| Gain of electrons. The definition of reduction has been steadily refined over the centuries, paralleling the clarification of its opposite, oxidation. Hence when oxygen reacts with metals, it formally gains electrons, to become O{TAG(tag=>sup)}2-{TAG} if the compound is ionic. Having gained electrons, it has been reduced. Other simple rules for recognizing reductions are as follows (all are opposite to the rules for oxidation): gain of hydrogen, as when Cl{TAG(tag=>sub)}2{TAG} is reduced to HC1; loss of oxygen, as when Fe{TAG(tag=>sub)}2{TAG}O{TAG(tag=>sub)}3{TAG} is reduced to Fe; and decrease in oxidation number, as when Fe{TAG(tag=>sup)}3+{TAG} is reduced to Fe{TAG(tag=>sup)}2+{TAG}. |
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