Solved Example: Redox Reaction | Chemistry for JEE Main & Advanced PDF Download

 Page 1


JEE Solved Example on Redox Reaction 
JEE Mains 
Q1:  The equivalent weight of ???????? ?? when it is oxidised by acidified ???????? ?? will be equal to 
(A) ?? ?? of ???????? ?? 
(B) 
?? ?? ???????? ?? ?? 
(C) ?? ?? ?? ???????? ?? 
(D) 
?? ?? ???????? ?? ?? 
 Ans:  (A) Equivalent weight = Molecular weight × ?? tastor 
 = (?? 0
)
FeSO
4
× 1
Fe
+2
? Fe
+3
 
 
Q2:  The equivalent weight of ?? ?? ????
?? ?? ?? when it is converted ????
?? +
 will be equal to 
(A) ?? ?? ?? ?? ?? ?? 
(B) 
?? ?? ?? ????
?? ?? ?? 
(C) 
?? ?? ?? ????
?? ?? ?? ?? 
(D) 
?? ?? ?? ?? ?? ?? ?? ?? 
 Ans: (D) Equivalent weight = Molecular weight × n
factor 
 = (M)
K
2
Cr
2
O
7
× 6
Cr
2
O
7
? Cr
+3
 
 
 
Q3:  The amount of ?? ?? ?? that can be oxidised to sulfur on oxidation using ?? . ???????? of ???????? ?? as 
oxidising agent in acidic medium will be 
(A) ?? . ?????????? 
(B) ?? . ???????? 
(C) ?? . ???????????? 
(D) None of these 
Ans: (A) 
 
Page 2


JEE Solved Example on Redox Reaction 
JEE Mains 
Q1:  The equivalent weight of ???????? ?? when it is oxidised by acidified ???????? ?? will be equal to 
(A) ?? ?? of ???????? ?? 
(B) 
?? ?? ???????? ?? ?? 
(C) ?? ?? ?? ???????? ?? 
(D) 
?? ?? ???????? ?? ?? 
 Ans:  (A) Equivalent weight = Molecular weight × ?? tastor 
 = (?? 0
)
FeSO
4
× 1
Fe
+2
? Fe
+3
 
 
Q2:  The equivalent weight of ?? ?? ????
?? ?? ?? when it is converted ????
?? +
 will be equal to 
(A) ?? ?? ?? ?? ?? ?? 
(B) 
?? ?? ?? ????
?? ?? ?? 
(C) 
?? ?? ?? ????
?? ?? ?? ?? 
(D) 
?? ?? ?? ?? ?? ?? ?? ?? 
 Ans: (D) Equivalent weight = Molecular weight × n
factor 
 = (M)
K
2
Cr
2
O
7
× 6
Cr
2
O
7
? Cr
+3
 
 
 
Q3:  The amount of ?? ?? ?? that can be oxidised to sulfur on oxidation using ?? . ???????? of ???????? ?? as 
oxidising agent in acidic medium will be 
(A) ?? . ?????????? 
(B) ?? . ???????? 
(C) ?? . ???????????? 
(D) None of these 
Ans: (A) 
 
m
34
× 2 =
1.58
158
× 5 = 0.85 
 
Q4:  The amount of nitric acid required to oxidise 127 gms of ?? ?? to ?? ?? ?? ?? will be   . Assume that 
during the reaction ?????? ?? gets converted to ????
?? . 
(A) 12.7 
(B) 3.15 
(C) 315 
(D) 31.5 
Ans: (C) HNO
3
+5
+ I
2
? I
2
O
5
+5
+ NO
2
+4
 
?? 63
× 1 =
127
127 × 2
× 10 = 315 
 
Q?? :  ???? ???? of oxalic acid was completely oxidised by ???? ???? of ?? . ?????? ???????? ?? . The normality of 
oxalic acid solution is 
(A) ?? . ???? ?? 
(B) ?? . ?? ?? 
(C) ?? . ?? ?? 
(D) ?? . ?????? ?? 
 Ans:  (C)N
1
 V
1
 = N
2
 V
2
 Oxalic acid  KMnO
4
10 × 10
-3
× N = 20 × 10
-3
× 0.02 × (5)
 n-factor = 0.2 N
 
 
Q6: ?? . ?? ?? of a sample of ?? ?? ?? ?? required ???? ???? of ?? ?? ???????? ?? in a titration in the presence of 
?? ?? ????
?? . Purity of ?? ?? ?? ?? is 
(A) ???? % 
(B) ???? % 
(C) ???? % 
(D) None of these 
Ans: (C) 
m
34
× 2 = 10 × 10
-3
× 1; m = 0.17 
? Purity =
0.17
0.2
× 100 = 85% 
 
Q7:  The number of moles of ???????? ?? that will be needed to react completely with one mole of 
ferrous oxalate in acidic solution is 
(A) 
?? ?? 
(B) 
?? ?? 
(C) 
?? ?? 
(D) 1 
Page 3


JEE Solved Example on Redox Reaction 
JEE Mains 
Q1:  The equivalent weight of ???????? ?? when it is oxidised by acidified ???????? ?? will be equal to 
(A) ?? ?? of ???????? ?? 
(B) 
?? ?? ???????? ?? ?? 
(C) ?? ?? ?? ???????? ?? 
(D) 
?? ?? ???????? ?? ?? 
 Ans:  (A) Equivalent weight = Molecular weight × ?? tastor 
 = (?? 0
)
FeSO
4
× 1
Fe
+2
? Fe
+3
 
 
Q2:  The equivalent weight of ?? ?? ????
?? ?? ?? when it is converted ????
?? +
 will be equal to 
(A) ?? ?? ?? ?? ?? ?? 
(B) 
?? ?? ?? ????
?? ?? ?? 
(C) 
?? ?? ?? ????
?? ?? ?? ?? 
(D) 
?? ?? ?? ?? ?? ?? ?? ?? 
 Ans: (D) Equivalent weight = Molecular weight × n
factor 
 = (M)
K
2
Cr
2
O
7
× 6
Cr
2
O
7
? Cr
+3
 
 
 
Q3:  The amount of ?? ?? ?? that can be oxidised to sulfur on oxidation using ?? . ???????? of ???????? ?? as 
oxidising agent in acidic medium will be 
(A) ?? . ?????????? 
(B) ?? . ???????? 
(C) ?? . ???????????? 
(D) None of these 
Ans: (A) 
 
m
34
× 2 =
1.58
158
× 5 = 0.85 
 
Q4:  The amount of nitric acid required to oxidise 127 gms of ?? ?? to ?? ?? ?? ?? will be   . Assume that 
during the reaction ?????? ?? gets converted to ????
?? . 
(A) 12.7 
(B) 3.15 
(C) 315 
(D) 31.5 
Ans: (C) HNO
3
+5
+ I
2
? I
2
O
5
+5
+ NO
2
+4
 
?? 63
× 1 =
127
127 × 2
× 10 = 315 
 
Q?? :  ???? ???? of oxalic acid was completely oxidised by ???? ???? of ?? . ?????? ???????? ?? . The normality of 
oxalic acid solution is 
(A) ?? . ???? ?? 
(B) ?? . ?? ?? 
(C) ?? . ?? ?? 
(D) ?? . ?????? ?? 
 Ans:  (C)N
1
 V
1
 = N
2
 V
2
 Oxalic acid  KMnO
4
10 × 10
-3
× N = 20 × 10
-3
× 0.02 × (5)
 n-factor = 0.2 N
 
 
Q6: ?? . ?? ?? of a sample of ?? ?? ?? ?? required ???? ???? of ?? ?? ???????? ?? in a titration in the presence of 
?? ?? ????
?? . Purity of ?? ?? ?? ?? is 
(A) ???? % 
(B) ???? % 
(C) ???? % 
(D) None of these 
Ans: (C) 
m
34
× 2 = 10 × 10
-3
× 1; m = 0.17 
? Purity =
0.17
0.2
× 100 = 85% 
 
Q7:  The number of moles of ???????? ?? that will be needed to react completely with one mole of 
ferrous oxalate in acidic solution is 
(A) 
?? ?? 
(B) 
?? ?? 
(C) 
?? ?? 
(D) 1 
 Ans: (B) KMnO
4
+ FeC
2
O
4
? Mn
2+
+ Fe
3+
+ CO
2
n
KMnO
4
× 5 = 1 × (1 + 2) =
3
5
 
 
Q8:  A metal oxide is reduced by heating it in a stream of hydrogen. It is found that after complete 
reduction, ?? . ???? ?? of the oxide has yielded ?? . ???? ?? of the metal. We may deduce that 
(A) The atomic weight of the metal is 8 
(B) The atomic weight of the metal is 4 
(C) The equivalent weight of the metal is 4 
(D) The equivalent weight of the metal is 8 
 Ans: (C) M
2
?? 2
+ ?? 2
? 2?? + ?? ?? 2
O
1 mole M
2
?? 2
 gives 2 moles ?? ?
3.15 g
(MW)
?
1.05
M
 ? 6?? = 2?? + ?? (16)
 ? 4?? = ?? (16)
 
 ? ?? = 4?? Now, (???? )
?? =
(???? )
?? ?? =
?? ?? ? (???? )
?? =
?? ?? = 4.
 
 
Q9:  Oxidation involves 
(A) Gain of electrons 
(B) Loss of electrons 
(C) Increase in the valency of negative part 
(D) Decrease in the valency of positive part 
Ans: (B) Oxidation means increase of oxidation number 
? So, there is loss of electrons. 
 
Q10:  The oxidation number of ???? in ?? ?? ????
?? ?? ?? 
(A) +2 
(B) -2 
(C) +6 
(D) -6 
 Ans: (C) K
2
Cr
2
O
7
2 K
+
2Cr
x+
7O
2-
 +2 + 2x- 14 = 0
?? = +6
 
 
Page 4


JEE Solved Example on Redox Reaction 
JEE Mains 
Q1:  The equivalent weight of ???????? ?? when it is oxidised by acidified ???????? ?? will be equal to 
(A) ?? ?? of ???????? ?? 
(B) 
?? ?? ???????? ?? ?? 
(C) ?? ?? ?? ???????? ?? 
(D) 
?? ?? ???????? ?? ?? 
 Ans:  (A) Equivalent weight = Molecular weight × ?? tastor 
 = (?? 0
)
FeSO
4
× 1
Fe
+2
? Fe
+3
 
 
Q2:  The equivalent weight of ?? ?? ????
?? ?? ?? when it is converted ????
?? +
 will be equal to 
(A) ?? ?? ?? ?? ?? ?? 
(B) 
?? ?? ?? ????
?? ?? ?? 
(C) 
?? ?? ?? ????
?? ?? ?? ?? 
(D) 
?? ?? ?? ?? ?? ?? ?? ?? 
 Ans: (D) Equivalent weight = Molecular weight × n
factor 
 = (M)
K
2
Cr
2
O
7
× 6
Cr
2
O
7
? Cr
+3
 
 
 
Q3:  The amount of ?? ?? ?? that can be oxidised to sulfur on oxidation using ?? . ???????? of ???????? ?? as 
oxidising agent in acidic medium will be 
(A) ?? . ?????????? 
(B) ?? . ???????? 
(C) ?? . ???????????? 
(D) None of these 
Ans: (A) 
 
m
34
× 2 =
1.58
158
× 5 = 0.85 
 
Q4:  The amount of nitric acid required to oxidise 127 gms of ?? ?? to ?? ?? ?? ?? will be   . Assume that 
during the reaction ?????? ?? gets converted to ????
?? . 
(A) 12.7 
(B) 3.15 
(C) 315 
(D) 31.5 
Ans: (C) HNO
3
+5
+ I
2
? I
2
O
5
+5
+ NO
2
+4
 
?? 63
× 1 =
127
127 × 2
× 10 = 315 
 
Q?? :  ???? ???? of oxalic acid was completely oxidised by ???? ???? of ?? . ?????? ???????? ?? . The normality of 
oxalic acid solution is 
(A) ?? . ???? ?? 
(B) ?? . ?? ?? 
(C) ?? . ?? ?? 
(D) ?? . ?????? ?? 
 Ans:  (C)N
1
 V
1
 = N
2
 V
2
 Oxalic acid  KMnO
4
10 × 10
-3
× N = 20 × 10
-3
× 0.02 × (5)
 n-factor = 0.2 N
 
 
Q6: ?? . ?? ?? of a sample of ?? ?? ?? ?? required ???? ???? of ?? ?? ???????? ?? in a titration in the presence of 
?? ?? ????
?? . Purity of ?? ?? ?? ?? is 
(A) ???? % 
(B) ???? % 
(C) ???? % 
(D) None of these 
Ans: (C) 
m
34
× 2 = 10 × 10
-3
× 1; m = 0.17 
? Purity =
0.17
0.2
× 100 = 85% 
 
Q7:  The number of moles of ???????? ?? that will be needed to react completely with one mole of 
ferrous oxalate in acidic solution is 
(A) 
?? ?? 
(B) 
?? ?? 
(C) 
?? ?? 
(D) 1 
 Ans: (B) KMnO
4
+ FeC
2
O
4
? Mn
2+
+ Fe
3+
+ CO
2
n
KMnO
4
× 5 = 1 × (1 + 2) =
3
5
 
 
Q8:  A metal oxide is reduced by heating it in a stream of hydrogen. It is found that after complete 
reduction, ?? . ???? ?? of the oxide has yielded ?? . ???? ?? of the metal. We may deduce that 
(A) The atomic weight of the metal is 8 
(B) The atomic weight of the metal is 4 
(C) The equivalent weight of the metal is 4 
(D) The equivalent weight of the metal is 8 
 Ans: (C) M
2
?? 2
+ ?? 2
? 2?? + ?? ?? 2
O
1 mole M
2
?? 2
 gives 2 moles ?? ?
3.15 g
(MW)
?
1.05
M
 ? 6?? = 2?? + ?? (16)
 ? 4?? = ?? (16)
 
 ? ?? = 4?? Now, (???? )
?? =
(???? )
?? ?? =
?? ?? ? (???? )
?? =
?? ?? = 4.
 
 
Q9:  Oxidation involves 
(A) Gain of electrons 
(B) Loss of electrons 
(C) Increase in the valency of negative part 
(D) Decrease in the valency of positive part 
Ans: (B) Oxidation means increase of oxidation number 
? So, there is loss of electrons. 
 
Q10:  The oxidation number of ???? in ?? ?? ????
?? ?? ?? 
(A) +2 
(B) -2 
(C) +6 
(D) -6 
 Ans: (C) K
2
Cr
2
O
7
2 K
+
2Cr
x+
7O
2-
 +2 + 2x- 14 = 0
?? = +6
 
 
 
Q11:  When ?? ?? ????
?? ?? ?? is converted into ?? ?? ????
?? ?? ?? the change in oxidation number of ???? is 
(A) 0 
(B) 6 
(C) 4 
(D) 3 
 Ans: (D) K
2
Cr
2
O
7
? K
2
Cr
2
O
7
 +6 ? +3
 
? Change in oxidation No. = [3]. 
 
Q12:  White ?? reacts with caustic soda. The products are ????
?? and ?????? ?? ????
?? . This reaction is an 
example of 
(A) Oxidation 
(B) Reduction 
(C) Oxidation and reduction 
(D) Neutralization 
Ans: (C) P + NaOH? PH
3
-3
+ NaH
2
PO
2
+1
 
?? is getting oxidised and also reduced 
? It is oxidation and reduction 
( ?? is proportionation) 
 
Q13:  The oxidation number of carbon in ????
?? ?? is 
(A) -2 
(B) +2 
(C) 0 
(D) +4 
Ans: (C) CH
2
O 
C
x
2H
+
O
2-
x + 2 - 2 = 0
x = 0
 
 
Q. 14 The oxidation number of ?? in ????
?? , ????
?? ???? , ????
?? ????
?? ???????? ?? , and ??????
?? are respectively 
(A) ?? , ?? , -?? , ?? , -?? 
(B) -?? , -?? , ?? , +?? , +?? 
(C) ?? , ?? , ?? , -?? , -?? 
(D) ?? , ?? , ?? , -?? , -?? 
Ans: (B) CH
4
? C
x+
+ 4H
+
 x = -4 
Page 5


JEE Solved Example on Redox Reaction 
JEE Mains 
Q1:  The equivalent weight of ???????? ?? when it is oxidised by acidified ???????? ?? will be equal to 
(A) ?? ?? of ???????? ?? 
(B) 
?? ?? ???????? ?? ?? 
(C) ?? ?? ?? ???????? ?? 
(D) 
?? ?? ???????? ?? ?? 
 Ans:  (A) Equivalent weight = Molecular weight × ?? tastor 
 = (?? 0
)
FeSO
4
× 1
Fe
+2
? Fe
+3
 
 
Q2:  The equivalent weight of ?? ?? ????
?? ?? ?? when it is converted ????
?? +
 will be equal to 
(A) ?? ?? ?? ?? ?? ?? 
(B) 
?? ?? ?? ????
?? ?? ?? 
(C) 
?? ?? ?? ????
?? ?? ?? ?? 
(D) 
?? ?? ?? ?? ?? ?? ?? ?? 
 Ans: (D) Equivalent weight = Molecular weight × n
factor 
 = (M)
K
2
Cr
2
O
7
× 6
Cr
2
O
7
? Cr
+3
 
 
 
Q3:  The amount of ?? ?? ?? that can be oxidised to sulfur on oxidation using ?? . ???????? of ???????? ?? as 
oxidising agent in acidic medium will be 
(A) ?? . ?????????? 
(B) ?? . ???????? 
(C) ?? . ???????????? 
(D) None of these 
Ans: (A) 
 
m
34
× 2 =
1.58
158
× 5 = 0.85 
 
Q4:  The amount of nitric acid required to oxidise 127 gms of ?? ?? to ?? ?? ?? ?? will be   . Assume that 
during the reaction ?????? ?? gets converted to ????
?? . 
(A) 12.7 
(B) 3.15 
(C) 315 
(D) 31.5 
Ans: (C) HNO
3
+5
+ I
2
? I
2
O
5
+5
+ NO
2
+4
 
?? 63
× 1 =
127
127 × 2
× 10 = 315 
 
Q?? :  ???? ???? of oxalic acid was completely oxidised by ???? ???? of ?? . ?????? ???????? ?? . The normality of 
oxalic acid solution is 
(A) ?? . ???? ?? 
(B) ?? . ?? ?? 
(C) ?? . ?? ?? 
(D) ?? . ?????? ?? 
 Ans:  (C)N
1
 V
1
 = N
2
 V
2
 Oxalic acid  KMnO
4
10 × 10
-3
× N = 20 × 10
-3
× 0.02 × (5)
 n-factor = 0.2 N
 
 
Q6: ?? . ?? ?? of a sample of ?? ?? ?? ?? required ???? ???? of ?? ?? ???????? ?? in a titration in the presence of 
?? ?? ????
?? . Purity of ?? ?? ?? ?? is 
(A) ???? % 
(B) ???? % 
(C) ???? % 
(D) None of these 
Ans: (C) 
m
34
× 2 = 10 × 10
-3
× 1; m = 0.17 
? Purity =
0.17
0.2
× 100 = 85% 
 
Q7:  The number of moles of ???????? ?? that will be needed to react completely with one mole of 
ferrous oxalate in acidic solution is 
(A) 
?? ?? 
(B) 
?? ?? 
(C) 
?? ?? 
(D) 1 
 Ans: (B) KMnO
4
+ FeC
2
O
4
? Mn
2+
+ Fe
3+
+ CO
2
n
KMnO
4
× 5 = 1 × (1 + 2) =
3
5
 
 
Q8:  A metal oxide is reduced by heating it in a stream of hydrogen. It is found that after complete 
reduction, ?? . ???? ?? of the oxide has yielded ?? . ???? ?? of the metal. We may deduce that 
(A) The atomic weight of the metal is 8 
(B) The atomic weight of the metal is 4 
(C) The equivalent weight of the metal is 4 
(D) The equivalent weight of the metal is 8 
 Ans: (C) M
2
?? 2
+ ?? 2
? 2?? + ?? ?? 2
O
1 mole M
2
?? 2
 gives 2 moles ?? ?
3.15 g
(MW)
?
1.05
M
 ? 6?? = 2?? + ?? (16)
 ? 4?? = ?? (16)
 
 ? ?? = 4?? Now, (???? )
?? =
(???? )
?? ?? =
?? ?? ? (???? )
?? =
?? ?? = 4.
 
 
Q9:  Oxidation involves 
(A) Gain of electrons 
(B) Loss of electrons 
(C) Increase in the valency of negative part 
(D) Decrease in the valency of positive part 
Ans: (B) Oxidation means increase of oxidation number 
? So, there is loss of electrons. 
 
Q10:  The oxidation number of ???? in ?? ?? ????
?? ?? ?? 
(A) +2 
(B) -2 
(C) +6 
(D) -6 
 Ans: (C) K
2
Cr
2
O
7
2 K
+
2Cr
x+
7O
2-
 +2 + 2x- 14 = 0
?? = +6
 
 
 
Q11:  When ?? ?? ????
?? ?? ?? is converted into ?? ?? ????
?? ?? ?? the change in oxidation number of ???? is 
(A) 0 
(B) 6 
(C) 4 
(D) 3 
 Ans: (D) K
2
Cr
2
O
7
? K
2
Cr
2
O
7
 +6 ? +3
 
? Change in oxidation No. = [3]. 
 
Q12:  White ?? reacts with caustic soda. The products are ????
?? and ?????? ?? ????
?? . This reaction is an 
example of 
(A) Oxidation 
(B) Reduction 
(C) Oxidation and reduction 
(D) Neutralization 
Ans: (C) P + NaOH? PH
3
-3
+ NaH
2
PO
2
+1
 
?? is getting oxidised and also reduced 
? It is oxidation and reduction 
( ?? is proportionation) 
 
Q13:  The oxidation number of carbon in ????
?? ?? is 
(A) -2 
(B) +2 
(C) 0 
(D) +4 
Ans: (C) CH
2
O 
C
x
2H
+
O
2-
x + 2 - 2 = 0
x = 0
 
 
Q. 14 The oxidation number of ?? in ????
?? , ????
?? ???? , ????
?? ????
?? ???????? ?? , and ??????
?? are respectively 
(A) ?? , ?? , -?? , ?? , -?? 
(B) -?? , -?? , ?? , +?? , +?? 
(C) ?? , ?? , ?? , -?? , -?? 
(D) ?? , ?? , ?? , -?? , -?? 
Ans: (B) CH
4
? C
x+
+ 4H
+
 x = -4 
CH
3
ClC
?? +
+ 3H
+
+ Cl
-
 ?? = -2
CH
2
Cl
2
x + 2 - 2 = 0 ?? = 0
CHCl
3
?? + 1 - 3 = 0 ?? = 2
CCl
4
 x - 4 = 0 x = +4
 
 
Q15:  Which of the following reactions is not redox type 
(A) ???????? + ?? ?? ? ?? ?????? ?? 
(B) ?? ???????? ?? ? ?? ???????? ?? + ?????? 
(C) ?????? ?? + ?? ?? ????
?? ? ???????? ?? + ?? ?? ?? ?? 
(D) ????
?? + ?? ?? ?? ?? ? ?? ?? ?? ?? + ?? ?? 
Ans:  (C) Redox: Exchange of electrons 
? Change in oxidation state. 
(c) Ba
2+
O
2
2-
+ H
2
SO
4
+6
? Ba
2+
SO
4
+6
+ H
2
O
2
 
No change in oxidation 
 
Q16:  In which of the following compounds iron has lowest oxidation state 
(A) ?? ?? ???? (???? )
?? 
(B) ?? ?? ??????
?? 
(C) ????
?? ?? 
(D) ???? (???? )
?? 
Ans: (D) (a) +4 - 6 + ?? = 0; ?? = +2 
(b) +2 + ?? - 8 = 0; ?? = +6 
(c) +2?? - 2 = 0; ?? = +1 
(d) ?? + 5(0) = 0; ?? = 0 
 
Q17:  Select the compound in which chlorine is assigned the oxidation number +5 
(A) ???????? 
(B) ???????? ?? 
(C) ???????? ?? 
(D) ???????? ?? 
Ans:  (C) (a) HClO
+1
+ 1 + ?? - 2 = 0; ?? = +1 
(b) HClO
2
+ 1 + ?? - 4 = 0; ?? = +3 
(c) HClO
3
+ 1 + ?? - 6 = 0; ?? = 5 
(d) HClO
4
+ 1 + ?? - 8 = 0; ?? = +7