1. Redox Reactions
Many practical or everyday examples of redox reactions:
Corrosion of iron (rust formation)
Forest fire
Charcoal grill
Natural gas burning
Batteries
Metabolic processes
combustion

2. CH4 (g) + 2 O2 (g)  CO2 (g) + 2 H2O (g)
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)

3. 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

4. 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)

5. 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.

6. 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)

7. Redox Reactions Oxidation of Metals by Acids or Metal Salts
Mg(s) HCl (aq)  MgCl2 (aq) + H2 (g) -1 +2 +1
Oxidation # of Mg increased oxidation
Oxidation # of H+ ion reduced reduction

8. 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) HCl (aq)  ZnCl2 (aq) + H2 (g)

9. 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) HCl (aq)  ZnCl2 (aq) + H2 (g)
oxidized
reduced +1 -1 +2

10. 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) 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)

11. 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)

12. 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)
oxidized -2 -2 +3 +2

13. 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)

14. 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

15. Activity Series