OxidationReduction Reactions

1
Oxidation/Reduction Reactions

• CHM1020
• Chapter 11

2
Oxidation Reduction Reactions(redox)

• In these reactions, atoms change charges.
• The loss of electrons is called oxidation
• The gain of electrons is called reduction.
• When something is being oxidized, something else
  must be reduced. Oxidation-Reduction reactions
  occur in pairs.
• A simple pneumonic
• LEO the lion says GER

3
A combination reaction A B ? AB
Mg0
O0
Mg2
O2-
2 Mg(s) O2(g) ?
2 MgO (s)
2 Mg ? 2 Mg2 4 e- oxidation
Mg is losing electrons
O2 4 e- ? 2 O2- reduction
O is gaining electrons
Most combination reactions are Redox
reactions. All elements in their elemental state
have a zero charge.
4
A decomposition reaction AB ? A B
Ag0
Ag
Br -
Br0
2AgBr (aq) light?
2Ag(s) Br2
2 Br- ? Br2 2 e-
oxidation Br is losing electrons
2 Ag 2 e- ? 2 Ag reduction Ag
is gaining electrons
These seem to be the opposite of combination
reactions and most are redox reactions.
5
It is this reaction that occurs in black white
film

• The light converts silver ions to elemental
  silver.
• The reduced silver is attracted to a sulfur.
• The metallic silver provides a catalyst for the
  reduction of the entire crystal.

6
A single replacement reaction A BC ? B AC
Fe0
Cu2
Cl-
Cu0
Fe2
Cl-
Fe(s) CuCl2(aq) ?
Cu(s) FeCl2(aq)
2 Fe0 ? Fe2 2 e-
oxidation Fe is losing electrons
Cu2 2 e- ? Cu0 reduction
Cu is gaining electrons
Single replacement reactions are redox reactions.
A is being oxidized and B is being reduced.
7
Copper plating a nail
8
Why will these reactions occur?

• Activity Series  
• Metal Oxidation reaction
• Potassium K - K e-
• Sodium Na - Na e-
• Magnesium Mg - Mg2 2e-
• Aluminum Al - Al3 3e-
• Zinc Zn - Zn2 2e-
• Iron Fe -Fe2 2e-
• Hydrogen H2 - 2H 2e-
• Copper Cu - Cu2 2e-
• Silver Ag -Ag e-
• Gold Au -Au3 3e-

• Some metals are more stable in their elemental
  state than others.
• Gold, is hard to oxidize.
• Potassium and Magnesium are easy to oxidize.