The following abbreviations are widely
used:
ox. no.oxidation number
ox. agt.oxidizing agent
red. agt.reducing agent142 CHAPTER 4: Some Types of Chemical Reactions
0 1 1 1 5 2 0 2 5 (^20)
8 n
888888 888n
888
88888888888888888888888888888888888888888888888888888888
888888888888
The following equations represent examples of redox reactions. Oxidation numbers are
shown above the formulas, and oxidizing and reducing agents are indicated:
2Fe(s)3Cl 2 (g)88n2FeCl 3 (s)
red. agt. ox. agt.
2FeBr 3 (aq)3Cl 2 (g)88n2FeCl 3 (aq)3Br 2 ()
red. agt. ox. agt.
Equations for redox reactions can also be written as total ionic and net ionic equations.
For example, the second equation may also be written as:
2[Fe^3 (aq)3Br(aq)]3Cl 2 (g)88n2[Fe^3 (aq)3Cl(aq)]3Br 2 ()
We distinguish between oxidation numbers and actual charges on ions by denoting oxida-
tion numbers as nor n in red circles just above the symbols of the elements,and actual
charges as nor nabove and to the right of formulas of ions. The spectator ions, Fe^3 ,
do not participate in electron transfer. Their cancellation allows us to focus on the oxidizing
agent, Cl 2 (g), and the reducing agent, Br(aq).
2Br(aq)Cl 2 (g)88n2Cl(aq)Br 2 ()
A disproportionation reactionis a redox reaction in which the same element is
oxidized and reduced. An example is:
Cl 2 H 2 O88nHClHClO
EXAMPLE 4-4 Redox Reactions
Write each of the following formula unit equations as a net ionic equation if the two differ.
Which ones are redox reactions? For the redox reactions, identify the oxidizing agent, the
reducing agent, the species oxidized, and the species reduced.
(a) 2AgNO 3 (aq)Cu(s)88nCu(NO 3 ) 2 (aq)2Ag(s)
heat
(b) 4KClO 3 (s)888nKCl(s)3KClO 4 (s)
(c) 3 AgNO 3 (aq)K 3 PO 4 (aq)88nAg 3 PO 4 (s)3KNO 3 (aq)
Plan
To write ionic equations, we must recognize compounds that are (1) soluble in water and (2)
ionized or dissociated in aqueous solutions. To determine which are oxidation–reduction reac-
tions, we should assign an oxidation number to each element.
Solution
(a) According to the solubility guidelines (page 134), both silver nitrate, AgNO 3 , and copper(II)
nitrate, Cu(NO 3 ) 2 , are water-soluble ionic compounds. The total ionic equation and oxidation
numbers are
2[Ag(aq)NO 3 (aq)]Cu(s)88n[Cu^2 (aq)2NO 3 (aq)]2Ag(s)
2
1
0 0 3 1
3 1 0 3 (^10)
Iron reacting with chlorine to form
iron(III) chloride.
Metallic silver formed by immersing
a spiral of copper wire in a silver
nitrate solution (see Example 4-4a).