OXIDATION AND REDUCTION: REDOX

OXIDATION AND REDUCTION: REDOX

Redox-       Is when oxidation and reduction are taking place at the same time(simultaneously) .
Oxidation-  Is the loss of electrons or oxidation is said to occur when there is an increase in oxidation                     state.
Reduction-   Is the gain of electrons or when there is a decrease in oxidation state .

Cu²⁺ + Zn --> Cu + Zn²⁺
For the example given above,Zn has been oxidised (lost electrons ) and Cu has been reduced (gain electrons ).
Remember when a specie losses electron(s) it becomes positively charged and when a specie gains electron(s) it becomes negatively charged .

OXIDATION STATES
Rules

• All elements in their standard state have zero(0) oxidation state .example Na ,Cl2
• Na+ has oxidation state of +1 and Mg2+ has oxidation state of +2
• Cl- has oxidation state of -1 
• Hydrogen has oxidation state of +1 except in the hydrides where it is -1

How to find the oxidation states of elements in a compound 

Eg  1.find the ox of c in Co2 

C -4 =0             note : O has ox of -2 and there are two molecules of it so the total oxidation state is 

                                  2 * -2 = -4 

C = +4

2. what is the oxidation state of 

 N in No3 - ?                                           3.Mn in MnO4 -

N- (3*2)= -1                                               Mn -(2*4) = -1

N-6 = -1                                                      Mn -8 = -1

N= -1+6                                                      Mn = -1 +8

N= +5                                                         Mn =+7

4.S in SO₄²⁻ 

S -(2*4) = -2 

S-8= -2

S= -2 +8 

S= +6

Role of oxidation state in naming species 

Manganese(iv) oxide -Mn has +4 oxidation state in MnO2 hence the name 

Sulphur (vi) oxide -    S has + 6 oxidation state 

dichromate (vi)    -      Cr has oxidation state of +6