1. Oxidation Reduction Reactions

2. Re-dox Reactions Oxidation is the loss of electrons
Reduction is a gain of electrons
Leo goes Grr!
Lose Electrons Oxidation
Gain electrons Reduce

3. “Redox Reactions”
Many reactions involve (or seem to involve) a transfer of electrons.
Such reactions always involve both:
Oxidation  Loss of electrons
Na  Na+ + e-
Reduction  Gain of electrons
Cl + e-  Cl-

4. Determine a Redox Reaction
To determine if what you have is a redox reaction, first rewrite the equation to include the oxidation number for each element
This includes every element in a polyatomic ion
The oxidation number is the charge an element has or appears to have when combining to form compounds

5. Oxidizing/Reducing Agents
The element that was oxidized is part of the reducing agent.
The element that was reduced is part of the oxidizing agent.

6. Assigning Oxidation Numbers
All pure elements and homogeneous molecules = 0
Elements in group IA = +1
Elements in group IIA = +2
Ag+, Zn+2, Al+3 (unless it is a pure metal)
In binary compounds the second element = anion charge
Oxygen is almost always = -2 *unless it is O2(g)
Hydrogen is almost always = +1 *unless it is H2(g)
The total charge of a compound is always = 0

7. A Sample Problem
What are the oxidation numbers of the elements in Na2SO4?
Na = +1 (times 2 atoms) = +2
O = -2 (times 4 atoms) = -8
= -6
If the compound must = 0, then S must = +6

8. Give the oxidation number for:
S in Na2SO3
Mn in KMnO4
N in Ca(NO3)2
C in Na2CO3
N in NO2-
S in SO4-2
S in H2S2O7
Fe in Fe(C2H3O2)2 +4 +7 +5 +3 +6 +2

9. Ammonia plus Oxygen NH3 + O2  NO + H2O Is this equation balanced?
No, it does not matter
Step 1: Rewrite the equation with the charges
N3-H+3 + O02  N2+O2- + H+2O2-

10. Ammonia plus Oxygen
Step 2: Determine the changes in the charges of each element
N3-H+3 + O02  N2+O2- + H+2O2-
Nitrogen changes from 3- to 2+
it lost an electron and was oxidized
Oxygen changes from 0 to 2-
it gains electrons and so is reduced

11. Last Step
Step 3: If there is a species oxidized and one reduced, then it is a redox equation