The reaction of AgNO 3 (aq) and K 3 PO 4 (aq) is a precipitation reaction (see Example 4-4c).
4-5 Oxidation–Reduction Reactions: An Introduction 143The nitrate ions, NO 3 , are spectator ions. Canceling them from both sides gives the net ionic
equation:
2Ag(aq)Cu(s)88nCu^2 (aq)2Ag(s)This is a redox equation. The oxidation number of silver decreases from 1 to zero; silver ion
is reduced and is the oxidizing agent. The oxidation number of copper increases from zero to
2; copper is oxidized and is the reducing agent.
(b) This reaction involves only solids, so there are no ions in solution and the formula unit
and net ionic equations are identical. It is a redox reaction:
4KClO 3 (s)88nKCl(s)3KClO 4 (s)
6
2Chlorine is reduced from 5 in KClO 3 to the 1 oxidation state in KCl; the oxidizing agent
is KClO 3. Chlorine is oxidized from 5 in KClO 3 to the 7 oxidation state in KClO 4. KClO 3
is also the reducing agent. This is a disproportionation reaction. We see that KClO 3 is both
the oxidizing agent and the reducing agent.
(c) The solubility guidelines indicate that all these salts are soluble except for silver phos-
phate, Ag 3 PO 4. The total ionic equation is
3[Ag(aq)NO 3 (aq)][3K(aq)PO 43 (aq)]88nAg 3 PO 4 (s)3[K(aq)NO 3 (aq)]Eliminating the spectator ions gives the net ionic equation:
3Ag(aq)PO 43 (aq)88nAg 3 PO 4 (s)There are no changes in oxidation numbers; this is not a redox reaction.
You should now work Exercises 44 and 47.
1 0 (^20)
1 5 2 1 1 1 7 2
8n
888 888n
8888
8888888888888888888888888
888888888888888
In Chapter 11 we will learn to balance redox equations and to carry out stoichiometric
calculations using the balanced equations.
Problem-Solving Tip:A Foolproof Way to Recognize a Redox Reaction
You can always recognize a redox reaction by analyzing oxidation numbers. First deter-
mine the oxidation number of each element wherever it appears in the reaction. If no
elements change in oxidation numbers, the reaction is not an oxidation–reduction reac-
tion. If changes do occur, the reaction is an oxidation–reduction reaction. Remember
that oxidation and reduction must always occur together; if some atoms increase in oxida-
tion numbers, then others must decrease.
1 5 2 1 5 2