Oxidation & Reduction
Definition of Redox Reaction
 Oxidation Reduction Reaction (Redox):
A reaction in which electrons are ___________________ from one substance to another.
Definition of Redox Reaction
 Oxidation cannot occur without ____________________
 Definition of Oxidized:
1. Losing of _________________________ (LEO)
2. Increasing the oxidation charge, ie: 0 to +1
-2 to -1
3. Gaining __________________________
 Definition of Reduced:
1. _______________________ of electrons (GER)
2. Reducing the oxidation charge, ie: -1 to -2
1 to 0
3. Losing _____________________________
Example of an electron transfer reaction

2Mg + O2  2MgO

Mg atom _______________________ two electrons to each oxygen atom.

As a result 2 Mg atoms become Mg2+ and two oxygen atoms become ______________

Mg _______________ two electrons

O ________________ two electrons
Examples of Oxidation Reduction

When an electron is _______________ (An electron is found on the product side) there is ______________
◦

X0  X+1 + e-
When an electron is _______________ (An electron is found on the reactant side) there is ______________
◦
e- +Y+1  Y0
1
Examples:

Ex5
start
Na0

finish
Na+1
Oxidation or Reduction
_____________________________________________

Ex6
Fe+3

Fe+2
_____________________________________________

Ex7
N+1

N+2
_____________________________________________

Ex8
Mg+2

Mg0
_____________________________________________
Vocabulary

Whatever is __________________________ is called the reducing agent

Whatever is _________________________ is called the oxidizing agent

Real Examples:
start
finish
Oxidizing agent or reducing agent

Ex5
Na0

Na+1
_____________________________________________

Ex6
Fe+3

Fe+2
_____________________________________________

Ex7
N+1

N+2
_____________________________________________

Ex8
Mg+2

Mg0
_____________________________________________
Redox Homework #1:
1. What is a redox reaction?
2. Can oxidation occur without reduction? Explain.
3. Define oxidation and reduction in terms of the gain or loss of oxygen.
4. Define oxidation and reduction in terms of the gain or loss of electrons.
5. How is a change in oxidation number related to the process of oxidation and reduction?
2
Half-Reactions for Oxidation/Reduction
A half-reaction is an equation just showing just the oxidation or just the reduction reaction that takes place
in a redox reaction.
State whether the half-reaction is oxidation or reduction.
K+ +e-  K
_____________________________
7. Ca  Ca2+ + 2e-
_____________________________
8. 2Br  Br2 + 2e-
_____________________________
9. S + 2e  S
_____________________________
10. F2 + 2e-  2F-
_____________________________
6.
-
2-
Write where the electron(s) is lost or gained. Then determine if each equation is oxidation or reduction.
11.
Na

Na+
__________________________
12.
Mg2+

Mg
__________________________
13.
K

K+
__________________________
14.
Fe2+

Fe3+
__________________________
15.
Ag+

Ag
__________________________
16.
I2

2I-
__________________________
17.
Zn2+

Zn
__________________________
18.
2F-

F2
__________________________
19.
Al3+

Al
__________________________
20.
Cl2

2Cl-
__________________________
Redox Rules:
Redox Rules to Learn for Ionic and Covalent Bonds
Electronegativity and Redox Rules

Definition: Electronegativity is the atom’s ability to _____________________ electrons.

__________________ is the most electronegative element
Electronegativity Trend
_________________EN More protons to attract electrons
_________________EN
electrons get further away
from protons
3
Rule #1
Oxidation number of an _______________________ atom = zero (no compounds or ions)
i.e
.
Mg, H2, Na
ie.
All H2 O2 N2 Cl2 Br2 I2 F2 ’s ox. # are zero
Rule #2
Oxidation number of a ____________________ ion = charge of the ion
i.e.
Mg2+ , O2- , Al3+ , Br –
Rule #3
The sum of the oxidation numbers of a ________________ compound = 0
i.e.
H2O
CO2
CO
NaCl
Rule #4
The oxidation number for H is _______
Exception: when bonded to a ____________ electronegative element (metal), then it is ___________.
i.e.
LiH
NaH
i.e.
HF
Cl
MgH2
Rule#5
Oxygen’s oxidation number is ______, in a compound
Two exceptions: peroxides and fluorine
in H2O2
where O is _______________
with OF2
where O is ________________
Rule#6
Oxidation number of
polyatomic ___________ = 0 (same as rule #3)
polyatomic _______ = the charge of the ion
i.e. compounds:
NH3
SiCl4
K3PO4
CO32-
SO42-
i.e. ions:
NH4+
NO34
Rule#7
Oxidation numbers for _____________ in:
Group 1A metal compound
+1
2A metal compound
+2
3A Aluminum compound+
+3
i.e.
NaCl
MgSO4
AlPO4
Rule#8
The most electronegative element __________________ ALWAYS has an oxidation number of -1 when it is bonded
to another element.
i.e.
HF
Question Time
Assign oxidation numbers to each element
1. Cl2
2. Cl-
3. MgCl2
4. NaH
5. HCl
6. K3PO4
7. CaSO4
8. KF
Classwork: Redox Rules
1. Give the oxidation numbers of all the elements in the following molecules and ions:
a. N2O
b. NO
c. N2O4
d. N2O5
e. NO2-
f. NO3-
e. HS-
f. SO2
2. Determine the oxidation number of the sulfur atom:
a. H2S
b. S
c. H2SO4
d. S2-
g. SO3
3. Indicate the oxidation number of phosphorus in each of the following compounds:
a. HPO3
b. H3PO2
c. H3PO3
d. H3PO4
5
e. H4P2O7
f. H5P3O10
Redox Homework #2: Oxidation Numbers and Rules Worksheet
The oxidation number of an atom is the apparent charge assigned to it in a particular molecule, ion or
compound. Certain rules are followed in assigning oxidation numbers. Use rules at the right to assign
oxidation numbers to each element in each of the given formulas.
Example
Oxidation Number Rules
OXIDATION NUMBER
H2O
N2
H=+1, O= −2
N=0
Rule #1: Oxidation number of an uncombined
atom = zero (no compounds or ions)
OXIDATION NUMBER
Rule #2: Oxidation number of a monatomic ion
1. Cl2
___________________
2. Cl−
___________________
3. Na
___________________
neutral compound = 0
+
___________________
Rule #4: The oxidation number for H is +1
5. KCl
___________________
except when bonded to a less electronegative
4. Na
= charge of the ion
Rule #3: The sum of the oxidation numbers of a
element (metal), then it is -1.
6. H2S
___________________
7. CaO
___________________
exceptions: peroxides and fluorine
8. H2SO4
___________________
Rule#6: Oxidation number of polyatomic
9. NO3−
___________________
compound = zero , polyatomic ion = the charge
10. Cr2O72-
___________________
11. NH4Cl
___________________
1A metal compound= +1, 2A metal compound=
12. NH3
___________________
+2, 3A metal compound= +3
13. NO2
___________________
Rule#8: The most electronegative element
14. CaH2 (calcium hydride)
___________________
Rule#5: Oxygen’s oxidation number is -2, 2
of the ion
Rule#7: Oxidation numbers for metals in: Group
fluorine ALWAYS has an oxidation number of -1
when it is bonded to another element.
15. Na2O2 (sodium peroxide) ___________________
Cw: Give oxidation numbers for the underlined atoms in these molecules and ions:
a. Cs2O
f. ClF3
k. MoO42b. PtCl62-
g. H3AsO3
l. MnO4-
c. CaI2
h. SbF6-
m. PtCl42-
d. SnF2
i. TiO2
n. O2
e. Al2O3
j. P4
o. O3
6
Redox Homework #3: Oxidation Numbers Worksheet
Directions: Use the Rules for Assigning Oxidation Numbers to determine the oxidation number assigned to each
element in each of the given chemical formulas.
Formula
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
Cl2
ClNa
Na+
O2
N2
Al+3
H2O
NO3NO2
Cr2O72KCl
NH3
CaH2
SO42-
Element and Oxidation
Number
Cl
Cl
Na
Na
O
N
Al
H
O
N
O
N
O
Cr
O
K
Cl
N
H
Ca
H
S
O
Formula
16.
17.
18.
19.
20.
21.
22.
23.
24.
25.
26.
27.
28.
29.
30.
Na2O2
SiO2
CaCl2
PO43MnO2
FeO
Fe2O3
H2O2
CaO
H2S
H2SO4
NH4Cl
K3PO4
HNO3
KNO2
Element and Oxidation Number
Na
Si
Ca
P
Mn
Fe
Fe
H
Ca
H
H
N
K
H
K
O
O
Cl
O
O
O
O
O
O
S
S
H
P
N
N
O
Cl
O
O
O
NT: Using the Rules (Last Lesson of the Year!)
Oxidation Number

If oxidation number goes ______________ it is ___________________.

If oxidation number goes ______________ it is ___________________.
Using the Rules
Balance the reactions, write the oxidation numbers for each atom and write the oxidizing and reducing agents.
Ex1
HCl
+
Zn

ZnCl2
Ex2
Mg
+
N2

Mg3N2
Ex3
H2S
+
Cl2

HCl
Ex4
Fe
+
O2

Fe2O3
+ H2
+ S
7
Summary of Oxidation/Reduction
There are three definitions of oxidation and reduction:
Oxidation
Reduction
1._________________________________
1._________________________________
2._________________________________
2._________________________________
3._________________________________
3._________________________________
Two ways to remember oxidation/reduction is:
L E O
goes
G E R
or
O I L
R I G
Classwork: Using Rules to Balance Equations
Assign oxidation numbers for each element. Then, for the following balanced redox reactions answer the
following questions:
1)
Fe(aq) + H2O2(aq)  Fe+2(aq) + 2 OH-1(aq)
a. What is the oxidation state of oxygen in H2O2?
b. What is the element that is oxidized?
c. What is the element that is reduced?
d. What is the oxidizing agent?
e. What is the reducing agent?
f. How many electrons are transferred in the reaction as it is balanced?
2) 4NaOH(aq) + Ca(OH)2(aq) + C(s) + 4ClO2(g)  4NaClO2(aq) + CaCO3(s) + 3H2O(l)
a. What is the oxidation state of Cl in ClO2(g)?
b. What is the oxidation state of C in C(s)?
c. What is the element that is oxidized?
d. What is the element that is reduced?
e. What is the oxidizing agent?
f. What is the reducing agent?
g. How many electrons are transferred in the reaction as it is balanced?
8
3) 16 HCl(aq) + 5 SnCl2(aq) + 2 KMnO4(aq)  2 MnCl2(aq) 5 SnCl4(aq) + 8 H2O(l) + 2 KCl(aq)
a. What is the oxidation state of Mn in KMnO4(aq)?
b. What is the oxidation state of Sn in SnCl2(aq)?
c. What is the element that is oxidized?
d. What is the element that is reduced?
e. What is the oxidizing agent?
f. What is the reducing agent?
g. How many electrons are transferred in the reaction as it is balanced?
Redox Homework #4: Using Rules to Balance Equations
Balance each equation. Assign oxidation numbers to each atom. Determine what is oxidized/reducing agent and
what is reduced/oxidizing agent. Tell the number of electrons transferred.
1. Na + Cl2 
NaCl
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
2. C + O2 
CO2
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
3. Zn + CuSO4 
ZnSO4 +
Cu
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
4.
Fe + O2 +
H2O 
Fe(OH)2
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
5. Cu +
H2SO4  CuSO4 + SO2 + H2O
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
6. Mg + HCl  MgCl2 + H2
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
9
Redox Homework #5: (Extra Practice)
Assign oxidation numbers to each atom. Determine what is oxidized/reducing agent and what is reduced/oxidizing
agent. Tell the number of electrons transferred.
1)
2 Na + FeCl2  2 NaCl + Fe
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
2)
2 C2H2 + 5 O2  4 CO2 + 2 H2O
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
3)
2 PbS + 3 O2  2 SO2 + 2 PbO
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
4)
2 H2 + O2  2 H2O
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
5)
Cu + HNO3  CuNO3 + H2
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
6)
AgNO3 + Cu  CuNO3 + Ag
Oxidized (Reducing Agent)_____________
Reduced (Oxidizing Agent) _____________
Electrons transferred = ________________
10