaCl

A : Na2CrO

4 B: Na

2Cr

2O

7

C : K2Cr

2O

7

(ii) Use of K2Cr

2O

7(C) : It is used as a strong oxidizing agent.

OR

(a) 8MnO4+ 3S

2O

32+ H

2O 8MnO

2+ 6SO

42+ 2OH

(b) Cr2O72

+ 3Sn2+

+ 14H+

2Cr3+

+ 7H2O + 3Sn4+

8. When a co-ordination compound CrCl3.6H

2O is mixed with AgNO

3, 2 moles of AgCl are

precipitated per mole of the compound. Write [2]

(i) Structural formula of the complex.

(ii) IUPAC name of the complex.

Ans. (a) [Cr(H2O)

5Cl]Cl

2H

2O

(b) Pentaaquachloridochromium (III) chloride mono hydrate

9. For a reaction: 2 33 2 2

NH N HPt( ) ( ) ( )g g g + ; Rate = k. [2]

(i) Write the order and molecularity for this reaction.

(ii) Write the unit of k.

Ans. (i) Order Zero Molecularity Two

(b) Units of K mol L1s1

10. Write the mechanism of the following reaction: [2]

2 3 2 413 3 2 2 32 4CH CH OH CH CH O CH CH

Conc. H SO

K

Ans. Step 1: CH CH O H + H CH CH O H3 2 3 2

+ +

H

Step 2: CH CH O H + CH CH O H CH CH O CH CH3 2 3 2 3 2 2 3

+ +

H

H

Step 3 : CH CH O CH CH CH CH O CH CH3 2 2 3 3 2 2 3

+

H

11. Give reasons: [3]

(i) CClbond length in chlorobenzene is shorter than CClbond length in CH3Cl.

(ii) The dipole moment of chlorobenzene is lower than that of cyclohexyl chloride.

(iii) SN1 reactions are accompanied by racemization in optically active alkyl halides.

Ans. (i) In chlorobenzene, due to resonance, there is a partial double bond character, so bond

length is short.

(ii) The dipole moment of chlorobenzene is lower as bond length is shorter (m= q d) due toresonance and sp2hybridized carbon.

(iii) Because SN1 reactions occurs via formation of carbocation which will lead to form

d- & l-products. hence racemization occurs.

12. An element crystalizes in a f.c.c. lattice with cell edge of 250 pm. Calculate the density if 300 g

of this element contain 2 1024atoms. [3]

Ans. a = 250 pm

Z = 4

d

Z M

N=

(a)3

0

3010

d =

4 90 33250 6 022 10 103 23 30

.( ) .

= 38.4 gm/cc


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13. The rate constant for the rst order decompositon of H2O

2is given by the following equation:

log . .

kT

K=

14 2 1 0 104

[3]

Calculate Eafor this reaction and rate constant k if its half-life period be 200 minutes. (Given:

R = 8.314 J K1mol1)

Ans. log . .

kT

K=

14 2 1 0 104

on comparing with log logk A E2.303 RT

= a , we get

E

2.303 R

a= 1 10

4

\ Ea= 2.303 R 104

= 2.303 8.314 104

= 19.14 104

= 1.91 105J = 191 kJ

k =

0 693

1 2

.

/t

= 0 693200

.

= 0.0034

= 3.4 103min1

14. (i) Differentiate between adsorption and absorption. [3]

(ii) Out of MgCl2and AlCl

3, which one is more effective in causing coagulation of negatively

charged sol and why?

(iii) Out of sulphur sol and proteins, which one forms multi-molecular colloids?

Ans. (i) Adsorption occurs only at surface of absorbent whereas absorptionoccurs throughout

bulk.

(ii) According to Hardy Schulze rule, AlCl3 with high positive charged cation (Al3+) will

coagulate more effectively.

(iii) Sulphur sol.

15. (i) Name the method of rening of metals such as Germanium. [3]

(ii) In the extraction of Al, impure Al2O

3is dissolved in conc. NaOH to form sodium aluminate

and leaving impurities behind. What is the name of this process?

(iii) What is the role of coke in the extraction of iron from its oxides?

Ans. (i) Zone rening method

(ii) Leaching

(iii) Coke act as a reducing agent

16. Calculate e.m.f. of the following cell at 298 K: [3]2Cr(s) + 3Fe2+(0.1M) 2Cr3+(0.01M) + 3Fe(s)

Given: E(Cr3+| Cr) = 0.74 V E (Fe2+| Fe) = 0.44 V

Ans. E En

P

R=

.log

0 0591

Cr Cr Fe Fe

Cr Cr e i

Fe e Fe ii

| || |

...( )

...( )

3 2

3

2

3 2

2

+ +

+

+

+

+ 33

2 3 3 2

0 44 0 74

0 0591

6

2 3Cr s Fe Fe s Cr

E

( ) ( )

( . ( . )

.

log

+ +

= [ ]

+ +

(( . )

( . )

0 01

0 1

2

3


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E = + 0 30 0 0591

6

1

10.

.log

= + 0 30

0 0591

61.

.( )

= + 0.30 + 0.01 = 0.31 V

17. Give reasons: [3] (i) Mn shows the highest oxidation state of +7 with oxygen but with uorine it shows the

highest oxidation state of +4.

(ii) Transition metals show variable oxidation states.

(iii) Actinoids show irregularities in their electronic congurations.

Ans. (i) Mn shows +7 oxidation state with oxygen because it can form multiple bond but uorine

can not.

(ii) Transition metals show variable oxidation state because the energy of ns and (n 1)d

orbitals are approximately same so they can loose different number of electrons depending

on requirement.

(iii) Due to less energy difference between 5f, 6d and 7s orbitals. Hence electron can

re-arrange for stable conguration.

18. Write the main product(s) in each of the following reactions: [3]

(i) CH C

CH

CH

O CH HI3 3

3

3

+

|

|

(ii) CH CH CH B H

H O OH3 2 3

2 6

2 2

=

( )

( ) /

i

ii

(iii) C H OH aq. NaOH

CO ,H6 5 2

+

( )

( )

i

ii

Ans. (i) CH C O CH + HI CH C I + CH OH3 3 3 3

CH3

CH3

CH3

CH3

(ii) CH CH = CH3 2 CH CH CH OH3 3 2(i) B H2 6

(ii) 3H O /OH2 2

(iii)

OH

(i) aq. NaOH

(ii) CO , H2+

OHCOOH

19. Write the structures of A, B and C in the following:

(a) C H CONH A B CBr aq KOH NaNO HCl

C

KI

6 5 2 0 52 2

+

/ .

(b) CH Cl A B CKCN LiAlH C HC l a lc K OH34 3

+ .

Ans. (a) C6H

5 CONH

2

B r KO H2 / C

6H

5NH

2[A]

NaNO HCl2 + C

6H

5N

2+Cl KI C

6H

5I

(b) CH3Cl

KCN CH

3CN [A] LiAlH4 CH

3CH

2NH

2[B]

CHCl KOH3 +

CH3CH

2NC

20. (i) What is the role of t-butyl peroxide in the polymerization of ethene?

(ii) Identify the monomers in the following polymer:

[ ( ) ( ) ]NH CH NH CO CH CO n2 6 2 4

(iii) Arrange the following polymers in the increasing order of their intermolecular forces:

Polystyrene, Terylene, Buna-S

OR Write the mechanism of free radical polymerization of ethene.

Ans. (i) Radical initiator


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(ii) NH2 (CH

2)6 NH

2 and HOOC (CH

2)4 COOH

Hexamethylene diamine Adipic acid

(iii) Buna-S < Polystyrene < Terylene

OR

Chain initiation step:

Chain propagating step:

Chain terminating step:

21. (i) Write the name of two monosaccharides obtained on hydrolysis of lactose sugar.

(ii) Why vitamin C cannot be stored in our body?

(iii) What is the difference between a nucleoside and nucleotide?

Ans. (i) b-D-Glucose and bDGalactose

(ii) It is water soluble, hence it is excreted through urine.

(iii) Nucleoside: It is formed when pentose sugar combines with nitrogen base.

Nucleotide: When Nucleoside bonds with phosphate group.

22. (a) For the complex [Fe(CN)6]3, write the hybridization type, magnetic character and spin

nature of the complex. (At. number : Fe = 26).

(b) Draw one of the geometrical isomers of the complex [Pt(en)2Cl

2]2+which is optically active.

Ans. (a) [Fe(CN)6]3

Fe in ground state

3d 4s

Fe(III)

3d 4s 4p 4d

Since CNis strong eld ligand, pairing takes place.

Fe

3d5 4s 4p

Hybridization d2sp3(octahedral)

Magnetic character Paramagnetic

Spin nature Low spin complex

(b)

cis

Pt

Cl

en

en

Cl

Pt

Cl

en

Cl

en

trans

2+ 2+

23. Due to hectic and busy schedule, Mr. Angad made his life full of tension and anxiety. He startedtaking sleeping pills to overcome the depression without consulting the doctor. Mr. Deepak, a

close friend of Mr. Angad, advised him to stop taking sleeping pills and suggested to change his

lifestyle by doing yoga, meditation and some physical exercise. Mr. Angad followed his friends


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advice and after few days he started feeling better.

After reading the above passage, answer the following

(a) What are the values (at least two) displayed by Mr. Deepak?

(b) Why is it not advisable to take sleeping pills without consulting doctor?

(c) What are tranquilizers ? Give two examples.

Ans. (a) Friendly

Knows harmful effects of sleeping pills. (b) It is not advisable to take sleeping pills without consulting doctor because it can be

dangerous and life threatning.

(c) Medicines which are used to cure anxiety & depression are called tranquilizers e.g.

equanil, phenelzine.

24. (a) Account for the following:

(i) Ozone is thermodynamically unstable.

(ii) Solid PCl5is ionic in nature.

(iii) Fluorine forms only one oxoacid HOF.

(b) Draw the structure of

(i) BrF5

(ii) XeF4

OR

(i) Compare the oxidizing action of F2

and Cl2 by considering parameters such as bond

dissociation enthalpy, electron gain enthalpy and hydration enthalpy.

(ii) Write the conditions to maximize the yield of H2SO

4by contact process.

(iii) Arrange the following in the increasing order of property mentioned:

(a) H3PO

3, H

3PO

4, H

3PO

2(Reducing character)

(b) NH3, PH

3, AsH

3, SbH

3, BiH

3(Base strength)

Ans. (i) O O O H ve3 2 + =

Ozone being thermodynamically unstable therefore its decomposition is exothermic and

its DS is +ve. So DG is always negative.

(ii) In solid state, PCl5exist as [PCl

4]+[PCl

6]because of unequal P-Cl bond lengths.

(iii) F can exhibit only one oxidation state i.e. 1 & in HOF it exhibits 1 oxidation state so it

can form only HOF also absence of d-orbital in F.

(b) (i) BrF5

Br

F

F F

F

Square pyramidal

F

(ii) XeF4 Xe

FF

F F

Squareplanar


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OR

X (g)2Hreaction

X (aq.)

Hhyd.

X (g)

2X(g) Heg

Hdiss.

DH reaction = DH dissociation + DH egain DH hydration

The dissociation enthalpy (DH diss.) of F2is less positive than that of Cl

2but the DH

egfor F

2

is +ve and for Cl2is ve. However since Fis a smaller anion it is move strongly hydrated

& hence DHhydration

for Fis more ve than Cl.

DH reaction for F2is more ve than Cl

2hence F

2is stronger oxidizing agent than Cl

2.

(ii) The main reaction in contact process is

2 22 2 3

SO O SO+

this reaction is reversible and in order to increase the yield of SO3 (i) High pressure (according to LCP)

(ii) High temperature should be maintained &

(ii) V2O

5catalyst.

(iii) (a) H3PO

4< H

3PO

3< H

3PO

2

(b) BiH3< SbH

3< AsH

3< PH

3< NH

3

25. (a) Write the structures of A, B, C, D and E in the following reactions:

C H A BCH COClanhyd AlCl

Zn Hg conc HCl i

6 63

3.

/ . ( )( ) KKMnO KOH

i i H OC

NaOH

D E

4

3

+

+

,

( )

OR

(a) Write the chemical equation for the reaction involved in Cannizzaro reaction.

(b) Draw the structure of the semicarbazone of ethanal.

(c) Why pKaof F CH

2 COOH is lower than that of Cl CH

2 COOH ?

(d) Write the product in the following reaction

CH CH CH CH CN i DIBAL H

i i H O3 2 2 =

( )

( )

(e) How can you distinguish between propanal and propanone ?

Ans. (a) C H6 6CH COCl3

Anhyd. AlCl3

C CH3

O

Acetophenone(A)

ZnHg/Conc. HCl

C H2 5

Ethylbenzene(B)

KMnO KOH4

H+

COOH

Benzoic acid(C)

COO Na +

Sodium. Benzoate(D)

+

Iodoform(E)

CHI3

(yellow ppt.)

OR

(i) 2 50

3HCHO CH OH HCOONa

NaOH% +

(ii) CH CH N NH CO NH3 2

=


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(iii) In FCH2 COOH uorine is more electron withdrawing than chlorine in ClCH

2 COOH

so FCH2COOH is more acidic than ClCH

2COOH hence its pK

a value is lesser than

ClCH2COOH

(iv) CH CH CH CH CN CHPent enenitrile

i DIBAL H

i i H O3 23

2 =

( )

( ) 33 23 1

=

CH CH CH CHOPent en al

(v) Propanal and propanone can be differentiate.

(i) By Tollens reagent i.e. propanal will give silver mirror but propanone will not.

CH CH CHO Ag NH CH CH COO Ag H O3 2 3 2 3 2 22 2 + [ ] + + ++

( )silvermirror

33 3NH

26. (a) Calculate the freezing point of solution when 1.9 g of MgCl2(M = 95 g mol1) was dissolved

in 50 g of water, assuming MgCl2undergoes complete ionization.

(Kffor water = 1.86 K kg mol1)

(b) (i) Out of 1 M glucose and 2 M glucose, which one has a higher boiling point and why?

(ii) What happens when the external pressure applied becames more than the osmotic

pressure of solution ?

OR

(a) When 2.56 g of sulphur was dissolved in 100 g of CS2, the freezing point lowered by 0.383

K. Calculate the formula of sulphur (SX).

(Kffor CS2= 3.83 K kg mol1, Atomic mass of Sulphur = 32 g mol1)

(b) Blood cells are isotonic with 0.9% sodium chloride solution. What happens if we place

blood cells in a solution containing.

(i) 1.2% sodium chloride solution ?

(ii) 0.4% sodium chloride solution?

Ans. (a) wB(solute) = 1.9 g w

(H2O)= 50 g

M(MgCl2)

= 95 g/mol i = 3 (for MgCl2)

DTf= iK

fm

DTf= 3 1 86

1 9

95

1000

50 .

.(kg)

DTf= 2.232 K Also, DT

f= T0

f T

f

Tf= T0

f DT

f

= 273.15 2.232

= 270.918 K

(b) (i) 2 M glucose, because more the concentration, more is elevation in boiling point.

DTbm

(ii) Reverse osmosis takes place.

OR

(a) DTf= K

fm

DTf= K wMM w

fB

B A

1 (Kg)

MMB=

K w

T wf B

f A

(kg)

=3 83 2 56 1000

0 383 100

. .

. (kg)

= 256 g/mol

M.M. = n Atomic mass

n =M M

Atomic mass

. .= =

256

328

\S8

(b) (i) Water moves out from blood cell, hence shrink.

(ii) Water will enter into blood cell, hence swell.

*****

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