CP NT Ch 20: Oxidation & Reduction
Intro to Redox
Definition
 Oxidation Reduction Reaction (Redox):
A reaction in which electrons are _______________ from one substance to another.
 Oxidation cannot occur without ____________________
 Oxidation:
1. Losing of _________________________
2. Increasing the oxidation charge, ie: 0 to +1 or -2 to -1
 Reduction
1. _______________________ of electrons
2. Reducing the oxidation charge, ie: -1 to -2 or 1 to 0
 Oxidation numbers—number of _________________ the atom would have in a molecule if
_________________ were transferred _______________________
Rule #1
Oxidation number of a ___________ element is ___________
Example:
Mg, H2, Na, P4, S8, K
Rule #2
Oxidation number of an __________ is the _______________ of the ion
Example:
Mg2+ , O2– , Al3+ , Br –
Rule #3
The oxidation number for H is _______ when bonded to a ________________
*Exception: when bonded to a ____________ it is _____
Example:
HCl
HF
LiH
H2O
NaH
MgH2
Rule#4
Oxygen’s oxidation number is ______
Two exceptions: peroxides and fluorine
in H2O2
where O is _____
with OF2
where O is _____
Practice: Assign oxidation numbers to each element
1. HNO3
2. NO3–
3. MgCl2
4. CO32–
5. NH3
6. K3PO4
7. CaSO4
8. SiCl4
Whiteboard Practice:
1. Give the oxidation number of the nitrogen atom:
a. N2
b. NO
c. N2O4
d. N2O5
e. NO2–
f. NH4+
e. HS–
f. SO2
e. H4P2O7
f. H5P3O10
2. Determine the oxidation number of the sulfur atom:
a. H2S
b. S
c. H2SO4
d. S2–
3. Indicate the oxidation number of phosphorus in each:
a. HPO3
b. H3PO2
c. H3PO3
d. H3PO4
1
g. SO3
Homework Day 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 electrons.
Directions: Use the Rules for Assigning Oxidation Numbers to determine the oxidation number assigned to
each element in each of the given chemical formulas.
Element and Oxidation
Formula
Formula
Element and Oxidation Number
Number
5. Cl2
Cl
0
6.
Na2O2
Na
O
7. Cl
Cl
8.
SiO2
Si
O
9. Na
Na
10.
CaCl2
Ca
Cl
11. Na+
Na +1
12.
PO43P
O
13. O2
O
14.
MnO2
Mn
O
15. N2
N
16.
FeO
Fe
+2
O -2
+3
17. Al
Al
18.
Fe2O3
Fe
O
19. H2O
H
+1
O
-2
20.
H2O2
H
O
21. NO3
N
O
22.
CaO
Ca
O
23. NO2
N
O
24.
H2S
H
S
225. Cr2O7
Cr
O
26.
H2SO4
H
S
O
27. KCl
K
Cl
28.
NH4Cl
N
H
Cl
29. NH3
N
H
30.
K3PO4
K
P
O
31. CaH2
Ca
H
32.
HNO3
H
N
O
233. SO4
S
O
34.
KNO2
K
N
O
Half Reactions
Redox reaction:
 2Mg + O2  2MgO
2
General example of Oxidation ½ reaction
 When an electron is _______________ (electrons appear as ________________)
◦ X0  X+1 + e―
 Oxidation number goes ______________
General example of Reduction ½ reaction
 When an electron is _______________ (electrons appear as ________________)
◦ e― +Y+1  Y0
 Oxidation number goes ______________
Two ways to remember oxidation/reduction is:
 L E O goes G E R
or
O I L
R I G
Examples:




Ex1
Ex2
Ex3
Ex4
start
Na0
Fe+3
N+1
Mg+2
finish
Na+1
Fe+2
N+2
Mg0




Oxidation or Reduction
______________
______________
______________
______________
Homework Day 2:
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.
1. K+ +e―  K
_____________________________
2. Ca  Ca2+ + 2e― _____________________________
3. 2Br―  Br2 + 2e― _____________________________
4. S + 2e―  S2―
_____________________________
5. F2 + 2e―  2F-―
_____________________________
Write where the electron(s) is lost or gained. Then determine if each equation is oxidation or reduction.
6.
Na

Na+
__________________________
2+
7.
Mg

Mg
__________________________
+
8.
K

K
__________________________
2+
3+
9.
Fe

Fe
__________________________
10.
Ag+

Ag
__________________________
―
11.
I2

2I
__________________________
2+
12.
Zn

Zn
__________________________
13.
2F― 
F2
__________________________
3+
14.
Al

Al
__________________________
―
15.
Cl2

2Cl
__________________________
NT: Redox Reactions (Last Lesson of the Year!)
Balance the reactions, write the oxidation numbers for each atom.
Ex1
HCl
+
Zn
 ZnCl2 + H2
3
Ex2
Mg
+
N2
 Mg3N2
Ex3
H2S
+
Cl2

HCl
Ex4
Fe
+
O2

Fe2O3
+ S
Classwork:
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. Write all the oxidation numbers.
b. Write the ½ reactions.
_______________________________
_______________________________
(oxidation or reduction)
(oxidation or reduction)
c. Add the electrons to each ½ reaction.
d. Identify each ½ reaction as oxidation or reduction.
2) Zn(s) + HCl(aq)  H2(g) + ZnCl2(aq)
a. Write all the oxidation numbers.
b. Write the ½ reactions.
_______________________________
_______________________________
(oxidation or reduction)
(oxidation or reduction)
c. Add the electrons to each ½ reaction.
d. Identify each ½ reaction as oxidation or reduction.
3) SbCl5 + 2 KI  SbCl3 + I2 + 2 KCl
a. Write all the oxidation numbers.
b. Write the ½ reactions.
_______________________________
_______________________________
(oxidation or reduction)
(oxidation or reduction)
c. Add the electrons to each ½ reaction.
d. Identify each ½ reaction as oxidation or reduction.
4
Homework Day 3:
Balance each equation. Assign oxidation numbers to each atom. Write the ½ reactions and determine what
is reduced or oxidized.
1.
Na + Cl2 
NaCl
2.
C + O2 
CO2
3.
Zn + CuSO4 
4.
Al + CuCl2 
ZnSO4 +
Cu +
Cu
AlCl3
H2SO4  CuSO4 + SO2 + H2O
5.
Cu +
6.
Mg + HCl  MgCl2 + H2
5