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OXIDATION

AND

REDUCTION

OXIDATION

AND

REDUCTION

1. CLASSICAL CONCEPT2. ELECTRONIC CONCEPT

OXIDISING

AGENT

A^ substance

which^

supplies

oxygen

or

removes

hydrogen

is^ called

oxidising agent

Or

oxidiser or

oxidant. e.g.^ O^2

and^ Br

act^ as 2 oxidising agents

in^ the

above^

reactions.

CLASSICAL

CONCEPT

•^ REDUCTION

:‐^ It^ is

defined

as^ the

process

which

involves

addition

of^ hydrogen

or

removal

of^ oxygen

e.g.^ H^2

+^ Cl^  2

2HCl^

(addition

of^ hydrogen)

H^ +^ Br^2

2HBr 2

(addition

of^ hydrogen)

ZnO +^ C

Zn^ +

CO^ (removal

of^ oxygen)

ELECTRONIC

CONCEPT

•^ OXIDATION

:‐^ it^ is^

defined

as^ the

process

in

which^ an

atom^ or

an^ ion

loses^ one

or^ more

electrons. • Loss^ of

electrons

either^

increases

positive

charge

or^ decreases

negative

charge

of^ the

atom^ or

ion.

•Examples showing increase in positivecharge

Mg^ ^

+2^ Mg+ 2e- +2^ Fe

+3^ Fe+ e- Examples showing decrease in negativecharge

-2^ S ^

S + 2e- 2-MnO 4 MnO

-^ + e- 4

The substance which loses electrons is called reducing agent

decrease in positive charge

3+^ Fe+ e-

^ Fe

2+ 4+^ Sn+ 2e-

^ Sn

2+

increase in negative charge

S + 2e-

2- S

• MnO 4
  • e-^ 

MnO^4

The substance which gains one or moreelectrons is called

oxidising agent.

Oxidation

and^ reduction

are

complementary

-^ Neither

oxidation

nor^ reduction

can^ occur

by

itself.^ A

substance

can^ lose

electrons

only^ if

there^ is

another

substance

to^ gain

those

electrons.

i.e.^ oxidation

occurs

at^ the^

cost^ of

reduction

and^ vice

versa.^

So,^ we^

can^ say

that

both^ oxidation

and^ reduction

go^ side

by^ side.

Actually,

these^

are^ accepted

by^ oxygen

which

changes

to^ oxide

ion^ as^

shown

below

O^ +^ 2e‐

2  O

‐^ OR

O^ +^ 4e^2

‐^ ^ 2O

2 ‐^ (reduction)

If^ we^ add

oxidation

and^ reduction,

we^ get

the

net^ reaction

as:

-^ 2Mg

+^ O^ ^2

2MgO

So,^ we^

can^ say

that^ both

oxidation

and^ reduction

are complementary

to^ each

other.

In^ the^ above

example,

Mg^ loses

electrons

and^ acts

as^ reducing agent

and^ oxygen

accepts

electrons

and^ act

as^ oxidising

agent.

Types

of^ Redox Reactions

•^ 1.^ Direct

redox reactions.

•^ 2.^ Indirect

redox reactions.

DIRECT

REDOX

REACTIONS

-^ The^ reactions

in^ which

both^ oxidation

and

reduction

take^ place

in^ the^

same^ vessel

are

called^ direct

redox^

reactions.

-^ e.g.^ Zn

rod^ dipped

in^ CuSO

Solution.

1.^ A^ part

of^ zinc

metal^

plate^ has

dissolved

and

has^ lost

weight.

2.^ Reddish

metallic

copper

has^ started

depositing

on^ the

zinc^ plate

or^ is^ settling

down

at^ the^ bottom

of^ the^

beaker.

3.^ The^

bluish^ colour of

the^ solution

gradually

fades^ away.4.^ Solution

becomes

hot^ after

sometime

5.^ Solution

remains

electrically

neutral.

EXPLANATION: