1. REDOX INTRODUCTION

2. What lost e-?s What gained e-? Zn (lost 2-)  OXIDATION
Cu2+ (gained 2-)  REDUCTION

3. Oxidation-Reduction Reactions
Also known as ‘redox’ reactions. Always occur as a pair (so 2 reactants) LEO the lion says GER OIL (oxidation is loss) RIG (reduction is gain)

4. Example #1 Identify the atoms being oxidized or reduced.
Ag+(aq) + e-  Ag(s)
Cu(s)  Cu2+(aq) + 2 e-
2 Na + Cl2  2 NaCl
Write your own example of
An oxidation:
A reduction:
Reduction
Oxidation
Oxidation of Na
Mg(s)  Mg 2+(aq) + 2e-
F2(g) +2 e-  2F – (aq)
Reduction of Cl2

5. Redox Reactions oxidizing agent – causes the other to be oxidized
(itself gets reduced)
Which one in this e.g.?
Cu2+ (aq)
reducing agent – the reactant which caused the other to be reduced (itself gets oxidized) Which one in this e.g.?
Zn (s)

6. Example #2 For the following reactions:
Which element is oxidized? reduced?
Identify the oxidizing agent. Reducing agent.
2 Ca + O2  2 CaO
Mg + Br2  MgBr2
Ca: Reducing agent
O2: Oxidizing agent
Oxidized
Reduced
Mg: Reducing agent
Br2: Oxidizing agent
Oxidized
Reduced

7. OXIDATION NUMBERS

8. OXIDATION NUMBERS
Oxidation numbers are used to keep track of electrons during reactions.
It is an arbitrary system based on:
ions charge of an atom
electronegativity
For any neutral compound, the oxidation numbers of the atoms must add up to zero.

9. compounds containing a single type of atom
OXIDATION NUMBERS
Atom or Ion
Oxidation Number
Examples
compounds containing a single type of atom Na
Cl2
H in most compounds +1
HCl
H in a hydride -1
LiH
O in most compounds -2
H2O
O in a peroxide
H2O2
monatomic ions
charge of ion
Na+ = +1
S2- = -2

10. Oxidation Numbers General steps to assign oxidation numbers:
Assign common oxidation numbers.
use your periodic table
The total oxidation number of a molecule or an ion is the value of the charge of the molecule or ion.
Unknown oxidation numbers can be assigned algebraically.

11. Example #3 OXIDATION NUMBERS Determine the oxidation numbers for:
MoS2:
H2O
ClO2-

12. Example #3 OXIDATION NUMBERS Determine the oxidation numbers for:
MoS2: S = 2- from the chart;
x + (2 x -2) = total charge = 0 (neutral)
x-4 = 0  Mo’s Oxidation No. = 4
H2O
ClO2-
X + (-2 x 2) =-1  x -4 = -1  x = +3

13. Example #3 OXIDATION NUMBERS SO32- x + 3.(-2) = -2  x = +4 Na3N
H2O x = 0  2x = -2  x= -1 +4 -2 +1 -3 +1 -1

14. Example #3 OXIDATION NUMBERS Determine the oxidation numbers for: MoS2
H2O
ClO2-
Finding oxidation # of Cl
x + 2 x (-2) = -1  x -4 = -1  x =3 +1 -2 +3 -2

15. 2 KCl + MnO2 + 2 H2SO4  K2SO4 + MnSO4 + Cl2 + H2O
Example #4
For the following reaction:
identify the substance oxidized / reduced
oxidizing / reducing agents
2 KCl + MnO2 + 2 H2SO4  K2SO4 + MnSO4 + Cl2 + H2O
oxidation +1 -1 +4 -2 +1 +6 -2 +1 +6 -2 +2 +6 -2 +1 -2
reduction
i. Cl atoms in KCl are oxidized (-1 to 0). Mn atoms in MnO2 are reduced (+4 to +2)
ii. KCl is a reducing agent. MnO2 is the oxidizing agent.

16. HALF REACTIONS

17. HALF REACTIONS
All redox reactions may be divided into half-reactions. One half represents the oxidation, while the other is the reduction. Half-reactions are always written for a single mole of a substance.
Zn(s) + Cu2+(aq)  Zn2+(aq) + Cu(s)
Oxidation: Zn(s)  Zn2+(aq) + 2e-
Reduction: Cu2+(aq) + 2e-  Cu(s)

18. HALF REACTIONS
Using the half-reactions table, one can predict whether a redox reaction will occur spontaneously. An oxidizing agent (left column) will always spontaneously react with a reducing agent (right column) lower on the list.

19. Yes
This table is similar. The higher the voltage, the more reactive the oxidizer.

20. Example #5 HALF REACTIONS
Will iodine be able to oxidize zinc metal to Zn2+ ions?
Name an oxidizing agent that can oxidize Br- to Br2, but cannot oxidize Cl- to Cl2.
Yes
MnO2