Redox reactions

What is oxidation? OIL - loss of electrons

gain in oxidation number

gain O2 and loses H2

What is reduction? RIG - gain of electrons

decrease in oxidation number

gain of H2 and loss of O2

What is the oxidation agent?

substance that causes another to be oxidised, while is itself reduced

What is the reducing agent?

substance that causes another to be reduced, while it is itself oxidised 

What are the oxidising and reducing agents in this equation: 2Al(s) + 3FeCl2(aq) → 2AlCl3(aq) + 3Fe(s)

Al is oxidised (increase in oxidation number from 0 to +3), so is the reducing agent. Fe2+ is reduced (decreases in oxidation number from +2 to 0) so is the oxidising agent.

What are the rules used to identify oxidation states of atoms?

• Oxidation number of elements is 0. E.g. Mg, O2.

Group 1 metals: +1. E.g. Na+ is +1. • Group 2 metals: +2. E.g. Mg2+ is +2.

• H is always +1 (except in metal hydrides when it’s -1.) • ‘O’ is always -2 (except in H2O2, when it’s -1)

• Monoatomic ions: oxidation is given by charge of the ion. E.g. Cu2+ is +2.

• Polyatomic ions: sum of oxidation numbers equals charge of the ion.

• Neutral compounds: oxidation no’s add to 0.

What are the types of redox reaction?

displacement of metals, combustion, corrosion and electrochemical processes

How does redox occur in the context of displacement of metals?

A more reactive metal is oxidised and replaces a less reactive metal, which is reduced

e.g Fe + CuSO4 → FeSO4 + Cu (Fe is oxidised and copper ion = reduced)

How does redox occur in the context of combustion?

In the combustion of a metal with oxygen, the metal is oxidised and oxygen is reduced

e.g 2Cu + O2 → 2CuO (copper is oxidised)

How does redox occur in the context of corrosion?

the process in which a metal is oxidised when it reacts with chemicals in the atmosphere

How do you balance redox equations in acidic conditions?

• Balance all elements other than H and O.

• Add H2O to balance O atoms.

• Add H+ to balance H atoms.

• Add e- to balance charge.

Balance the following redox equation in acidic conditions:

Cr2O7 2- (aq) + Fe2+(aq) → Cr3+(aq) + Fe3+(aq)

Cr2O7 2- (aq) + 14H+ (aq) + 6e - → 2Cr3+(aq) + 7H2O

Balanced Cr, added H2O to balance O; added H+ to balance H; added electrons to balance charge.

( Fe2+(aq) → Fe3+(aq) + e- ) x 6

Overall: Cr2O7 2- (aq) + 6Fe2+(aq) + 14H+→ 2Cr3+(aq) + 6Fe 3+ (aq) + 7H2O

half equation and net ionic equation for Fe + Cl2 → FeCl3?

Oxidation: Fe → Fe3+ + 3e-

Reduction: 3Cl2 +6e- → 6Cl-

Net ionic equation : 2Fe + 3Cl2 → 2Fe3+ + 6Cl