Download Redox

Sodium loses an electron
- oxidation
2Na  Cl2  2Na Cl

Chlorine gains an electron
- reduction

Magnesium loses an electron
- oxidation
2Mg  O2  2Mg O
2
Oxygen gains an electron
- reduction
2
Oxidation Numbers
• In order to keep track of
electrons during chemical
reactions, the idea of
oxidation numbers (oxidation
states) was introduced.
Oxidation Number
• Is the charge which an atom has, or
appears to have, in a compound.
Rules for Assigning Oxidation
Numbers
1. The oxidation number of any
uncombined element is zero.
Na
O2
Cl2
Fe
2. The oxidation number of an ion is
the same as its charge.
O
-2
Fe
has an oxidation number of  2
2
has an oxidation number of  2
Na  has an oxidation number of  1
3. The sum of all the Oxidation numbers in
a compound must equal zero.
4. Oxygen always has an oxidation number
of -2 except in peroxides ( when it has
an oxidation number of -1) and in the
compound OF2 (where it has an oxidation
number +2.)
5. Hydrogen is always +1 except in metal
hydrides where it is -1.
6. In simple compounds, Halogens have an
oxidation number of -1.
7. In a complex ion, the sum of the
oxidation numbers should equal the
charge on the ion.
1.
The oxidation number of any uncombined element is zero.
2.
The oxidation number of an ion is the same as its charge.
3.
The sum of all the Oxidation numbers in a
compound must equal zero.
4. Oxygen always has an oxidation number of -2
except in peroxides ( when it has an oxidation
number of -1) and in the compound OF2 (where
it has an oxidation number +2.)
5. Hydrogen is always +1 except in metal hydrides
where it is -1.
6. In simple compounds, Halogens have an oxidation number of -1.
7. In a complex ion, the sum of the oxidation numbers should equal
the charge on the ion.
Loses 2e
MnO  2H  2Cl  Mn
+7

4
-8

+2

-2
 Cl2  H2 O
2
+2
0
+2 -2
Gains 5e
Loses 10e
2MnO  2H  10Cl  2Mn

4

Gains 10e

2
 5Cl2  H2 O
Loses 10e
2MnO  16H  10Cl  2Mn

4

Gains 10e

2
 5Cl2  8H2O
Loses 2e
MnO  H2 S  2H  Mn
4
+7 -8

+2 -2
Gains 5e
+2
+2
2
 S  H2 O
0
+2
-2
Loses 2e
0
+4
+6
-2
Gains 2electrons
Reduction
Loses 2e
2
0
+4 -6
+2-2
Reduced
Gains 2 electrons
-2
+6 -8
+1