Redox Reactions
13.1a Electron Transfer Theory
Overview
• oxidation and reduction rxtns always occur
together (redox rxtn)
– you can’t have one without the other
• examples
– extracting metal from an ore
– electroplating of metals
– salt on roads (corrosion)
• salt accelerates the reaction between oxygen and metal
• makes electron transfer easier
3 perspectives of oxidation/reduction
• 1) oxygen
– oxidation gains and reduction loses
• 2) hydrogen
– oxidation loses and reduction gains
• 3) electrons (modern view)
– oxidation loses and reduction gains
– most fundamental explanation, what we will
be working with the most
Sample Rxtn.
We convert iron ore to metallic iron using
carbon. What is being oxidized?
2Fe2O3 + 3C  4Fe + 3CO2
– we removed oxygen from the iron(III)oxide
and the carbon gained oxygen
– carbon was oxidized because it gained an
oxygen
Sample Rxtns. con’t
Fe2O3 (s) + 3 CO(g)
2 Fe (s) + 3CO2 (g)
SnO2 (s) + C(s)
Sn(s) + CO2 (g)
CuS(s) + H2(g)
Cu(s) + H2S(g)
Oxidation
Reduction
Gains oxygen
Lose Oxygen
Oxygen
Lose Hydrogen
Gains hydrogen
Hydrogen
Lose Electrons
Gains electrons
e-
Redox with Electrons
many reactions may not even involve oxygen
redox currently refers to electrons being
transferred between reactants
Mg
+
S
Mg2+
+
S2-
(MgS)
•the magnesium atom (which has zero charge) changes to a magnesium ion by
losing 2 electrons, and is oxidized to Mg2+
•the sulfur atom (which has no charge) is changed to a sulfide ion by gaining 2
electrons, and is reduced to S2•Mg is the reducing agent and S is the oxidizing agent
• agents cause the other half of the rxtn. to occur
Examples
• Is the reactant oxidized or reduced?
•
•
•
•
•
Pb  PbO3
SnO2  SnO
KClO3 KCl
C2H6O  C2H4O
C2H2  C2H6
oxidized
reduced
reduced
oxidized
reduced
Homework
Textbook p. 559 #1-4
Redox Reactions
13.1a1 Electron Transfer Theory
Leo the Lion!
• LEO the lion says GER
– Loss of electrons is oxidation, gain of
electrons is reduction
LEO says GER
Lose Electrons = Oxidation
1
0
Na  Na  e

Sodium is oxidized
Gain Electrons = Reduction
0

1
Cl  e  Cl
Chlorine is reduced
LEO says GER con’t
- losing electrons is oxidation, and the
substance that loses the electrons is
called the reducing agent.
- gaining electrons is reduction, and the
substance that gains the electrons is
called the oxidizing agent.
Mg is the
reducing
agent
Mg is oxidized: loses e-, becomes a Mg2+ ion
Mg(s) + S(s)
S is the oxidizing agent
MgS(s)
S is reduced: gains e- = S2- ion
Oxidizing and Reducing Agents
CuO + H2  Cu + H2O
• Cu goes from 2+ to 0
– Cu is reduced, therefore it is called an
oxidizing agent because it causes some
other substance to be oxidized
• H goes from 0 to 1+
– H is oxidized, therefore it is called a reducing
agent because it causes some other
substance to be reduced
Identifying Agents in an Equation
Reduction: CuO is
the oxidizing agent
• CuO + H2  Cu + H2O
Oxidation: H2 is
the reducing
agent
Examples
• A) H2(g) + Cl2 (g)
• H2 oxidized
2HCl(g)
Cl2 reduced
• B) S(s) + Cl2 (g)
• S oxidized
• C) N2 + 2O2
• N2 oxidized
• D) 2Li + F2
Cl2 reduced
2NO2
O2 reduced
2LiF
• Li oxidized
• E) H2 + S
SCl2(g)
F2 reduced
H2S
• H2 oxidized
S reduced
Half-Cell Reactions
The overall reaction:
2Fe + 3Cl2
2Fe3+ + 6Clmay be written as the sum of two half-cell
reactions:
2Fe  2Fe3+ + 6e(oxidation)
3Cl2 + 6e-  6Cl(reduction)
Complete redox reactions can be expressed as the
sum of two half reactions, one reduction and one
oxidation.
Homework
Textbook p.564 #7-11
LSM 13.1B,C summary