CBSE Class 11 Chemistry Redox Reactions Notes Set B

Redox Reactions MCQ Questions with Answers Class 11 Chemistry

Question. When SO₂ is passed in acidified potassium dichromate solution, the oxidation number of S is changed from

(1) + 4 to zero

(2) + 4 to + 2

(3) + 4 to + 6

(4) + 6 to + 4

Answer (3)

Question. A compound of Xe and F is found to have 53.3% Xe (At. mass = 133). Oxidation number of Xe in this compound is

(1) +2

(2) 0

(3) +4

(4) +6

Answer (4)

Question. Which of the following is not a redox reaction?

(1) H₂+ Cl₂→ 2 HCl

(2) NaOH + HCl → NaCl + H₂O

(3) Photosynthesis

(4) Cell respiration

Answer (2)

Question. How many mole of FeSO₄ reacted with one mole of KMnO ₄ in acidic medium?

(1)2/5

(2) 5

(3)1/2

(4) 1/5

Answer (2)

Question. Redox reaction have no concern with

(1) Neutralization of acid bases

(2) Salt hydrolysis

(3) Esterification

(4) All of these

Answer (4)

Question.In the process of photosynthesis, which takes place in green plants which undergoes reduction?

(1) Water

(2) CO₂

(3) Protons

(4) Photons

Answer (2)

Question. The ratio of number of moles of KMnO4 and K₂Cr₂O₇ required to oxidise 0.1 mol Sn²⁺ to Sn⁺⁴ in acidic medium

(1) 6 : 5

(2) 5 : 6

(3) 1 : 2

(4) 2 : 1

Answer (1)

Question. Which of the following is not correct for electrochemical cell?

(1) Convert chemical energy to electrical energy

(2) Anode is –ve terminal

(3) Cathode is –ve terminal

(4) Cathode is +ve terminal

Answer (3)

Question. KCl is used as an electrolyte in salt bridge because

(1) K+ and Cl– are isoelectronic

(2) Monovalent ions are required

(3) Both the ions have almost same velocity

(4) They are having similar size

Answer (3)

Question. Electrode potential depends upon

(1) Size of electrode

(2) Surface area of electrode

(3) Temperature

(4) Shape of electrode

Answer (3)

Question.  The number of moles of H₂O₂ required to completely react with 400 ml of 0.5 N KMnO₄ in acidic medium are

(1) 0.1

(2) 0.2

(3) 1.0

(4) 0.5

Answer (1)

Question. Number of electrons involved in the reaction when 0.1 mol NH₃ dissolved in water

(1) 2

(2) 0.4

(3) 0.9

(4) Zero

Answer (4)

Question.  Three metals A, B and C are arranged in increasing order of standard reduction electrode potential, hence their chemical reactivity order will be

(1) A < B < C

(2) A > B > C

(3) B > C > A

(4) A = B = C

Answer (2)

Question. Find the incorrect statement

(1) Higher reduction potential of non-metal means stronger reducing agent

(2) Lower oxidation potential of a metal means strong oxidising agent

(3) Oxidation state of oxygen in O₃ is –1

(4) All of these

Answer (4)

Question. When an alkali metal is reacted with hydrogen then metallic hydride is formed. In this reaction

(1) Hydrogen is oxidised

(2) Hydrogen is reduced

(3) Hydrogen is neither oxidised nor reduced

(4) Hydrogen is oxidised as well as reduced

Answer (2)

Question. Which of the following is incorrect regarding salt bridge solution?

(1) Solution must be a strong electrolyte

(2) Solution should be inert towards both electrodes

(3) Size of cations and anions of salt should be much different

(4) Salt bridge solution is prepared in gelatin or agar-agar to make it semi-solid

Answer (3)

Top concepts

1. Redox reactions are those reactions in which oxidation and reduction takes place simultaneously

2. Classical view of redox reactions

• Oxidation is addition of oxygen / electronegative element to a substance or removal of hydrogen / electropositive element from a substance

• Reduction is removal of oxygen / electronegative element from a substance or addition of hydrogen / electropositive element to a substance

3. Redox reactions in terms of Electron transfer

• Oxidation is defined as loss of electrons by any species

• Reduction is defined as gain of electrons by any species

4. In oxidation reactions there is loss of electrons or increase in positive charge or decrease in negative charge

5. In reduction reactions there is gain of electrons or decrease in positive charge or increase in negative charge

6. Oxidising agents are species which gain one or more electrons and get reduced themselves

7. Reducing agents are the species which lose one or more electrons and gets oxidized themselves

8. Oxidation number denotes the oxidation state of an element in a compound ascertained according to a set of rules. These rules are formulated on the basis that electron in a covalent bond belongs entirely to the more electronegative element.

9. Rules for assigning oxidation number to an atom

• Oxidation number of Hydrogen is always +1 (except in hydrides, it is -1).

• Oxidation number of oxygen in most of compounds is -2. In peroxides it is (-1). In superoxides, it is (-1/2). In OF₂ oxidation number of oxygen is +2.In O₂F₂ oxidation number of oxygen is +1

• Oxidation number of Fluorine is -1 in all its compounds

• For neutral molecules sum of oxidation number of all atoms is equal to zero

• In the free or elementary state, the oxidation number of an atom is alwayszero. This is irrespective of its allotropic form

• For ions composed of only one atom, the oxidation number is equal t thecharge on the ion

• The algebraic sum of the oxidation number of all the atoms in a compoundmust be zero

• For ions the sum of oxidation number is equal to the charge on the ion

• In a polyatomic ion, the algebraic sum of all the oxidation numbers of atomsof the ion must be equal to the charge on the ion

10. Oxidation state and oxidation number are often used interchangeably

11. According to Stock notation the oxidation number is expressed by putting aRoman numeral representing the oxidation number in parenthesis after the symbol of the metal in the molecular formula

12.Types of Redox Reactions

• Combination Reactions: Chemical reactions in which two or moresubstances (elements or compounds) combine to form a single substance

• Decomposition Reactions: Chemical reactions in which a compoundbreak up into two or more simple substances

• Displacement Reactions: Reaction in which one ion(or atom)in acompound is replaced by an ion(or atom) of other element

a. Metal Displacement Reactions: Reactions in which a metal in acompound is displaced by another metal in the uncombined state

b. Non-metal Displacement Reactions: Such reactions are mainlyhydrogen displacement or oxygen displacement reactions

• Disproportionation Reactions: Reactions in which an element in oneoxidation state is simultaneously oxidized and reduced

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