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Redox Reactions
Day One
REDOX-OXIDATION STATES
16.2-16.3
Oxidation-Reduction
• Process of gaining or losing electrons
• Oxidation: losing electrons
• Reduction: Gaining Electrons
OIL RIG
How do we Identify if something is
being reduced or oxidized?
• Oxidation States (Oxidation Numbers)
– Computed for each element based on the number
of electrons assigned
• There are FIVE (5) Rules for assigning
Oxidation States
Oxidation State RULES
1. Oxidation state of an atom in a free element
is ZERO (0).
2. Hydrogen always has an oxidation number of
(+1) , except in hydrides
3. Oxygen always has an oxidation number of
(-2), except in peroxides
Oxidation State Rules
4. The sum of oxidation states of all atoms in:
– Molecule = (0)
– Ion = charge of the ion
5. In their compounds,
– Group I metal = (+1)
– Group II metals (+2)
LETS TRY A FEW!!!
•
•
•
•
•
•
Br2
K+1
LiF
CO2
SO4-2
Na2O2
Br = 0, Br= 0
1+
Li = 1+, F = 1- total = 0
O = -2 each = -4 Total = 0
C = +4
O= -2 ea. = -8
S = +6
Total = -2
Na = +1ea. = +2
O = -2 ea. = -4
Na has priority so it sets the rule so
O will have a -1ea so the total = 0
Identify Redox Reaction
• You can identify a redox by checking to see if
one compound was reduced and the other
was oxidized.
• Remember:
– Oxidation = an increase in oxidation state
– Reduction = a decrease in oxidation state
Day Two
½ REACTIONS
16.4
Balancing Redox Reactions
1. Assign Oxidation Numbers
2. Split reaction into two ½ reactions
3. Balance all elements except H and O
- balance O by adding H2O
- balance H by adding H+1
4. Add electrons to show lose or gain of charge
5. Balance number of electrons
6. Add together the two half reactions & verify
Al(s) + Ag+1  Al+3 + Ag(s)
Fe+2 + MnO4-1  Fe+3 + Mn+2
Day Three
½ REACTIONS
ACIDIC AND BASIC SOLN
Balancing Redox Reactions
in Acidic Solutions
1.
2.
3.
4.
5.
6.
Split reaction into two ½ reactions
Balance all elements except H and O
Add electrons to show lose or gain of charge
Balance number of electrons
Add Water to balance O
Add H+1 to balance H
** NO DIFFERENCE THAN WHAT WE HAVE BEEN
DOING!!!!!!!!!!!
HNO3 + H2S  S + NO
Acidic Solution
Balancing Redox Reactions
in Basic Solutions
1.
2.
3.
4.
5.
6.
Split reaction into two ½ reactions
Balance all elements except H and O
Add electrons to show lose or gain of charge
Balance number of electrons
Add Water to balance O
Add H+1 to balance H
7. Neutralize H+1 by adding the
appropriate amount of OH-1 to EACH
SIDE
NO2  NO-2 + NO3-1
Basic Soln