Redox Equations (AQA A Level Chemistry)

Balancing Redox Reactions

• Balancing equations using redox principles is a useful skill and is best illustrated by following an example

• It is important to follow a methodical step-by-step approach so that you don't get lost:

Redox & Disproportionation Reactions

Oxidation

• Oxidation is the gain of oxygen, eg:

Cu + H₂O → CuO + H₂

(Cu has gained an oxygen and is oxidised)

• Oxidation is also the loss of hydrogen, eg:

2NH₃ + 3Br₂ → N₂ + 6HBr

(NH₃ has lost hydrogen and is oxidised)

• Oxidation is also the loss of electrons, eg:

Cu²⁺ + Mg → Mg²⁺ + Cu

(Mg has lost two electrons and is oxidised)

• Oxidation causes an increase in oxidaiton state, eg:

Cu²⁺ + Mg → Mg²⁺ + Cu

(change in ox. no. of Mg is +2 thus Mg is oxidised)

Reduction

• Reduction is the loss of oxygen, eg:

Cu+ H₂O → 2CuO + H₂

(H₂O has been reduced)

• Reduction is also the gain of hydrogen, eg:

2NH₃+ 3Br₂ → N₂ + 6HBr

(Br has been reduced)

• Reduction is also the gain of electrons, eg:

Cu²⁺ + Mg → Mg²⁺ + Cu

(Cu has been reduced)

• Reduction causes a decrease in oxidation number, eg:

Cu²⁺ + Mg → Mg²⁺ + Cu

(the change in oxidation state of Cu is -2 thus Cu is reduced)

Redox reactions

• Redox reactions are reactions in which oxidation and reduction take place simultaneously

• While one species is oxidising, another is reducing in the same reaction, eg:

Cu²⁺+ Mg → Mg²⁺ + Cu

(Cu has been reduced and Mg has been oxidised)

Disproportionation reactions

• A disproportionation reaction is a reaction in which the same species is both oxidised and reduced

Example of a disproportion reaction in which the same species (chlorine in this case) has been both oxidised and reduced