Oxidation, Reduction and Redox

What is Oxidation and Reduction?

Oxidation - A reaction in which an atom or a group of atoms loses electrons.

Reduction - A reaction in which an atom or group of atoms gain electrons.

What is a Oxidising or Reducing Agent?

Oxidising Agent - A reagent that oxidises another species. This means that it is accepting electrons, so its oxidation state decreases, and is being reduced itself.

Reducing Agent - A reagent that reduces another species. This means that it is donating electrons, so its oxidation state increases, and is being oxidised itself.

What is a Redox Reaction?

A reaction in which electrons are transferred from one species to another.

What is a Spectator Ion?

Ions that are unchanged during a chemical reaction as they take no part in the reaction.

What are Oxidation States and What are the rules of Oxidation States?

Oxidation State - The number of electrons lost or gained by an atom in a compound compared to the uncombined atom.

Rules:

• Every element in its uncombined state has an oxidation number of 0

• A positive number shows that the element has lost electrons and has therefore been oxidised

• A negative number shows that the element has gained electrons and has therefore been reduced

• The more positive/negative the number, the more it has been oxidised/reduced

• They always have a + or - sign unless they are 0

How can you find the Oxidation State of Elements in a Compound?

For Elements - The oxidation state = 0

For Neutral Compounds - The oxidation state = 0

For Complex Ions - The oxidation state = Total charge

In a compound, the most electronegative element always has a negative oxidation state.

Common Oxidation States:

• Hydrogen = +1

• Oxygen = -2

• Group 1 = +1

• Group 7 = -1

How can Half Equations be used in Redox Reactions?

Half Equations can be used to show separate oxidation and reduction reactions that occur. They must be balanced in terms of species present and the charges of the species both sides of the equation.

Half Equations can be balanced by:

• Calculating Oxidation states and adding electrons to balance charges

• Add H₂O to balance any oxygen

• Add H⁺ ions to balance any hydrogen

Two redox half equations can be combined, but if the amount of electrons are not the same on both sides then you may need to scale up the moles for the equations.