chem oxidation states / redox reactions

Define oxidation

• Loss of electrons

• Reducing agent

• Increase in oxidation state

Define Reduction

• gain of electrons

• Oxidising agent

• Decrease in oxidation state

Oxidation states rules, in order

1. atom in a free element = 0

2. Monatomic ion = to its charge

3. The sum of oxidation states in a neutral molecule = 0, in a polyatomic ion = to its charge

4. Group 1 metals = +1, Group 2 metals = +2

5. Non metals, F = -1, H = +1, O = -2, Group 17 = -1, Group 16 = -2, Group 15 = -3

Balancing redox reactions

1. Assign oxidation states

2. Split into two half reactions

3. Balance the two half reactions by stoichiometric ratio - balance O with H2O, balance H with H+

4. Balance by charges by adding electrons

5. Make the number of electrons in both half reactions equal by multiplying

6. Verify by mass and charge that it’s balanced

“Which has the least tendency to be oxidised”

• lowest on the list

“Which metal cation has the greatest tendency to be reduced”

• Lowest on the list

“Best reducing agent”

• highest on the list