Oxidation and reduction are such useful concepts that they have
been extended from cases of outright electron gain or loss, to reactions
involving varying degrees of electron sharing.
When copper oxide ore is reduced to metallic copper by roasting
with charcoal (below), copper ions are reduced and carbon is oxidized:
2Cu2O + C ------> 4Cu + CO2
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The reduction of copper is obvious; each Cu+
ion accepts one electron and becomes a copper atom.
But in what sense is carbon oxidized? It does not
give up its outer electrons and become a C4+
ion in CO2.
Each carbon atom of coke initially shared its four
electrons equally with other carbon atoms. It continues to share
electron pairs with oxygen in CO2,
but on an unequal basis.
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