Oxidation–Reduction . In each equation, identify the substance that is oxidized, the substance that is reduced, the oxidizing agent, and the reducing agent.
Strategy : The substance that is oxidized loses electrons and is a reducing agent.
The substance that gains electrons is the oxidizing agent and is reduced.
(a) Al(s) loses three electrons and becomes Al^{3+} ; therefore, aluminum is oxidized. In the process of being oxidized, Al(s) gives its electrons to Fe^{3+} , and so Al(s) is the reducing agent. Fe31 gains three electrons and becomes Fe^{3+} and is reduced. In the process of being reduced, Fe^{3+} accepts three electrons from Al(s), and so Fe^{3+} is the oxidizing agent. To summarize:
(b) Because it is not easy to see the loss or gain of electrons in this example,
we apply the second set of definitions. In converting CH_{3} OH to HCOOH , CH_{3} OH both gains oxygens and loses hydrogens; it is oxidized. In being converted to H_{2} O , O_{2} gains hydrogens; it is reduced. The compound oxidized is the reducing agent; CH_{3} OH is the reducing agent. The compound reduced is the oxidizing agent; O_{2} is the oxidizing agent. To summarize:
