Reduction and Oxidation

Reduction

Gain of electrons, decrease of oxidation number

Reducing Agent

The specie that loses electrons (is oxidised)

Oxidation

Loss of electrons, increase of oxidation number

Oxidising Agent

The specie that gains electrons (is reduced)

Examples of redox reactions

Combustion, corrosion, photosynthesis, respiration, batteries

Oxidation Numbers

A system for keeping track of the gain and loss of electrons in redox reactions. The greater an atom’s oxidation number, the more electrons it has lost.

Oxidation number rules

1. Elements have an oxidation state of 0

2. Monatomic ions have oxidation numbers equal to their charge (Aluminium, halides, etc)

3. Hydrogen has an oxidation state of +1, except in metal hydrides where it is -1

4. Oxygen has an oxidation state of -2, except in peroxides where it is -1

5. For polyatomic ions, the sum of the oxidation states of its atoms is equal to its charge

6. For compounds, the sum of the oxidation states of its atoms is 0

What changes about redox (half-)equations in acidic solutions?

H₂O may be added to balance O and H⁺ may be added to balance H

How do you balance reduction and oxidations half-reactions

Equalise the number of electrons by multiplying the half-equations