How do you determine the oxidizing or reducing agent in a redox equation?

1 Answer
Sep 16, 2016

If the oxidation number increases upon reaction, the species is a reducing agent. And if the oxidation number decreases, the species is an oxidizing agent.


Redox transfer is formalized on the basis of loss or gain or electrons. Recall the old mnemonic: #"LEO SAYS GER"#, #"loss of electrons = oxidation; gain of electrons = reduction."#

And thus if something has been oxidized, it is A SOURCE of electrons; likewise, if something has been reduced it is an electron sink, and has ACCEPTED electron from somewhere.

We can go to a simple redox reaction; the oxidation of elemental carbon:

#C + O_2 rarr CO_2#

Zerovalent carbon has been oxidized to #C^(IV+)#. But while carbon has been oxidized, its very oxidation has provided electrons to the dioxygen oxidant; i.e. carbon is here the reducing agent.