Class 11 Chemistry: Redox Reactions

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Question 1:

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

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Question 2:

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

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Question 3:

Which of the following arrangements represents an increasing oxidation number of the central atom?

• (i) CrO₂^–, ClO₃^–, CrO₄^2-, MnO₄^–
• (ii) ClO₃^–, CrO₄^2-, MnO₄^–, CrO₂^–
• (iii) CrO₂^–, ClO₃^–, MnO₄^–, CrO₄^2-
• (iv) CrO₄^2-, MnO₄^–, CrO₂^–, ClO₃^–

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Question 4:

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 uncombined state bears oxidation number zero.
• (iv) In all its compounds, the oxidation number of fluorine is -1.

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Question 5:

Using the standard electrode potential, find out the pair between which redox reaction is not feasible.

E° values: Fe³⁺/Fe²⁺ = +0.77 V; I₂/I^– = +0.54 V; Cu²⁺/Cu = +0.34 V; Ag⁺/Ag = +0.80 V

• (i) Fe³⁺ and I^–
• (ii) Ag⁺ and Cu
• (iii) Fe³⁺ and Cu
• (iv) Ag and Fe³⁺

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Question 6:

The more positive the value of E°, the greater 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.

E° values: Fe³⁺/Fe²⁺ = +0.77 V; I₂(s)/I^– = +0.54 V; Cu²⁺/Cu = +0.34 V; Ag⁺/Ag = +0.80 V

• (i) Fe³⁺
• (ii) I₂(s)
• (iii) Cu²⁺
• (iv) Ag⁺

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Question 7:

What is an oxidation reaction?

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Question 8:

What is the reduction reaction?

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Question 9:

What are the most essential conditions that must be satisfied in a redox reaction?

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Question 10:

What happens to the oxidation number of an element in oxidation?

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Question 11:

Name the different types of redox reactions.

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Question 12:

All decomposition reactions are not redox reactions. Give justification.

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Question 14:

What is the role of a salt bridge in an electrochemical cell?

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Question 15:

Define a redox couple.

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Question 16:

Explain why:

3Fe₃O₄(s) + 8Al(s) → 9Fe(s) + 4Al₂O₃(s)

is an oxidation reaction?

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Question 17:

The reaction

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 their oxidising action.

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Question 18:

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.

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Question 19:

MnO₄^2- undergoes a disproportionation reaction in an acidic medium but MnO₄^– does not. Give a reason.

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Question 20:

Write the formula 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

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Question 21:

PbO and PbO₂ react with HCl according to the following chemical equations:

2PbO + 4HCl → 2PbCl₂ + 2H₂O

PbO₂ + 4HCl → PbCl₂ + Cl₂ + 2H₂O

Why do these compounds differ in their reactivity?

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Question 22:

Nitric acid is an oxidising agent and reacts with PbO, but it does not react with PbO₂. Explain why.

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Question 23:

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

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Question 24:

Calculate the oxidation number of phosphorus in the following species.

• (a) HPO₃^2-
• (b) PO₄^3-

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Question 25:

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

(CN)₂(g) + 2OH^–(aq) → CN^–(aq) + CNO^–(aq) + H₂O(l)

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Question 26:

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) Fe₂O₃(s) + 3CO(g) → 2Fe(s) + 3CO₂(g)
• (iv) PCl₃(l) + 3H₂O(l) → 3HCl(aq) + H₃PO₄(aq)
• (v) 4NH₃ + 3O₂(g) → 2N₂(g) + 6H₂O(g)

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Question 27:

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

• (a) Select the possible non-metals that can show a disproportionation reaction.
• (b) Select three metals that can show a disproportionation reaction.

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Question 28:

Explain redox reactions on the basis of electron transfer. Give suitable examples.

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Question 29:

Arrange the given metals in the order in which they displace each other from the solution of their salts.

• (i) Al
• (ii) Fe
• (iii) Cu
• (iv) Zn
• (v) Mg

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Question 30:

Why does fluorine not show a disproportionation reaction?

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Question 31:

Which method can be used to find out the strength of the reductant/oxidant in a solution? Explain with an example.