REDOX REACTION 1

EXERCISE - 1 : BASIC LEVEL OBJECTIVE QUESTIONS

Concept of Oxidation and Reduction
1. Which of the following behaves as both oxidising and 4. Which substance serves as reducing agents in the following
reducing agents? reaction?
(a) H2SO4 (b) SO2 14H+ + Cr2O72– + 3Ni ® 2Cr3+ + 7 H2O + 3Ni2+
(c) H2S (d) HNO3 (a) H2O (b) Ni
Ans. (b) (c) H+ (d) Cr2O72–
Oxi Ans. (b)
Sol. S+4 ® S+6

+4
Red
2-
Sol. 14 H+ + Cr O + 3Ni ® 2Cr +3 +7H O+ 3Ni 2+
S ®S 2 7
¯
2
¯ ¯
¯ +2
+6 0 +3

2. The compound that can work both as an oxidising as well as Reducing agents are those which reduce others and oxidises
a reducing agent is : itself
(a) KMnO4 (b) H2O2 Ni ® Ni +2
0
(c) Fe2(SO4)3 (d) K2Cr2O7
Ans. (b)
Sol. In all other options the inspecting elements are either in 5. Which of the following reactions depicts the oxidising
property of SO2?
their highest or lowest oxidation states. Hence they can be
only reduced or only oxidized. In H 2 O 2 the 'O' atom is in (a) SO2 + H2O ¾¾
® H2SO3
oxidation state (-1). Which is not its highest O.S. Hence it
(b) 2H2S + SO2 ¾¾
® 3S + 2H2O
can be further reduced or oxidized. Hence it can act as both
a reducing and oxidizing agent. (c) Cl2 + SO2 ¾¾
® SO2Cl2

(d) 2MnO4– + 5SO2 + 2H2O ¾¾

® 5SO42– + 2Mn2+ + 4H +
3. Which of the following is not a redox reaction?
Ans. (b)
(a) CaCO3 ® CaO + CO2
(b) O2 + 2H2 ® 2H2O Sol. 2H 2 S+ SO 2 ® 3S+ 2H 2 O
¯ ¯
+2 0 SO 2 OxidizedH 2S to S
(c) Na + H2O ® Na OH + 1/2 H2
(d) MnCl3 ® MnCl2 + 1/2 Cl2
6. Nitric oxide acts as a reducing agent in the reaction
Ans. (a)
(a) 4NH3 + 5O2 ¾¾
® 4NO + 6H2O
Sol. Ca C O3 ® Ca O + C O3
¯ ¯ ¯ ¯ ¯ ¯ ¯ (b) 2NO + 3I2 + 4H2O ¾¾
® 2NO3– + 6I– + 8H +
+2 +4 -2 +2 -2 +4 -2

There is no change in O.S. of any of the elements in the (c) 2NO + H2SO3 ¾¾
® N2O + H2SO4
course of reaction. Hence it is not a redox reaction. In all
other options the O.S. of one or more element changes. (d) 2NO + H2S ¾¾
® N2O + S + H2O
Ans. (b)

Sol. 2NO + 3I 2 + 4H 2O ® 2NO3- + 6I - + 8H +

I 2 is reduced to I–
 REDOX REACTION 2

Oxidation Number 12. In which of the following reactions is there a change in the
oxidation number of nitrogen atom?
7. The oxidation stae of osmium (Os) in OsO4 is
(a) + 7 (b) + 5 (a) 2 NO2 ® N2O4

(c) + 4 (d) + 8 (b) NH3 + H2O ® NH4+ + OH–

Ans. (d) (c) N2O5 + H2O ® 2HNO3

Sol. OsO 4 (d) None of these

Ans. (d)
x + 4(-2) = 0
x =8 Sol. NO
+4
2 ® N 2O 4
+4

NH 3 + H 2 O ® NH 4+ + O 2
8. Oxidation number of nitrogen in (NH4)2SO4 is ¯ ¯
-3 -3
(a) – 1/3 (b) – 1
N 2 O5 + H2 O ® 2HNO3
(c) + 1 (d) – 3 ¯ ¯
+5 +5
Ans. (d)
Sol. NH +4
13. When SO 2 is passed through an acidified solution of
x + 4(1) = +1 potassium dichromate the oxidation state of S changes from:
x = -3 (a) + 4 to 0 (b) + 4 to + 2
(c) + 4 to + 6 (d) + 6 to + 4
9. The oxidation number of Phosphorus in Mg2P2O7 is : Ans. (c)
(a) + 3 (b) + 2
Sol. SO 2 + K 2 Cr2 O 7 ® Cr2 SO 4 3
(c) + 5 (d) – 3 ¯ ¯ ¯ ¯
+4 +6 +3 +6
Ans. (c)
Sol. Mg 2 P2 O7 14. Oxidation state of nitrogen is correctly given for
2(2) + 2x + ( -14) = 0 Compound Oxidation state
x=5 (a) [Co(NH3)5 Cl]Cl2 0
(b) NH2OH +1
10. In which of the following compounds, nitrogen has an (c) (N2H5)2SO4 +2
oxidation state of – 1?
(d) Mg3N2 – 3
(a) N2O (b) NO2 –
Ans. (d)
(c) NH2OH (d) N2H4
Ans. (c) éCo NH3 5 Cl ù
ê ú
a ê ¯ ú Cl 2
Sol. x+2-1=0 Sol.
êë (-3) úû
x=-1
NH 2 OH
11. A metal ion M3 + loses 3 electrons, its oxidation number will b ¯
be : (-1)
(a) + 3 (b) + 6 æ N 2 H5 ö
(c) 0 (d) – 3 ç ÷
C ç ¯ ÷ SO 4
Ans. (b) ç -2 ÷
è ø2
Sol. M3+ ® M6+ + 3e
Mg 3 N 2 Hence option 'd '
¯ ¯
æ
çç +2 ö÷÷ æ
çç -3ö÷÷
è ø è ø
 REDOX REACTION 3

15. The oxidation state of chromium in Cr(CO)6 is :

(a) 0 (b) + 2 18. Which of the following elements has least oxidation number?
(c) – 2 (d) + 6 (a) Ni(CN)4 (b) Ni(CO)4
Ans. (a) (c) Fe2O3 (d) SF6
Ans. (b)
Cr CO
Sol. ¯ 6
0 Sol. a Ni(CN) 4 Þ CN - –1
The above compound is an example of a co-ordination \ Ni(4+ )
compound where 'CO' is a neutral ligand. Hence O.S. of Cr Ni(CO) 4 CO(0)
should be zero. CO carbon monoxide when CO acts like a b
\ Ni(0)
ligand [Lenius base] it is known as carbonyl ligand.
c Fe 2 O 4
C O as a molecule CO is neutral ¯ ¯
¯ ¯ ( +3) -2
( +2) ( -2)

d S F6
¯ ¯
+6 -1
16. In which of the following pairs, there is greatest difference
in the oxidation number of the underlined elements?
(a) NO2 and N2O4 (b) P2O5 and P4O10 19. The oxidation number of sulphur in S8,S2F2, H2S respectively
(c) N2O and NO (d) SO2 and SO3 are :
Ans. (d) (a) 0, + 1 and –2 (b) + 2, + 1 and –2
Sol. (a) N O 2 and N 2 O4 (c) 0, + 1 and + 2 (d) –2, + 1 and – 2
¯ ¯ ¯ ¯
+4 -2 +4 -2 Ans. (a)

b P2 O5 and P4 O10 Sol. S8 ® 0, S2 F2 , H 2 S

¯ ¯ ¯ ¯
¯ ¯ ¯ ¯ +1 -1 + 1 -2
+5 -2 +5 -2
Types & Balancing of Redox Reactions
c N 2 O and N O
¯ ¯ ¯ ¯ 20. In which of the following reactions, there is no change in
+1 -2 +2 -2
valency?
d S O 2 and S O 3 (a) 4KClO3 ¾¾
® 3KClO4 + KCl
¯ ¯ ¯ ¯
+4 -2 +6 -2
(b) SO2 + 2H2S ¾¾
® 2H2O + 3S

17. In which of the compounds does manganese exhibit highest (c) BaO2 + H2SO4 ¾¾
® BaSO4 + H2O2
oxidation number?
(d) 2BaO + O2 ¾¾
® 2BaO2
(a) MnO2 (b) Mn3O4
Ans. (c)
(c) K2MnO4 (d) MnSO4
Ans. (c) Sol. BaO 2 + H 2 SO 4 ® BaSO 4 + H 2 O 2

Sol. a Mn O 2 This is a double displacement reaction

¯ ¯
+4 -2

21. Which of the following is a disproportionation reaction ?

b Mn 3 O4
¯ ¯ (a) Cu 2 O + 2H Å ¾¾
® Cu + Cu 2 + + H 2 O
æ +8/3ö -2
ç ÷
è ø

c K 2 Mn O4 Hence option ‘c’ (b) 2CrO 24 - + 2H Å ¾¾

® Cr2 O 72 - + H 2 O
¯ ¯
+6 -2
(c) CaCO 3 + 2H Å ¾¾
® Ca 2 + + H 2 O + CO 2
d) Mn SO4 Q
+2 2-
-2 ® 2CrO 42 - + H 2 O
(d) Cr2 O7 + 2 O H ¾¾
 REDOX REACTION 4

Ans. (a) Ans. (a)

Sol. Sol. 2+
Mn O -4 + C 2 O 42- + H + ® Mn + C O 2 + H 2 O
¯ ¯ ¯ ¯
+4 +2 +4
+3

-
é 5e
- 2+ ù
ê MnO 4 ® Mn ú
ë û
22. For the redox reaction, 2MnO -4 + 5C 2 O42 - ® 2Mn 2 + + 10CO 2
MnO4– + C2O42– + H + ¾¾ ® Mn2 + + CO2 + H2O the correct 2MnO -4 + 5C 2 O 42 - + 16H + ® 2Mn 2 + + 10CO 2 + 8H 2 O
coefficients of the reactants for the balanced reaction are:
MnO4– C 2O 4 2 – H+
26. In the chemical reaction, K 2 Cr2 O 7 + XH 2SO 4 + YSO 2 ®
(a) 2 5 16
(b) 16 5 2 K 2SO 4 + Cr2 SO4 3
+ ZH 2 O, X, Y and Z are
(c) 5 16 2 (a) 1,3,1 (b) 4,1,4
(d) 2 16 5 (c) 3,2,3 (d) 2,1,2
Ans. (a) Ans. (a)
- 2- + Sol.
Sol. Mn O4 C 2 O4 H
¯ ¯ ¯
2 5 16 K 2 Cr2 O 7 + XH 2SO4 + YSO2 ® K 2SO4 + Cr2 SO 4 3 + ZH 2 O
¯ ¯ ¯
2MnO -4 + 5C 2 O 42 - + 16H + ® 2Mn 2 + + 10CO 2 + 8H 2 O +6 +4 +3
-
23. What is the coefficient of oxalate ion in the following é 2-
6e
3+ ù
êCr2 O 7 ® 2Cr ú
reaction? ë û
-

MnO4– + C2O42– + H + ¾¾
® Mn2 + + CO2 + H2O é 2e
2- ù
êSO 2 ® SO 4 ú ´ 3
(a) 4 (b) 2 ë û
(c) 3 (d) 5 Cr2 O72- + 3SO 2 + 2H + ® 2Cr 3+ + 3SO 42 - + H 2 O
Ans. (d) K 2 Cr2 O7 + 3SO 2 + H 2SO4 ® K 2SO 4 + Cr2 SO4 3
+ H 2O

Sol. 2MnO -4 + 5C 2 O 42 - + 16H + ® 2Mn 2 + + 10CO 2 + 8H 2 O X=1,Y=3,Z=1

24. In the equation

27. In the chemical reaction,
NO 2 Q + H 2 O ¾¾
® NO 3 Q + 2H Å + ne - K2Cr2O7 + xH2SO4 + ySO2 ¾¾
® K2SO4 + Cr2(SO4)3 + zH2O
n stands for x, y and z are
(a) 1 (b) 2 (a) 1, 3, 1 (b) 4, 1, 4
(c) 3 (d) 4 (c) 3, 2, 3 (d) 2, 1, 2
Ans. (b) Ans. (a)
Sol.
Sol.
K 2 Cr2 O 7 + XH 2SO4 + YSO2 ® K 2SO4 + Cr2 SO 4 3 + ZH 2 O
¯ ¯ ¯
+6 +4 +3
-
25. For the redox reaction MnO-4 + C2 O42 - + H + é 2-
6e
3+ ù
êCr2 O 7 ® 2Cr ú
ë û
® Mn 2+ + CO2 + H 2 O, The correct stoichiometric é
-
2- ù
2e

êSO 2 ® SO 4 ú ´ 3
coefficients of MnO-4 , C2 O42- and H + are respectively: ë û

(a) 2,5,16 (b) 16,5,2 Cr2 O72- + 3SO 2 + 2H + ® 2Cr 3+ + 3SO 42 - + H 2 O

(c) 5,16,2 (d) 2,16,5 K 2 Cr2 O7 + 3SO 2 + H 2SO4 ® K 2SO 4 + Cr2 SO4 3
+ H 2O
 REDOX REACTION 5

X=1,Y=3,Z=1 (b) Oxidation occurs at anode

28. In the balanced chemical reaction (c) Electrons flow from anode to cathode

IO3Q + aIQ + bH Q ¾¾
® cH 2 O + dI 2 (d) All the statements are correct
Ans. (d)
a, b, c and d respectively, correspond to
Sol. Electrode at which reduction takes place Þ cathode
(a) 5, 6, 3, 3 (b) 5, 3, 6, 3
Electrode at which reduction takes place Þ anode
(c) 3, 5, 3, 6 (d) 5, 6, 5, 5
Ans. (a) By definition

Sol. I O3- + I- + H+ ® H2O + I2 In a galvanic cell the anode is e- rich while the cathode
¯ ¯ ¯
+5 -1 0 is e- deficient \ e - flow from anode to cathode via the
-
é - 10e ù internal circuit.
ê2IO3 ® I2 ú
ë û
é 2e ù
- 31. The correct order of reactivity of K, Mg, Zn and Cu with
ê 2I ® I 2 ú ´ 5 water according to the electrochemical series is
ë û
(a) K > Mg > Zn > Cu (b) Mg > Zn > Cu > K
2IO 3- + 10I - ® 6I2
(c) K > Zn > Mg > Cu (d) Cu > Zn > Mg > K
+ - -
6H + IO + 5I ® 3I 2 + 3H 2 O
3
Ans. (a)

a Þ 5, b Þ 6, c Þ 3,d Þ 3 Sol. K > Mg > Zn > Cu

32. Consider the following standard reduction potentials:
29. How many moles of MnO Q4 ion will react with 1 mol of ferrous
oxalate in acidic medium ? Ca 2+ + 2e - ¬¾
® Ca; E o = -2.76 V
¾¾
¾
1 2 Pb 2+ + 2e- ¬¾
® Pb; E o = -0.13 V
¾¾
¾
(a) (b)
5 5
Cu 2 + + 2e - ¬¾
® Cu; E o = 0.34 V
¾¾
¾
3 5 2+
(c) (d) Hg 2 + 2e - ¬¾
¾¾
¾® Hg; E o = 0.80 V
5 3
Ans. (c) Pt 2+ + 2e - ¬¾
® Pt; E o = 1.20 V
¾¾
¾
Sol. Fe2 + + C2 O-4 2 ® Fe3+ + 2CO2 + 3e - Which of the following metals is the strongest reducing
agent?
MnO -4 + 5e- ® Mn 2+ (a) Ca (b) Pb
5FeC 2 O 4 = 3MnOQ
4 (c) Cu (d) Hg

3 Ans. (a)
1FeC 2 O 4 = MnO -4
5 Sol. Ca 2 + + 2e - ƒ Ca; E0 = -2.76V
Redox Reactions and Electrode Processes Pb 2 + + 2e - ƒ Pb; E 0 = -0.13V
30. Which of the following statement is correct for a galvanic Cu 2+ + 2e - ƒ Cu; E 0 = 0.34V
cell ? Hg 22 + + 2e - ƒ Hg; E 0 = 0.80V
(a) Reduction occurs at cathode Pt 2 + + 2e - ƒ Pt; E 0 = 1.20V
 REDOX REACTION 6

The strongest reducing agent will be the one which most 35. In the reaction VO + Fe 2 O3 ® FeO + V2 O5 the eq. wt. of
readily oxidise.
V2O5 is equal to its
\ Ca is the strongest reducing agent.
(a) mol. wt. (b) mol. wt./8
(c) mol. wt./6 (d) none of these
33. Consider the following electrodes potentials:
Ans. (c)
2+ - o
(a) V + 2e ® V; E = -1.18V
Sol. 2VO
+4
® V2 O5
+10

(b) Cu 2+ + e- ® Cu + ; E o = 0.15V MW
EW V2 O5 =
6
(c) 2H + + 2e - ® H 2 ; Eo = 0.00V

(d) Mg 2+ + 2e- ® Mg; Eo = -2.37 V 36. The eq. wt. of K2CrO4 as an oxidising agent in acid medium
is
Based on the above data, state which of the following is
2 ´ mol. wt.
the strongest reducing agent ? (a) mol. wt./2 (b)
3
Ans. (d) mol. wt. mol. wt.
(c) (d)
Sol. Mg ® Mg 2+ + 2e - E o = 2.37 V 3 6
Ans. (c)
Note : EO data given is SRP
Sol. Cr +6 ® Cr3 +
\ SOP will have opposite sign
MW
\Mg is the strongest reducing agent EW=
3
34. The standard reduction potentials at 298 K are given against
37. In the conversion NH2OH ® N2O, the equivalent weight
each of the following half cell reactions :
of NH2OH will be :
Q Q
I. E Zn 2+ |Zn = -0.76 V II. E Cr 3+ |Cr = -0.74 V (a)M/4 (b)M/2
(c)M/5 (d)M/1
Q Q
III. E H Å |H 2 = 0.00 V IV. E Fe3+ |Fe+2 = +0.77 V (M = molecular weight of NH2OH)
Based on the above data, state which of the following is the Ans. (b)
strongest reducing agent ?
Sol. 2NH 2-OH
1
® N2O
+1
(a) Zn (b) Cr
For 2 moles of NH 2OH 4e- transfer
(c) H2 (d) Fe
Ans. (a) \1mole ® 2e -
M
Sol. From the given data \ EW =
2
Zn ® Zn2+ E0 = 0.76V
­
SOP 38. The mass of oxalic acid crystals (H2C2O4.2H2O) required to
Note E o data given is SRP prepare 50 mL of a 0.2 N solution is :
(a) 4.5 g (b) 6.3 g
\ SOP will have opposite sign
(c) 0.63 g (d) 0.45 g
\ Zn is the strongest reducing agent
Ans. (c)
Equivalent Concept
Sol. C 2 O 24 - ® 2CO2
 REDOX REACTION 7

M 126
\ EW H 2 C 2 O4 × 2H 2 O = = = 63
2 2
50ml of a 0.2N = 10 -2 equivalent
Sol.
63 ´10 -2 = 0.63g

39. M is molecular weight of KMnO4.. The equivalent weight of

KMnO4 when it is converted into K2MnO4 is :
\Total e’ change = 24 + 4 = 28e -
(a) M (b) M/3
(c) M/5 (d) M/7 MW
Ans. (a) EW =
n factor
Sol. K Mn O 4 ® K 2 Mn O4
¯ ¯ 42. Equivalent weight of H3PO2 (molecular weight = M) when it
+7 +6
disproportionates into PH3 and H3PO3 is
The change in Oxidation State per KMnO 4 molecule is 1
M
\ n Factor = 1 (a) M (b)
2
MW M 3M
\ Eq wt = (c) (d)
1 4 4
Ans. (d)
40. The equivalent mass of oxidising agent in the following
reaction is MW
Sol. H3 P O2 ® P H3 = EW
SO2 + 2H2S ® 3S + 2H2O
¯
+1
¯
-3
4
(a) 32 (b) 64 MW
H3 P O2 ® H3PO3 = EW
(c) 16 (d) 8 ¯
+1 ¯
+3
2
Ans. (c) é 1 1 ù 3M
EWnet = MW ê + ú =
Sol. SO 2 show Reduction ë4 2û 4

4e - + SO 2 ® S
+4 0
43. Equivalent weight of MnO 4 Q in acidic, neutral and basic
n Factor = 4 media are in ratio of :
MW 64 (a) 3 : 5 : 15 (b) 5 : 3 : 1
= EW = = 16
4 4
(c) 5 : 1 : 13 (d) 3 : 15 : 5
Ans. (a)
41. In the following reaction :
Sol. é5e - +MnO - ¾Acidic
¾¾¾ ® Mn +2 ù n = 5
4
NO 3Q + As 2S3 + H 2 O ¾¾
® AsO 4 3- + NO + SO 42 - + H Å ë û

the equivalent weight of As2S3 (with molecular weight M) é1e- MnO- ¾neutral
¾¾¾ ® MnO2 ù n = 3
4
ë û
is:
é ù
3M M Basic
ê MnO - ¾¾ -2 ú
(a) (b) ¾® MnO n =1
28 4 ê æ - ö4 4
ú
1e
ëê è ø
ç ÷ úû
M M
(c) (d) M M M
24 28 : :
5 3 1
Ans. (d)
Þ 3 : 5 :15

44. K2CrO4 oxidises KI in the presence of HCl to I 2. The

 REDOX REACTION 8

equivalent weight of the K2CrO4 is = 0.6V

Mw 2 Since eq of K 2 Cr2 O 7 is more

(a) (b) Mw ´
2 3
So, Fe+2 is oxidised more by K 2 Cr2 O 7 .
Mw Mw
(c) (d)
3 6
47. Volume V1 mL of 0.1M K2Cr2O7 is needed for complete
Ans. (c) oxidation of 0.678 g N2H4 in acidic medium. The volume of
0.3 M KMnO4 needed for same oxidation in acidic medium
é +3 ù
Sol. êCr O 24 - ® 2 Cr ú n = 3 will be :
¯ ¯
ë +6 +3 û (a) 2/5 V1 (b) 5/2 V1
Mw (c) 113 V1 (d) Can not be determined
=
3
Ans. (a)

Sol. The amount of N 2 H 4 reacting in both case is same.

45. The equivalent weight of MnSO4 is half its molecular weight
when it is converted to \ The number of equvalents required for K2Cr2O7 and KMnO4
(a) Mn2O3 (b) MnO2 should be same.
\ N1V1 = N 2 V2
(c) MnO 4 Q (d) MnO 4 2 -
­ ­
Ans. (b) For For
Sol. MnSO4 Mn 2O3 MnO2 MnO-4 MnO24- K 2 Cr2 O 7 KMnO 4
¯ ¯ ¯ ¯ ¯
+2 +3 +4 +7 +6
(0.1 ´ 6) ´ V1 = (0.3 ´ 5)V2
é 2e + Mn SO ® Mn O ù n = 2
- 0.1´ 6
ëê +2 4
+4 2 ûú \ V2 = ´ V1
0.3 ´ 5
MW 2
EW = \ V2 = V1
2 5
48. 80 mL of KMnO4 solution reacts with 3.4 g of Na2 C2O4.2H2O
Redox Titrations in acidic medium. The molarity of the KMnO4 solution is
(a) 0.5 M (b) 0.1 M
46. If equal volumes of 0.1 M KMnO4 and 0.1 M K2Cr2O7
solutions are allowed to oxidise Fe2+ to Fe3+ in acidic medium, (c) 5 M (d) 1 M
then Fe2+ will be oxidised : Ans. (b)
(a) More by KMnO4 (b) More by K2Cr2O7
Sol. No. of Eq of KMnO 4 = no. of Eq Na 2 C 2 O7 × 2H 2 O
(c) Equal in both cases (d) Cannot be determined.
5 ´ no. of moles = 2 ´ no. moles
Ans. (b)
2
Sol. 5Fe 2 + + MnO 4- + 8H + ® 5Fe3 + + 4H 2 O + Mn 2 + M ´ 80 ´10 -3 = ´ 0.02
5

6Fe 2 + + Cr2 O 27 - + 14H + ® 6Fe3+ + 7H 2 O + 2Cr 3+ \ M = 0.1 M

+7 +2
ù
KMnO 4 ® Mn ú n = 5 49. What weight of NaHSO3 is required to react with 100 mL of
û solution containing 0.33 g of NaIO 3 according to the
ù following reaction
K 2 Cr2 O7 ® Cr +3 ú n = 6
+6 +3´ 2 û IO3Q + HSO3Q ¾¾
® IQ + SO 42 -
eq of KMnO 4 = m ´ n ´ v = 0.1´ 5 ´ Vol (a) 0.52 g (b) 5.2 g
eq of K 2 Cr2 O 7 = 0.1 ´ 6 ´ Vol
 REDOX REACTION 9

(c) 1.04 g (d) 10.4 g W2

Sol. N = EW ×V
Ans. (a) 2

Sol. I O3- + HS O3- ® I - +SO24- 34 200

¯ ¯ ¯ ¯ N= =
+5 +4 -1 +6 17 ´1.12 112
- -
6e é 2e ù 1 N of H 2 O 2 = 5.6 volume strength
IO3- ® I- ê HSO 3- ® SO 24 - ú ´ 3
ë û 200
- - 2-
5.6 ´ = 10 Vol
NaIO + 3NaHSO3 ® I + 3SO
3 4
112
eq. of NaIO 3 = eq . Of NaHSO3
53. A 5.0 mL solution of H2O2 liberates 1.27 g of iodine from an
x = 0.52g acidified KI solution. The percentage strength of H2O2 is
(a) 11.2 (b) 5.6
50. What volume of 0.05 M K2Cr2O7 in acidic medium is needed (c) 1.7 (d) 3.4
for complete oxidation of 200 mL of 0.6 M FeC2O4 solution? Ans. (d)
(a) 1.2 mL (b) 1.2 L Sol. H 2 O 2 º KI º I 2
(c) 120 mL (d) 800 mL mEq of H 2 O 2 = 5×N
Ans. (b) W 1.27
mEq of I 2 = ×1000 = ×1000 = 10m Eq
EW 127
Sol. CrO72 - + Fe+2 C2 O 4 ® Fe3+ + 2CO 2 + Cr3+
I 2 = MW = 254
MW
EW FeC2 O 4 = 254
3 EW= =127
2
MW 5 ´ N = 10 \ N = 2
EW Cr2 O 72- =
6
1N of H 2 O 2 =1.7% H 2 O 2
Eq of FeC2O 4 = Eq of Cr2O -72
2N Þ 3.4
= 1.2L
54. The volume strength of 1.5 N H2O2 solution is
51. KI reacts with H2SO4 producing I2 and H2S. The volume of
(a) 4.8 (b) 8.4
0.2 M H2SO4 required to produce 0.1 mol of H2S is
(a) 4 L (b) 2.5 L (c) 3.0 (d) 8.0
(c) 3.8 L (d) 5 L Ans. (b)
Ans. (b) Sol. 2H 2 O 2 ® 2H 2 O + O 2
Sol. 8KI + 5H 2SO 4 ® 4K 2SO 4 + 4I 2 + H 2S + 4H 2 O
5 mole 1 mole 68 gm 22.4L (at STP)

Mole of H 2S = 0.1mol Mass of H 2 O 2 in 1.5N = EW ´1.5 = 17 ´1.5 = 25.5g

Mole of H 2SO 4 = 0.1´ 5 = 0.5 22.4L ´ 25.5g

\ Vol. strength = = 8.4L
68.0
0.2 ´ V = 0.5
V = 2.5L

Volume Strength of Hydrogen Peroxide

52. 34 g of H2O2 is present in 1120 mL of solution. This solution
is called
(a) 10 vol solution (b) 20 vol solution
(c) 34 vol solution (d) 32 vol solution
Ans. (a)