Redox Reaction a reaction where both

oxidation & reduction occurs at the same time.

Credits

• Chem Notes • http://www.chemguide.co.uk/inorganic/redox

/oxidnstates.html

• Xinle, jengsuan , angeline , shiyun 4E1

Reducing ?Oxidizing ?

:Reducing Agent Reduces others, but itself is being oxidized.

Oxidizing Agent : Oxidizes others, but itself is being reduced.

Reduction & Oxidation

DEFINITION OXIDATION REDUCTION

#1 0XYGEN TRANSFER Gain Oxygen (+) Lose Oxygen (-)

#2 HYDROGEN TRANSFER

Lose Hydrogen (-) Gain Hydrogen(-)

#3 ELECTRON TRANSFER

Lose Electron (-)

Gain Electron(+)

#4 OXIDATION STATE Increase (+) Decrease (-)

Oxygen Transfer Oxidizing:Gains O Reducing: Loses O

Oxygen Transfer

•CuO + H2 -> Cu + H2O

• oxidizing agent-Oxygen • reducing agent Hydrogen• Note: Oxidising & Reducing agents only

refer to reactants.

Gains O₂

Loses O₂

HYDROGEN TRANSFER Oxidation: loses H Reduction Gains H

Hydrogen Transfer

•H2S + Cl2 -> S + 2HCl

• .

• Oxidizing Agent Cloride,Cl₂• Reducing Agent Hydrogen Sulfur , H₂S

Loses H

Gains H

Electron TransferOxidation: Loses E¯Reduction: Gains E¯

Electron transfer

Oxidised ? ALUMINIUM Reduced? OXYGEN

Oxidation stateThe oxidation state is the charge and atom

of an ion in a compound.

A.K.A oxidation number. OS

Either a positive number(+) or a negative number(-) or zero(0) .

RULES EXAMPLES OXIDATION STATE

1. The oxidation state of an elements in the uncombined state (free state) is zero.

Sodium (Na)Carbon ( C ) Magnesium ( Mg )Oxygen (O2)

0000

2. The oxidation state of a simple ion is equal to the charge on the ion.

Na+

Fe3+

O2-

P3-

+1 +3-2-3

3.The Oxidation states of group I and II elements in their compounds are fixed.

ALL group I and group II elements.

Group 1: +1

Group 2: +2

4. The oxidation states of hydrogen and oxygen in their compound are fixed.

* H2O2 is the only exception where the O.S of oxygen is -1

H ( in H2 O )

O ( in CuO )

+1

-2

• Oxidation occurs when the O.S of an element increases (+)

• Reduction occurs when the O.S of an element decreases (-)

!Oxidation and reduction always occur together

(+2) (+3)

2FeCl2 (s) + Cl2 (g) 2FeCl3•

(a)Oxidation state of Iron increases from +2 in FeCl2 to +3 in 2FeCl3 .

(b)Oxidation state of Chlorine decreases from 0 in Cl2 to -1 in Cl- .

oxidation ----increase in oxidation state

REDUCTION----decrease in oxidation state

Example:

Question

• (NH4)2SO4

since (NH4) has a oxidation state of +1 , (NH4)2 = +2

Oxidation state of nitrogen in (NH4)2 is N2 + 8(+1)= 2(+1)

N2 = +2 -8

N2 = -6

N = -3

Oxidation state of hydrogen in (NH4)2 = +1

since SO4 an oxidation state of -2 ,

oxidation state of sulfur in SO4 is S +4(-2)=-2

S= -2+8 S =+6 Oxidation state of oxygen in SO4 is -2