Oxidation, reduction and redox equations (3.1.7)

What is meant by the terms oxidation and reduction?

Oxidation - the loss of electrons/ hydrogen and gain of oxygen

Reduction - the gain of electrons/ hydrogen and loss of oxygen

OIL RIG

What is meant by the terms oxidising and reducing agent?

Oxidising agent - the species that removes electrons from another (gets reduced)

Reducing agent - the species that gives electrons to another (gets oxidised)

What is a redox reaction and what is another type?

Redox reaction - a chemical reaction in which both reduction and oxidation occurs simultaneously

Disproportionation reactions are also redox but one species is simultaneously oxidised and reduced:

Cl₂ + H₂O → HOCl + HCl

Cl:

• 0 → +1 in HOCl - oxidised

• 0 → -1 in HCl - reduced

How do oxidation states relate to oxidation and reduction?

If the oxidation state goes up, the species is oxidised

If the oxidation state goes down, the species is reduced

What are the main rules when calculating oxidation state?

Rules:

• Elements have a oxidation state of 0

• Ions have the same oxidation state as their charge

• Hydrogen has a oxidation state of +1 (except in hydrides)

• Oxygen has am oxidation state of -2 (except in H₂O₂ where -1)

• Group 1,2,3 have oxidation states of +1,+2,+3

• Usually group 7 have an oxidation state of -1

• Oxidation states of the elements add up to the charge of the whole species

What are half-equations and how do you form them?

Half-equations - equations that show the separate oxidation and reduction reactions that occur in a redox reaction

How to form them:

1) Balance non O/H elements

2) Balance O with H₂O

3) Balance H with H⁺

4) Balance charge with e^-

How do you add half-equations?

1) Multiply the equations to get the same number of electrons on each side

2) Combine them and cancel out the electrons