Chemistry

Redox Reactions

Question:

Fluorine reacts with ice and results in the change:
H20(S) + F2 (g) ——-> HF(g) + HOF(g)
Justify that this reaction is a redox reaction.

Answer:

Writing the O.N. of each atom above its symbol, we have,
ncert-solutions-for-class-11-chemistry-chapter-8-redox-reactions-10
Here, the O.N. of F decreases from 0 in F2 to -1 in HF and increases from 0 in F2 to +1 in HOF. Therefore, F2 is both reduced as well as oxidised. Thus, it is a redox reaction and more specifically, it is a disproportionation reaction.

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Redox Reactions

Q 1.

What is salt bridge?

Q 2.

Identify the correct statements with reference to the given reaction.
P4 + 30H + 3H20→ PH3 + 3H2 P02
(a) Phosphorus is undergoing reduction only.
(b) Phosphorus is undergoing oxidation only.
(c) Phosphorus is undergoing oxidation as well as reduction.
(d) Hydrogen is undergoing neither oxidation nor reduction

Q 3.

While sulphur dioxide and hydrogen peroxide can act as an oxidising as well as reducing agents in their reactions, ozone and nitric acid act only as oxidants. Why?

Q 4.

Arrange the following metals in the order in which they displace each other from the solution of their salts.Al, Cu, Fe, Mg and Zn.

Q 5.

How can CuS04 solution not be stored in an iron vessel?

Q 6.

Predict the products of electrolysis in each of the folloxving:
(i) An aqueous solution of AgNO3 with silver electrodes.
(ii) An aqueous solution of silver nitrate with platinum electrodes.
(iii) A dilute solution of  H2S04with platinum electrodes.
(iv) An aqueous solution of  CuCl2  with platinum electrodes.

Q 7.

What is meant by reducing agent? Name the best reducing agent.

Q 8.

Why is standard hydrogen electrode called reversible electrode?

Q 9.

In the reaction .
M4O2 + 4HCI ————-> M4Cl2 + Cl2 + 2H20
which species is oxidised.

Q 10.

Define Oxidation and Reduction in terms of oxidation number.

Q 11.

What is oxidation number of Fe in [Fe(CO)5] ?

Q 12.

What is a disproportionation reaction ? Give one example.

Q 13.

Calculate the oxidation number of phosphorus in the following species.
(a) HPO32- and (b) P043-

Q 14.

Balance the following redox reactions by ion-electron method.
(a) MnO4(aq) +I(aq) ———>Mn02(s) + I2 (s) (in basic medium)
(b) MnO4(aq) + S02(g) ——-> Mn2+(aq) +H2S04(in acidic solution)
(c) H2O2(aq) + Fe2+(aq) ———-> Fe3+(aq) + H2O(l) (in acidic solution)
(d) Cr2O72-  (aq) + S02 (g)——> Cr3+  (aq) + SO42-(aq) (in acidic solution)

Q 15.

Which of the following electrodes will act as anodes, when connected to Standard Hydrogen Electrode?
(a)     A13-/A1;  E °= -1.66 V
(b)       Fe2+ /Fe;  E °= -0.44 V
(c) Cu2+/ Cu E °=34 V
(d) F2(g)/2F(aq) E °= 2.87 V

Q 16.

What is standard hydrogen electrode? For what purpose it is used? What are signs of oxidation potential and reduction potential decided by using SHE (Standard hydrogen electrode)?

Q 17.

Which of the following statement(s) is/are not true about the following decomposition reaction?
2KCIO3 →2KC1 + 302
(a) Potassium is undergoing oxidation.
(b) Chlorine is undergoing oxidation.
(c) Oxygen is reduced.
(d) None of the species are undergoing oxidation or reduction.

Q 18.

Define EMF of cell.

Q 19.

In Ostwald’s process for the manufacture of nitric add, the first step involves the oxidation of ammonia gas by oxygen gas to give nitric oxide gas and steam. What is the maximum wight of nitric oxide that can be obtained starting only with 10.0 g of ammonia and 20.0 g of oxygen?

Q 20.

Identify the oxidant and the reductant in the following reaction.  
N2H4(g) + ClO4(aq) ———–> NO(g) + Cr(aq)

Q 21.

What is a standard hydrogen electrode?

Q 22.

Write the cell reactions:
ncert-solutions-for-class-11-chemistry-chapter-8-redox-reactions-11

Q 23.

Nitric acid is an oxidizing agent and reacts with PbO but it does not react with Pb02. Explain why?

Q 24.

Which of the following elements does not show disproportionation tendency?
(a) Cl
(b) Br  
(c) F  
(d) I

Q 25.

What is meant by cell potential?

Q 26.

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/their compounds.
(a) 3s1
(b) 3dl4s2                                  
(c)  3d24s2
(d) 3s23p3

Q 27.

Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions.
ncert-solutions-for-class-11-chemistry-chapter-8-redox-reactions-21

Q 28.

E ° values of some redox complexes are given below. On the basis of these values choose the correct option.
E ° values: Br2/Br = +1.90; Ag+/Ag(s) = +0.80 Cu2+/Cu(s) = +0.34; I2(s)/I = +0.54 V
(a) Cu will reduce Br
(b) Cu will reduce Ag
(c) Cu will reduce I                                                              
(d) Cu will reduce Br2

Q 29.

Justify-giving reactions that among halogens, fluorine is the best oxidant and among hydrohalic compounds, hydroiodic add is the best reductant.

Q 30.

How will you identify cathode and anode in electrochemical cell ?

Q 31.

Justify that the following reactions are redox reactions:
(a) CuO(s) + H2(g) —–> Cu(s) + H20(g)
(b) Fe2O3(s) +3CO(g) —-> 2Fe(s) + 3CO2(g)
(c) 4BCl3(g) +3LiAlH4(s) ——> 2B2H6(g) + 3LiCl(s) + 3AlCl3(s)
(d) 2K(s) +F2(g)——> 2K+F(s)

Q 32.

Write formulas for the following compounds:
(a) Mercury (II) chloride, (b) Nickel (II) sulphate, (c) Tin (IV) oxide, (d) Thallium
(I) sulphate, (e) Iron (III) sulphate, (f) Chromium (III) oxide.

Q 33.

Consider the reactions:
ncert-solutions-for-class-11-chemistry-chapter-8-redox-reactions-23
Why does the same reductant, thiosulphate react difforerently with iodine and bromine?

Q 34.

(a) Arrange the following in order of increasing O.N of iodine:
I2, HI, HIO2, KIO3, ICl.
(b) Identify the oxidant and reductant in the following redox reaction:
2K2Mn04 + Cl2 ———–> 2KCl + 2KMnO4

Q 35.

(a) Balance the following equation by oxidation number method or by ion electron (half reaction) method.
ncert-solutions-for-class-11-chemistry-chapter-8-redox-reactions-12

Q 36.

Fluorine reacts with ice and results in the change:
H20(S) + F2 (g) ——-> HF(g) + HOF(g)
Justify that this reaction is a redox reaction.

Q 37.

Consider the reactions:
(a) 6CO2(g) 6H2O(l) ———> C6H12O6(s) + 6O6(g) (b) O3(g) + H2O2(l) H2O(l) + 2O2(g)
Why it is more appropriate to write these reactions as:
(a) 6CO2(g) + 12H2O(l) ————-> C6H12O6(s) + 6H2O(l) + 6O2(g)
(b) O3(g) + H2O2 (l) ———–> H2O(l) + O2(g) + O2(g)
Also suggest a technique to investigate the path of above (a) and (b) redox reactions.

Q 38.

PbO and Pb02 react with HC1 according to following chemical equations:
2PbO + 4HCl → 2PbCl2 + 2H20
Pb02 + 4HC1 → PbCl2 + Cl2 + 2H20
Why do these compounds differ in their  reactivity?

Q 39.

Calculate the oxidation number of sulphur, chromium and nitrogen in H2SO5,  Cr2O2  and NOT. Suggest structure of these compounds. Count for the fallacy.

Q 40.

Whenever a reaction between an oxidising agent and a reducing agent is carried out, a compound of lower oxidation state is formed if the reducing agent is in excess and a compound of higher oxidation state is formed if oxidising agent is in excess. Justify this statement giving three illustrations.

Q 41.

Define oxidation in terms of electronic concept.

Q 42.

What is the source of electrical energy in a galvanic cell?

Q 43.

What is the oxidation state of Ni in  Ni (CO)4?

Q 44.

Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions.
ncert-solutions-for-class-11-chemistry-chapter-8-redox-reactions-14

Q 45.

In which of the following compounds, an element exhibits two different oxidation states.
(a) NH2OH
(b) NH4NO3
(c) N2H4
(d) N3H

Q 46.

Identify the correct statement(s) in relation to the following reaction:
Zn + 2HCl → ZnCl2 + H2
(a) Zinc is acting as an oxidant.
(b) Chlorine is acting as a reductant.
(c) Hydrogen ion is acting as an oxidant.
(d) Zinc is acting as a reductant.
ncert-exemplar-problems-class-11-chemistry-chapter-8-redox-reactions-7

Q 47.

Balance the following equations by the oxidation number method.
(i) Fe2+ + H+ + Cr2072- →Cr3+ + Fe3+ + H20
(ii) I2 + N03→ N02 +I03
(iii) I2 + S2032- →I + S4062-
(iv) MnO, + C2042-→ Mn2+ + CO2

Q 48.

Why does the following reaction occur?
ncert-solutions-for-class-11-chemistry-chapter-8-redox-reactions-24

Q 49.

Write Jour informations about the reaction:
(CN)2(g) + 2OH(aq) —–> CN(aq) + CNO(aq) + H2O(l)

Q 50.

Given the standard electrode potentials,
K+/K = -2.93 V, Ag+/Ag = 0.80 V, Hg2+/Hg = 0.79 V, Mg2+/Mg = -2.37 V,
Cr3+/Cr = -0.74 V. Arrange these metals in increasing order of their reducing power.