CBSE Chemistry Past year paper (Solutions) - 2013, Class 12 Class 12 Notes | EduRev

Chemistry Class 12

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Class 12 : CBSE Chemistry Past year paper (Solutions) - 2013, Class 12 Class 12 Notes | EduRev

 Page 1


  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
CBSE 
Class XII Chemistry – Set 1 
Board Paper – 2013 (Solution) 
Time: 3 hours Total Marks: 70 
 
1. Number of atoms present in one face-centred cubic crystal: 
 
Number of atoms present at corners per unit cell =  
8 corner atoms × 
1
8
 atom per unit cell = 1 atom  
Number of atoms present at faces per unit cell = 6 face-centred atoms ×
1
2
 atom per unit 
cell = 3 atoms 
?Total number of atoms per unit cell = 4 atoms. 
 
2. Mond’s process is the method used for refining of nickel metal. In this process, nickel is 
heated in a steam of carbon monoxide to form volatile nickel carbonyl Ni(CO)4. 
Nickel carbonyl vapour on further heating decomposes to give pure nickel. 
 
               
330 350K 450 470K
4
Impure                                               
Ni 4CO Ni
     Pur
(CO) Ni 4CO
e
??
? ? ? ? ? ? ? ? ? ? ? ?
 
 
3.  
 
Covalence of nitrogen in nitrogen pentoxide is 4. 
 
 
4.  
3 2 2
 5      4     3      2      1
CH CH CH CH CH
        |
        Cl
? ? ? ?
  
IUPAC name: 4-chloropent-1-ene 
 
 
 
 
Page 2


  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
CBSE 
Class XII Chemistry – Set 1 
Board Paper – 2013 (Solution) 
Time: 3 hours Total Marks: 70 
 
1. Number of atoms present in one face-centred cubic crystal: 
 
Number of atoms present at corners per unit cell =  
8 corner atoms × 
1
8
 atom per unit cell = 1 atom  
Number of atoms present at faces per unit cell = 6 face-centred atoms ×
1
2
 atom per unit 
cell = 3 atoms 
?Total number of atoms per unit cell = 4 atoms. 
 
2. Mond’s process is the method used for refining of nickel metal. In this process, nickel is 
heated in a steam of carbon monoxide to form volatile nickel carbonyl Ni(CO)4. 
Nickel carbonyl vapour on further heating decomposes to give pure nickel. 
 
               
330 350K 450 470K
4
Impure                                               
Ni 4CO Ni
     Pur
(CO) Ni 4CO
e
??
? ? ? ? ? ? ? ? ? ? ? ?
 
 
3.  
 
Covalence of nitrogen in nitrogen pentoxide is 4. 
 
 
4.  
3 2 2
 5      4     3      2      1
CH CH CH CH CH
        |
        Cl
? ? ? ?
  
IUPAC name: 4-chloropent-1-ene 
 
 
 
 
  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
5. CH3Br reacts with KCN to form CH3CN. It is a nucleophilic substitution reaction. 
 
33
CH Br  KCN  CH CN  KBr
Methyl
nitrite
? ? ?
 
6. Structure of 3-methyl butanal 
32
3
H C CH CH CHO
        |
       CH
? ? ?
 
 
7.  
3 3 3 2 3 2
o o o
(CH ) N CH NH (CH ) NH
3               1             2
??
 
As a consequence of combined effects of inductive effects and solvation, the secondary 
amines are the strongest bases. 
 
8. There are three types of RNA molecules: Messenger RNA (mRNA), transfer RNA (tRNA) 
and ribosomal RNA (rRNA). 
 
9. w1 = weight of solvent (H2O) = 1  
kg = 1000 gm w2 = weight of solute 
(C6H12O6) =18 gm 
M2 = Molar mass of solute (C6H12O6) =180 g mol
-1
 
Kb = 0.52 K kg mol
-1 
o
b
b
b
b b b
b
b
T . K
Kw
T
MW
.
.K
TTT
. T .
T . K
?
??
??
? ? ?
?
??
?
?
?
? ? ?
??
??
2
21
37315
1000
052 1000 18
180 1000
0052
0052 37315
373202
 
 
  
Page 3


  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
CBSE 
Class XII Chemistry – Set 1 
Board Paper – 2013 (Solution) 
Time: 3 hours Total Marks: 70 
 
1. Number of atoms present in one face-centred cubic crystal: 
 
Number of atoms present at corners per unit cell =  
8 corner atoms × 
1
8
 atom per unit cell = 1 atom  
Number of atoms present at faces per unit cell = 6 face-centred atoms ×
1
2
 atom per unit 
cell = 3 atoms 
?Total number of atoms per unit cell = 4 atoms. 
 
2. Mond’s process is the method used for refining of nickel metal. In this process, nickel is 
heated in a steam of carbon monoxide to form volatile nickel carbonyl Ni(CO)4. 
Nickel carbonyl vapour on further heating decomposes to give pure nickel. 
 
               
330 350K 450 470K
4
Impure                                               
Ni 4CO Ni
     Pur
(CO) Ni 4CO
e
??
? ? ? ? ? ? ? ? ? ? ? ?
 
 
3.  
 
Covalence of nitrogen in nitrogen pentoxide is 4. 
 
 
4.  
3 2 2
 5      4     3      2      1
CH CH CH CH CH
        |
        Cl
? ? ? ?
  
IUPAC name: 4-chloropent-1-ene 
 
 
 
 
  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
5. CH3Br reacts with KCN to form CH3CN. It is a nucleophilic substitution reaction. 
 
33
CH Br  KCN  CH CN  KBr
Methyl
nitrite
? ? ?
 
6. Structure of 3-methyl butanal 
32
3
H C CH CH CHO
        |
       CH
? ? ?
 
 
7.  
3 3 3 2 3 2
o o o
(CH ) N CH NH (CH ) NH
3               1             2
??
 
As a consequence of combined effects of inductive effects and solvation, the secondary 
amines are the strongest bases. 
 
8. There are three types of RNA molecules: Messenger RNA (mRNA), transfer RNA (tRNA) 
and ribosomal RNA (rRNA). 
 
9. w1 = weight of solvent (H2O) = 1  
kg = 1000 gm w2 = weight of solute 
(C6H12O6) =18 gm 
M2 = Molar mass of solute (C6H12O6) =180 g mol
-1
 
Kb = 0.52 K kg mol
-1 
o
b
b
b
b b b
b
b
T . K
Kw
T
MW
.
.K
TTT
. T .
T . K
?
??
??
? ? ?
?
??
?
?
?
? ? ?
??
??
2
21
37315
1000
052 1000 18
180 1000
0052
0052 37315
373202
 
 
  
  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
10.  
m
1
m
21
k 1000
()
C
Given :
k 0.025Sc
Mola
m
C 0.02 M
0.025 1000
()
r conducti
0.20
125Scm l
v
m
it
 o
y
?
?
?
??
?
?
?
??
?
 
 
Molar conductivity is 125 Scm
2
 mol
-1
.  
 
11.  
 
(i) Smoke 
Dispersed phase: Solid  
Dispersion medium: Gas 
(i) Milk 
Dispersed phase: Liquid  
Dispersion medium: Liquid 
 
OR 
 
Lyophilic colloids:  
Colloidal solutions in which the particles of the dispersed phase have a 
great affinity for the dispersion medium are called lypophilic colloids. 
These are reversible in nature. These are stable and cannot be easily 
coagulated by small amounts of electrolytes. 
 
Lyophobic colloids:  
Colloidal solutions in which there is no affinity between particles of the dispersed phase 
and the dispersion medium are called lyophobic colloids. These are irreversible in nature. 
These are unstable and can be easily coagulated on addition of a small amount of 
electrolyte due to the lack of protecting layer around the charged colloidal particles. 
 
 
 
 
 
 
Page 4


  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
CBSE 
Class XII Chemistry – Set 1 
Board Paper – 2013 (Solution) 
Time: 3 hours Total Marks: 70 
 
1. Number of atoms present in one face-centred cubic crystal: 
 
Number of atoms present at corners per unit cell =  
8 corner atoms × 
1
8
 atom per unit cell = 1 atom  
Number of atoms present at faces per unit cell = 6 face-centred atoms ×
1
2
 atom per unit 
cell = 3 atoms 
?Total number of atoms per unit cell = 4 atoms. 
 
2. Mond’s process is the method used for refining of nickel metal. In this process, nickel is 
heated in a steam of carbon monoxide to form volatile nickel carbonyl Ni(CO)4. 
Nickel carbonyl vapour on further heating decomposes to give pure nickel. 
 
               
330 350K 450 470K
4
Impure                                               
Ni 4CO Ni
     Pur
(CO) Ni 4CO
e
??
? ? ? ? ? ? ? ? ? ? ? ?
 
 
3.  
 
Covalence of nitrogen in nitrogen pentoxide is 4. 
 
 
4.  
3 2 2
 5      4     3      2      1
CH CH CH CH CH
        |
        Cl
? ? ? ?
  
IUPAC name: 4-chloropent-1-ene 
 
 
 
 
  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
5. CH3Br reacts with KCN to form CH3CN. It is a nucleophilic substitution reaction. 
 
33
CH Br  KCN  CH CN  KBr
Methyl
nitrite
? ? ?
 
6. Structure of 3-methyl butanal 
32
3
H C CH CH CHO
        |
       CH
? ? ?
 
 
7.  
3 3 3 2 3 2
o o o
(CH ) N CH NH (CH ) NH
3               1             2
??
 
As a consequence of combined effects of inductive effects and solvation, the secondary 
amines are the strongest bases. 
 
8. There are three types of RNA molecules: Messenger RNA (mRNA), transfer RNA (tRNA) 
and ribosomal RNA (rRNA). 
 
9. w1 = weight of solvent (H2O) = 1  
kg = 1000 gm w2 = weight of solute 
(C6H12O6) =18 gm 
M2 = Molar mass of solute (C6H12O6) =180 g mol
-1
 
Kb = 0.52 K kg mol
-1 
o
b
b
b
b b b
b
b
T . K
Kw
T
MW
.
.K
TTT
. T .
T . K
?
??
??
? ? ?
?
??
?
?
?
? ? ?
??
??
2
21
37315
1000
052 1000 18
180 1000
0052
0052 37315
373202
 
 
  
  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
10.  
m
1
m
21
k 1000
()
C
Given :
k 0.025Sc
Mola
m
C 0.02 M
0.025 1000
()
r conducti
0.20
125Scm l
v
m
it
 o
y
?
?
?
??
?
?
?
??
?
 
 
Molar conductivity is 125 Scm
2
 mol
-1
.  
 
11.  
 
(i) Smoke 
Dispersed phase: Solid  
Dispersion medium: Gas 
(i) Milk 
Dispersed phase: Liquid  
Dispersion medium: Liquid 
 
OR 
 
Lyophilic colloids:  
Colloidal solutions in which the particles of the dispersed phase have a 
great affinity for the dispersion medium are called lypophilic colloids. 
These are reversible in nature. These are stable and cannot be easily 
coagulated by small amounts of electrolytes. 
 
Lyophobic colloids:  
Colloidal solutions in which there is no affinity between particles of the dispersed phase 
and the dispersion medium are called lyophobic colloids. These are irreversible in nature. 
These are unstable and can be easily coagulated on addition of a small amount of 
electrolyte due to the lack of protecting layer around the charged colloidal particles. 
 
 
 
 
 
 
  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
12.  
S. No. Point of 
difference 
Physiosorption Chemisorption 
(i) Specificity It is not specific in nature. It is highly specific in nature. 
(ii) Temperature 
Dependence 
Usually occurs at low 
temperature and decreases 
with an increase in 
temperature. 
Occurs at high temperature 
and increases with the 
increase in temperature. 
(iii) Reversibility It is reversible in nature. It is irreversible in nature. 
(iv) Enthalpy 
change 
Enthalpy of adsorption is 
low; it is of the order of 20–
40 KJmol
-1
. 
Enthalpy of adsorption is high; 
it is of the order of 80–240 
KJmol
-1
. 
 
13.  
(a) Dilute solution (0.5%) of NaCN or KCN is used for leaching of silver metal in the presence 
of air in the metallurgy of silver. 
(b) Out of C and CO, CO is a better reducing agent at the lower temperature range because the 
CO, CO2 line lies below the Fe, FeO line, i.e. ?G
(CO, CO
2) 
< ?G
(Fe, FeO)
. So, CO will reduce FeO 
and will itself be oxidised to CO2. 
 
14.  
(i) PCl5 on heating decomposes to give PCl3 and Cl2 
5   3 2
  PCl PCl Cl ? ? 
(ii) H3PO3 on heating gives orthophosphoric acid and phosphine 
3 3 3 4 3
4H PO  3H PO PH ?? 
15.  
(a) Cu metal in the first transition series (3d series) shows the +1 oxidation state most 
frequently. This is because the electronic configuration of Cu is 3d
10 
4s
1 
and after 
losing one electron, it acquires the stable 3d
10 
fully filled electronic configuration. 
 
(b) The colour of cations is dependent on the number of unpaired electrons present in the 
d-orbital. The electronic configuration of the following cations is 
(c)  
Sc (Z = 21) = 3d
1 
4s
2 
and Sc
3+ 
= 3d
0 
4s
0
 
As the d-orbital is empty, it is colourless. 
 
V (Z = 23) = 3d
3 
4s
2 
and V
3+ 
= 3d
2 
4s
0
  
As the d-orbital has 2 unpaired electrons, it undergoes d–d transition and is green. 
Page 5


  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
CBSE 
Class XII Chemistry – Set 1 
Board Paper – 2013 (Solution) 
Time: 3 hours Total Marks: 70 
 
1. Number of atoms present in one face-centred cubic crystal: 
 
Number of atoms present at corners per unit cell =  
8 corner atoms × 
1
8
 atom per unit cell = 1 atom  
Number of atoms present at faces per unit cell = 6 face-centred atoms ×
1
2
 atom per unit 
cell = 3 atoms 
?Total number of atoms per unit cell = 4 atoms. 
 
2. Mond’s process is the method used for refining of nickel metal. In this process, nickel is 
heated in a steam of carbon monoxide to form volatile nickel carbonyl Ni(CO)4. 
Nickel carbonyl vapour on further heating decomposes to give pure nickel. 
 
               
330 350K 450 470K
4
Impure                                               
Ni 4CO Ni
     Pur
(CO) Ni 4CO
e
??
? ? ? ? ? ? ? ? ? ? ? ?
 
 
3.  
 
Covalence of nitrogen in nitrogen pentoxide is 4. 
 
 
4.  
3 2 2
 5      4     3      2      1
CH CH CH CH CH
        |
        Cl
? ? ? ?
  
IUPAC name: 4-chloropent-1-ene 
 
 
 
 
  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
5. CH3Br reacts with KCN to form CH3CN. It is a nucleophilic substitution reaction. 
 
33
CH Br  KCN  CH CN  KBr
Methyl
nitrite
? ? ?
 
6. Structure of 3-methyl butanal 
32
3
H C CH CH CHO
        |
       CH
? ? ?
 
 
7.  
3 3 3 2 3 2
o o o
(CH ) N CH NH (CH ) NH
3               1             2
??
 
As a consequence of combined effects of inductive effects and solvation, the secondary 
amines are the strongest bases. 
 
8. There are three types of RNA molecules: Messenger RNA (mRNA), transfer RNA (tRNA) 
and ribosomal RNA (rRNA). 
 
9. w1 = weight of solvent (H2O) = 1  
kg = 1000 gm w2 = weight of solute 
(C6H12O6) =18 gm 
M2 = Molar mass of solute (C6H12O6) =180 g mol
-1
 
Kb = 0.52 K kg mol
-1 
o
b
b
b
b b b
b
b
T . K
Kw
T
MW
.
.K
TTT
. T .
T . K
?
??
??
? ? ?
?
??
?
?
?
? ? ?
??
??
2
21
37315
1000
052 1000 18
180 1000
0052
0052 37315
373202
 
 
  
  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
10.  
m
1
m
21
k 1000
()
C
Given :
k 0.025Sc
Mola
m
C 0.02 M
0.025 1000
()
r conducti
0.20
125Scm l
v
m
it
 o
y
?
?
?
??
?
?
?
??
?
 
 
Molar conductivity is 125 Scm
2
 mol
-1
.  
 
11.  
 
(i) Smoke 
Dispersed phase: Solid  
Dispersion medium: Gas 
(i) Milk 
Dispersed phase: Liquid  
Dispersion medium: Liquid 
 
OR 
 
Lyophilic colloids:  
Colloidal solutions in which the particles of the dispersed phase have a 
great affinity for the dispersion medium are called lypophilic colloids. 
These are reversible in nature. These are stable and cannot be easily 
coagulated by small amounts of electrolytes. 
 
Lyophobic colloids:  
Colloidal solutions in which there is no affinity between particles of the dispersed phase 
and the dispersion medium are called lyophobic colloids. These are irreversible in nature. 
These are unstable and can be easily coagulated on addition of a small amount of 
electrolyte due to the lack of protecting layer around the charged colloidal particles. 
 
 
 
 
 
 
  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
12.  
S. No. Point of 
difference 
Physiosorption Chemisorption 
(i) Specificity It is not specific in nature. It is highly specific in nature. 
(ii) Temperature 
Dependence 
Usually occurs at low 
temperature and decreases 
with an increase in 
temperature. 
Occurs at high temperature 
and increases with the 
increase in temperature. 
(iii) Reversibility It is reversible in nature. It is irreversible in nature. 
(iv) Enthalpy 
change 
Enthalpy of adsorption is 
low; it is of the order of 20–
40 KJmol
-1
. 
Enthalpy of adsorption is high; 
it is of the order of 80–240 
KJmol
-1
. 
 
13.  
(a) Dilute solution (0.5%) of NaCN or KCN is used for leaching of silver metal in the presence 
of air in the metallurgy of silver. 
(b) Out of C and CO, CO is a better reducing agent at the lower temperature range because the 
CO, CO2 line lies below the Fe, FeO line, i.e. ?G
(CO, CO
2) 
< ?G
(Fe, FeO)
. So, CO will reduce FeO 
and will itself be oxidised to CO2. 
 
14.  
(i) PCl5 on heating decomposes to give PCl3 and Cl2 
5   3 2
  PCl PCl Cl ? ? 
(ii) H3PO3 on heating gives orthophosphoric acid and phosphine 
3 3 3 4 3
4H PO  3H PO PH ?? 
15.  
(a) Cu metal in the first transition series (3d series) shows the +1 oxidation state most 
frequently. This is because the electronic configuration of Cu is 3d
10 
4s
1 
and after 
losing one electron, it acquires the stable 3d
10 
fully filled electronic configuration. 
 
(b) The colour of cations is dependent on the number of unpaired electrons present in the 
d-orbital. The electronic configuration of the following cations is 
(c)  
Sc (Z = 21) = 3d
1 
4s
2 
and Sc
3+ 
= 3d
0 
4s
0
 
As the d-orbital is empty, it is colourless. 
 
V (Z = 23) = 3d
3 
4s
2 
and V
3+ 
= 3d
2 
4s
0
  
As the d-orbital has 2 unpaired electrons, it undergoes d–d transition and is green. 
  
 
CBSE XII  |  Chemistry  
Board Paper Solution - 2013 
 
  
Ti (Z = 22) = 3d
2 
4s
2 
and Ti
4+ 
= 3d
0 
4s
0
.  
As the d-orbital is empty, it is colourless. 
 
Mn (Z =25) = 3d
5
4s
2 
and Mn
2+ 
=3d
5 
4s
0
.  
As the d-orbital has 5 unpaired electrons, it is pink. 
 
16. Chlorobenzene is less reactive towards a nucleophilic substitution reaction because  
of the following reasons: 
? Resonance effect: The electron pair on the chlorine atom is in conjugation with the p 
electrons of the benzene ring which results in the following resonance structures: 
 
 
It results in delocalisation of the electrons of C–Cl bond and a partial double bond 
character develops in the bond, which makes it difficult for the nucleophile to cleave 
the C–Cl bond. 
? Polarity of the C–Cl bond: The sp
2 
hybridised carbon atom involved in C–Cl bond in 
chlorobenzene is more electronegative than the sp
3 
hybrid carbon atom in alkyl halide. 
Therefore, this sp
2 
hybridised carbon atom has less tendency to release electrons to the 
Cl atom. Thus, lower the polarity of C–Cl, lesser is the reactivity. 
 
17. Mechanism for the reaction: 
 
 
 
 
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