# NCERT solutions for Class 11 Chemistry Textbook chapter 8 - Redox Reactions [Latest edition]

## Chapter 8: Redox Reactions

[Pages 272 - 275]

### NCERT solutions for Class 11 Chemistry Textbook Chapter 8 Redox Reactions [Pages 272 - 275]

Q 1.1 | Page 272

Assign oxidation numbers to the underlined elements in each of the following species:

NaH2PO4

Q 1.3 | Page 272

Assign oxidation numbers to the underlined elements in each of the following species

H4P2O7

Q 1.4 | Page 272

Assign oxidation numbers to the underlined elements in each of the following species:

K2MnO4

Q 1.5 | Page 272

Assign oxidation numbers to the underlined elements in each of the following species

CaO2

Q 1.6 | Page 272

Assign oxidation numbers to the underlined elements in each of the following species:

NaBH4

Q 1.7 | Page 272

Assign oxidation numbers to the underlined elements in each of the following species:

H2S2O7

Q 1.8 | Page 272

Assign oxidation numbers to the underlined elements in each of the following species:

KAl(SO4)2.12 H2O

Q 2.1 | Page 272

What are the oxidation numbers of the underlined elements in each of the following and how do you rationalise your results?

KI3

Q 2.2 | Page 272

What are the oxidation numbers of the underlined elements in each of the following and how do you rationalise your results?

H2S4O6

Q 2.3 | Page 272

What are the oxidation numbers of the underlined elements in each of the following and how do you rationalise your results?

Fe3O4

Q 2.4 | Page 272

What are the oxidation numbers of the underlined elements in each of the following and how do you rationalise your results?

CH3CH2OH

Q 2.5 | Page 272

What are the oxidation numbers of the underlined elements in each of the following and how do you rationalise your results?

CH3COOH

Q 3.1 | Page 272

Justify that the following reactions are redox reactions:

CuO(s) + H2(g) → Cu(s) + H2O(g)

Q 3.2 | Page 272

Justify that the following reactions are redox reactions:

Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)

Q 3.3 | Page 272

Justify that the following reactions are redox reactions:

4BCl3(g) + 3LiAlH4(s) → 2B2H6(g) + 3LiCl(s) + 3 AlCl3 (s)

Q 3.4 | Page 272

Justify that the following reactions are redox reactions:

2K(s) + F2(g) → 2K+F– (s)

Q 3.5 | Page 272

Justify that the following reactions are redox reactions:

4 NH3(g) + 5 O2(g) → 4NO(g) + 6H2O(g)

Q 4 | Page 272

Fluorine reacts with ice and results in the change: H2O(s) + F2(g) → HF(g) + HOF(g)

Justify that this reaction is a redox reaction.

Q 5 | Page 272

Calculate the oxidation number of sulphur, chromium and nitrogen in H2SO5, Cr_2O_7^(2-) and NO_3^-. Suggest structure of these compounds. Count for the fallacy.

Q 6.1 | Page 272

Write the formulae for the following compounds: Mercury(II) chloride

Q 6.2 | Page 272

Write the Formulae for the Following Compounds : Nickel(II) Sulphate

Q 6.3 | Page 272

Write formulas for the following compounds: Tin(IV) oxide

Q 6.3 | Page 272

Write the formulae for the following compounds: Thallium(I) sulphate

Q 6.5 | Page 272

Write the Formulae for the Following Compounds: Iron(III) Sulphate

Q 6.6 | Page 272

Write the Formulae for the Following Compounds: Chromium(III) Oxide

Q 7 | Page 272

Suggest a list of the substances where carbon can exhibit oxidation states from –4 to +4 and nitrogen from –3 to +5.

Q 8 | Page 272

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

Q 9 | Page 272

Consider the reactions:

(a) 6 CO2(g) + 6H2O(l) → C6 H12 O6(aq) + 6O2(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) → C6 H12 O6(aq) + 6H2O(l) + 6O2(g)

(b) O3(g) + H2O2 (l) → H2O(l) + O2(g) + O2(g)

Also suggest a technique to investigate the path of the above (a) and (b) redox

reactions

Q 10 | Page 273

The compound AgF2 is an unstable compound. However, if formed, the compound acts as a very strong oxidizing agent. Why?

Q 11 | Page 273

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 the oxidising agent is in excess. Justify this statement giving three illustrations.

Q 12.1 | Page 273

How do you count for the following observations?

Though alkaline potassium permanganate and acidic potassium permanganate both are used as oxidants, yet in the manufacture of benzoic acid from toluene we use alcoholic potassium permanganate as an oxidant. Why? Write a balanced redox equation for the reaction.

Q 12.2 | Page 273

How do you count for the following observations?

When concentrated sulphuric acid is added to an inorganic mixture containing chloride, we get colourless pungent smelling gas HCl, but if the mixture contains bromide then we get red vapour of bromine. Why?

Q 13.1 | Page 273

Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions:

2AgBr (s) + C6H6O2(aq) → 2Ag(s) + 2HBr (aq) + C6H4O2(aq)

Q 13.2 | Page 273

Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions:

HCHO(l) + 2[Ag (NH3)2]+(aq) + 3OH(aq) → 2Ag(s) + HCOO(aq) + 4NH3(aq) + 2H2O(l)

Q 13.3 | Page 273

Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions:

HCHO (l) + 2Cu2+(aq) + 5 OH(aq) → Cu2O(s) + HCOO(aq) + 3H2O(l)

Q 13.4 | Page 273

Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions:

N2H4(l) + 2H2O2(l) → N2(g) + 4H2O(l)

Q 13.5 | Page 273

Identify the substance oxidised, reduced, oxidising agent and reducing agent for each of the following reactions:

Pb(s) + PbO2(s) + 2H2SO4(aq) → 2PbSO4(s) + 2H2O(l)

Q 14 | Page 273

Consider the reactions:

2S_2O_3^(2-)(aq) + l_2(S) -> S_4O_6^(2-)(aq) + 2l^(-)(aq)

S_2O_3^(2-)(aq) + 2Br_2(l) + 5H_2O(l) -> 2SO_4^(2-) (aq) + 4Br^(-)(aq) + 10H^(+) (aq)

Why does the same reductant, thiosulphate react differently with iodine and bromine?

Q 15 | Page 273

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

Q 16 | Page 273

Why does the following reaction occur?

XeO_6^(4-) (aq) + 2F^(-) (aq) + 6H^(+) (aq) -> XeO_3(g) + F_2(g) + 3H_2O(l)

What conclusion about the compound Na4XeO6 (of which XeO_6^(4+) is a part) can be drawn from the reaction.

Q 17 | Page 273

Consider the reactions:

(a) H3PO2(aq) + 4 AgNO3(aq) + 2 H2O(l) → H3PO4(aq) + 4Ag(s) + 4HNO3(aq)

(b) H3PO2(aq) + 2CuSO4(aq) + 2 H2O(l) → H3PO4(aq) + 2Cu(s) + H2SO4(aq)

(c) C6H5CHO(l) + 2[Ag (NH3)2]+(aq) + 3OH(aq) → C6H5COO(aq) + 2Ag(s) + 4NH3 (aq) + 2 H2O(l)

(d) C6H5CHO(l) + 2Cu2+(aq) + 5OH(aq) → No change observed.

What inference do you draw about the behaviour of Ag+ and Cu2+ from these reactions?

Q 18 | Page 274

Balance the following redox reactions by ion-electron method:

a) MnO_4^(-) (aq) + I (aq) → MnO2 (s) + I2(s) (in basic medium)

(b) MnO_4^(-) (aq) + SO2 (g) → Mn2+ (aq) +HSO_4^(-)  (aq) (in acidic solution)

(c) H2O2 (aq) + Fe2+ (aq) → Fe3+ (aq) + H2O (l) (in acidic solution)

(d)Cr_2O_7^(2-) + SO2(g) → Cr3+ (aq) + SO_4^(2-) (aq) (in acidic solution)

Q 19.1 | Page 274

Balance the following equations in basic medium by ion-electron method and oxidation number methods and identify the oxidising agent and the reducing agent.

P4(s) + OH(aq) ———> PH3(g) + H2PO2(aq)

Q 19.2 | Page 274

Balance the following equations in the basic medium by ion-electron method and oxidation number methods and identify the oxidising agent and the reducing agent.

N2H4(l) + ClO-3(aq) → NO(g) + Cl(g)

Q 19.3 | Page 274

Balance the following equations in basic medium by ion-electron method and oxidation number methods and identify the oxidising agent and the reducing agent.

Cl_2O_(7(g)) + H_2O_(2(aq)) -> ClO_(2(aq))^- + O_(2(g)) + H_(aq)^+

Q 20 | Page 274

What sorts of informations can you draw from the following reaction ?

(CN)_(2(g)) + 2OH_((aq))^(-) -> CN_((aq))^(-) + CNO_((aq))^(-) + H_2O_(l)

Q 21 | Page 274

The Mn3+ ion is unstable in solution and undergoes disproportionation to give Mn2+, MnO2, and H+ ion. Write a balanced ionic equation for the reaction.

Q 22.1 | Page 274

Consider the elements: Cs, Ne, I and F

Identify the element that exhibits only negative oxidation state.

Q 22.2 | Page 274

Consider the elements: Cs, Ne, I and F

Identify the element that exhibits only postive oxidation state.

Q 22.3 | Page 274

Consider the elements: Cs, Ne, I and F

Identify the element that exhibits both positive and negative oxidation states.

Q 22.4 | Page 274

Consider the elements : Cs, Ne, I and F

Identify the element which exhibits neither the negative nor does the positive oxidation state.

Q 23 | Page 274

Chlorine is used to purify drinking water. Excess of chlorine is harmful. The excess of chlorine is removed by treating with sulphur dioxide. Present a balanced equation for this redox change taking place in water.

Q 24.1 | Page 274

Refer to the periodic table given in your book and now answer the following questions:

Select the possible non-metals that can show disproportionation reaction.

Q 24.2 | Page 274

Refer to the periodic table given in your book and now answer the following questions:

Select three metals that can show disproportionation reaction.

Q 25 | Page 274

In Ostwald’s process for the manufacture of nitric acid, the first step involves the oxidation of ammonia gas by oxygen gas to give nitric oxide gas and steam. What is the maximum weight of nitric oxide that can be obtained starting only with 10.00 g. of ammonia and 20.00 g of oxygen?

Q 26.1 | Page 274

Using the standard electrode potentials given in the Table 8.1, predict if the reaction between the following is feasible:

Fe3+(aq) and I(aq)

Q 26.2 | Page 274

Using the standard electrode potentials given in the Table 8.1, predict if the reaction between the following is feasible:

Ag+(aq) and Cu(s)

Q 26.3 | Page 274

Using the standard electrode potentials given in the Table 8.1, predict if the reaction between the following is feasible

Fe3+ (aq) and Cu(s)

Q 26.5 | Page 274

Using the standard electrode potentials given in the Table 8.1, predict if the reaction between the following is feasible:

Br2(aq) and Fe2+(aq)

Q 27.1 | Page 275

Predict the products of electrolysis in each of the following:

An aqueous solution of AgNO3 with silver electrodes

Q 27.2 | Page 275

Predict the products of electrolysis in each of the following:

An aqueous solution AgNO3 with platinum electrodes

Q 27.3 | Page 275

Predict the products of electrolysis in the following:

A dilute solution of H2SO4 with platinum electrodes

Q 27.4 | Page 275

Predict the products of electrolysis in the following:

An aqueous solution of CuClwith platinum electrodes.

Q 28 | Page 275

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 29 | Page 275

Given the standard electrode potentials,

K+/K = –2.93V, Ag+/Ag = 0.80V,

Hg2+/Hg = 0.79V

Mg2+/Mg = –2.37V. Cr3+/Cr = –0.74V

Arrange these metals in their increasing order of reducing power.

Q 30 | Page 275

Depict the galvanic cell in which the reaction Zn(s) + 2Ag+(aq) → Zn2+(aq) + 2Ag(s) takes place, further show:

(i) which of the electrode is negatively charged,

(ii) the carriers of the current in the cell, and

(iii) individual reaction at each electrode.

## NCERT solutions for Class 11 Chemistry Textbook chapter 8 - Redox Reactions

NCERT solutions for Class 11 Chemistry Textbook chapter 8 (Redox Reactions) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CBSE Class 11 Chemistry Textbook solutions in a manner that help students grasp basic concepts better and faster.

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Concepts covered in Class 11 Chemistry Textbook chapter 8 Redox Reactions are Classical Idea of Redox Reactions - Oxidation and Reduction Reactions, Redox Reactions in Terms of Electron Transfer Reactions - Introduction, Redox Reactions in Terms of Electron Transfer Reactions - Competitive Electron Transfer Reactions, Oxidation Number - Introduction, Types of Redox Reactions, Balancing of Redox Reactions, Redox Reactions as the Basis for Titrations, Limitations of Concept of Oxidation Number, Redox Reactions and Electrode Processes.

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