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Oxidation-Reduction: Transfer Of Electrons
Oxidation and
Reduction
Wait
Cu metal
and Ag+
ions
Ag metal
and Cu2+
ions
Chapter 9.1
Concepts In Oxidation-Reduction
• Oxidation-reduction reactions involve a
transfer of electrons from one species to
another.
• Oxidation – loss of e- or oxidation # increases
• Reduction – gain of e- or oxidation #
decreases
• The species that loses electrons is oxidized
and is an reducing agent.
• The species that gains electrons is reduced
and is an oxidizing agent.
However, we never “see” electrons in the final
balanced chemical equation:
2 Ag+ + Cu
Concepts In Oxidation-Reduction
Ag+ + e¯ -->Ag
Reduction of silver
Silver is the oxidizing agent
Cu -->Cu2+ + 2e¯
Oxidation of copper
Copper is the reducing agent
Oxidation-Reduction Reactions
2 Ag + Cu2+
Can only “see” electrons when the reaction is
broken down into “half” reactions:
Ag+ + e¯--> Ag
 Oxidation number - In order to keep
track of electrons in chemical reactions,
chemists assign an oxidation number to
each element.
Cu --> Cu2+ + 2e¯
Number of electrons produced and consumed in
half reactions must be balanced so that they cancel
out in the final chemical equation.
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Determining Oxidation States
 Oxidation number of an element in its
native state is zero.
 Alkali metals have an oxidation number
of +1
 Alkaline earth elements have an
oxidation number of +2
 The oxidation number of monatomic
ions is the same as the charge.
Try Some
 Ga2O3
Fe2(CrO4)3
 K2MnO4
Hg2(BrO3)2
 H2PO4-
KClO4
Determining Oxidation States
 Fluorine is 1 except for F2.
 Cl, Br, and I are 1 in binary
compounds.
 O is usually 2 (except for peroxides
O2 2 and superoxides O2 1).
 H is usually +1 (except for hydrides H 1)
 The sum of the oxidation numbers
equals the charge on ion or molecule.
Oxidation-Reduction Recall
 Oxidation – process in which an
element loses one or more
electrons with an increase in the
oxidation number.
 Reduction – process in which an
element gains one or more
electrons with a decrease in
oxidation number.
 Oxidizing agent – Substance that
causes another substance to be
oxidized. The oxidizing agent is
always reduced.
 Reducing agent – Substance that
causes another substance to be
reduced. The reducing agent is
always oxidized.
 WO3(s) + 3 H2(g)  W(s) + 3 H2O(l)
 Element oxidized –
 Element reduced –
 Oxidizing agent –
 Reducing agent –
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WO3(s) + 3 H2(g)  W(s) + 3 H2O(l)
Element oxidized –
Element reduced –
Oxidizing agent –
Reducing agent –
hydrogen
tungsten
WO3
H2
 SnO2(s) + 2 C(s)  Sn(l) + 2 CO(g)
 Element oxidized –
 Element reduced –
 Oxidizing agent –
 Reducing agent –
SnO2(s) + 2 C(s)  Sn(l) + 2 CO(g)
Element oxidized –
Element reduced –
Oxidizing agent –
Reducing agent –
Carbon
Tin
SnO2(s)
C(s)
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