Two Hands Clapping

I promised in Reactions 3 and 4 to lead you to the promised land of the modern understanding of oxidation and reduction reactions. This is the section where these two great chemical rivers flow together and acquire great explanatory power and wide applicability. 1 have already shown that one great class of reactions, those between acids and bases (Reaction 2), takes place by the transfer of one fundamental particle, the proton. I shall now show you that oxidation and reduction reactions all take place by the transfer of another fundamental particle, in this case the proton s cousin, the electron. 

My aim here is to show you that everything I discussed in Reactions 3 and 4 boils down to the consequences of the transfer of electrons from one species to another. You have already caught a glimpse of that process as we stood together perilously deep inside the blast furnace in Reaction 4 and saw that ions transfer electrons to Fe ions to bring about the reduction of the ore to the metal. 

To see the truth of this electrons in transit view we need to stand back a little. You might already have noticed the first clue oxidation never occurs without reduction, and vice versa. Oxidation and reduction are the Tweedledum and Tweedledee, the Castor and Pollux, of chemistry. There is never one without the other. For instance, when iron ore is reduced by carbon monoxide in a blast furnace, the carbon monoxide is oxidized to carbon dioxide. Because oxidation is always accompanied by reduction chemists take the view that it is inappropriate to speak of an oxidation reaction alone or of a reduction reaction alone. Instead, they think of them jointly as a reduction-oxida- 

This point, that two hands need to clap, should be easy to understand once you accept that redox reactions are electron transfer reactions, for there cannot be electron donation without electron acceptance. You saw exactly the same reciprocity, the same need for two hands to clap, in the discussion of neutralization and proton transfer in Reaction 2 an acid, a proton donor, cannot donate into a vacuum it needs a base, a proton acceptor, to participate in the transfer. 

Let s look at the oxidation and reduction reactions we have already encountered, but do so in the expectation of winkling out the fact that they all take place by the transfer of electrons. A good place to start is the combustion of magnesium (Reaction 3). 

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