C.B.S.E. CLASS XII 2012 CHEMISTRY (Theory) SET I (DELHI BOARD) · (i) Nitrobenzene to benzoic acid....

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1 2012 C.B.S.E CHEMISTRY DELHI

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C.B.S.E. CLASS–XII–2012

CHEMISTRY (Theory)

SET–I (DELHI BOARD)

Time allowed: 3 hours Maximum Marks: 70

Q1. What is meant by ‘doping in a semiconductor?

Q2. What is the role of graphite in the electrometallurgy of aluminium?

Q3. Which one of 4PCl is not likely to exist and why?

Q4. Give the IUPAC name of the following compound.

2 2

3

CH C CH Br

CH|

Q5. Draw the structural formula of 2-methylpropan-2 ol molecule.

Q6. Arrange the following compound in an increasing order of their reactivity in nucleophilic addition

reaction: ethanal, propanal, butanone.

Q7. Arrange the following in the decreasing order of their basic strength in aqueous solutions:

3 2 3 2 3 3 3CH NH ,(CH ) NH,(CH ) NandNH

Q8. Define the term, homopolymerisation’ giving example.

Q9. A 1.00 molal aqueous solution of trichloroacetic acid 3(CCl COOH) is heated to its boiling point. The

solution has the boiling point of 100.180 C. Determine the Van’t Hoff factor for trichloro-acetic acid. (Kb

for water= 0.512 k kgmol-1)

or

Define the following terms:

(i) Molo fraction

(ii) Isotonic solution

(iii) Van’t Hoff factor

(iv) Ideal solution

Q10. What do you understand by the order of a reaction’? Identify the reaction order from each of the

following units of reaction rate constant:

(i) 1 1L mols

(ii) 1 1Lmol s

Q11. Name the two group into which phenomenon of catalysis can be divided. Give an example of each group

with the chemical equation involved.

Q12. What is meant by coagulation of colloidal solution? Describe briefly and three methods by which

coagulation of lyophobic sols can be carried out.

Q13. Describe the principle involved in each of the following processes.

(i) Mond process for refining of Nickel.

(ii) column chromatography for purification of rate elements.

Q14. Explain the following giving an appropriate reason in each case.

(i) O2 and F2 both stabilize higher oxidation state of metals but O2 exceeds F2 in doing so.

(ii) Structures of Xenon fluorides cannot be explained by Valence Bond approach.




Q15. Complete the following chemical equation:

2O H I2 7Cr

NO H4 2MnO

Q16. What is meant by

(i) Peptide linkage

(ii) Biocatalysts?

Q17. Write any two reactions Glucose which cannot be explained be the open chain structure of glucose

molecule.

Q18. Draw the structure of the monomer for each of the following polymers:

(i) Nylon6

(ii) Polypropene

Q19. Tungsten crystallizes in body centred cubic unit cell. If the edge of the unit cell is 316.5 pm, what is the

radius of tungsten atom?

OR

Iron has a body centred cubic unit cell with a cell dimension of 286.65 pm. The density of iron is 7.874

g cm-3 . use this information to calculate Avogadro’s number. (At. Mass of Fe = 55.845 u)

Q20. Calculate the amount of KCl which must be added to 1 kg of water so that the freezing point is

depressed by 2K. (Kf for water=1.86 K Kg mol-1)

Q21. For the reaction (g) 2(g) (g)2NO CI 2NOCl the following data were collected. AL the measurements

were taken at 263 K:

Experiment

No.

Initial [NO] (M) Initial [Cl2] (M) Initial rate of

disappearance of Cl2

(M/min)

1

2

3

4

0.15

0.15

0.30

0.25

0.15

0.30

0.15

0.25

0.60

1.20

2.40

?

(a)write the expression for rate law.

(b)calculate the value of rate constant and specify its units.

(c)what is the initial rate of disappearance of CI2 in exp. 4?

Q22. How would you account for the following?

(i) Many of the transition elements are known to form interstitial compounds.

(ii) The metallic radii of the third (5d) series of transition metals are virtually the same as those of

the corresponding group members of the second (4d) series.

(iii) Lanthanoids form primarily + 3 ions, while the actinoids usually have higher oxidation states

in their compounds, +4 or even +6 being typical.

Q23. Give the formula of each of the following coordination entities:

(i) 3Co ion is bound to one Cl , one NH3 molecules and two bidentate ethylene diamine (en)

molecules.

(ii) 2Ni ion is bound to two water molecules and two oxalate ions.

Write the name and magnetic behavior of each of the above coordination entities.

(At. nos. nos. Co =27, Ni=28)

Q24. Although chlorine is an electron withdrawing group, yet it is ortho-,para-directing in electrophilic

aromatic substitution reactions. Explain why it is so?

Q25. Draw the structure and name the product formed if the following alcohols are oxidized. Assume that an

excess of oxidizing agent is used.

(i) 3 2 2 2CH CH CH CH OH

(ii) 2-butenol

(iii) 2-methyl-1-propanol




Q26. Write chemical equations for the following:

(i) Nitrobenzene to benzoic acid.

(ii) Benzyl chloride to 2-phenylethanamine.

(iii) Aniline to benzyl alcohol.

Q27. What are the following substances? Give one example of each one of them.

(i) Tranquilizers

(ii) Food preservatives

(iii) Synthetic detergents

Q28. (a) what type of a battery is the lead storage battery? Write the anode and the cathode reactions and

the overall reaction occurring in a lead storage battery when current is drawn form it.

(b) In the button cell, widely used in watches, the following reaction takes place.

2

(s) 2 (s) 2 l (s) (aq)Zn Ag O H O Zn (aq) 2Ag 2OH

Determine E0 and ΔG0 for the reaction.

(given : 0

Ag /Ag(E 0.80V) , 0

Zn /Zn(E 2 0.76V)

or

(a) Define molar conductivity of a solution and explain how molar conductivity change with change in

concentration of solution for a weak and a strong electrolyte.

(b) The resistance of conductivity cell containing 0.001 M KCl solution at 298 K is 1500 Ώ. What is the

cell constant if the conductivity of 0.001 M KCl solution at 298 K is 3 10 146 10 Scm. ?

Q29. (a) complete the following chemical reaction equation:

(i) 4 2 2P SO Cl

(ii) 6 2XeF H O

(b)Predict the shape and the asked angle (900 or more or less) in each of the following cases:

(i) 23SO and the angle O S O

(ii) 3C / F and angle F Cl F

(iii) 2XeF and angle F Xe F

or

(a) Complete the following chemical equation:

(i) 2NaOH Cl(hot and cone.)

(ii) 4 2 2XeF O F

(b)Draw the structure of the following molecules:

(i) 3 2H PO

(ii) 2 2 7H S O

(iii) 4XeOF

Q30. Illustrate the following name reactions giving suitable example in each case:

(i)clemmensen reduction

(ii)Hell-Volhard-Zelinsky reaction

(b)How are the following conversions carried out?

(i)Ethylcyanide to tehanoic acid

(ii)Benzoic acid to m-bromobenzoic acid

or

(a)illustrate the following reactions giving a suitable example for each.

(i) Cross aldol condensation

(ii) Decarboxylation

(b) Give simple tests to distinguish between the following pairs of compounds

(i) Pentan-2 one and pentan-3-one

(ii) Benzaldehyde and Acetophenone

(iii)Phenol and Benzoic acid




SOLUTION C.B.S.E. CLASS–XII–2012

CHEMISTRY (Theory)

SET–I (DELHI BOARD)

1. Introducing impurities into elements of Group 13 [B] or Group [P] into the elements of Group 14 [Si or

Ge] this improves conductivity of Group in 14 elements.

2. Graphite Is used as anode and cathode during electrolysis of fused alumina in molten cryolite.

3. 4Pcl cannot exit, because ‘P’ cannot withdraw C from more electronegative Cl.

4. 3-Bromo-2-methyl propane.

5.

6. Butanone < Propanone < Propanol < Ethanol.

7. 3 2 3 2 3 3 3(CH ) NH CH NH (CH ) N NH

8. A polymer from a single Monomer, called homopolymerisation, and this process called

homopolymerisation e.g. polythene formed by polymerization of ethylene.

9. M = 1, Tb = 100. 180C

T 0b = 100 0C I = ? Δtb = 0.18 0C

Kb = 0.512 K kg 1 mol.

ΔTb (th10 ) = Kb ˟ M

ΔTb (thco ) = 0.512 ˟ 1= 0.512

L= b

b

T (obs) 0.180.35156

T (theo) 0.512

(i) Mole fraction: It may be defined as the ratio of the number of moles of one component (solute or

solvent) to the total number of all the component present in the solution.

(ii)Isotonic solutions: two solution are said to be isotonic when they exert the same osmotic pressure

because they have the same molar concentration. All intravenous injection must be isotonic with body

fluids.

(iii)Van’t Hoff factor: It may be defined as the ratio of normal molecular mass to the observed

molecular mass of the solute.

i = observed Colligative property

Calculated colligative property

i =

Total number of moles of particle after

association

Number of association moles of

Particules before

i = normal mass

abnormal mass

CH3–C–CH3

CH3

OH




(iv) Ideal solution : Ideal solution is the solution which follow Raoult’s law, ΔHmix =0, ΔVmix =0. In ab

Ideal solution force attraction between A-B are equal to that in A-A and B-B.

10. Order of raction : the sum of the exponents (power) of the concentration of reactants in the rate law

is termed as order of reaction. It can be zero also.

(i)L-s mol S-1 zero order reaction.

(ii)L mol-1 second order reaction.

11. In the same phase of the reactants is mentioned as homogeneous catalyst. Example of this catalyst is

the extraction of methyl acetate from the acetic acid

(g )NO

2 2 32SO (g) O (g) 2SO (g) oxidation of Sulphur dioxide into tri-oxide with dioxygen in presence

of oxides of nitrogen as the catalyst in the in lead chamber process.

(ii)Heterogenous catalysis : This catalyst provides a medium for the performance of the reactions.

Heterogenous catalysis is defined as the catalytic process in which the reactants catalysis are in

different phases e. g.

(g )NO

2 2 32SO (g) O (g) 2SO (g) Oxidation of Sulphur dioxide into tri-oxide with dioxygen in

presence of oxides of nitrogen as the catalyst in the lead chamber process.

(iii)Heterogenous catalysis : This catalyst provides a medium for the performance of the reactions.

Heterogenous catalysis is defined as the catalytic process in which the reactants catalysis are in

different phases e. g.

Pt(s)2 32SO (g) 2SO (g) Oxidation of Sulphur trioxide from sulphur dioxide in the presence of Pt.

12. The process of settling of colloidal particular is called coagulation or precipitation of the sol.

Method of which coagulation of lyophobic sols can be carried out.

(i)By electrophoresis : the colloidal particles move towards opposite charged electrodes, electrodes

get discharged and precipitated under an applied electric field.

(ii) By mixing two oppositely charged sols: oppositely charged sols when mixed is almost equal

properties, neutralize their charge and get partially or completely precipitated. Mixing of hydrated

ferric oxide (+Ve sols) and arsenious sulphide (-ve sol ) bring them is the precipitated forms.This type

of coagulation is called mutual coagulation.

(iii)By Boiling: when a solution is boiled, the adsorbed layer is disturbed due to increase colloisions

with the molecules of dispersion medium. This reduce the charge on the particles and ultimately lead to

setting down in the form of precipitate.

13. (i) Mond process for refining nickel: the mond process for refining nickel is based on some feature.

In this process, impure nickel is exposed to carbon monoxide gas at 50 C0 whereby volatile nickel tetra

carbonyl forms .No impurity present in the crude nickel reacts with carbon monoxide e.g.

4Ni(s) 4CO(g) NiCO (g)

2 4Ti(s) 2I (g)OTiI (g)

330 350K

4Ni 4CO Ni(Co)

Impure Tetra carboyl nickel.

450 470K

Ni 4CO

pure

(ii)Column Chromatography : Different components of mixture are absorbed to different extents,

depanding upon their polarity.

14. (i) The ability of O2 to stabilize higher oxidation states exceeds that of fluorine because oxygen can

form multiple bonds with metals.




(ii)According to VBT if electrons in an orbital are raised ( especially of noble gases) then they do not

participate in bond formation or (undergo hybridization).

15. (i) 2 32 7 2 2Cr O H 6I 2Cr 7H O2I I 2e ]X3

2 32 7 2 2Cr O 6I 14H 2Cr 3I 7H O

(ii) 24 2 2 22MnO 5NO 6H 2Mn 5NO 3H O

16. (i) Peptide linkage : the amide linkage O O

( C|

H|

N ) formed between two α-amino acid

molecules with the loss of a water molecule in a polypeptide is called a peptide linkage.

(ii)Bio catalysts: It is the use of natural catalysis, such as protein enzymes, to perform chemical

transformations or organic compound. Both enzymes that have been more or less isolated and enzymes

still residing inside living cells are employed for this task.

17. (i) Despite having the aldehyde group, glucose does not give, 2,-4-DNP test, schiff’s test and it does not

form the hydrogen sulphite addition product with NaHSO3.

(ii) the penta acetate of glucose does not react with hydroxilamine indicating the absence fo free-CHO

group.

(iii)Glucose is found to exist in two different crystalline forms which are named as α and β. The α-form

of glucose (M.P. 419K) is obtained by crystallization from concentrated solution of glucose at 303 K

while the β-form (M.P. 423 K) is obtained by crystallization from not saturated aqueous solution at 371

K.

18. (i) Nylon6: Monomers- Caprolactum

H C2

H C2

H C2

-CH2

CH2

C=0

H

N

ε-Caprolactum

(ii)Polypropene

Monomer – propene

3 2H C CH CH or

(-CH -CH-)

2 n

CH3

propene.

19. For a body centred cubic, unit cell arrangement, ( 3) 4a r

3 316.54

4

r

r = 137.04 pm

OR

d =7.87 g cm-3

For bec, Z=2, M = 56 g mol1

A = 286.65pm = 286.65 x 10-10 cm, NA =?

D= 3

A

Z M

N a

NA = 3

Z M

d a




NA = 10 3

2 55.845

7.874 (286.65 10 cm)

NA = 235.931 10 atom/mol.

20. Assuming 100% dissociation of KCI,

fi 2, T 2K

1fK 1.86kkgmol

BW ?

1BM 74.5gmol

f fT i K M

massof KCI

2 2 1.86 174.5

= 2 1.86 massof KCI

74.5

74.5

Mass of KCI1.86

40.05gm.

21. (a)

d[R]R

dt

2 12K [NO] [CI ]

(b) 2 1

2R K [NO] [Cl ]

2 1 2 12

R 0.6K

[NO] [Cl ] [0.15] [0.15]

3

0.6177.75

(0.15)

[using experiment (1)]

(c) 2

2R K [NO] [Cl ]

2R 177.78 (0.25) 0.25

R 2.78M/ Min.

22. (i) Many of the transition elements are known to form interstial compounds.Transition elements from

interstial compounds as they are capable of entrapping small atoms like H, C or N in the interstitial

sites in their crystal Lattice.

(ii)The metallic radii of the third (5d) series of transition metals are virtually the same as those of the

corresponding group members of second (4d) series. This is due to filing 4f orbitals which have poor

shielding effect or due to lanthanoid contraction.

(iii)This is attributed to the fact that 5f, 6d and 7s levels are of comparable energies in case of actinoids.

23. (i) 23 2[Co (NH ) (en) C1]

IUPAC name: Amminechloridobis

(ethane, -1, 2, -diamine Cobalt III ion.

Magnetic behavior: Diamagnetic (d2 sp3 ) hybridisation




(ii) 22 2 4 2Ni H O C O[ ( )( ) ]

IUPAC name: Diaquadioxalationickelate

(II) ion.

Magnetic behavior: Peramagnetic ( 3 2sp d ) hybridization.

24. Chlorine with draws electrons through inductive effect and release electrons though resonance. Though

inductive effect, chlorine destabilizes the intermediate carbocation formed during the electrolphilic

substitution.

Cl

+ E

Cl

EEH

Inductive effectdestabilises the intermediate carbocation

Cl

+ E

Cl

EH

(attack at ortho-position)

Cl

+ E

Cl

E H (attack at para-position)

Resonance effect stabilizes the intermediate carbocations. Through resonance, halogen tends to

estabilise the carbocation and the effect is more pronounced and ortho-and para position. The inductive

effect is stronger than resonance and cause net electron withdrawl and thus cause net deactivation the

resonance effect tends to oppose the inductive effect for the attack at ortho-and para-position and hence

makes the deactivation less for ortho-and para attack. Reactivity is thus controlled by the stronger

inductive effect and orientation is conrolled by resonance effect.

25. (i) 2 2 7K Cr O /H

3 2 2 2

3 2 2

CH CH CH CH OH

CH CH CH COOH

Type equation here.

Butanoic acid

(ii) PCC

2 2

3

CH CH CH CH

CH CH CH CHO

(iii)

2 2 7K Cr O /H3 2

3

CH||CH CH CH OH

CH

3

3

CH CH COOH|

CH

2-Methyl propanoic acid

26. (i) Nitrobenzene to benzoic acid

NO2

Sn/HCl

6[H]

NH2

2NaNO /HCl

(273 280K)

N Cl2

2Cu(CN)

KCN

Nitrobenzene Aniline

CN

Benzonitrile

22H O/H

COOH

Benzoic acid




(ii)Benzyl chloride to 2-phenylethanamine.

CH Cl2

Benzyl

chloride

KCN(ag)

CH CN2

Phenyletthanenitrile

CH2CH NH2 2

2-Phenylethanamine

2Li Al H

(iii)Aniline to benzyl alcohol.

NH2

Aniline

2NaNO /HCl

(273 280K)

N Cl2

Benzenediazonium

chloride

CuCN/KCN

CN

Benzonitrile

22H O/H

COOH

Benzoic acid

4Li Al H

CH OH2

Benzylalcohol

27. (i) Tranquilizers: These area class of chemical, compounds used for the treatment of stress fatigue,

and mild or even severe mental disease. These relieve anxiety, stress, irritability or excitement by

inducing a sense of well- being.

(ii) Food preservatives: It is the process of treating and handling food to stop or slow down spoilage

and thus allow for longer storage. Preservation usually involves preventing the growth of bacteria,

yeasts, fungi, and other micro-organisms, as well as retarding the oxidation of fats.

(iii)Synthetic detergents: Synthetic detergents have similar molecular structure and properties as

soap. Although the cleansing action is similar, the detergents do not react as readily with hard water

ions of calcium and magnesium.

28. (a) It is a secondary cell.

Anode : 24 4Pb SO Pb SO 2e

Cathode : 22 4 4 2PbO 4H SO 2e PbSO 2H O

Overall reaction : 22 4 4 2Pb PBO 4H 2SO PbSO 2H O

(b)Zn is oxidized and 2Ag O is reduced.

22

0 0 0cell Ag O reduction Zn Zn oxidation

E E Ag E, ( ) / ( )

= 0.8 -(-0.76)

= 1.564 V

ΔG0 = -n 0cellFF = 2 x 96500 x 1.56=3010801

or

Molar conductivity of a solution at a given concentration is the conductance of the volume V of solution

containing one mole of electrolyte kept between two electrodes with area of cross section A and distance

of unit length.

2 1m

K 1000S cm mol

C

Molar conductivity increase marginally with decrease in concentration/ increases in dilution for a

strong electrolyte.




KCl

CH COOH3

m

For weak electrolyte increase steeply with decrease in concentration / increases in dilution. This is in

accordance with Le Chatelier principle.

(b)1 l 1

K or K Gp A p

G* =1

A=cell constant= G* = p ˟ k.

=1500 ohms x 0.146 x 10-3 ohm-1 cm-1

=1500 x 0.146 x 10-3 cm-1

=219 x 10-3 cm-1

29. (a) (i) 4 2 2 3 2 2 2P 8SO Cl 4PCl 4SO 2S Cl

(ii) 6 2 4XeF H O 2HF XeOF

(b)(i) structure: See Q. 24, set=II, O.D., 2008 (Comptt.).

Shape of 23SO pyramidal bond angle more than 900

(ii)structure:

F Cl

F

F CIF3 Bent T-shape

Bond angle = More than 900

(iii)Structure:

Cl F3 (T-shaped)

Xe

F

F

XeF2 Linear

XeF2 Linear shape

Bond angle = More than 900

Or

(a)(i) 2 3 26NaOH 3Cl 5NaCl NaClO 3H O

(hot and conc.)

(ii) 4 2 2 6 2XeF O F XeF O




(b)(i) 3 2H PO

O

P

HO

HO

H

Diabasic Orthophosphorous acid

(ii)H2S2O7

O

S

O

H

O

O

S

OH

O

Pyrosulphuric acid

(iii)XeOF4

Xe

O

F

F

F

F

Square pyramidal.

30. (a) (i) Clemmensen reduction:

Zn(Hg)in3 3 3Conc.HCl

O

CH C H H C

||

CH

Ethanol Ethane

Zn(Hg)in3 3 3 2 3Conc.HCl

|

O

H C C CH

|

H C CH CH

Propene Propane

(ii)Hell-Volhard.

2

2

1.Cl /Red.P3 2 2.H O

H C CH COOH

Propanoic acid

3H C CH C

CI

OOH|

α-Chloropropanoic acid

(b) (i) 3 3H O NH D3 2 3 2 3 2 2 2CH CH CN CH CH COOH CH CH CONH NaOH,Br

HONO3 2 3 2 2 3CH CH OH CH CH NH [O]CH COOH

(ii) 2 2 7 2 4K Cr O /dil H SO3 2 2 2 3 2Oxidation

CH CH CH CH OH H C CH -

2

|CH O

O|C H

Butanoic acid




(iii)

C-OH

O

Benzoic acid

+Br2

3 3Al Br Or FeBr

C-OH

O

Br m-Bromobezoic acid

Or

(a) (i) Cross aldol condensation : when aldol condensation is carried out between two different

aldehydes and ketones, it is called cross aldol condensation. Ketones can also be used as one

compound in cross aldol reaction.

CH3 CHO

+

1.NaOH3 2 2.NaOH

CH CH CHO

3 3 2 3CH CH CH CHO CH CH CH C CHO CH

But-2-enal from two molecules of ethanal 2-methyl pent-2-enal from two molecules of propanal

3 3 2

3

CH CH C CHO CH CH CH CH CHO|CH

2-methylbut-2-enal

From one molecule of ethanol and one molecule of propnal

(ii)Decarboxylation: Carboxylic acid lose carbon dioxide to from hydrocarbons when their sodium

salts are heated with sodaline. The reaction is known as decarboxylation.

NaOH&CaO2 3Heat

R COONa R H Na CO

electrolysis2 22CH COONa(ag) 2H O

3 3 2 2CH CH 2CO 2NaOH H

(b)(i)

3 2 2 3

||CH C C H

O

H CH C

Gives yellow precipitate of Iodoform with NaOH and iodine.

3 2 2 2

||H C CH

O

C CH CH

Pentane-Zone

Does not give yellow precipitate

(ii)

C-OH

O

Benzaldehyde No reaction

C-CH3

O

Acetophenone

Give yellow precipitate of iodoform with NaOH and iodine.

(iii)Benzoic acid decomposes NaHCO3 and gives effervescence due to evolution of CO2 but

phenol does not decomposes NaHCO3 .

6 5 3 6 5 2 2C H COOH NaHCO C H COONa CO H O

6 5 3C H COH NaHCO No reaction.




OH

COOH

(i)Gives violet colouration (i) No reaction

with neutral FeCl3 solution

(ii)No reaction (ii)Gives brisk efferve scene with 3NaHCO

(iii) The role of carbon monoxide in the refining of crude nickel.

(i) In the metallurgy of aluminium, purified Al2 O3 is mixed with cryolite lowers melting point of

the mix and brings conductivity.

(ii) Co-form a volatile complex (Nickel tetralabonyl)

300 350K4Ni 4Co Ni(Co)

The carbonyl is subjected to higher temperature so that it is decomposed giving a pure metal.

450 410K4Ni[Co] Ni 4Co.

C.B.S.E. CLASS XII 2012 CHEMISTRY (Theory) SET I (DELHI BOARD) · (i) Nitrobenzene to benzoic acid....

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Transcript of C.B.S.E. CLASS XII 2012 CHEMISTRY (Theory) SET I (DELHI BOARD) · (i) Nitrobenzene to benzoic acid....