Oxidation & Reduction

Addition of Oxygen

Oxidation is the addition of oxygen

E.g. C + O₂ —→ CO₂ The carbon gains oxygen, therefore the carbon is oxidised

Removal of Oxygen

Reduction is the removal of oxygen

E.g. CuO + H₂ —→ Cu + H₂O The copper loses oxygen, therefore the cooper is reduced

Addition of Hydrogen

Oxidation is the removal of hydrogen

Removal of Hydrogen

Reduction is the addition of hydrogen

Electron Transfer

Oxidation is the loss of electrons

Reduction is the gain of electrons

Oxidation Is Loss Reduction Is Gain

Change in Oxidation Number

Oxidation is an increase in oxidation number

Reduction is a decrease in oxidation number

Oxidising Agent

is a substance that brings about oxidation in other substances by being reduced

Reducing Agent

is a substance that brings about reduction in other substances by being oxidised

Oxidation Number

is the apparent charge an atom has when electrons are distributed according to certain rules

Oxidation Number Rules

1. The oxidation number of any element that isn’t bond to another different element is 0

2. The oxidation number of an ion of an element is the same as its charge

3. The total of the oxidation numbers in a neutral compound must add to give 0

4. Oxygen has an oxidation number of -2

Exceptions: Peroxides like H₂O₂,O.N of H = +1, each O must have an O.N. of -1 to give a total of 0

In OF₂, as O.N. of F = -1, O must have an O.N. of +2

5. Hydrogen has an oxidation number of +1

Exceptions: In metal hydrides (H after a metal) like NaH, CaH₂. Here H has an O.N. of -1

6. Halogens (Groups VII elements) have an oxidation number of -1

Exceptions: When bonded to a more electronegative element (O or F), halogens can have other oxidation numbers which are calculated using rule 3

7. The total of the oxidation numbers in a complex ion must add to give the charge on the ion

Oxidation States

Mn has different oxidation numbers depending on the elements it’s combined with