Transcript Redox Reactions - NordoniaHonorsChemistry

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)
Summary of Rules
1st- There are many that don’t have rules and are exceptions!
• Rule Number One
All free, uncombined elements have an oxidation number of zero.
This includes diatomic elements such as O2 or others like P4 and S8.
• Rule Number Two
Hydrogen, in all its compounds except hydrides, has an oxidation number of
+1
• Rule Number Three
Oxygen, in all its compounds except peroxides, has an oxidation number of -2
• We can also assume in most cases group 1’s are +1
• With polyatomics- look at each ion separate and then assign numbers
• Oxidation #’s are the # of atoms- not after multiplication.
LETS TRY A FEW!!!
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•
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 only the atom undergoing the change
4. Count up the # of electrons transferred
5. Balance the electrons by multiplying the ½ rxn
6. Bring the equation back together
7. Balance the rest of the reaction
Al(s) + Ag+1  Al+3 + Ag(s)
Ag+1 = +1 → Al+3 = +3
Al = 0
Ag= 0
Al → Al +3
Ag + → Ag
0
+1
3+
0
3e-
1eAl →Al +3
3 Ag +→ 3Ag
Al + 3Ag+ → Al +3 + 3Ag
SnCl3 + Fe  SnCl2 + FeCl2
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