AP Chemistry Unit 2
Oxidation­Reduction Reactions
Reactions involving a transfer of electrons
from one species to another
This is reflected in a change in
OXIDATION NUMBERS
Fe (s) + CuSO4 (aq)
Fe (s) + Cu+2 (aq)
FeSO4 (aq) + Cu (s)
Fe+2 (aq) + Cu (s)
Assigning Oxidation Numbers
Redox Intro
NaCl
HCO3­1
Br2
HClO4
SO2
ClO3­1
AP Chemistry Unit 2
Half­Reactions
+2
0
+2
Fe (s) + Cu+2 (aq)
0
Fe+2 (aq) + Cu (s)
2 electrons lost by iron
+2
0
Fe+2 (aq) + 2e­
Fe (s) +2
0
Cu (s)
Cu+2 (aq) + 2e­
2 electrons gained by copper
oxidation
0
+2
Fe (s) + Cu+2 (aq)
+2
Fe+2 (aq) + Cu (s)
reduction
LEO
goes
GER
Redox Intro
0
AP Chemistry Unit 2
Examples of Oxidation­Reduction Reactions
Combination (Synthesis)
Not all, but when 2 elements react to form a compound, yes!
2 Al (s) + 3 Cl2 (g)
2 AlCl3 (s)
CaO (s) + SO2 (g)
CaSO3 (s)
Decomposition
Not all, but when a compound breaks into 2 elements, yes!
2 HgO (s) 2 Hg (l) + O2 (g)
Examples of Oxidation­Reduction Reactions
Displacement (Single­Replacement)
Involve an element and one of its compounds, so ALL of them...well, those that will occur based on the Activity Series!
2 Al (s) + 3 CuSO4 (aq)
Redox Intro
3 Cu (s) + Al2(SO4)3 (aq)
AP Chemistry Unit 2
Examples of Oxidation­Reduction Reactions
Combustion
A substance reacts with oxygen, usually releasing heat, along with a flame.
Oxygen's oxidation number changes from 0 to ­2, so all combustion reactions are oxidation­reduction reactions.
0
0
4 Fe (s) + 3 O2 (g)
Redox Intro
+3 ­2
2 Fe2O3 (s)
AP Chemistry Unit 2
Balancing Oxidation­Reduction Reactions
Half­Reaction Method
MgBr2 (aq) + Al (s)
Net Ionic:
Mg2+ (aq) + Al (s)
AlBr3 (aq) + Mg (s)
Al3+ (aq) + Mg (s)
Oxidation:
Al Al3+ + 3 e­
Reduction:
Mg2+ + 2 e­
Mg
Al Cancel out electrons:
Mg2+ + 2 e­
2 Al + 3 Mg+2 + 6 e­
Al3+ + 3 e­
Mg
2 Al+3 + 6 e­ + 3 Mg
Balanced oxidation­reduction reaction:
2 Al + 3 Mg+2 Redox Intro
2 Al+3 + 3 Mg