Electrochemistry Solved Examples | Chemistry for JEE Main & Advanced PDF Download

 Page 1


Solved Examples on Electrochemistry 
JEE Mains 
Q. 1 One gm. metal ?? +?? was discharged by the passage of ?? . ???? × ????
????
 electrons. 
What is the atomic weight of metal? 
(A) 33.35 
(B) 133.4 
(C) 66.7 
(D) 55 
Ans: Zn
( ?? )
|Zn
( aq)
2+
||Ag
( aq)
+
|Ag
( s)
 
(i) Zinc electrode is negatively charged 
(ii) At anode: 
Zn( s) ? Zn
(aq) 
2+
+ 2e
-
 
At cathode 
Ag
+
( aq )+ e
-
? Ag ( s) 
 
Q2. The equilibrium constant for the reaction ???? ( ?? )+ ????
+?? ( ???? ) ? ????
+?? ( ???? )+ ???? ( ?? ) 
is ?? . ???? × ????
????
 at ????
°
?? 
Ans: ?
?? = 1000×
?? ?? =
1000×7.896×10
-5
0.00241
 
 ?
?? = 32.765 cm
2
 mol
-1
q =
?
m
?
?? 
m
=
32.76
390.5
?? = 0.084
k
a
=
C?? 2
1 - ?? ; k
a
= 2.2 × 10
-4
 
 
Q3. The ?? °
 for a cell made up of the ???? /????
+?? and ????
+?? /???? half-cells 
(A) ?? . ???????? ?? 
(B) ?? . ???????? ?? 
(C) ?? . ???????? ?? 
(D) ?? . ???????? ?? 
Ans: (A) We have, 
?? °
=
0.0591
2
log ?? ?? ?? °
=
0.0591
2
log ( 2.69 × 10
12
)= 0.3667 V
 
 
Page 2


Solved Examples on Electrochemistry 
JEE Mains 
Q. 1 One gm. metal ?? +?? was discharged by the passage of ?? . ???? × ????
????
 electrons. 
What is the atomic weight of metal? 
(A) 33.35 
(B) 133.4 
(C) 66.7 
(D) 55 
Ans: Zn
( ?? )
|Zn
( aq)
2+
||Ag
( aq)
+
|Ag
( s)
 
(i) Zinc electrode is negatively charged 
(ii) At anode: 
Zn( s) ? Zn
(aq) 
2+
+ 2e
-
 
At cathode 
Ag
+
( aq )+ e
-
? Ag ( s) 
 
Q2. The equilibrium constant for the reaction ???? ( ?? )+ ????
+?? ( ???? ) ? ????
+?? ( ???? )+ ???? ( ?? ) 
is ?? . ???? × ????
????
 at ????
°
?? 
Ans: ?
?? = 1000×
?? ?? =
1000×7.896×10
-5
0.00241
 
 ?
?? = 32.765 cm
2
 mol
-1
q =
?
m
?
?? 
m
=
32.76
390.5
?? = 0.084
k
a
=
C?? 2
1 - ?? ; k
a
= 2.2 × 10
-4
 
 
Q3. The ?? °
 for a cell made up of the ???? /????
+?? and ????
+?? /???? half-cells 
(A) ?? . ???????? ?? 
(B) ?? . ???????? ?? 
(C) ?? . ???????? ?? 
(D) ?? . ???????? ?? 
Ans: (A) We have, 
?? °
=
0.0591
2
log ?? ?? ?? °
=
0.0591
2
log ( 2.69 × 10
12
)= 0.3667 V
 
 
Q4.  During electrolysis of an aqueous solution of ???????? ?? using copper 
electrodes, if ?? . ?? ?? of ???? is deposited at cathode, then at anode 
(A) ?????????? of ????
?? at STP is liberated 
(B) ?????????? of ?? ?? at STP is liberated 
(C) ?? . ?? ?? of copper is deposited 
(D) A decrease of ?? . ?? ?? of mass takes place 
Ans: (B) At cathode 
Cu
2+
+ 2e
-
? Cu 
At anode 
2H
2
O ? O
2
+ 4H
+
+ 4e
-
Moles n
O
2
=
1
2
nC
2
 V
O
2
= 22400 n
O
2
= 22400×
1
2
×
2.5
63.5
= 441 mL
 ˜ 445 mLO
2
 is liberated 
 
 
Q5.  The cost at 5 paise / KWH of operating an electric motor for 8 hours which 
takes ?????????? at ?????? ?? is 
(A) Rs 66 
(B) 66 paise 
(C) 37 paise 
(D) Rs. 6.60 
Ans: (B) ?? = ???? 
?? = 1.65 kW
?? = 1.65 × 8kWh = 13.2kWh
 Cost = 13.2 × 5 paise = 66 paise 
 
 
Q6.  Equivalent conductance of ?? . ???????? (weak acid) solution is ???? ?? ????
?? 
equivalent  
-?? and that at infinite dilution is ?????? ?? ????
?? equivalent  
-?? Hence ???? of 
HA solution is 
(A) 1.3 
(B) 1.7 
(C) 2.3 
(D) 3.7 
Ans: (C) ?? =
?
?? ?
?? 0
=
10
200
= 0.05 
[H
+
] = C?? = 0.005
pH = -log [H
+
] = log [200 ] = 2.3
 
 
 
Page 3


Solved Examples on Electrochemistry 
JEE Mains 
Q. 1 One gm. metal ?? +?? was discharged by the passage of ?? . ???? × ????
????
 electrons. 
What is the atomic weight of metal? 
(A) 33.35 
(B) 133.4 
(C) 66.7 
(D) 55 
Ans: Zn
( ?? )
|Zn
( aq)
2+
||Ag
( aq)
+
|Ag
( s)
 
(i) Zinc electrode is negatively charged 
(ii) At anode: 
Zn( s) ? Zn
(aq) 
2+
+ 2e
-
 
At cathode 
Ag
+
( aq )+ e
-
? Ag ( s) 
 
Q2. The equilibrium constant for the reaction ???? ( ?? )+ ????
+?? ( ???? ) ? ????
+?? ( ???? )+ ???? ( ?? ) 
is ?? . ???? × ????
????
 at ????
°
?? 
Ans: ?
?? = 1000×
?? ?? =
1000×7.896×10
-5
0.00241
 
 ?
?? = 32.765 cm
2
 mol
-1
q =
?
m
?
?? 
m
=
32.76
390.5
?? = 0.084
k
a
=
C?? 2
1 - ?? ; k
a
= 2.2 × 10
-4
 
 
Q3. The ?? °
 for a cell made up of the ???? /????
+?? and ????
+?? /???? half-cells 
(A) ?? . ???????? ?? 
(B) ?? . ???????? ?? 
(C) ?? . ???????? ?? 
(D) ?? . ???????? ?? 
Ans: (A) We have, 
?? °
=
0.0591
2
log ?? ?? ?? °
=
0.0591
2
log ( 2.69 × 10
12
)= 0.3667 V
 
 
Q4.  During electrolysis of an aqueous solution of ???????? ?? using copper 
electrodes, if ?? . ?? ?? of ???? is deposited at cathode, then at anode 
(A) ?????????? of ????
?? at STP is liberated 
(B) ?????????? of ?? ?? at STP is liberated 
(C) ?? . ?? ?? of copper is deposited 
(D) A decrease of ?? . ?? ?? of mass takes place 
Ans: (B) At cathode 
Cu
2+
+ 2e
-
? Cu 
At anode 
2H
2
O ? O
2
+ 4H
+
+ 4e
-
Moles n
O
2
=
1
2
nC
2
 V
O
2
= 22400 n
O
2
= 22400×
1
2
×
2.5
63.5
= 441 mL
 ˜ 445 mLO
2
 is liberated 
 
 
Q5.  The cost at 5 paise / KWH of operating an electric motor for 8 hours which 
takes ?????????? at ?????? ?? is 
(A) Rs 66 
(B) 66 paise 
(C) 37 paise 
(D) Rs. 6.60 
Ans: (B) ?? = ???? 
?? = 1.65 kW
?? = 1.65 × 8kWh = 13.2kWh
 Cost = 13.2 × 5 paise = 66 paise 
 
 
Q6.  Equivalent conductance of ?? . ???????? (weak acid) solution is ???? ?? ????
?? 
equivalent  
-?? and that at infinite dilution is ?????? ?? ????
?? equivalent  
-?? Hence ???? of 
HA solution is 
(A) 1.3 
(B) 1.7 
(C) 2.3 
(D) 3.7 
Ans: (C) ?? =
?
?? ?
?? 0
=
10
200
= 0.05 
[H
+
] = C?? = 0.005
pH = -log [H
+
] = log [200 ] = 2.3
 
 
 
 
Q7.  For the cell 
???? ? ??? ?? ( ?? . ?? ?????? ) |?? +
( ???? = ?? ) ? ?? +
( ???? = ?? ) |?? ?? ( ?? . ?? ?????? ) | ???? 
The measured potential at ????
°
?? is 
(A) -?? . ?? ?? 
(B) -0.5 
(C) -0.041 
(D) None of these 
Ans: (C) At cathode, 
H
+
+ e
-
?
1
2
H
2
 
At anode 
1
2
H
2
? H
+
+ e
-
1
2
H
2
+ H
+
?
1
2
H
2
+ H
+
0.410
-20
? 10
-1
E = -0.0591log 
10
-1
· ( 0.1)
1/2
10
-2
· ( 0.4)
1/2
E = -0.041 V
 
 
Q8. For the fuel cell reaction: 
?? ?? ?? ( ?? )+ ?? ?? ( ?? ) ? ?? ?? ?? ?? ( ?? ) ; ?? ?? ?? ??????
°
( ?? ?? ?? ( ?? )= -?????? . ?????? /???????? 
What is ?? ?? ??????
°
 for the given fuel cell reaction? 
Given ?? ?? ( ?? )+ ?? ?? +
( ???? )+ ?? ?? -
? ?? ?? ?? ?? (I) ?? °
= ?? . ???? ?? 
(A) -?? . ?????? ?? /?? 
(B) -?? . ?????? ???? /?? 
(C) ?? . ???? ???? /?? 
(D) -?? . ?????? ???? /?? 
Ans: (D) O
2
( g)+ 4H
+
( aq )+ 4e
-
? 2H
2
O( l) 
?? °
= 1.23 V
??? °
= -?????? = -474.78 kJ
??? ?? ( ?? 2
) = 0
??? ?? = 2??? 4
( ?? 2
?? 1
l) = -2 × 285.5 kJ = -571 kJ
??? = ??? - ?? ??? ??? =
??? - ??? ?? = -0.322 kJ/k
 
 
 
Page 4


Solved Examples on Electrochemistry 
JEE Mains 
Q. 1 One gm. metal ?? +?? was discharged by the passage of ?? . ???? × ????
????
 electrons. 
What is the atomic weight of metal? 
(A) 33.35 
(B) 133.4 
(C) 66.7 
(D) 55 
Ans: Zn
( ?? )
|Zn
( aq)
2+
||Ag
( aq)
+
|Ag
( s)
 
(i) Zinc electrode is negatively charged 
(ii) At anode: 
Zn( s) ? Zn
(aq) 
2+
+ 2e
-
 
At cathode 
Ag
+
( aq )+ e
-
? Ag ( s) 
 
Q2. The equilibrium constant for the reaction ???? ( ?? )+ ????
+?? ( ???? ) ? ????
+?? ( ???? )+ ???? ( ?? ) 
is ?? . ???? × ????
????
 at ????
°
?? 
Ans: ?
?? = 1000×
?? ?? =
1000×7.896×10
-5
0.00241
 
 ?
?? = 32.765 cm
2
 mol
-1
q =
?
m
?
?? 
m
=
32.76
390.5
?? = 0.084
k
a
=
C?? 2
1 - ?? ; k
a
= 2.2 × 10
-4
 
 
Q3. The ?? °
 for a cell made up of the ???? /????
+?? and ????
+?? /???? half-cells 
(A) ?? . ???????? ?? 
(B) ?? . ???????? ?? 
(C) ?? . ???????? ?? 
(D) ?? . ???????? ?? 
Ans: (A) We have, 
?? °
=
0.0591
2
log ?? ?? ?? °
=
0.0591
2
log ( 2.69 × 10
12
)= 0.3667 V
 
 
Q4.  During electrolysis of an aqueous solution of ???????? ?? using copper 
electrodes, if ?? . ?? ?? of ???? is deposited at cathode, then at anode 
(A) ?????????? of ????
?? at STP is liberated 
(B) ?????????? of ?? ?? at STP is liberated 
(C) ?? . ?? ?? of copper is deposited 
(D) A decrease of ?? . ?? ?? of mass takes place 
Ans: (B) At cathode 
Cu
2+
+ 2e
-
? Cu 
At anode 
2H
2
O ? O
2
+ 4H
+
+ 4e
-
Moles n
O
2
=
1
2
nC
2
 V
O
2
= 22400 n
O
2
= 22400×
1
2
×
2.5
63.5
= 441 mL
 ˜ 445 mLO
2
 is liberated 
 
 
Q5.  The cost at 5 paise / KWH of operating an electric motor for 8 hours which 
takes ?????????? at ?????? ?? is 
(A) Rs 66 
(B) 66 paise 
(C) 37 paise 
(D) Rs. 6.60 
Ans: (B) ?? = ???? 
?? = 1.65 kW
?? = 1.65 × 8kWh = 13.2kWh
 Cost = 13.2 × 5 paise = 66 paise 
 
 
Q6.  Equivalent conductance of ?? . ???????? (weak acid) solution is ???? ?? ????
?? 
equivalent  
-?? and that at infinite dilution is ?????? ?? ????
?? equivalent  
-?? Hence ???? of 
HA solution is 
(A) 1.3 
(B) 1.7 
(C) 2.3 
(D) 3.7 
Ans: (C) ?? =
?
?? ?
?? 0
=
10
200
= 0.05 
[H
+
] = C?? = 0.005
pH = -log [H
+
] = log [200 ] = 2.3
 
 
 
 
Q7.  For the cell 
???? ? ??? ?? ( ?? . ?? ?????? ) |?? +
( ???? = ?? ) ? ?? +
( ???? = ?? ) |?? ?? ( ?? . ?? ?????? ) | ???? 
The measured potential at ????
°
?? is 
(A) -?? . ?? ?? 
(B) -0.5 
(C) -0.041 
(D) None of these 
Ans: (C) At cathode, 
H
+
+ e
-
?
1
2
H
2
 
At anode 
1
2
H
2
? H
+
+ e
-
1
2
H
2
+ H
+
?
1
2
H
2
+ H
+
0.410
-20
? 10
-1
E = -0.0591log 
10
-1
· ( 0.1)
1/2
10
-2
· ( 0.4)
1/2
E = -0.041 V
 
 
Q8. For the fuel cell reaction: 
?? ?? ?? ( ?? )+ ?? ?? ( ?? ) ? ?? ?? ?? ?? ( ?? ) ; ?? ?? ?? ??????
°
( ?? ?? ?? ( ?? )= -?????? . ?????? /???????? 
What is ?? ?? ??????
°
 for the given fuel cell reaction? 
Given ?? ?? ( ?? )+ ?? ?? +
( ???? )+ ?? ?? -
? ?? ?? ?? ?? (I) ?? °
= ?? . ???? ?? 
(A) -?? . ?????? ?? /?? 
(B) -?? . ?????? ???? /?? 
(C) ?? . ???? ???? /?? 
(D) -?? . ?????? ???? /?? 
Ans: (D) O
2
( g)+ 4H
+
( aq )+ 4e
-
? 2H
2
O( l) 
?? °
= 1.23 V
??? °
= -?????? = -474.78 kJ
??? ?? ( ?? 2
) = 0
??? ?? = 2??? 4
( ?? 2
?? 1
l) = -2 × 285.5 kJ = -571 kJ
??? = ??? - ?? ??? ??? =
??? - ??? ?? = -0.322 kJ/k
 
 
 
 
Q9.  The standard reduction potentials of ????
?? +
/???? and ????
?? +
/????
+
are 0.337 and 
?? . ?????? ?? respectively. The standard electrode potential of ????
+
/???? half-cell is: 
(A) ?? . ?????? ?? 
(B) ?? . ?????? ?? 
(C) ?? . ?????? ?? 
(D) ?? . ?????? ?? 
Ans: (C) Cu
2+
+ 2e
-
? Cu
2
; E
°
= 0.337 
?G
1
°
= -nFE
°
= -0.674 F
Cu
2+
+ eCu
+
; E
°
= 0.153
Cu
+
? Cu
2+
+ e
-
; E
°
= -0.153
?G
2
a
= -nFE
°
= +0.153 F
 
Adding, 
Cu
+
+ e
-
? Cu
?G = ?G
1
o
+ ?G
2
s
 -FE
°
= -0.674 F + 0.153 F
E
°
= 0.521 V
 
 
Q10.  One mole of electron passes through each of the solution of ???????? ?? , ???????? ?? 
and ???????? ?? when ???? , ???? and ???? are deposited at cathode. The molar ratio of ???? , ???? 
and ???? deposited are: 
(A) ?? : ?? : ?? 
(B) ?? : ?? : ?? 
(C) 6:3:1 
(D) ?? : ?? : ?? 
Ans: ?
m
=
?? ×1000
?? =
2.48×10
-2
×1000
0.2
 ?
m
= 124O
-1
 cm
2
 mol
-1
 
 
Q11.  Salts of A (atomic weight = ?? ), B (atomic weight = 27) and ?? (atomic 
weight = ???? ) were electrolyzed under identical conditions using the same 
quantity of electricity. It was found that when ?? . ?? ?? of A was deposited, the 
weights of B and C deposited were 2.7 and ?? . ?? ?? . The valencies of ?? , ?? and ?? 
respectively are: 
(A) 3,1 and 2 
(B) 1, 3 and 2 
(C) 3, 1 and 3 
(D) 2, 3 and 2 
Ans: (i) Reaction: 
Page 5


Solved Examples on Electrochemistry 
JEE Mains 
Q. 1 One gm. metal ?? +?? was discharged by the passage of ?? . ???? × ????
????
 electrons. 
What is the atomic weight of metal? 
(A) 33.35 
(B) 133.4 
(C) 66.7 
(D) 55 
Ans: Zn
( ?? )
|Zn
( aq)
2+
||Ag
( aq)
+
|Ag
( s)
 
(i) Zinc electrode is negatively charged 
(ii) At anode: 
Zn( s) ? Zn
(aq) 
2+
+ 2e
-
 
At cathode 
Ag
+
( aq )+ e
-
? Ag ( s) 
 
Q2. The equilibrium constant for the reaction ???? ( ?? )+ ????
+?? ( ???? ) ? ????
+?? ( ???? )+ ???? ( ?? ) 
is ?? . ???? × ????
????
 at ????
°
?? 
Ans: ?
?? = 1000×
?? ?? =
1000×7.896×10
-5
0.00241
 
 ?
?? = 32.765 cm
2
 mol
-1
q =
?
m
?
?? 
m
=
32.76
390.5
?? = 0.084
k
a
=
C?? 2
1 - ?? ; k
a
= 2.2 × 10
-4
 
 
Q3. The ?? °
 for a cell made up of the ???? /????
+?? and ????
+?? /???? half-cells 
(A) ?? . ???????? ?? 
(B) ?? . ???????? ?? 
(C) ?? . ???????? ?? 
(D) ?? . ???????? ?? 
Ans: (A) We have, 
?? °
=
0.0591
2
log ?? ?? ?? °
=
0.0591
2
log ( 2.69 × 10
12
)= 0.3667 V
 
 
Q4.  During electrolysis of an aqueous solution of ???????? ?? using copper 
electrodes, if ?? . ?? ?? of ???? is deposited at cathode, then at anode 
(A) ?????????? of ????
?? at STP is liberated 
(B) ?????????? of ?? ?? at STP is liberated 
(C) ?? . ?? ?? of copper is deposited 
(D) A decrease of ?? . ?? ?? of mass takes place 
Ans: (B) At cathode 
Cu
2+
+ 2e
-
? Cu 
At anode 
2H
2
O ? O
2
+ 4H
+
+ 4e
-
Moles n
O
2
=
1
2
nC
2
 V
O
2
= 22400 n
O
2
= 22400×
1
2
×
2.5
63.5
= 441 mL
 ˜ 445 mLO
2
 is liberated 
 
 
Q5.  The cost at 5 paise / KWH of operating an electric motor for 8 hours which 
takes ?????????? at ?????? ?? is 
(A) Rs 66 
(B) 66 paise 
(C) 37 paise 
(D) Rs. 6.60 
Ans: (B) ?? = ???? 
?? = 1.65 kW
?? = 1.65 × 8kWh = 13.2kWh
 Cost = 13.2 × 5 paise = 66 paise 
 
 
Q6.  Equivalent conductance of ?? . ???????? (weak acid) solution is ???? ?? ????
?? 
equivalent  
-?? and that at infinite dilution is ?????? ?? ????
?? equivalent  
-?? Hence ???? of 
HA solution is 
(A) 1.3 
(B) 1.7 
(C) 2.3 
(D) 3.7 
Ans: (C) ?? =
?
?? ?
?? 0
=
10
200
= 0.05 
[H
+
] = C?? = 0.005
pH = -log [H
+
] = log [200 ] = 2.3
 
 
 
 
Q7.  For the cell 
???? ? ??? ?? ( ?? . ?? ?????? ) |?? +
( ???? = ?? ) ? ?? +
( ???? = ?? ) |?? ?? ( ?? . ?? ?????? ) | ???? 
The measured potential at ????
°
?? is 
(A) -?? . ?? ?? 
(B) -0.5 
(C) -0.041 
(D) None of these 
Ans: (C) At cathode, 
H
+
+ e
-
?
1
2
H
2
 
At anode 
1
2
H
2
? H
+
+ e
-
1
2
H
2
+ H
+
?
1
2
H
2
+ H
+
0.410
-20
? 10
-1
E = -0.0591log 
10
-1
· ( 0.1)
1/2
10
-2
· ( 0.4)
1/2
E = -0.041 V
 
 
Q8. For the fuel cell reaction: 
?? ?? ?? ( ?? )+ ?? ?? ( ?? ) ? ?? ?? ?? ?? ( ?? ) ; ?? ?? ?? ??????
°
( ?? ?? ?? ( ?? )= -?????? . ?????? /???????? 
What is ?? ?? ??????
°
 for the given fuel cell reaction? 
Given ?? ?? ( ?? )+ ?? ?? +
( ???? )+ ?? ?? -
? ?? ?? ?? ?? (I) ?? °
= ?? . ???? ?? 
(A) -?? . ?????? ?? /?? 
(B) -?? . ?????? ???? /?? 
(C) ?? . ???? ???? /?? 
(D) -?? . ?????? ???? /?? 
Ans: (D) O
2
( g)+ 4H
+
( aq )+ 4e
-
? 2H
2
O( l) 
?? °
= 1.23 V
??? °
= -?????? = -474.78 kJ
??? ?? ( ?? 2
) = 0
??? ?? = 2??? 4
( ?? 2
?? 1
l) = -2 × 285.5 kJ = -571 kJ
??? = ??? - ?? ??? ??? =
??? - ??? ?? = -0.322 kJ/k
 
 
 
 
Q9.  The standard reduction potentials of ????
?? +
/???? and ????
?? +
/????
+
are 0.337 and 
?? . ?????? ?? respectively. The standard electrode potential of ????
+
/???? half-cell is: 
(A) ?? . ?????? ?? 
(B) ?? . ?????? ?? 
(C) ?? . ?????? ?? 
(D) ?? . ?????? ?? 
Ans: (C) Cu
2+
+ 2e
-
? Cu
2
; E
°
= 0.337 
?G
1
°
= -nFE
°
= -0.674 F
Cu
2+
+ eCu
+
; E
°
= 0.153
Cu
+
? Cu
2+
+ e
-
; E
°
= -0.153
?G
2
a
= -nFE
°
= +0.153 F
 
Adding, 
Cu
+
+ e
-
? Cu
?G = ?G
1
o
+ ?G
2
s
 -FE
°
= -0.674 F + 0.153 F
E
°
= 0.521 V
 
 
Q10.  One mole of electron passes through each of the solution of ???????? ?? , ???????? ?? 
and ???????? ?? when ???? , ???? and ???? are deposited at cathode. The molar ratio of ???? , ???? 
and ???? deposited are: 
(A) ?? : ?? : ?? 
(B) ?? : ?? : ?? 
(C) 6:3:1 
(D) ?? : ?? : ?? 
Ans: ?
m
=
?? ×1000
?? =
2.48×10
-2
×1000
0.2
 ?
m
= 124O
-1
 cm
2
 mol
-1
 
 
Q11.  Salts of A (atomic weight = ?? ), B (atomic weight = 27) and ?? (atomic 
weight = ???? ) were electrolyzed under identical conditions using the same 
quantity of electricity. It was found that when ?? . ?? ?? of A was deposited, the 
weights of B and C deposited were 2.7 and ?? . ?? ?? . The valencies of ?? , ?? and ?? 
respectively are: 
(A) 3,1 and 2 
(B) 1, 3 and 2 
(C) 3, 1 and 3 
(D) 2, 3 and 2 
Ans: (i) Reaction: 
Mg( s)+ Cu
2+
 (aq. )? Cu ( s)+ Mg
2+
( aq. )
 0. 0001M
 0. 001M
?? = ?? °
-
2.303 ????
????
log (
[Cu
2+
]
[Mg
2+
]
)
-1
?? = ?? °
-
0.0591
2
log 
0.001
0.0001
?? = ?? °
- 0.02955
?? = ?? °
- 0.03
 = 2.70 - 0.03
 = 2.67 V
 
 (ii) Fe+ 2H
+
? Fe
2+
+ H
2
1 0.001
n = 2
E = E
°
-
0.0591
2
log 
[Fe
2+
]P
H
2
[H
+
]
2
E = E
0
- 0.03log 
0.001× 1
1
E = E
0
+ 0.09 = 0.44 + 0.09
 ? E = 0.53 V
 
 
Q12.  The density of ???? is ?? . ???? ?? ????
-?? . The quantity of electricity needed to plate 
an area ???? ???? × ???? ???? to a thickness of ????
-?? ???? using ???????? ?? solution would be 
(A) ???????????? 
(B) ???????????? 
(C) 40758 
(D) ???????????? 
Ans: The formula of standard cell potential is 
?? cell 
°
= ?? right 
°
- ?? left 
°
 
Use this link to get all values 
?? cell 
0
= 0.344 - ( -0.76)
?? cell 
0
= 0.344 + 0.076 V
?? cell 
0
= +1.104 V
 
In balanced reaction there are 2 electron are transferring so that n = 2 
Faraday constant, F = 96500C mol
-1
 
E
cell
°
= +1.104 V 
Use formula 
Plug the value we get