REDOX REACTIONS AND ELECTROCHEMISTRY – 4

1) A buffer solution is prepared by mixing 10 ml of 1.0 M CH3COOH and 20 ml of 0.5 M CH3COONa and then diluted to 100 ml with distilled water. If pKa of CH3COOH is 4.76 , what is the pH of the buffer solution ?.
a) 5.21
b) 4.76
c) 4.34
d) 5.8

2) The degree of dissociation of 0.1N CH3COOH is: (Dissociation constant = 1 x 10-5)
a)
b)
c)
d)

3) In the reaction 3 Mg + N2 Mg3N2.
a) Mg is reduced
b) Mg is oxidised
c) Nitrogen is oxidised
d) None of these

4) Which of the following metals exhibits more than one oxidation state ?
a) Na
b) Mg
c) Fe
d) Al

5) The equivalent weight of KMnO4 in an acid solution is
a) 158
b) 31.6
c) 52.16
d) 79

6) The oxidation number of the As atom in H3AsO4 is
a) – 3
b) – 1
c) + 3
d) + 5

7) The oxidation number of N in C6H5NH2 (aniline) is

a) + 2
b) – 3
c) – 1
d) + 1

8) In an acidic medium, how many moles of electrons are accepted by one mole of MnO4 in a redox process ?

a) 1
b) 3
c) 5
d) 6

9) In an acidic medium potassium dichromate acts as an oxidant according to the equation

.What is the equivalent weight of K2Cr2O7 ?

a) M
b) M/2
c) M/3
d) M/6

10) Which of the following metals has the least oxidation number ?
a)
b)
c)
d)

11) Which one of the following elements shows the maximum number of different oxidation states in its compounds ?
a) Am
b) Gd
c) La
d) Eu

12) If the molecular weight of KMnO4 is M, then its equivalent weight in an acidic medium would be
a) M
b) M/2
c) M/5
d) M/4

13) In the reaction, 4Fe + 3O2 4Fe3 + + 6, which of the following statements is not correct ?
a) It is a redox reaction
b)
c) Metallic iron is a reducing agent
d)

14) The oxidation number of hydrogen in KH, HgH2 and NaH are respectively
a) -1,-2,-1
b) + 1,+ 1 and +1
c) + 2, + 1 and – 2
d) – 2, – 3 and – 1

15) Which one is an oxidising agent ?
a)
b)
c)
d) None

16) Which of the following can act as a reducing agent as well as an oxidising agent ?
a)
b)
c)
d) None

17) The strongest reducing agent among the following is
a)
b)
c)
d)

18) Identify the element among the following which can have the highest oxidation number.

a) N
b) O
c) Cl
d) C

19) The number of moles of oxalate ions oxidised by one mole of MnO4 is
a) 1/5
b) 2/5
c) 5/2
d) 5

20) Which of the following is the weakest oxidising agent ?

a)
b)
c)
d)

21) The oxidation number of N in (NH4)2SO4 is
a) – 1/3
b) – 1
c) + 1
d) – 3

22) H2S is passed through an acidified solution of CuSO4 and a black precipitate is formed. This is due to
a)
b)
c) Double decomposition
d) Reduction and oxidation

23) In an acidic solution the reaction MnMn2 + involves
a) Oxidation by 3 electrons
b) Reduction by 3 electrons
c) Oxidation by 3 electrons
d) Reduction by 5 electrons

24) In the reaction between acidified K2Cr2O7 and Fe (II) ions shown by the equation.
Cr2 (aq) + 6Fe2+ (aq) + 14H+ (aq) 2Cr3+ (aq) + 7H2O (e) + 6Fe3+ (aq)
a) The colour of the solution changes from green to yellow
b) The Fe (II) ions are reduced
c)
d) Hydrogen ions are reduced

25) The strongest reducing agent among the following is.
a)
b)
c)
d)

26) The number of moles of KMnO4 required to oxidise one mole of FeC2O4 in an acidic medium is
a) 0.6
b) 1.67
c) 0.2
d) 0.4

27) When KMnO4 reacts with acidified FeSO4,
a) ,nothing is reduced
b)
c)
d) None of the above

28) Acidified K2Cr2O7 is treated with H2S. In the reaction the oxidation number of Cr
a) Increases from + 3 to + 6
b) Decreases from + 6 to + 3
c) Remains unchanged
d) Decreases from + 6 to + 2

29) The oxidation number of S in S2 is

a) + 2
b) – 2
c) + 4
d) 0

30) The oxidation number of P in P2 is.
a) + 3
b) + 4
c) + 5
d) + 6

31) The oxidation state of I in H4IO6 is
a) + 7
b) – 1
c) +5
d) + 6

32) The oxidation number of Fe in K3[Fe(CN)6] is
a) + 2
b) + 3
c) + 4
d) + 1

33) The oxidation state of oxygen in H2O2 is
a) – 2
b) – 1
c) + 1
d) + 2

34) The oxidation number of Pt in [Pt(C2H4)Cl3] is
a) + 1
b) + 2
c) + 3
d) +4

35) In the brown ring complex [Fe(H2O)5NO] SO4 the oxidation number of Fe is
a) + 1
b) + 2
c) + 3
d) + 4

36) Which of the following sequences is correct with reference to the oxidation number of iodine ?
a)
b)
c)
d)

37) The oxidation number of N in HNO3 is
a) – 3.5
b) + 3.5
c) – 3, + 5
d) + 5

38) If HNO3 changes into N2O the oxidation number decreases by
a) + 2
b) – 1
c) 1
d) + 4

39) When CuSO4 reacts with KI, the oxidation state of Cu decreases by
a) 0
b) – 1
c) 1
d) + 2

40) When P reacts with NaOH to form PH3 and NaH2PO2, this reaction is an example of
a) Oxidation
b) Reduction
c) Neutralisation
d) Disproportionation

41) Which one of the following is a strong reducing agent ?
a)
b) Na
c) Cl
d) Cr

42) The 3d-elements show variable oxidation states. What is the maximum oxidation state shown by the element Mn ?
a) + 4
b) + 5
c) +6
d) + 7

43) The partial ionic equation, Cr2 + 14H+ + 6e 2Cr3+ + 7H2O, suggests that the equivalent weight of Cr2 will be equal to its formula weight divided by.
a) 1
b) 3
c) 6
d) 14

44) The oxidation number of Fe and S in iron pyrites is

a) 4, – 2
b) 2, – 1
c) 3, – 1.5
d) 3, 1

45) The oxidation numbers of As are
a) + 2 and + 3
b) + 3 and + 5
c) + 3 and + 4
d) None

46) The reaction 2CuI Cu + CuI2 is
a) Redox
b) Neutralisation
c) Oxidation
d) Reduction

47) Reductants are substances which
a) Show a decrease in their oxidation number during a change
b) Gain electrons during a change
c) Get reduced during a change
d) Show an increase in oxidation number during a change

48) Oxidants are substances which
a) Show an increase in their oxidation number during a change
b) lose electrons during a change
c) are oxidized during a reaction
d) Show a decrease in oxidation number during a change

49) Which of the following shows the highest oxidation number in its compounds?
a) Na
b) Mg
c) Cl
d) C

50) In a conjugate pair of reductant and oxidant, the oxidant has
a) a higher oxidation number
b) a lower oxidation number
c) the same oxidation number
d) any of these

51) In reality with which does SO2 act as an oxidant ?
a) Acidified KMnO4
b) acidified K2Cr2O7
c)
d)

52) In which compound does iron have the lowest oxidation state ?

a)
b)
c)
d)

53) The compound that can act both as an oxidising and reducing agent is
a)
b)
c)
d)

54) The oxidation number and covalency of sulphur in the sulphur molecule (S8) are respectively.
a) 0 and 2
b) + 6 and 8
c) 0 and 8
d) + 6 and 2

55) In the reaction 3Br2 + 6C + 3H2O 5Br + Br + 6HCO3
a) Bromine is oxidised and carbonate is reduced
b) Bromine is reduced and carbonate is oxidised
c) Bromine is neither reduced nor oxidised
d) Bromine is reduced as well oxidised

56) In which of the following is the oxidation number of oxygen +2 ?
a)
b) H2O2
c)
d)

57) In the balanced equation for the reaction MnO4 + H+ + C2 Mn2+ + CO2 + H2O, the moles of CO2 formed are
a) 2
b) 4
c) 5
d) 10

58) In the balanced equation MnO4 + H + ClMn2++H2O + Cl2, the correct coefficient for Cl (aq) is
a) 8
b) 5
c) 10
d) 16

59) For the reaction MnO4 + 8H+ + 5e Mn2+ + 4H2O taking place in an acidic medium, the true oxidation numbers of Mn changes from
a) +7 to +6
b) +7 to +2
c) +4 to +2
d) +6 to +7

60) In the conversion of Br2 to BrO3, the oxidation state of bromine changes from
a) 0 to 5
b) 1 to 5
c) 0 to -3
d) 2 to 5

61) How many moles of electrons are involved in the reduction of one mole of MnO4 ions to MnO3in an alkaline medium ?
a) 2
b) 1
c) 3
d) 4

62) In the reduction of dichromate by Fe (II), the number of electrons involved per chromium atom is
a) 3
b) 1
c) 2
d) 4

63) In the balanced equation I2 + HNO3 HIO3 + NO2 + H2O the coefficient for HIO3 is
a) 1
b) 5
c) 2
d) 10

64) In the following reaction, 4P + 3KOH + 3H2O 3KH2PO2 + PH3,
a) Only P is oxidised
b) Only P is reduced
c) P is oxidised as well as reduced
d) P is neither oxidised nor reduced

65) Which of the following shows the maximum number of oxidation states ?
a) Bi
b) N
c) P
d) As

66) In the reduction of ferric salt by hydrazine 4Fe3+ + N2H4 4Fe2+ + N2 + 4H+ the number of electrons lost per mole of N2H4 is
a) 2
b) 4
c) 6
d) Zero

67) Which of the following is an oxidation and reduction reaction ?
a)
b)
c)
d)

68) Bromide ions can reduce
a) Iodine atoms
b) Iodine ions
c) Chlorine atoms
d) Chloride ions

69) A compound contains atoms X, Y, Z. The oxidation number of X is +2, Y is +5, and Z is -2. The possible formula of the compound is
a)
b)
c)
d)

70) In the reaction Cr2 + H+ + Br 2Cr3+ + Br2 + H2O, the reducing agent is
a)
b)
c)
d)

71) The bleaching action of SO2 is due to
a) its reducing property
b) its oxidizing property
c) Hydrolysis
d) its acidic nature

72) The oxidation number of Ni in K4[Ni(CN)6] is
a) +6
b) +4
c) +2
d) +3

73) In which of the following are the compounds arranged in the order of the increasing oxidation number of nitrogen ?
a)
b)
c)
d)

74) When H2S is passed through iodine solution,
a) It is oxidised to H2SO4
b) It is oxidised to S
c) Thiosulphuric acid is formed
d)

75) In CH2Cl2, the oxidation number of C is
a) -4
b) +2
c) 0
d) +4

76) The bleaching action of chlorine in the presence of moisture is due to its
a) Reducing property
b) Oxidizing property
c) Hydrolysis
d) Substitution

77) The oxidation state of manganese in the product formed by the reduction of potassium permanganate in an acid medium is
a) +8
b) +7
c) +2
d) +5

78) In which reaction is there a change in the oxidation number of N ?
a)
b)
c)
d)

79) The oxidation number of sulphur in H2S2O8 is
a) +2
b) +6
c) +7
d) +14

80) In the reaction H2O2 + Na2CO3 Na2O2 + CO2+ H2O, the substance undergoing oxidation is
a)
b)
c)
d) None

81) The conversion of KMnO4 to MnSO4 is a process of
a) Oxidation
b) Reduction
c) Dehydration
d) Both oxidation and reduction

82) The oxidation state of +1 for phosphorus is found in
a)
b)
c)
d)

83) The maximum oxidation state is exhibited by
a) V
b) Fe
c) Mn
d) Cr

84) The oxidation state of the oxygen atom in potassium super oxide is
a) -1/2
b) 0
c) +1/2
d) -2

85) Which one of the following reactions does not involve oxidation-reduction ?
a)
b)
c)
d)

86) In which reaction is H2 acting as an oxidising agent ?
a)
b)
c)
d)

87) In which series does the oxidation state show an ascending order ?
a)
b)
c)
d)

88) In which of the following reactions is H2O2 a reducing agent ?
a)
b) Cl2 + H2O2O2 + 2Cl + 2H+
c)
d)

89) Which of the following reactions indicates the oxidising behaviour of H2SO4 ?
a)
b)
c)
d)

90) In the-reaction 2Ag + 2H2SO4 Ag2SO4 + SO2 + 2H2O, H2SO4 acts as a/an
a) Oxidising agent
b) Reducing agent
c) Catalyst
d) Acid as well as an oxidant

91) The oxidation number of S in S is
a) +8
b) +6
c) +4
d) +2

92) When Sn (IV) chloride is treated with excess HCl, the complex [SnCl6]2- is formed. The oxidation state of Sn in this complex is
a) +6
b) -2
c) +4
d) -5

93) Co (s) + Cu2+ (aq) Co2+ (aq) + Cu (s). This reaction is a/an
a) Oxidation reaction
b) Reduction reaction
c) Redox reaction
d) None

94) In which of the following is the oxidation number of sulphur least ?
a)
b)
c)
d)

95) The oxidation number of sulphur in the gas evolved when copper is heated with conc. H2SO4 is
a) +1
b) +2
c) +3
d) +4

96) The oxidation number of P in Mg2P2O7 is
a) +3
b) +2
c) +5
d) -3

97) When ethylene is passed through aqueous KMnO4 solution, the oxidation state of Mn changes from
a) + 7 to + 2
b) + 7 to + 4
c) + 7 to + 6
d) None of these

98) The oxidation number of N in N3H is
a) -3
b) +3
c) 0
d) -1/3

99) In which of the following compounds of Cr is the oxidation state of Cr not + 6 ?
a)
b)
c)
d)

100) Which of the following statements is false ?
a) All reactions are oxidation and reduction reactions
b) The oxidising agent is itself reduced
c) Oxidation and reduction always go side by side
d) The oxidation number decreases during reduction


Answer :

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