Question

Chemistry class 11 redox reactions notes

Answer 1

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

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

Answer 2

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