Redox Reactions
 Many practical or everyday examples of
redox reactions:
Corrosion of iron (rust formation)
Forest fire
combustion
Charcoal grill
Natural gas burning
Batteries
Metabolic processes
Redox Reactions
 There are many different kinds of redox
reactions.
Combustion
CH4 (g) + 2 O2 (g)  CO2 (g) + 2 H2O (g)
Oxidation of Metals by Acids or Metal
Salts
Cu (s) + H2SO4 (aq)  CuSO4 (aq) + H2 (g)
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
 The reaction between a metal and an acid
or between a metal and a metal salt is
called a displacement reaction.
a reaction in which an element reacts
with a compound and displaces an
element from that compound
A
+
BX

AX
+
B
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
Examples:
Mg (s) + 2HCl (aq)  MgCl2 (aq) + H2 (g)
Zn (s) + 2 HBr (aq)  ZnBr2 (aq) + H2 (g)
Mn (s) + Pb(NO3)2 (aq)  Mn(NO3)2 (aq) + Pb (s)
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
 How do you know if a redox reaction has
occurred?
 You must examine the oxidation number of
each of the elements present in the reactants
and products.
If the oxidation number changes, then a
redox reaction has occurred.
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
 When oxidation occurs:
Electrons are lost
Oxidation number increases
 When reduction occurs:
Electrons are gained
Oxidation number is reduced (decreases)
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
Mg(s) + 2HCl (aq)  MgCl2 (aq) + H2 (g)
-1
0
+1
Oxidation # of Mg
increased
oxidation
Oxidation # of H+ ion
reduced
reduction
-1
+2
0
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
Example: Identify the element that has been
oxidized and the one that has been reduced.
Zn (s) + 2 HCl (aq)  ZnCl2 (aq) + H2 (g)
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
 To determine which components have been
oxidized and reduced, find the oxidation
numbers:
Zn (s) + 2 HCl (aq)  ZnCl2 (aq) + H2 (g)
-1
0
oxidized
reduced
+1
+2
-1
0
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
 You can also write a net ionic equation to
describe the reaction:
Write all soluble strong electrolytes as ions
Eliminate the spectator ions
Zn (s) + 2 HCl (aq)  ZnCl2 (aq) + H2 (g)
Zn (s) + 2 H+ (aq) + 2 Cl- (aq)  Zn2+ (aq) + 2 Cl- (aq)
+ H2 (g)
Zn (s) + 2H+ (aq)  Zn2+ (aq) + H2 (g)
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
Example: Write the complete ionic and net
ionic equations for the reaction. Which
element is oxidized?
2 Al (s) + 3 Ni(NO3)2 (aq)  2 Al(NO3)3 (aq) + 3 Ni (s)
2 Al (s) + 3 Ni2+(aq) + 6 NO3- (aq)  2 Al3+ (aq) +
6 NO3- (aq) + 3 Ni (s)
2 Al (s) + 3 Ni 2+(aq)  2 Al3+ (aq) + 3 Ni (s)
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
+5
+5
2 Al (s) + 3 Ni(NO3)2 (aq) 2 Al(NO3)3 (aq) + 3 Ni (s)
0
oxidized
+2
-2
+3
-2
0
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
 Based on the previous equation, we wouldn’t
want to store a solution of Ni(NO3)3 in an
aluminum container.
The aluminum container would react and
dissolve!!!
 Metals differ in the ease with which they are
oxidized.
Al (s) is oxidized by Ni(NO3)3 (aq)
Ag(s) is NOT oxidized by Ni(NO3)3 (aq)
Redox Reactions
Oxidation of Metals by Acids or Metal Salts
 Activity series:
A list of metals arranged in order of
decreasing ease of oxidation
Used to predict whether a metal will react
with an acid or with a metal salt
See table 4.5
Activity Series