REDOX REACTIONSTIONSTIONSTIONS
嚜燃nit
8
REDOX REAC
TIONS
REACTIONS
I. Multiple Choice Questions (Type-I)
1.
2.
Which of the following is not an example of redox reaction?
(i)
CuO + H2 ?↙ Cu + H2O
(ii)
Fe2O3 + 3CO ?↙ 2Fe + 3CO2
(iii)
2K + F2 ?↙ 2KF
(iv)
BaCl2 + H2SO4 ?↙ BaSO4 + 2HCl
V
The more positive the value of E , the greater is the tendency of the species to
get reduced. Using the standard electrode potential of redox couples given
below find out which of the following is the strongest oxidising agent.
V
每
E values: Fe3+/Fe2+ = + 0.77; I2(s)/I = + 0.54;
Cu2+/Cu = + 0.34; Ag+/Ag = + 0.80V
3.
(i)
Fe3+
(ii)
I2(s)
(iii)
Cu2+
(iv)
Ag+
V
E values of some redox couples are given below. On the basis of these values
choose the correct option.
V
每
E values : Br2/Br = + 1.90; Ag+ /Ag(s) = + 0.80
每
Cu2+/Cu(s) = + 0.34; I2(s)/I = + 0.54
每
(i)
Cu will reduce Br
(ii)
Cu will reduce Ag
(iii)
Cu will reduce I
(iv)
Cu will reduce Br2
每
16-04-2018
4.
Using the standard electrode potential, find out the pair between which redox
reaction is not feasible.
V
3+
2+
E values : Fe /Fe
每
= + 0.77; I2/I = + 0.54;
+
2+
Cu /Cu = + 0.34; Ag /Ag = + 0.80 V
5.
3+
and I
每
(i)
Fe
(ii)
Ag and Cu
(iii)
Fe
(iv)
Ag and Fe
+
3+
and Cu
3+
Thiosulphate reacts differently with iodine and bromine in the reactions given
below:
2每
2每
每
2S2O3 + I2 ↙ S4O6 + 2I
2每
2每
每
S2O3 + 2Br2 + 5H2O ↙ 2SO4 + 2Br + 10 H
+
Which of the following statements justifies the above dual behaviour of
thiosulphate?
6.
7.
8.
(i)
Bromine is a stronger oxidant than iodine.
(ii)
Bromine is a weaker oxidant than iodine.
(iii)
Thiosulphate undergoes oxidation by bromine and reduction by iodine
in these reactions.
(iv)
Bromine undergoes oxidation and iodine undergoes reduction in these
reactions.
The oxidation number of an element in a compound is evaluated on the basis
of certain rules. Which of the following rules is not correct in this respect?
(i)
The oxidation number of hydrogen is always +1.
(ii)
The algebraic sum of all the oxidation numbers in a compound is zero.
(iii)
An element in the free or the uncombined state bears oxidation
number zero.
(iv)
In all its compounds, the oxidation number of fluorine is 每 1.
In which of the following compounds, an element exhibits two different
oxidation states.
(i)
NH2OH
(ii)
NH4NO3
(iii)
N2H4
(iv)
N3H
Which of the following arrangements represent increasing oxidation number
of the central atom?
每
每
每
2每
2每
每
, CrO4 , MnO4
(i)
CrO2 , ClO3
(ii)
ClO3 , CrO4 , MnO4 , CrO2
每
每
105 Redox Reactions
16-04-2018
每
每
2每
每
(iii)
CrO2 , ClO3 , MnO4 , CrO4
(iv)
CrO4 , MnO4 , CrO2 , ClO3
2每
每
每
每
9. The largest oxidation number exhibited by an element depends on its outer
electronic configuration. With which of the following outer electronic
configurations the element will exhibit largest oxidation number?
(i)
3d 4s
1
2
(ii)
3d 4s
3
2
(iii)
3d 4s
5
1
(iv)
3d 4s
5
2
10. Identify disproportionation reaction
(i)
CH4 + 2O2 ?↙ CO2 + 2H2O
(ii)
CH4 + 4Cl2 ?↙ CCl4 + 4HCl
(iii)
2F2 + 2OH ?↙ 2F + OF2 + H2O
(iv)
2NO2 + 2OH ?↙ NO2 + NO3 + H2O
每
每
每
每
每
11. Which of the following elements does not show disproportionation tendency?
(i)
Cl
(ii)
Br
(iii)
F
(iv)
I
II. Multiple Choice Questions (Type-II)
In the following questions two or more options may be correct.
12. Which of the following statement(s) is/are not true about the following
decomposition reaction.
2KClO3 ↙ 2KCl + 3O2
(i)
Potassium is undergoing oxidation
(ii)
Chlorine is undergoing oxidation
(iii)
Oxygen is reduced
(iv)
None of the species are undergoing oxidation or reduction
13. Identify the correct statement (s) in relation to the following reaction:
Zn + 2HCl ↙ ZnCl2 + H2
(i)
Zinc is acting as an oxidant
(ii)
Chlorine is acting as a reductant
(iii)
Hydrogen ion is acting as an oxidant
(iv)
Zinc is acting as a reductant
Exemplar Problems, Chemistry 106
16-04-2018
14. The exhibition of various oxidation states by an element is also related to the
outer orbital electronic configuration of its atom. Atom(s) having which of the
following outermost electronic configurations will exhibit more than one oxidation
state in its compounds.
1
(i)
3s
(ii)
3d 4s
1
2
(iii)
3d 4s
2
2
(iv)
3s 3p
2
3
15. Identify the correct statements with reference to the given reaction
每
每
P4 + 3OH + 3H2O ↙ PH3 + 3H2PO2
(i)
Phosphorus is undergoing reduction only.
(ii)
Phosphorus is undergoing oxidation only.
(iii)
Phosphorus is undergoing oxidation as well as reduction.
(iv)
Hydrogen is undergoing neither oxidation nor reduction.
16. Which of the following electrodes will act as anodes, when connected to
Standard Hydrogen Electrode?
V
3+
(i)
Al/Al
E = 每1.66
(ii)
Fe/Fe
(iii)
Cu/Cu
(iv)
F2 (g)/2F (aq)
V
2+
E = 每 0.44
V
2+
E = + 0.34
V
每
E = + 2.87
III. Short Answer Type
17. The reaction
每
每
每
Cl2 (g) + 2OH (aq) ?↙ ClO (aq) + Cl (aq) + H2O (l )
represents the process of bleaching. Identify and name the species that
bleaches the substances due to its oxidising action.
18.
每
MnO 24 每 undergoes disproportionation reaction in acidic medium but MnO4
does not. Give reason.
19. PbO and PbO2 react with HCl according to following chemical equations :
2PbO + 4HCl ?↙ 2PbCl2 + 2H2O
PbO2 + 4HCl ?↙ PbCl2 + Cl2 + 2H2O
Why do these compounds differ in their reactivity?
20. Nitric acid is an oxidising agent and reacts with PbO but it does not react
with PbO2. Explain why?
107 Redox Reactions
16-04-2018
21. Write balanced chemical equation for the following reactions:
每
(i) Permanganate ion (MnO4 ) reacts with sulphur dioxide gas in acidic
medium to produce Mn2+ and hydrogensulphate ion.
(Balance by ion electron method)
每
(ii) Reaction of liquid hydrazine (N2H4) with chlorate ion (ClO3 ) in basic
medium produces nitric oxide gas and chloride ion in gaseous state.
(Balance by oxidation number method)
(iii) Dichlorine heptaoxide (Cl2O7) in gaseous state combines with an aqueous
solution of hydrogen peroxide in acidic medium to give chlorite ion
每
(ClO2 ) and oxygen gas.
(Balance by ion electron method)
22. Calculate the oxidation number of phosphorus in the following species.
2每
3每
(a) HPO 3 and
(b) PO 4
23. Calculate the oxidation number of each sulphur atom in the following
compounds:
(a) Na2S2O3
(b) Na2S4O6
(c) Na2SO3
(d) Na2SO4
24. Balance the following equations by the oxidation number method.
3+
2每
3+
(i)
Fe2+ + H+ + Cr2 O7 ?↙ Cr + Fe + H2O
(ii)
I2 + N O3 ?↙ NO2 + I O 3
(iii)
I2 + S2 O3 ?↙ I + S4 O6
(iv)
MnO2 + C2 O 4 ?↙ Mn + CO2
每
每
每
2每
2每
2+
2每
25. Identify the redox reactions out of the following reactions and identify the
oxidising and reducing agents in them.
(i)
3HCl(aq) + HNO3 (aq) ?↙ Cl2 (g) + NOCl (g) + 2H2O (l )
(ii)
HgCl2 (aq) + 2KI (aq) ?↙ HgI2 (s) + 2KCl (aq)
(iii)
? ↙ 2Fe (s) + 3CO (g)
Fe2O3 (s) + 3CO (g) ???
2
(iv)
PCl3 (l) + 3H2O (l) ?↙ 3HCl (aq) + H3 PO3 (aq)
(v)
4NH3 + 3O2 (g) ?↙ 2N2 (g) + 6H2O (g)
26. Balance the following ionic equations
2每
+
每
3+
(i)
Cr2 O7 + H + I ?↙ Cr + I2 + H2O
(ii)
Cr2 O7 + Fe + H ?↙ Cr + Fe + H2O
(iii)
Mn O 4 + S O 3 + H ?↙ Mn + S O 4 + H2O
(iv)
Mn O 4 + H + Br ?↙ Mn + Br2 + H2O
2+
2每
每
每
+
+
2每
+
3+
每
3+
2+
2每
2+
Exemplar Problems, Chemistry 108
16-04-2018
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