Reduction and Oxidation (Redox)
Objectives
Be able to...
• Define the terms oxidation and reduction in
terms of changes in oxidation number
• Determine whether elements have been oxidised
or reduced in a reaction using their oxidation
states
• Confidently use half equations to describe redox
reactions
Specification...
Where this comes from...
Oxidation-number Changes in
Chemical Reactions
• If the oxidation number increases for an atom
▫ Oxidation has occurred
• If the oxidation number decreases for an atom
▫ Reduction has occurred
+1 +5 –2
0
+2 +5 –2
0
2AgNO3(aq) + Cu(s)  Cu(NO3)2(aq) + 2Ag(s)
• What is being oxidized? What is being reduced?
Remember OIL RIG
• Oxidation
• Is
• Loss
• Reduction
• Is
• Gain
▫ (Of electrons)
Or...
LEO
LEO says
GER!
LEO
says
GER!
Loss of Electrons = Oxidation
Gain of Electrons = Reduction
• Use the changes in oxidation numbers to identify
which atoms are oxidized, and which atoms are
reduced:
1. 2H2 (g) + O2 (g)  2H2O (l)
2. 2KNO3 (s)  2KNO2 (s) + O2 (g)
3. NH4NO3 (s)  N2 (g) + 2H2O (g)

(HINT: consider each N separately)
4. PbO2 (aq) + 4HI (aq)  I2 (aq) + PbI2 (s) + 2H2O (l)
And some more...
Home Learning
• Complete worksheet on Redox and Oxidation
States