Chemistry: CBSE Marking Scheme with Solution (2019-20) Notes | EduRev

 Page 1


   MS CLASS XII CHEMISTRY 2019-20 
Q.No. Value points Marks  
 SECTION:A  
1. Reaction taking place at cathode when the battery is in use: 
) ( 2 ) ( 2 ) ( 4 ) ( ) (
2 4
2
4 2
l O H s PbSO e aq H aq SO s PbO ? ? ? ? ?
? ? ?
 
 
 
 
1 
2. 2 F  
 
1 
3. 
M Molarity 02 . 5
100 98
1000 294 . 1 38
?
?
? ?
? 
1 
4. It can be recharged after use. 
 
1 
 
5. At anode: O
2
 (g)  
At cathode: H
2
 (g) 
 
½ 
½ 
 
6. Sodium cyanide. 1 
7. Nucleotide  
              
1 
8. Zwitterion / dipolar ion 1 
9. Condensation  1 
10. Benzaldehyde 1 
11. (c) 1 
12. (b) 1 
13. (b) 1 
14. (a) 1 
15. (b) 1 
16. (c) 1 
17. (a) 1 
18. (d) 1 
19. (d) 1 
20. (d) 1 
 SECTION:B  
21. Lone pairs : 2 
Geometry : Square planar 
1 
1 
22. 
(i) 
 
(ii) 
R
E
Slope
a
303 . 2
? ?
 
 
k 
1
> k
2
 
1 
 
 
 
1 
23. When there is dissociation of solute into ions, in dilute solutions (ignoring 
interionic attractions) the number of particles increases. As the value of 
colligative properties depends on the number of particles of the solute , the 
experimentally observed  value of colligative property will be higher than 
the true value, therefore the experimentally determined (observed) molar 
mass is always lower than the true value. 
 
For KCl(electrolyte) the experimentally determined molar mass is always 
1 
 
 
 
 
 
 
½ 
Page 2


   MS CLASS XII CHEMISTRY 2019-20 
Q.No. Value points Marks  
 SECTION:A  
1. Reaction taking place at cathode when the battery is in use: 
) ( 2 ) ( 2 ) ( 4 ) ( ) (
2 4
2
4 2
l O H s PbSO e aq H aq SO s PbO ? ? ? ? ?
? ? ?
 
 
 
 
1 
2. 2 F  
 
1 
3. 
M Molarity 02 . 5
100 98
1000 294 . 1 38
?
?
? ?
? 
1 
4. It can be recharged after use. 
 
1 
 
5. At anode: O
2
 (g)  
At cathode: H
2
 (g) 
 
½ 
½ 
 
6. Sodium cyanide. 1 
7. Nucleotide  
              
1 
8. Zwitterion / dipolar ion 1 
9. Condensation  1 
10. Benzaldehyde 1 
11. (c) 1 
12. (b) 1 
13. (b) 1 
14. (a) 1 
15. (b) 1 
16. (c) 1 
17. (a) 1 
18. (d) 1 
19. (d) 1 
20. (d) 1 
 SECTION:B  
21. Lone pairs : 2 
Geometry : Square planar 
1 
1 
22. 
(i) 
 
(ii) 
R
E
Slope
a
303 . 2
? ?
 
 
k 
1
> k
2
 
1 
 
 
 
1 
23. When there is dissociation of solute into ions, in dilute solutions (ignoring 
interionic attractions) the number of particles increases. As the value of 
colligative properties depends on the number of particles of the solute , the 
experimentally observed  value of colligative property will be higher than 
the true value, therefore the experimentally determined (observed) molar 
mass is always lower than the true value. 
 
For KCl(electrolyte) the experimentally determined molar mass is always 
1 
 
 
 
 
 
 
½ 
lower than the true value when water is used as solvent. 
 Glucose (non-electrolyte) does not show a large variation from the true 
value. 
 
½ 
24. 
(a) 
 
 
(b) 
 
CH3-CH(Cl)-COOH 
 
C6H5CHO 
 
 
 
1 
 
 
1 
25.  
 
 
IUPAC Name of the entity:  
Dichloridobis(ethane-1,2-diamine)platinum(IV) ion 
 
OR 
Bonding in   
? 3
6 3
] ) ( [ NH CO
 
d
2
sp
3
 hybridisation
 
  
   
 
Geometry: Octahedral      
   
Diamagnetic         
1 
 
 
 
 
 
 
 
 
 
 
 
 
 
1 
 
 
 
½ 
 
 
 
½ 
 
 
 
 
 
½ 
 
½ 
 
 
26. Vapour phase refining: It is a refining method in which the metal is 
converted into its volatile compound and collected elsewhere. It is then 
decomposed to give pure metal.                              
Example:Mond’s Process for refining of Nickel / van Arkel method for 
refining of Zirconium         
   
1 
 
 
1 
 
 
Page 3


   MS CLASS XII CHEMISTRY 2019-20 
Q.No. Value points Marks  
 SECTION:A  
1. Reaction taking place at cathode when the battery is in use: 
) ( 2 ) ( 2 ) ( 4 ) ( ) (
2 4
2
4 2
l O H s PbSO e aq H aq SO s PbO ? ? ? ? ?
? ? ?
 
 
 
 
1 
2. 2 F  
 
1 
3. 
M Molarity 02 . 5
100 98
1000 294 . 1 38
?
?
? ?
? 
1 
4. It can be recharged after use. 
 
1 
 
5. At anode: O
2
 (g)  
At cathode: H
2
 (g) 
 
½ 
½ 
 
6. Sodium cyanide. 1 
7. Nucleotide  
              
1 
8. Zwitterion / dipolar ion 1 
9. Condensation  1 
10. Benzaldehyde 1 
11. (c) 1 
12. (b) 1 
13. (b) 1 
14. (a) 1 
15. (b) 1 
16. (c) 1 
17. (a) 1 
18. (d) 1 
19. (d) 1 
20. (d) 1 
 SECTION:B  
21. Lone pairs : 2 
Geometry : Square planar 
1 
1 
22. 
(i) 
 
(ii) 
R
E
Slope
a
303 . 2
? ?
 
 
k 
1
> k
2
 
1 
 
 
 
1 
23. When there is dissociation of solute into ions, in dilute solutions (ignoring 
interionic attractions) the number of particles increases. As the value of 
colligative properties depends on the number of particles of the solute , the 
experimentally observed  value of colligative property will be higher than 
the true value, therefore the experimentally determined (observed) molar 
mass is always lower than the true value. 
 
For KCl(electrolyte) the experimentally determined molar mass is always 
1 
 
 
 
 
 
 
½ 
lower than the true value when water is used as solvent. 
 Glucose (non-electrolyte) does not show a large variation from the true 
value. 
 
½ 
24. 
(a) 
 
 
(b) 
 
CH3-CH(Cl)-COOH 
 
C6H5CHO 
 
 
 
1 
 
 
1 
25.  
 
 
IUPAC Name of the entity:  
Dichloridobis(ethane-1,2-diamine)platinum(IV) ion 
 
OR 
Bonding in   
? 3
6 3
] ) ( [ NH CO
 
d
2
sp
3
 hybridisation
 
  
   
 
Geometry: Octahedral      
   
Diamagnetic         
1 
 
 
 
 
 
 
 
 
 
 
 
 
 
1 
 
 
 
½ 
 
 
 
½ 
 
 
 
 
 
½ 
 
½ 
 
 
26. Vapour phase refining: It is a refining method in which the metal is 
converted into its volatile compound and collected elsewhere. It is then 
decomposed to give pure metal.                              
Example:Mond’s Process for refining of Nickel / van Arkel method for 
refining of Zirconium         
   
1 
 
 
1 
 
 
Equations involved: 
4
350 330
) ( 4 CO Ni CO Ni
K
? ? ? ? ? ?
?
     
   
CO Ni CO Ni
K
4 ) (
470 450
4
? ? ? ? ? ?
?
      
  
OR 
Extraction of gold involves leaching the metal with CN
-
 
Oxidation reaction: 
4 Au (s) + 8 CN- (aq.) + 2H
2
O (aq.) + O
2
 (g) ?4[Au(CN)
2
]
-
(aq.) + 4 OH
-
 
                                                                                                               (aq.) 
 The metal is recovered by displacement method: 
2[Au(CN)
2
]- (aq.) + Zn (s) ? 2 Au (s) + [Zn(CN)
4
]
2-
 (aq.) 
 
Zinc acts as a reducing agent.
 
 
½ 
 
½ 
 
 
 
½ 
 
½ 
 
½ 
 
½ 
 
27. The following compound will undergo S
N
1 faster: 
CH
2
Cl
 
Greater the stability of the carbocation, greater will be its ease of formation 
from the corresponding halide and faster will be the rate of reaction. 
The benzylic carbocation formed gets stabilised through resonance. 
 
 
CH
3
CH
2
CH
2
Cl forms a 1
0
 carbocation, which is less stable than benzylic 
carbocation. 
 
 
 
 
 
 
½ 
 
 
 
 
½ 
 
 
 
 
 
½ 
 
 
 
 
 
 
 
 
 
 
½ 
 
 SECTION :C  
28. KCl  ?  K
+
 + Cl
-
 
n =2 
?
? ?
? ?
? ? ?
1
1
i
n i
 
 
½ 
 
½ 
½ 
 
Page 4


   MS CLASS XII CHEMISTRY 2019-20 
Q.No. Value points Marks  
 SECTION:A  
1. Reaction taking place at cathode when the battery is in use: 
) ( 2 ) ( 2 ) ( 4 ) ( ) (
2 4
2
4 2
l O H s PbSO e aq H aq SO s PbO ? ? ? ? ?
? ? ?
 
 
 
 
1 
2. 2 F  
 
1 
3. 
M Molarity 02 . 5
100 98
1000 294 . 1 38
?
?
? ?
? 
1 
4. It can be recharged after use. 
 
1 
 
5. At anode: O
2
 (g)  
At cathode: H
2
 (g) 
 
½ 
½ 
 
6. Sodium cyanide. 1 
7. Nucleotide  
              
1 
8. Zwitterion / dipolar ion 1 
9. Condensation  1 
10. Benzaldehyde 1 
11. (c) 1 
12. (b) 1 
13. (b) 1 
14. (a) 1 
15. (b) 1 
16. (c) 1 
17. (a) 1 
18. (d) 1 
19. (d) 1 
20. (d) 1 
 SECTION:B  
21. Lone pairs : 2 
Geometry : Square planar 
1 
1 
22. 
(i) 
 
(ii) 
R
E
Slope
a
303 . 2
? ?
 
 
k 
1
> k
2
 
1 
 
 
 
1 
23. When there is dissociation of solute into ions, in dilute solutions (ignoring 
interionic attractions) the number of particles increases. As the value of 
colligative properties depends on the number of particles of the solute , the 
experimentally observed  value of colligative property will be higher than 
the true value, therefore the experimentally determined (observed) molar 
mass is always lower than the true value. 
 
For KCl(electrolyte) the experimentally determined molar mass is always 
1 
 
 
 
 
 
 
½ 
lower than the true value when water is used as solvent. 
 Glucose (non-electrolyte) does not show a large variation from the true 
value. 
 
½ 
24. 
(a) 
 
 
(b) 
 
CH3-CH(Cl)-COOH 
 
C6H5CHO 
 
 
 
1 
 
 
1 
25.  
 
 
IUPAC Name of the entity:  
Dichloridobis(ethane-1,2-diamine)platinum(IV) ion 
 
OR 
Bonding in   
? 3
6 3
] ) ( [ NH CO
 
d
2
sp
3
 hybridisation
 
  
   
 
Geometry: Octahedral      
   
Diamagnetic         
1 
 
 
 
 
 
 
 
 
 
 
 
 
 
1 
 
 
 
½ 
 
 
 
½ 
 
 
 
 
 
½ 
 
½ 
 
 
26. Vapour phase refining: It is a refining method in which the metal is 
converted into its volatile compound and collected elsewhere. It is then 
decomposed to give pure metal.                              
Example:Mond’s Process for refining of Nickel / van Arkel method for 
refining of Zirconium         
   
1 
 
 
1 
 
 
Equations involved: 
4
350 330
) ( 4 CO Ni CO Ni
K
? ? ? ? ? ?
?
     
   
CO Ni CO Ni
K
4 ) (
470 450
4
? ? ? ? ? ?
?
      
  
OR 
Extraction of gold involves leaching the metal with CN
-
 
Oxidation reaction: 
4 Au (s) + 8 CN- (aq.) + 2H
2
O (aq.) + O
2
 (g) ?4[Au(CN)
2
]
-
(aq.) + 4 OH
-
 
                                                                                                               (aq.) 
 The metal is recovered by displacement method: 
2[Au(CN)
2
]- (aq.) + Zn (s) ? 2 Au (s) + [Zn(CN)
4
]
2-
 (aq.) 
 
Zinc acts as a reducing agent.
 
 
½ 
 
½ 
 
 
 
½ 
 
½ 
 
½ 
 
½ 
 
27. The following compound will undergo S
N
1 faster: 
CH
2
Cl
 
Greater the stability of the carbocation, greater will be its ease of formation 
from the corresponding halide and faster will be the rate of reaction. 
The benzylic carbocation formed gets stabilised through resonance. 
 
 
CH
3
CH
2
CH
2
Cl forms a 1
0
 carbocation, which is less stable than benzylic 
carbocation. 
 
 
 
 
 
 
½ 
 
 
 
 
½ 
 
 
 
 
 
½ 
 
 
 
 
 
 
 
 
 
 
½ 
 
 SECTION :C  
28. KCl  ?  K
+
 + Cl
-
 
n =2 
?
? ?
? ?
? ? ?
1
1
i
n i
 
 
½ 
 
½ 
½ 
 
C T
T T T
T
m iK T
f
f f f
f
f f
0 '
' 0
24 . 0
24 . 0
100 5 . 74
1000 5 . 0
86 . 1 ) 92 . 0 1 (
? ?
? ? ?
? ?
? ?
? ?
x
x
x x
 
 
½ 
 
½ 
 
 
½ 
 
 
29. 
) .......( ] 1 . 0 [ ] 2 . 0 [ 10 . 0
) ......( ] 1 . 0 [ ] 1 . 0 [ 05 . 0
] [ ] [
ii k
i k
B A k rate
y x
y x
y x
?
?
?
 
1
) 2 (
05 . 0
10 . 0
) ( ) (
) ......( ] 2 . 0 [ ] 1 . 0 [ 05 . 0
?
?
?
?
x
i ii
iii k
x
y x
 
0
) 2 (
05 . 0
05 . 0
) ( ) (
?
?
?
y
i iii
y
 
0 1
] [ ] [ B A k rate ?
 
It is a first order reaction. 
 
s t
k
t
s o
A
rate
k
386 . 1
5 . 0
693 . 0 693 . 0
5 .
] [
2
1
2
1
1
?
? ?
? ?
?
 
 
OR 
 
2
300
50
693 . 0
350
25
693 . 0
693 . 0
1
2
1
2
2
1
?
?
?
?
k
k
K k
K k
k
t
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
½ 
 
 
 
 
½ 
 
½ 
 
 
½ 
 
 
½ 
 
½ 
 
 
½ 
 
 
 
 
 
 
 
½ 
Page 5


   MS CLASS XII CHEMISTRY 2019-20 
Q.No. Value points Marks  
 SECTION:A  
1. Reaction taking place at cathode when the battery is in use: 
) ( 2 ) ( 2 ) ( 4 ) ( ) (
2 4
2
4 2
l O H s PbSO e aq H aq SO s PbO ? ? ? ? ?
? ? ?
 
 
 
 
1 
2. 2 F  
 
1 
3. 
M Molarity 02 . 5
100 98
1000 294 . 1 38
?
?
? ?
? 
1 
4. It can be recharged after use. 
 
1 
 
5. At anode: O
2
 (g)  
At cathode: H
2
 (g) 
 
½ 
½ 
 
6. Sodium cyanide. 1 
7. Nucleotide  
              
1 
8. Zwitterion / dipolar ion 1 
9. Condensation  1 
10. Benzaldehyde 1 
11. (c) 1 
12. (b) 1 
13. (b) 1 
14. (a) 1 
15. (b) 1 
16. (c) 1 
17. (a) 1 
18. (d) 1 
19. (d) 1 
20. (d) 1 
 SECTION:B  
21. Lone pairs : 2 
Geometry : Square planar 
1 
1 
22. 
(i) 
 
(ii) 
R
E
Slope
a
303 . 2
? ?
 
 
k 
1
> k
2
 
1 
 
 
 
1 
23. When there is dissociation of solute into ions, in dilute solutions (ignoring 
interionic attractions) the number of particles increases. As the value of 
colligative properties depends on the number of particles of the solute , the 
experimentally observed  value of colligative property will be higher than 
the true value, therefore the experimentally determined (observed) molar 
mass is always lower than the true value. 
 
For KCl(electrolyte) the experimentally determined molar mass is always 
1 
 
 
 
 
 
 
½ 
lower than the true value when water is used as solvent. 
 Glucose (non-electrolyte) does not show a large variation from the true 
value. 
 
½ 
24. 
(a) 
 
 
(b) 
 
CH3-CH(Cl)-COOH 
 
C6H5CHO 
 
 
 
1 
 
 
1 
25.  
 
 
IUPAC Name of the entity:  
Dichloridobis(ethane-1,2-diamine)platinum(IV) ion 
 
OR 
Bonding in   
? 3
6 3
] ) ( [ NH CO
 
d
2
sp
3
 hybridisation
 
  
   
 
Geometry: Octahedral      
   
Diamagnetic         
1 
 
 
 
 
 
 
 
 
 
 
 
 
 
1 
 
 
 
½ 
 
 
 
½ 
 
 
 
 
 
½ 
 
½ 
 
 
26. Vapour phase refining: It is a refining method in which the metal is 
converted into its volatile compound and collected elsewhere. It is then 
decomposed to give pure metal.                              
Example:Mond’s Process for refining of Nickel / van Arkel method for 
refining of Zirconium         
   
1 
 
 
1 
 
 
Equations involved: 
4
350 330
) ( 4 CO Ni CO Ni
K
? ? ? ? ? ?
?
     
   
CO Ni CO Ni
K
4 ) (
470 450
4
? ? ? ? ? ?
?
      
  
OR 
Extraction of gold involves leaching the metal with CN
-
 
Oxidation reaction: 
4 Au (s) + 8 CN- (aq.) + 2H
2
O (aq.) + O
2
 (g) ?4[Au(CN)
2
]
-
(aq.) + 4 OH
-
 
                                                                                                               (aq.) 
 The metal is recovered by displacement method: 
2[Au(CN)
2
]- (aq.) + Zn (s) ? 2 Au (s) + [Zn(CN)
4
]
2-
 (aq.) 
 
Zinc acts as a reducing agent.
 
 
½ 
 
½ 
 
 
 
½ 
 
½ 
 
½ 
 
½ 
 
27. The following compound will undergo S
N
1 faster: 
CH
2
Cl
 
Greater the stability of the carbocation, greater will be its ease of formation 
from the corresponding halide and faster will be the rate of reaction. 
The benzylic carbocation formed gets stabilised through resonance. 
 
 
CH
3
CH
2
CH
2
Cl forms a 1
0
 carbocation, which is less stable than benzylic 
carbocation. 
 
 
 
 
 
 
½ 
 
 
 
 
½ 
 
 
 
 
 
½ 
 
 
 
 
 
 
 
 
 
 
½ 
 
 SECTION :C  
28. KCl  ?  K
+
 + Cl
-
 
n =2 
?
? ?
? ?
? ? ?
1
1
i
n i
 
 
½ 
 
½ 
½ 
 
C T
T T T
T
m iK T
f
f f f
f
f f
0 '
' 0
24 . 0
24 . 0
100 5 . 74
1000 5 . 0
86 . 1 ) 92 . 0 1 (
? ?
? ? ?
? ?
? ?
? ?
x
x
x x
 
 
½ 
 
½ 
 
 
½ 
 
 
29. 
) .......( ] 1 . 0 [ ] 2 . 0 [ 10 . 0
) ......( ] 1 . 0 [ ] 1 . 0 [ 05 . 0
] [ ] [
ii k
i k
B A k rate
y x
y x
y x
?
?
?
 
1
) 2 (
05 . 0
10 . 0
) ( ) (
) ......( ] 2 . 0 [ ] 1 . 0 [ 05 . 0
?
?
?
?
x
i ii
iii k
x
y x
 
0
) 2 (
05 . 0
05 . 0
) ( ) (
?
?
?
y
i iii
y
 
0 1
] [ ] [ B A k rate ?
 
It is a first order reaction. 
 
s t
k
t
s o
A
rate
k
386 . 1
5 . 0
693 . 0 693 . 0
5 .
] [
2
1
2
1
1
?
? ?
? ?
?
 
 
OR 
 
2
300
50
693 . 0
350
25
693 . 0
693 . 0
1
2
1
2
2
1
?
?
?
?
k
k
K k
K k
k
t
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
½ 
 
 
 
 
½ 
 
½ 
 
 
½ 
 
 
½ 
 
½ 
 
 
½ 
 
 
 
 
 
 
 
½ 
 
?
?
?
?
?
? ?
?
?
?
?
?
?
?
? ?
300 350
300 350
314 . 8 303 . 2
2 log
1 1
303 . 2
log
2 1 1
2
x x
a
a
E
T T R
E
k
k
 
 
 Ea = 12.104 kJ / mol. 
 
 
½ 
 
 
½ 
 
 
(1/2 
+1/2) 
30. 
 
(a) 
 
(b) 
 
 
(c) 
 
K
4
[Fe(CN)
6
] 
Fe(OH)
3
  is converted into colloidal state by preferential adsorption of Fe
3+
 
ions. 
Proteins 
 
 
 
1 
 
1 
 
 
1 
31. 
(a) 
 
(b) 
 
(c) 
 
 
 
 
 
 
Moist sulphur dioxide behaves as a reducing agent, reduces MnO
4
-
 to Mn
2+
. 
X –X’ bond in interhalogens is weaker than X-X bond in halogensexcept F-
F bond. 
 
Due to the ease with which it liberates atoms of nascent oxygen. 
 
 
1 
 
1 
 
1 
 
32. 1-Propoxypropane is formed. 
Mechanism involved: 
Step 1 :Formation of protonated alcohol 
 
 
 
1 
 
½ 
 
 
 
1 
 
 
 
 
½ 
 
33. 
(a) 
(i)