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Oxidation and Reduction
Chem 1061 – Tro, Chapter 4
Lance S. Lund
Assigning Oxidation Numbers
1.
The oxidation number of an element is zero.
2.
The oxidation number of an atom in a monoatomic ion
equals the charge on the ion.
3.
The oxidation number of oxygen is -2 in most of its
compounds. Exception: In peroxides, the oxidation
number of oxygen is -1.
4.
The oxidation number of hydrogen is +1 in most of its
compounds. Exception: In hydrides, the oxidation
number of hydrogen is -1.
Assigning Oxidation Numbers
5.
The oxidation number of fluorine is -1 in all of its
compounds. Each of the halogens has an oxidation
number of -1 in binary compounds, except when the
other element is a halogen above it in the Periodic
Table or the other element is oxygen.
6.
The sum of oxidation numbers of the atoms in a
compound is zero. The sum of the oxidation numbers
of the atoms in a polyatomic ion equals the charge on
the ion.
Determine the Oxidation Numbers
• Determine the oxidation numbers of each
element in the following species:
– K2SO4
H3PO4
– Cr2O72-
Br2
Redox Reactions
• The Loss of Electrons is Oxidation
– An element that loses electrons is said to be oxidized.
The species in which that element is present in a
reaction is called the reducing agent.
• The Gain of Electrons is Reduction
– An element that gains electrons is said to be reduced.
The species in which that element is present in a
reaction is called the oxidizing agent.