Reduction and Oxidation
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Reduction and oxidation reactions (also known as redox reactions) are a key part of the process of extracting metals from their ores.
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Oxidation refers to the process where a substance gains oxygen during a chemical reaction. For instance, when copper ore is heated in air, it reacts with oxygen to form copper oxide, an oxidation reaction.
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Reduction, on the other hand, involves a substance losing oxygen. The copper oxide produced above can be reduced to copper metal by heating it with carbon, which removes the oxygen.
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In the context of metals, oxidation can also be understood as a process where a metal loses electrons to form positive ions. For example, in extracting aluminium from its ore, the aluminium ions are reduced to aluminium atoms, each by gaining three electrons.
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Simultaneously, there is a corresponding oxidation reaction where the negative oxide ions each lose two electrons to form oxygen molecules.
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Hence, in redox reactions, there is always a substance being reduced (gaining electrons or losing oxygen) and another being oxidised (losing electrons or gaining oxygen).
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It is important to remember that more reactive metals are harder to reduce (require more energy to remove oxygen or gain electrons) than less reactive metals.
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Also, using carbon to reduce metal oxides is only successful if the metal is less reactive than carbon. Otherwise, alternative methods, such as electrolysis, need to be used.
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Understanding of redox reactions is vital in the context of the reactivity series of metals, as it helps predict whether a particular metal can displace another from its compound.
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It should be noted that in the wider chemical context, reduction can also refer to a process where a substance gains electrons, and oxidation to a process where a substance loses electrons. This definition enables us to understand and explain more complex redox reactions.
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The mnemonic ‘OIL RIG’ can be used to remember the concept: Oxidation Is Loss (of electrons); Reduction Is Gain (of electrons).