OxidationReduction Redox Reactions

1
Oxidation-Reduction (Redox) Reactions

• Oxidation-reduction reactions involve the
  transfer of electrons from one species to
  another.
• Oxidation is defined as the loss of electrons.
• Reduction is defined as the gain of electrons.
• Oxidation and reduction always occur
  simultaneously.

2
An Example
Consider the following reaction
3
An Example
Consider the reaction of Cu(s) with Ag

• Cu (s) 2 Ag (aq) ?? Cu2 (aq) 2 Ag (s)

4
Oxidation-Reduction Reactions
5
Describing Oxidation-Reduction Reactions

• Look again at the reaction of iron with
  copper(II) sulfate.

• We can write this reaction in terms of two
  half-reactions.

6
A Half-Reaction
Oxidation Reduction Reaction
7
The Net Ionic Equation
8
Oxidation Numbers
How can we identify oxidized and reduced species?
By keeping track of the oxidation number

• The oxidation number (or oxidation state) of an
  atom in a substance is the actual charge of the
  atom if it exists as a monatomic ion.
• Alternatively, it is hypothetical charge assigned
  to the atom in the substance by simple rules.

9
Oxidation Number Rules
10
Oxidation Number Rules (Cont.)
11
Examples (Oxidation Number)
1. What is the oxidation number of chlorine in
HClO4
?Oxn (Cl) 8-1 7
12
Examples (Oxidation Number)
2. What is the oxidation number of chlorine in
chlorate ion
?Oxn (Cl) 5
13
Some Common Oxidation-Reduction Reactions

• Combination Reactions
• Decomposition Reactions
• Displacement Reactions
• Combustion Reactions

14
Combination Reactions

• A combination reaction is a reaction in which two
  substances combine to form a third substance.

15
Decomposition Reactions

• A decomposition reaction is a reaction in which a
  single compound reacts to give two or more
  substances.

16
Displacement Reactions
17
Combustion Reactions
18
Balancing Simple Oxidation-Reduction Reactions
Is the equation balanced?

• The masses are balanced but the charges are not
  balanced.
• a balanced equation must have a charge balance as
  well as a mass balance.

19
1. Write the Half-Equations
Masses are balanced
20
2. Balance Charges

• Add the half-equations to obtain the
• balanced redox equation

21
Activity Series
22
Balancing Oxidation-Reduction Reactions in Acidic
Solution
Balancing Oxidation-Reduction Reactions in Basic
Solution