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Oxidation-Reduction Reactions
“Redox”
LEO SAYS GER
Oxidation and Reduction (Redox)
Electrons are transferred
Spontaneous redox rxns can transfer
energy
Electrons (electricity)
Heat
Non-spontaneous redox rxns can be
made to happen with electricity
Oxidation Reduction Reactions
(Redox)
0
1
0
1
2 Na Cl 2 2 Na Cl
Each sodium atom loses one electron:
0
1
Na Na e
Each chlorine atom gains one electron:
0
1
Cl e Cl
LEO says GER :
Lose Electrons = Oxidation
1
0
Na Na e
Sodium is oxidized
Gain Electrons = Reduction
0
1
Cl e Cl
Chlorine is reduced
Rules for Assigning Oxidation Numbers
Rules 1 & 2
1. The oxidation number of any uncombined
element is zero
2. The oxidation number of a monatomic ion
equals its charge
0
0
1
1
2 Na Cl 2 2 Na Cl
Rules for Assigning Oxidation Numbers
Rules 3 & 4
3. The oxidation number of oxygen in
compounds is -2
4. The oxidation number of hydrogen in
compounds is +1
1
2
H2O
Rules for Assigning Oxidation Number
Rule 5
5. The sum of the oxidation numbers
in the formula of a compound is 0
1
2
H2O
2(+1) + (-2) = 0
H
O
2
2 1
Ca (O H ) 2
(+2) + 2(-2) + 2(+1) = 0
Ca
O
H
Rules for Assigning Oxidation Numbers
Rule 6
6. The sum of the oxidation numbers in the
formula of a polyatomic ion is equal to
its charge
? 2
N O3
? 2
S O4
2
X + 3(-2) = -1
N
O
X + 4(-2) = -2
S
O
X = +5
X = +6
The Oxidation Number Rules SIMPLIFIED
1. The sum of the oxidation numbers in
ANYTHING is equal to its charge
2. Hydrogen in compounds is +1
3. Oxygen in compounds is -2
Not All Reactions are Redox Reactions
Reactions in which there has been no change
in oxidation number are not redox rxns.
Examples:
1 5 2
1
1
1
1
1 5 2
Ag N O3 (aq) Na Cl (aq) Ag Cl (s) Na N O 3 (aq )
1 2 1
1
6 2
1
6 2
1
2
2 Na O H (aq) H 2 S O 4 (aq) Na 2 S O 4 (aq) H 2 O(l )
This slide refers to vocabulary that has been excluded from AP
Chemistry by the College Board, and will not be tested.
Reducing Agents and Oxidizing Agents
The substance reduced is the oxidizing agent
The substance oxidized is the reducing agent
0
1
Na Na e
Sodium is oxidized – it is the reducing agent
0
1
Cl e Cl
Chlorine is reduced – it is the oxidizing agent
Trends in Oxidation and Reduction
Active metals:
Lose electrons easily
Are easily oxidized
Active nonmetals:
Gain electrons easily
Are easily reduced
Redox Reaction Prediction
#1
Reduced in reaction
Formed in reaction
MnO4- (acid solution)
MnO4- (basic solution)
MnO2 (acid solution)
Cr2O72- (acid)
CrO42HNO3, concentrated
HNO3, dilute
H2SO4, hot conc
Metallic Ions
Free Halogens
HClO4
Na2O2
H2O2
Mn(II)
MnO2
Mn(II)
Cr(III)
Cr(III)
NO2
NO
SO2
Metallous Ions
Halide ions
ClOHO2
Redox Reaction Prediction
#2
Oxidized in reaction
Formed in reaction
Halide Ions
Free Metals
Metalous Ions
Nitrite Ions
Sulfite Ions
Free Halogens (dil, basic sol)
Free Halogens (conc, basic sol)
C2O42-
Halogens
Metal Ions
Metallic ions
Nitrate Ions
SO42Hypohalite ions
Halate ions
CO2