CHM 2046/Myers
Class Worksheet 19
February 22,
2010
1.
Oxidation Number = Oxidation State – Review
(Text section 5.7)
An atomic charge, sometimes fictional, calculated by assigning any shared electrons in
a bond to the more electronegative element.
The following are used to calculate this:
Elements:
O. N. = 0
(O
2
, N
2
, etc.)
Monatomic ions:
O. N. = actual charge (Na
+
, Mg
+2
, Cl

, etc.)
Usually:
O =

2,
H = +1
Molecules and Polyatomic Ions:
Sum of O. N. = Total Charge
Examples
:
H
3
PO
4
ClO
4

Cr
2
O
7

2
2. OxidationReduction (Redox) Reactions.
(
Rxns where there are O. N. changes.)
Oxidation = an increase in O. N.
Reduction = a decrease in O. N.
Oxidizing Agent =
Reducing Agent
=
Examples
 Identify the OA and RA in these reactions:
2 SO
2
+
O
2
→
2 SO
3
2 Na
+
Cl
2
→
2 NaCl
3.
Balancing Equations for Redox Reactions.
(Text section 21.1)
Balancing equations that involve redox is tricky but, once you get the hang of it,
is sort of fun!
A few of these equations, particularly combustion reactions, you can
balance simply “by inspection.”
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 Spring '08
 Staff
 Chemistry, Electron, Oxidation Number, Redox, Oxidizing agent, O. N.

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