Chapter 20 Outline
Oxidation Reduction Reactions
Section 20.1 – Oxidation vs. Reduction
reactions are also
reactions.

known as
of electrons or the
gain of
is the
.
of electrons or the
loss of
is the
.


 The substance that
called the
is
.
 In other words, the substance that is
the oxidizing agent, and the substance that is
_______________ is the reducing agent.
 The way to remember the difference in oxidation
and reduction is
.
O=
R=
I=
I=
L=
G=
Sample Problem
Mg(s) + S(s)  Mg+2S-2(s)
 Mg has a
charge and changes to _____, so it
________ electrons and is
.
 S has a
charge and changes to
________ electrons and is
 The substance that
the
, so it
.
is called
.
1. Determine what is oxidized and what is reduced.
Identify the oxidizing agent and the reducing
agent.
2AgNO3(aq) + Cu(s)  Cu(NO3)2(aq) + 2Ag(s)
is
Practice Problem
1. Determine which substance is oxidized and which
is reduced. Identify the oxidizing agent and the
reducing agent.
4Al(s) + 3O2(g)  2Al2O3(s)
Section 20.1 Assessment
1. Define oxidation and reduction in terms of loss or
gain of oxygen.
2. Define oxidation and reduction in terms of loss or
gain of electrons.
3. How do you identify the oxidizing agent and the
reducing agent in a redox reaction?
Section 20.2 – Oxidation Numbers
 An
is a positive or negative
______________ assigned to an atom to indicate its
______________ of oxidation or reduction.
 A
atom’s oxidation number is the
_____________ that it would have if the electrons in
the bonded were assigned to the atom of the
more
element.
Rules for Oxidation Numbers
1. The oxidation number of a
equal to its
is
.
Ex: Br- =
Fe+3 =
2. The oxidation number for
is
________________________ where it is
except in
.
Ex: HCl, H =
NaH, H =
4. Determine which substance is oxidized and which
is reduced. Identify the oxidizing agent and
reducing agent.
Mg(s) + Cu(NO3)2(aq)  Mg(NO3)2(aq) + Cu(s)
3. The oxidation number for
in
where it is
Ex: MgO, O =
H2O2, O =
is
.
except
4. The oxidation number of a
element
is
.
Ex: Ag =
N2 =
5. For a
, the sum of the
oxidation numbers must equal
.
Ex: NaCl =
H2O =
6. For a
, the sum of the
oxidation numbers must equal the
_____________________ of the ion.
Ex: CO3-2, O = , so C =
Sample Problem
1. What is the oxidation number of each element in
Na2SO4?
Practice Problems
1. Assign the oxidation numbers for each element in
SO2.
2. Assign the oxidation number for each element in
(NH4)2S.
 In some
, it is necessary to
look at
instead of just
using charges.
Sample Problem
1. Identify which atoms are oxidized and which are
reduced in the reaction.
2KNO3(s)  2KNO2(s) + O2(g)
Practice Problem
1. Identify which atoms are oxidized and which are
reduced in the reaction.
2HNO3(aq) + 6HI(aq)  2NO(g) + 3I2(s) + 4H2O(l)
Section 20.2 Assessment
1. What is the general rule for assigning oxidation
numbers?
2. Identify which atoms are oxidized and which are
reduced.
2Na(s) + Cl2(g)  2NaCl(s)