# NCERT solutions for Chemistry Part 1 and 2 Class 11 chapter 8 - Redox Reactions [Latest edition]

## Chapter 8: Redox Reactions

EXERCISES
EXERCISES [Pages 280 - 283]

### NCERT solutions for Chemistry Part 1 and 2 Class 11 Chapter 8 Redox Reactions EXERCISES [Pages 280 - 283]

EXERCISES | Q 8.1 - (a) | Page 280

Assign oxidation numbers to the underlined element in the following species:

NaH2PO4

EXERCISES | Q 8.1 - (b) | Page 280

Assign oxidation numbers to the underlined element in the following species:

NaHSO4

EXERCISES | Q 8.1 - (c) | Page 280

Assign oxidation numbers to the underlined element in the following species:

H4P2O7

EXERCISES | Q 8.1 - (d) | Page 280

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

K2MnO4

EXERCISES | Q 8.1 - (e) | Page 280

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

CaO2

EXERCISES | Q 8.1 - (f) | Page 280

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

NaBH4

EXERCISES | Q 8.1 - (g) | Page 280

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

H2S2O7

EXERCISES | Q 8.1 - (h) | Page 280

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

KAl(SO4)2.12 H2O

EXERCISES | Q 8.2 - (a) | Page 280

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

KI3

EXERCISES | Q 8.2 - (b) | Page 280

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

H2S4O6

EXERCISES | Q 8.2 - (c) | Page 280

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

Fe3O4

EXERCISES | Q 8.2 - (d) | Page 280

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

CH3CH2OH

EXERCISES | Q 8.2 - (e) | Page 280

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

CH3COOH

EXERCISES | Q 8.3 - (a) | Page 280

Justify that the following reaction is redox reaction:

$\ce{CuO(s) + H2(g) → Cu(s) + H2O(g)}$

EXERCISES | Q 8.3 - (b) | Page 280

Justify that the following reaction is redox reaction:

$\ce{Fe2O3(s) + 3CO(g) → 2Fe(s) + 3CO2(g)}$

EXERCISES | Q 8.3 - (c) | Page 280

Justify that the following reaction is redox reaction:

$\ce{4BCl3(g) + 3LiAlH4(s) → 2B2H6(g) + 3LiCl(s) + 3 AlCl3(s)}$

EXERCISES | Q 8.3 - (d) | Page 280

Justify that the following reaction is redox reaction:

$\ce{2K(s) + F2(g) → 2K+F– (s)}$

EXERCISES | Q 8.3 - (e) | Page 280

Justify that the following reaction is redox reaction:

$\ce{4 NH3(g) + 5 O2(g) → 4NO(g) + 6H2O(g)}$

EXERCISES | Q 8.4 | Page 280

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

Justify that this reaction is a redox reaction.

EXERCISES | Q 8.5 | Page 280

Calculate the oxidation number of sulphur, chromium and nitrogen in H2SO5, "Cr"_2"O"_7^(2-) and "NO"_3^-. Suggest structure of these compounds. Count for the fallacy.

EXERCISES | Q 8.6 - (a) | Page 280

Write the formulae for the following compound:

Mercury(II) chloride

EXERCISES | Q 8.6 - (b) | Page 280

Write the Formulae for the Following Compound:

Nickel(II) Sulphate

EXERCISES | Q 8.6 - (c) | Page 280

Write formulas for the following compound:

Tin(IV) oxide

EXERCISES | Q 8.6 - (d) | Page 280

Write the formulae for the following compound:

Thallium(I) sulphate

EXERCISES | Q 8.6 - (e) | Page 280

Write the Formulae for the Following Compound:

Iron(III) Sulphate

EXERCISES | Q 8.6 - (f) | Page 280

Write the Formulae for the Following Compound:

Chromium(III) Oxide

EXERCISES | Q 8.7 | Page 280

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

EXERCISES | Q 8.8 | Page 280

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?

EXERCISES | Q 8.9 (a) | Page 280

Consider the reaction:

$\ce{6 CO2(g) + 6H2O(l) → C6 H12O6(aq) + 6O2(g)}$

Why it is more appropriate to write these reaction as:

$\ce{6CO2(g) + 12H2O(l) → C6 H12O6(aq) + 6H2O(l) + 6O2(g)}$

Also, suggest a technique to investigate the path of the redox reactions.

EXERCISES | Q 8.9 (b) | Page 280

Consider the reaction:

$\ce{O3(g) + H2O2(l) → H2O(l) + 2O2(g)}$

Why it is more appropriate to write these reaction as:

$\ce{O3(g) + H2O2 (l) → H2O(l) + O2(g) + O2(g)}$

Also, suggest a technique to investigate the path of the redox reactions.

EXERCISES | Q 8.10 | Page 281

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

EXERCISES | Q 8.11 | Page 281

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.

EXERCISES | Q 8.12 - (a) | Page 281

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.

EXERCISES | Q 8.12 - (b) | Page 281

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?

EXERCISES | Q 8.13 - (a) | Page 281

Identify the substance oxidised, reduced, oxidising agent and reducing agent for the following reaction:

$\ce{2AgBr (s) + C6H6O2(aq) → 2Ag(s) + 2HBr (aq) + C6H4O2(aq)}$

EXERCISES | Q 8.13 - (b) | Page 281

Identify the substance oxidised, reduced, oxidising agent and reducing agent for the following reaction:

$\ce{HCHO(l) + 2[Ag (NH3)2]+(aq) + 3OH–(aq) → 2Ag(s) + HCOO–(aq) + 4NH3(aq) + 2H2O(l)}$

EXERCISES | Q 8.13 - (c) | Page 281

Identify the substance oxidised, reduced, oxidising agent and reducing agent for the following reaction:

$\ce{HCHO (l) + 2Cu^{2+}(aq) + 5 OH–(aq) → Cu2O(s) + HCOO–(aq) + 3H2O(l)}$

EXERCISES | Q 8.13 - (d) | Page 281

Identify the substance oxidised, reduced, oxidising agent and reducing agent for the following reaction:

$\ce{N2H4(l) + 2H2O2(l) → N2(g) + 4H2O(l)}$

EXERCISES | Q 8.13 - (e) | Page 281

Identify the substance oxidised, reduced, oxidising agent and reducing agent for the following reaction:

$\ce{Pb(s) + PbO2(s) + 2H2SO4(aq) → 2PbSO4(s) + 2H2O(l)}$

EXERCISES | Q 8.14 | Page 281

Consider the reactions:

$\ce{2S_2O_3^{(2-)}(aq) + l_2(S) -> S_4O_6^{(2-)}(aq) + 2l-(aq)}$

$\ce{S_2O_3^{(2-)}(aq) + 2Br_2(l) + 5H_2O(l) -> 2SO_4^{2-} (aq) + 4Br-(aq) + 10H+ (aq)}$

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

EXERCISES | Q 8.15 | Page 281

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

EXERCISES | Q 8.16 | Page 281

Why does the following reaction occur?

$\ce{XeO^{4-}_6 (aq) + 2F- (aq) + 6H+ (aq) -> XeO3(g) + F_2(g) + 3H_2O(l)}$

What conclusion about the compound Na4XeO6 (of which "XeO"_6^(4+) is a part) can be drawn from the reaction.

EXERCISES | Q 8.17 | Page 281

Consider the reactions:

1. $\ce{H3PO2(aq) + 4 AgNO3(aq) + 2 H2O(l) → H3PO4(aq) + 4Ag(s) + 4HNO3(aq)}$
2. $\ce{H3PO2(aq) + 2CuSO4(aq) + 2 H2O(l) → H3PO4(aq) + 2Cu(s) + H2SO4(aq)}$
3. $\ce{C6H5CHO(l) + 2[Ag (NH3)2]+(aq) + 3OH–(aq) → C6H5COO–(aq) + 2Ag(s) + 4NH3 (aq) + 2 H2O(l)}$
4. $\ce{C6H5CHO(l) + 2Cu^{2+}(aq) + 5OH–(aq) → No change observed}$

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

EXERCISES | Q 8.18 | Page 282

Balance the following redox reactions by ion-electron method:

1. $\ce{MnO-_4 (aq) + I– (aq) → MnO2 (s) + I2(s) (in basic medium)}$
2. $\ce{MnO-_4 (aq) + SO2 (g) → Mn^{2+} (aq) + HSO-_4 (aq) (in acidic solution)}$
3. $\ce{H2O2 (aq) + Fe^{2+} (aq) → Fe^{3+} (aq) + H2O (l) (in acidic solution)}$
4. $\ce{Cr_2O^{2-}_7 + SO2(g) → Cr^{3+} (aq) + SO^{2-}_4 (aq) (in acidic solution)}$
EXERCISES | Q 8.19 - (a) | Page 282

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

$\ce{P4(s) + OH–(aq) —> PH3(g) + HPO^–_2(aq)}$

EXERCISES | Q 8.19 - (b) | Page 282

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

$\ce{N2H4(l) + ClO^-_3 (aq) → NO(g) + Cl–(g)}$

EXERCISES | Q 8.19 - (c) | Page 282

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

$\ce{Cl_2O_{7(g)} + H_2O_{2(aq)} -> ClO-_{2(aq)} + O_{2(g)} + H+_{(aq)}}$

EXERCISES | Q 8.20 | Page 282

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

$\ce{{(CN)}_{2(g)} + 2OH-_{(aq)} -> CN-_{(aq)} + CNO-_{(aq)} + H_2O_{(l)}}$

EXERCISES | Q 8.21 | Page 282

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.

EXERCISES | Q 8.22 - (a) | Page 282

Consider the elements: Cs, Ne, I and F

Identify the element that exhibits only negative oxidation state.

EXERCISES | Q 8.22 - (b) | Page 282

Consider the elements: Cs, Ne, I and F.

Identify the element that exhibits only postive oxidation state.

EXERCISES | Q 8.22 - (c) | Page 282

Consider the elements: Cs, Ne, I and F

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

EXERCISES | Q 8.22 - (d) | Page 282

Consider the elements : Cs, Ne, I and F

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

EXERCISES | Q 8.23 | Page 282

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.

EXERCISES | Q 8.24 - (a) | Page 282

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.

EXERCISES | Q 8.24 - (b) | Page 282

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

Select three metals that can show disproportionation reaction.

EXERCISES | Q 8.25 | Page 282

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?

EXERCISES | Q 8.26 - (a) | Page 282

Using the standard electrode potential, predict if the reaction between the following is feasible:

Fe3+(aq) and I(aq)

EXERCISES | Q 8.26 - (b) | Page 282

Using the standard electrode potential, predict if the reaction between the following is feasible:

Ag+(aq) and Cu(s)

EXERCISES | Q 8.26 - (c) | Page 282

Using the standard electrode potential, predict if the reaction between the following is feasible.

Fe3+(aq) and Cu(s)

EXERCISES | Q 8.26 - (d) | Page 282

Using the standard electrode potential, predict if the reaction between the following is feasible:

Ag(s) and Fe3+ (aq)

EXERCISES | Q 8.26 - (e) | Page 282

Using the standard electrode potential, predict if the reaction between the following is feasible:

Br2(aq) and Fe2+(aq)

EXERCISES | Q 8.27 - (i) | Page 283

Predict the product of electrolysis in the following:

An aqueous solution of AgNO3 with silver electrodes.

EXERCISES | Q 8.27 - (ii) | Page 283

Predict the product of electrolysis in the following:

An aqueous solution AgNO3 with platinum electrodes.

EXERCISES | Q 8.27 - (iii) | Page 283

Predict the product of electrolysis in the following:

A dilute solution of H2SO4 with platinum electrodes

EXERCISES | Q 8.27 - (iv) | Page 283

Predict the product of electrolysis in the following:

An aqueous solution of CuClwith platinum electrodes.

EXERCISES | Q 8.28 | Page 283

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.

EXERCISES | Q 8.29 | Page 283

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.

EXERCISES | Q 8.30 | Page 283

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

1. which of the electrode is negatively charged,
2. the carriers of the current in the cell, and
3. individual reaction at each electrode.

EXERCISES

## NCERT solutions for Chemistry Part 1 and 2 Class 11 chapter 8 - Redox Reactions

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Concepts covered in Chemistry Part 1 and 2 Class 11 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 Redox Reactions in Terms of Loss and Gain of Electrons, Redox Reactions as the Basis for Titrations, Limitations of Concept of Oxidation Number, Redox Reactions and Electrode Processes.

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